Effect of photosystem I inactivation on chlorophyll a fluorescence induction in wheat leaves: Does activity of photosystem I play any role in OJIP rise?

Interpretation of the fast chlorophyll a fluorescence induction is still a subject of continuing discussion. One of the contentious issues is the influence of photosystem I (PSI) activity on the kinetics of the thermal JIP-phase of OJIP rise. To demonstrate this influence, we realized a series of measurements in wheat leaves subjected to PSI photoinactivation by the sequence of red saturation pulses (15,000 μmol photons m(-2) s(-1) for 0.3 s, every 10 s) applied in darkness. Such a treatment led to a moderate decrease of maximum quantum efficiency of PSII (by ~8%), but a strong decrease of the number of oxidizable PSI (by ~55%), which considerably limited linear electron transport and CO2 assimilation. Surprisingly, the PSI photoinactivation had low effects on OJIP kinetics of variable fluorescence. In particular, the amplitude of variable fluorescence of IP-step (ΔVIP), which has been considered to be a measure of PSI content, was not decreased, despite the low content of photooxidizable PSI. On the other hand, the slower relaxation of chlorophyll fluorescence after saturation pulse as well as the results of the double-hit method suggest that PSI inactivation treatment led to an increase of the fraction of QB-nonreducing PSII reaction centers. Our results somewhat challenge the mainstream interpretations of JIP-thermal phase, and at least suggest that the IP amplitude cannot serve to estimate reliably the PSI content or the PSI to PSII ratio. Moreover, these results recommend the use of the novel method of PSI inactivation, which might help clarify some important issues needed for the correct understanding of the OJIP fluorescence rise.

Low PSI content limits the photoprotection of PSI and PSII in early growth stages of chlorophyll b-deficient wheat mutant lines

In vivo analyses of electron and proton transport-related processes as well as photoprotective responses were carried out at different stages of growth in chlorophyll b (Chl b)-deficient mutant lines (ANK-32A and ANK-32B) and wild type (WT) of wheat (Triticum aestivum L.). In addition to a high Chl a-b ratio, ANK mutants had a lower content of photo-oxidizable photosystem I (PSI, P m), and several parameters indicated a low PSI/PSII ratio. Moreover, simultaneous measurements of Chl fluorescence and P700 indicated a shift of balance between redox poise of the PSII acceptor side and the PSII donor side, with preferential reduction of the plastoquinone pool, resulting in an over reduced PSI acceptor side (high Φ NA values). This was the probable reason for PSI inactivation observed in the ANK mutants, but not in WT. In later growth phases, we observed partial relief of "chlorina symptoms," toward WT. Measurements of ΔA 520 decay confirmed that, in early growth stages, the ANK mutants with low PSI content had a limited capacity to build up the transthylakoid proton gradient (ΔpH) needed to trigger non-photochemical quenching (NPQ) and to regulate the electron transport by cytochrome b 6/f. Later, the increase in the PSI/PSII ratio enabled ANK mutants to reach full NPQ, but neither over reduction of the PSI acceptor side nor PSI photoinactivation due to imbalance between the activity of PSII and PSI was mitigated. Thus, our results support the crucial role of proper regulation of linear electron transport in the protection of PSI against photoinhibition. Moreover, the ANK mutants of wheat showing the dynamic developmental changes in the PSI/PSII ratio are presented here as very useful models for further studies.

Photosynthetic characteristics, antioxidant capacity and biomass yield of wheat exposed to intermittent light irradiation with millisecond-scale periods

Energy consumption and output are two very important standards for evaluating the reliability of electric light sources when plants are grown in a controlled environment. As a primary source of energy, light is one of the most important environmental factors for wheat growth. The objective of this study was to investigate the influences of light/dark cycle operation with millisecond-scale period on the growth of wheat, photosynthetic characteristics, antioxidant capacity and biomass yield and quality during their life cycle. Four types of intermittent lighting with the same intensity were employed: a light/dark (0.5/0.5 ms) light (50%), a light/dark (0.7/0.3 ms) light (70%), a light/dark (0.8/0.2 ms) light (80%) and a continuous light (100%). The results showed that the wheat cultivated in the 80% light was characterized by highest photosynthetic rate and lowest lignin in inedible biomass, which was more beneficial to recycle substances in the processes of the environment regeneration. The data were comparable to those under continuous light condition in terms of chlorophyll concentration, antioxidant capacity, harvest index (HI) and thousand kernel weight (TKW). Wheat was sensitive to intermittent illumination which significantly affected those indices of growth and physiology, especially at heading and flowering stages.

[Analysis of Polarization Characteristics of Wheat and Maize Crops Using Land-Based Remote Sensing Measurements]

The paper presents analysis of a study of the polarized component of the reflectance factor (Rq) and the degree of polarization (P) of wheat and maize crops depending on the wavelength. Registration of polarization characteristics was carried out in the field from the elevated work platform at heights of 10 to 18 m in June and July. Measurements were performed using a double-beam spectrophotometer with a polarized light filter attachment, within the spectral range from 400 to 820-nm. The viewing angle was no greater than 20 degree with respect to the nadir. The reflection spectra of wheat and maize crops obtained using a polarizer adjusted to transmit the maximum and minimum amounts of light (R(max) and R(min)) were studied. Based on these reflection spectra polarization characteristics, which. differ in the visible and infrared spectral region, were determined and analyzed.

Responses of wheat (Triticum aestivum) and turnip (Brassica rapa) to the combined exposure of carbaryl and ultraviolet radiation

The increase of ultraviolet (UV) radiation reaching the Earth's surface as a result of increased ozone layer depletion has affected crop production systems and, in combination with pesticides used in agricultural activities, can lead to greater risks to the environment. The impact of UV radiation and carbaryl singly and in combination on Triticum aestivum (wheat) and Brassica rapa (turnip) was studied. The combined exposure was analyzed using the MixTox tool and was based on the conceptual model of independent action, where possible deviations to synergism or antagonism and dose-ratio or dose-level response pattern were also considered. Compared with the control, carbaryl and UV radiation individually led to reductions in growth, fresh and dry weight, and water content for both species. Combined treatment of UV and carbaryl was more deleterious compared with single exposure. For T. aestivum length, no interaction between the 2 stressors was found (independent action), and a dose-level deviation was the best description for the weight parameters. For B. rapa, dose-ratio deviations from the conceptual model were found when length and dry weight were analyzed, and a higher than expected effect on the fresh weight (synergism) occurred with combined exposure.

Variance components, heritability and correlation analysis of anther and ovary size during the floral development of bread wheat

Anther and ovary development play an important role in grain setting, a crucial factor determining wheat (Triticum aestivum L.) yield. One aim of this study was to determine the heritability of anther and ovary size at different positions within a spikelet at seven floral developmental stages and conduct a variance components analysis. Relationships between anther and ovary size and other traits were also assessed. The thirty central European winter wheat genotypes used in this study were based on reduced height (Rht) and photoperiod sensitivity (Ppd) genes with variable genetic backgrounds. Identical experimental designs were conducted in a greenhouse and field simultaneously. Heritability of anther and ovary size indicated strong genetic control. Variance components analysis revealed that anther and ovary sizes of floret 3 (i.e. F3, the third floret from the spikelet base) and floret 4 (F4) were more sensitive to the environment compared with those in floret 1 (F1). Good correlations were found between spike dry weight and anther and ovary size in both greenhouse and field, suggesting that anther and ovary size are good predictors of each other, as well as spike dry weight in both conditions. Relationships between spike dry weight and anther and ovary size at F3/4 positions were stronger than at F1, suggesting that F3/4 anther and ovary size are better predictors of spike dry weight. Generally, ovary size showed a closer relationship with spike dry weight than anther size, suggesting that ovary size is a more reliable predictor of spike dry weight.

An assessment of heavy ion irradiation mutagenesis for reverse genetics in wheat (Triticum aestivum L.)

Reverse genetic techniques harnessing mutational approaches are powerful tools that can provide substantial insight into gene function in plants. However, as compared to diploid species, reverse genetic analyses in polyploid plants such as bread wheat can present substantial challenges associated with high levels of sequence and functional similarity amongst homoeologous loci. We previously developed a high-throughput method to identify deletions of genes within a physically mutagenized wheat population. Here we describe our efforts to combine multiple homoeologous deletions of three candidate disease susceptibility genes (TaWRKY11, TaPFT1 and TaPLDß1). We were able to produce lines featuring homozygous deletions at two of the three homoeoloci for all genes, but this was dependent on the individual mutants used in crossing. Intriguingly, despite extensive efforts, viable lines possessing homozygous deletions at all three homoeoloci could not be produced for any of the candidate genes. To investigate deletion size as a possible reason for this phenomenon, we developed an amplicon sequencing approach based on synteny to Brachypodium distachyon to assess the size of the deletions removing one candidate gene (TaPFT1) in our mutants. These analyses revealed that genomic deletions removing the locus are relatively large, resulting in the loss of multiple additional genes. The implications of this work for the use of heavy ion mutagenesis for reverse genetic analyses in wheat are discussed.

Light regulation of mitochondrial alternative oxidase pathway during greening of etiolated wheat seedlings

This study deals with effects of de-etiolation (48h) of spring wheat (Triticum aestivum L., var. Irgina) seedlings on differential expression of AOX1 genes, levels of AOX protein and the alternative respiratory pathway (AP) capacity. As a result of exposure to continuous irradiation of dark-grown wheat seedlings, the respiratory activity and AP capacity in leaves significantly increased during the first 6h of studies. Expression of AOX1a was up-regulated by light and proved consistent with changes in the AP capacity. Effects on expression of AOX1c were less pronounced. Immunoblot analysis showed three distinct bands of AOX with molecular weights of 34, 36 and 38kDa, with no significant changes in the relative levels during de-etiolation. The lack of a clear correlation between AOX protein amount, AOX1a expression, and AP capacity suggests post-translational control of the enzyme activation. The AOX1a suppression and a decrease in the AP capacity correlated with the sugar pool depletion after 24h of the de-etiolation, which may mean a possible substrate dependence of the AOX activity in the green cells. More efficient malate oxidation by mitochondria as well as the higher AOX capacity during the first 6h of de-etiolation was detected, whereas respiration and AOX capacity with exogenous NADH and glycine increased after 6 and 24h, respectively. We conclude that AOX plays an important role during development of an actively photosynthesizing cell, and can rapidly adapt to changes in metabolism and photosynthesis.

Predictions of heading date in bread wheat (Triticum aestivum L.) using QTL-based parameters of an ecophysiological model

Prediction of wheat phenology facilitates the selection of cultivars with specific adaptations to a particular environment. However, while QTL analysis for heading date can identify major genes controlling phenology, the results are limited to the environments and genotypes tested. Moreover, while ecophysiological models allow accurate predictions in new environments, they may require substantial phenotypic data to parameterize each genotype. Also, the model parameters are rarely related to all underlying genes, and all the possible allelic combinations that could be obtained by breeding cannot be tested with models. In this study, a QTL-based model is proposed to predict heading date in bread wheat (Triticum aestivum L.). Two parameters of an ecophysiological model (V sat and P base , representing genotype vernalization requirements and photoperiod sensitivity, respectively) were optimized for 210 genotypes grown in 10 contrasting location × sowing date combinations. Multiple linear regression models predicting V sat and P base with 11 and 12 associated genetic markers accounted for 71 and 68% of the variance of these parameters, respectively. QTL-based V sat and P base estimates were able to predict heading date of an independent validation data set (88 genotypes in six location × sowing date combinations) with a root mean square error of prediction of 5 to 8.6 days, explaining 48 to 63% of the variation for heading date. The QTL-based model proposed in this study may be used for agronomic purposes and to assist breeders in suggesting locally adapted ideotypes for wheat phenology.

Impact of UV-B on drought- or cadmium-induced changes in the fatty acid composition of membrane lipid fractions in wheat

UV-B radiation may have either a positive or negative impact under the same conditions in wheat, depending on the type of secondary abiotic stressor: Cd or drought. Supplemental UV-B prevented the wilting and leaf rolling induced by PEG treatment. In contrast, combined UV-B and Cd treatment resulted in pronounced oxidative stress. The opposite effect of UV-B radiation in the case of drought or cadmium stress may be related to the alteration induced in the fatty acid composition. UV-B caused changes in the unsaturation of leaf phosphatidylglycerol fractions, and the accumulation of flavonoid in the leaves may prevent the stress induced by subsequent drought treatment. However it resulted in pronounced injury despite the increased flavonoid content in roots exposed to Cd. This was manifested in a drastic decrease in the unsaturation of the leaf monogalactosyldiacylglycerol and the root phosphatidylglycerol and digalactosyldiacylglycerol fractions. Data on the flavonoid content and fatty acid composition showed that oxidative stress was induced by drought in the leaves, by Cd in the roots, and interestingly, by UV-B radiation in both the leaves and roots. The additive effect of the combined stresses was also detected in the roots. The results presented here suggest a relationship between the capacity of the plant to remodel the fatty acid composition and its resistance to various stress factors.

Assessing the effects of architectural variations on light partitioning within virtual wheat-pea mixtures

BACKGROUND AND AIMS

Predicting light partitioning in crop mixtures is a critical step in improving the productivity of such complex systems, and light interception has been shown to be closely linked to plant architecture. The aim of the present work was to analyse the relationships between plant architecture and light partitioning within wheat-pea (Triticum aestivum-Pisum sativum) mixtures. An existing model for wheat was utilized and a new model for pea morphogenesis was developed. Both models were then used to assess the effects of architectural variations in light partitioning.

METHODS

First, a deterministic model (L-Pea) was developed in order to obtain dynamic reconstructions of pea architecture. The L-Pea model is based on L-systems formalism and consists of modules for 'vegetative development' and 'organ extension'. A tripartite simulator was then built up from pea and wheat models interfaced with a radiative transfer model. Architectural parameters from both plant models, selected on the basis of their contribution to leaf area index (LAI), height and leaf geometry, were then modified in order to generate contrasting architectures of wheat and pea.

KEY RESULTS

By scaling down the analysis to the organ level, it could be shown that the number of branches/tillers and length of internodes significantly determined the partitioning of light within mixtures. Temporal relationships between light partitioning and the LAI and height of the different species showed that light capture was mainly related to the architectural traits involved in plant LAI during the early stages of development, and in plant height during the onset of interspecific competition.

CONCLUSIONS

In silico experiments enabled the study of the intrinsic effects of architectural parameters on the partitioning of light in crop mixtures of wheat and pea. The findings show that plant architecture is an important criterion for the identification/breeding of plant ideotypes, particularly with respect to light partitioning.

Mycorrhizal responses in wheat: shading decreases growth but does not lower the contribution of the fungal phosphate uptake pathway

Effects have been investigated of reduced C supply (induced by shade) on arbuscular mycorrhizal (AM) colonisation, mycorrhizal growth responses (MGRs) and on AM-mediated and direct uptake of phosphate (Pi) (using (32)P) in wheat, a plant that does not usually respond positively to AM colonisation. Shading markedly reduced growth and shoot/root dry weight ratios of both AM and non-mycorrhizal wheat, indicating decreased photosynthetic C supply. However, shading had very little effect on percent root length colonised by Rhizophagus irregularis or Gigaspora margarita or on MGRs, which remained slightly positive or zero, regardless of shade; there were no growth depressions under shade. By 6 weeks, when the contributions of the AM pathway were measured with (32)P supplied in small hyphal compartments, R. irregularis had supplied 23 to 28% of shoot P with no significant effect of shading. Data show that reduced C availability did not reduce the contribution of the AM pathway to plant P, so the fungi were not acting physiologically as parasites. These results support our previous hypothesis that lack of positive MGR is not necessarily the outcome of excessive C use by the fungi or failure to deliver P via the AM pathway.

Induced and constitutive DNA methylation in a salinity-tolerant wheat introgression line

Cytosine methylation is a well recognized epigenetic mark. Here, the methylation status of a salinity-tolerant wheat cultivar (cv. SR3, derived from a somatic hybridization event) and its progenitor parent (cv. JN177) was explored both globally and within a set of 24 genes responsive to salinity stress. A further comparison was made between DNA extracted from plants grown under control conditions and when challenged by salinity stress. The SR3 and JN177 genomes differed with respect to their global methylation level, and methylation levels were reduced by exposure to salinity stress. We found the genetic stress- (triggered by a combination of different genomes in somatic hybridization) induced methylation pattern of 13 loci in non-stressed SR3; the same 13 loci were found to undergo methylation in salinity-stressed JN177. For the salinity-responsive genes, SR3 and JN177 also showed different methylation modifications. C methylation polymorphisms induced by salinity stress were present in both the promoter and coding regions of some of the 24 selected genes, but only the former were associated with changes in transcript abundance. The expression of both TaFLS1 (encoding a flavonol synthase) and TaWRSI5 (encoding a Bowman-Birk-type protease inhibitor), which showed both a different expression and a different DNA methylation level between SR3 and JN177, enhanced the salinity tolerance of Arabidopsis thaliana. C methylation changes appear to be a common component of the plant response to stress, and methylation changes triggered by somatic hybridization may contribute to the superior salinity tolerance of SR3.

A high throughput gas exchange screen for determining rates of photorespiration or regulation of C4 activity

Large-scale research programmes seeking to characterize the C4 pathway have a requirement for a simple, high throughput screen that quantifies photorespiratory activity in C3 and C4 model systems. At present, approaches rely on model-fitting to assimilatory responses (A/C i curves, PSII quantum yield) or real-time carbon isotope discrimination, which are complicated and time-consuming. Here we present a method, and the associated theory, to determine the effectiveness of the C4 carboxylation, carbon concentration mechanism (CCM) by assessing the responsiveness of V O/V C, the ratio of RuBisCO oxygenase to carboxylase activity, upon transfer to low O2. This determination compares concurrent gas exchange and pulse-modulated chlorophyll fluorescence under ambient and low O2, using widely available equipment. Run time for the procedure can take as little as 6 minutes if plants are pre-adapted. The responsiveness of V O/V C is derived for typical C3 (tobacco, rice, wheat) and C4 (maize, Miscanthus, cleome) plants, and compared with full C3 and C4 model systems. We also undertake sensitivity analyses to determine the impact of R LIGHT (respiration in the light) and the effectiveness of the light saturating pulse used by fluorescence systems. The results show that the method can readily resolve variations in photorespiratory activity between C3 and C4 plants and could be used to rapidly screen large numbers of mutants or transformants in high throughput studies.

Effects of modification and incorporation techniques on disintegrant properties of wheat (Triticum aestivum) starch in metronidazole tablet formulations

BACKGROUND

Natural polymers serve as cheap, non-toxic, biocompatible excipients in drug delivery.

OBJECTIVES

Starch from wheat (Triticum aestivum) was investigated as a disintegrant in metronidazole tablet formulations in comparison with sodium starch glycolate (SSG), a standard, synthetic but relatively more expensive disintegrant.

MATERIAL AND METHODS

Native wheat starch (NAS) was modified by pregelatinization (PGS) and microwave irradiation (MCW). The starches were characterized using swelling capacity, angle of repose, density measurements, Carr's index and Hausner's ratio. Metronidazole tablet formulations were made with the starches incorporated by intragranular (IG), extra-granular (EG) or intra/extragranular (IG/EG) methods. Tablet properties of crushing strength, disintegration time and dissolution tests were determined.

RESULTS

Native wheat starch had better hydration capacity than the modified starches, with PGS having a higher swelling capacity than the MCW. Modified starches formed better compacts than both NAS and SSG as indicated by the higher crushing strength of tablets containing modified starches. Intragranular incorporation gave a higher crushing strength than both EG and IG/EG methods. The ranking for disintegration time of tablets was IG/EG > IG > EG among the incorporation methods and SSG > PGS > MCW > NAS among the starches (EG > IG/EG). The difference between IG/EG and EG was significant (p < 0.05) but not significant between IG and other incorporation methods (MCW > SSG > PGS). Native and modified wheat starches exhibited better disintegrant properties than sodium starch glycolate in metronidazole tablet formulations.

CONCLUSIONS

The mode of disintegrant incorporation and modification of wheat starch had different effects on tablet properties of metronidazole formulations. The modification technique and method of disintegrant incorporation should be determined based on desired tablet properties.

Genetic analysis of biomass and photosynthetic parameters in wheat grown in different light intensities

Growth light intensities largely determine photosynthesis, biomass, and grain yield of cereal crops. To explore the genetic basis of light responses of biomass and photosynthetic parameters in wheat (Triticum aestivum L.), a quantitative trait locus (QTL) analysis was carried out in a doubled haploid (DH) population grown in low light (LL), medium light (ML), and high light (HL), respectively. The results showed that the wheat seedlings grown in HL produced more biomass with lower total chlorophyll content (Chl), carotenoid content, and maximum photochemical efficiency of photosystem II (Fv/Fm) while the wheat seedlings grown in LL produced less biomass with higher Chl compared with those grown in ML. In total, 48 QTLs were identified to be associated with the investigated parameters in relation to growth light intensities. These QTLs were mapped to 15 chromosomes which individually explained 6.3%-36.0% of the phenotypic variance, of which chromosomes 3A, 1D, and 6B were specifically involved in LL response, 5D and 7A specifically involved in ML response, and 4B specifically involved in HL response. Several light-responsive QTLs were co-located with QTLs for photosynthetic parameters, biomass, and grain weight under various conditions which may provide new hints to uncover the genetic control of photosynthesis, biomass, and grain weight.

100 Gy 60 Co γ-ray induced novel mutations in tetraploid wheat

10 accessions of tetraploid wheat were radiated with 100 Gy (60)Co γ -ray. The germination energy, germination rate, special characters (secondary tillering, stalk with wax powder, and dwarf), meiotic process, and high-molecular-weight glutenin subunits (HMW-GSs) were observed. Different species has different radiation sensibility. With 1 seed germinated (5%), T. dicoccum (PI434999) is the most sensitive to this dose of radiation. With a seed germination rate of 35% and 40%, this dose also affected T. polonicum (As304) and T. carthlicum (As293). Two mutant dwarf plants, T. turgidum (As2255) 253-10 and T. polonicum (As302) 224-14, were detected. Abnormal chromosome pairings were observed in pollen mother cells of both T. dicoccoides (As835) 237-9 and T. dicoccoides (As838) 239-8 with HMW-GS 1Ax silent in seeds from them. Compared with the unirradiated seed of T. polonicum (As304) CK, a novel HMW-GS was detected in seed of T. polonicum (As304) 230-7 and its electrophoretic mobility was between 1By8 and 1Dy12 which were the HMW-GSs of Chinese Spring. These mutant materials would be resources for wheat breeding.

Interactive effect of ultraviolet-B and mineral nutrients on accumulation and translocation of trace elements in wheat crop

Field study was conducted in two wheat cultivars (Triticum aestivum L. cv. HD 2329 and HUW 234) by supplimenting UV-B irradiation with different levels of mineral nutrients in order to evaluate the accumulation and translocation of trace elements. sUV-B significantly affected accumulation and translocation of most of the metals studied. Application of nutrients at higher doses enhanced the accumulation of trace elements in plants and grains of both cultivars. A higher dose of nutrient along with sUV-B resulted in increased accumulation of lead both in plants and grains, cadmium and chromium in grains, and copper in plants and decreased accumulation of cadmium in plants, copper in grains, chromium in plants and iron in plants and grains of both the tested cultivars. Nickel concentration increased in plants of HUW 234 due to simultaneous stress. Trace element concentration did not differ noticeably in the tested cultivars but the stress response differed perceptibly. Cultivar HD 2329 showed more significant interaction than HUW 234.

The transcriptional network of WRKY53 in cereals links oxidative responses to biotic and abiotic stress inputs

The transcription factor WRKY53 is expressed during biotic and abiotic stress responses in cereals, but little is currently known about its regulation, structure and downstream targets. We sequenced the wheat ortholog TaWRKY53 and its promoter region, which revealed extensive similarity in gene architecture and cis-acting regulatory elements to the rice ortholog OsWRKY53, including the presence of stress-responsive abscisic acid-responsive elements (ABRE) motifs and GCC-boxes. Four proteins interacted with the WRKY53 promoter in yeast one-hybrid assays, suggesting that this gene can receive inputs from diverse stress-related pathways such as calcium signalling and senescence, and environmental cues such as drought and ultraviolet radiation. The Ser/Thr receptor kinase ORK10/LRK10 and the apoplastic peroxidase POC1 are two downstream targets for regulation by the WRKY53 transcription factor, predicted based on the presence of W-box motifs in their promoters and coregulation with WRKY53, and verified by electrophoretic mobility shift assay (EMSA). Both ORK10/LRK10 and POC1 are upregulated during cereal responses to pathogens and aphids and important components of the oxidative burst during the hypersensitive response. Taken with our yeast two-hybrid assay which identified a strong protein-protein interaction between microsomal glutathione S-transferase 3 and WRKY53, this implies that the WRKY53 transcriptional network regulates oxidative responses to a wide array of stresses.

Pulsed light inactivation of naturally occurring moulds on wheat grain

BACKGROUND

Pulsed light (PL) is emerging as a non-thermal technology with excellent prospects for the decontamination of foods and food contact surfaces. Its application for mould inactivation on cereal grains would allow a reduction of storage losses as well as the prevention of mycotoxin contamination at a post-harvest level. The potential of PL for the decontamination of naturally occurring moulds on wheat grain was investigated in this study.

RESULTS

Treatments of up to 40 flashes of a fluence of 0.4 J cm⁻² per pulse were applied to both sides of the grain, with an overall energy release ranging from 6.4 to 51.2 J g⁻¹. The most powerful treatment applied to wheat in this study (51.2 J g⁻¹) resulted in a mould reduction of approximately 4 log cycles on samples displaying an initial mould contamination level of 2.2 × 10⁵ CFU g⁻¹. At the same time, the seed germination percentage was only slightly affected. For PL treatments causing an inactivation of 3-4 log cycles, only 14-15% of the germination power of the wheat seeds was lost.

CONCLUSION

The PL treatments attained greater microbial reductions for higher treatment times and lower initial mould loads. The absence of the UV portion of the radiation spectrum was found to significantly reduce the treatment effectiveness.

Biophysical controls on light response of net CO2 exchange in a winter wheat field in the North China Plain

To investigate the impacts of biophysical factors on light response of net ecosystem exchange (NEE), CO2 flux was measured using the eddy covariance technique in a winter wheat field in the North China Plain from 2003 to 2006. A rectangular hyperbolic function was used to describe NEE light response. Maximum photosynthetic capacity (P max) was 46.6 ± 4.0 µmol CO2 m(-2) s(-1) and initial light use efficiency (α) 0.059 ± 0.006 µmol µmol(-1) in April-May, two or three times as high as those in March. Stepwise multiple linear regressions showed that P max increased with the increase in leaf area index (LAI), canopy conductance (g c) and air temperature (T a) but declined with increasing vapor pressure deficit (VPD) (P<0.001). The factors influencing P max were sorted as LAI, g c, T a and VPD. α was proportional to ln(LAI), g c, T a and VPD (P<0.001). The effects of LAI, g c and T a on α were larger than that of VPD. When T a>25°C or VPD>1.1-1.3 kPa, NEE residual increased with the increase in T a and VPD (P<0.001), indicating that temperature and water stress occurred. When g c was more than 14 mm s(-1) in March and May and 26 mm s(-1) in April, the NEE residuals decline disappeared, or even turned into an increase in g c (P<0.01), implying shifts from stomatal limitation to non-stomatal limitation on NEE. Although the differences between sunny and cloudy sky conditions were unremarkable for light response parameters, simulated net CO2 uptake under the same radiation intensity averaged 18% higher in cloudy days than in sunny days during the year 2003-2006. It is necessary to include these effects in relevant carbon cycle models to improve our estimation of carbon balance at regional and global scales.

Early competition shapes maize whole-plant development in mixed stands

Mixed cropping is practised widely in developing countries and is gaining increasing interest for sustainable agriculture in developed countries. Plants in intercrops grow differently from plants in single crops, due to interspecific plant interactions, but adaptive plant morphological responses to competition in mixed stands have not been studied in detail. Here the maize (Zea mays) response to mixed cultivation with wheat (Triticum aestivum) is described. Evidence is provided that early responses of maize to the modified light environment in mixed stands propagate throughout maize development, resulting in different phenotypes compared with pure stands. Photosynthetically active radiation (PAR), red:far-red ratio (R:FR), leaf development, and final organ sizes of maize grown in three cultivation systems were compared: pure maize, an intercrop with a small distance (25cm) between maize and wheat plants, and an intercop with a large distance (44cm) between the maize and the wheat. Compared with maize in pure stands, maize in the mixed stands had lower leaf and collar appearance rates, increased blade and sheath lengths at low ranks and smaller sizes at high ranks, increased blade elongation duration, and decreased R:FR and PAR at the plant base during early development. Effects were strongest in the treatment with a short distance between wheat and maize strips. The data suggest a feedback between leaf initiation and leaf emergence at the plant level and coordination between blade and sheath growth at the phytomer level. A conceptual model, based on coordination rules, is proposed to explain the development of the maize plant in pure and mixed stands.

The Calvin cycle inevitably produces sugar-derived reactive carbonyl methylglyoxal during photosynthesis: a potential cause of plant diabetes

Sugar-derived reactive carbonyls (RCs), including methylglyoxal (MG), are aggressive by-products of oxidative stress known to impair the functions of multiple proteins. These advanced glycation end-products accumulate in patients with diabetes mellitus and cause major complications, including arteriosclerosis and cardiac insufficiency. In the glycolytic pathway, the equilibration reactions between dihydroxyacetone phosphate and glyceraldehyde 3-phosphate (GAP) have recently been shown to generate MG as a by-product. Because plants produce vast amounts of sugars and support the same reaction in the Calvin cycle, we hypothesized that MG also accumulates in chloroplasts. Incubating isolated chloroplasts with excess 3-phosphoglycerate (3-PGA) as the GAP precursor drove the equilibration reaction toward MG production. The rate of oxygen (O2) evolution was used as an index of 3-PGA-mediated photosynthesis. The 3-PGA- and time-dependent accumulation of MG in chloroplasts was confirmed by HPLC. In addition, MG production increased with an increase in light intensity. We also observed a positive linear relationship between the rates of MG production and O2 evolution (R = 0.88; P < 0.0001). These data provide evidence that MG is produced by the Calvin cycle and that sugar-derived RC production is inevitable during photosynthesis. Furthermore, we found that MG production is enhanced under high-CO2 conditions in illuminated wheat leaves.

Ultrasonic vibration-assisted pelleting of wheat straw: a predictive model for energy consumption using response surface methodology

Cellulosic biomass can be used as a feedstock for biofuel manufacturing. Pelleting of cellulosic biomass can increase its bulk density and thus improve its storability and reduce the feedstock transportation costs. Ultrasonic vibration-assisted (UV-A) pelleting can produce biomass pellets whose density is comparable to that processed by traditional pelleting methods (e.g. extruding, briquetting, and rolling). This study applied response surface methodology to the development of a predictive model for the energy consumption in UV-A pelleting of wheat straw. Effects of pelleting pressure, ultrasonic power, sieve size, and pellet weight were investigated. This study also optimized the process parameters to minimize the energy consumption in UV-A pelleting using response surface methodology. Optimal conditions to minimize the energy consumption were the following: ultrasonic power at 20%, sieve size at 4 mm, and pellet weight at 1g, and the minimum energy consumption was 2.54 Wh.

Photosynthetic electron transport and specific photoprotective responses in wheat leaves under drought stress

The photosynthetic responses of wheat (Triticum aestivum L.) leaves to different levels of drought stress were analyzed in potted plants cultivated in growth chamber under moderate light. Low-to-medium drought stress was induced by limiting irrigation, maintaining 20 % of soil water holding capacity for 14 days followed by 3 days without water supply to induce severe stress. Measurements of CO2 exchange and photosystem II (PSII) yield (by chlorophyll fluorescence) were followed by simultaneous measurements of yield of PSI (by P700 absorbance changes) and that of PSII. Drought stress gradually decreased PSII electron transport, but the capacity for nonphotochemical quenching increased more slowly until there was a large decrease in leaf relative water content (where the photosynthetic rate had decreased by half or more). We identified a substantial part of PSII electron transport, which was not used by carbon assimilation or by photorespiration, which clearly indicates activities of alternative electron sinks. Decreasing the fraction of light absorbed by PSII and increasing the fraction absorbed by PSI with increasing drought stress (rather than assuming equal absorption by the two photosystems) support a proposed function of PSI cyclic electron flow to generate a proton-motive force to activate nonphotochemical dissipation of energy, and it is consistent with the observed accumulation of oxidized P700 which causes a decrease in PSI electron acceptors. Our results support the roles of alternative electron sinks (either from PSII or PSI) and cyclic electron flow in photoprotection of PSII and PSI in drought stress conditions. In future studies on plant stress, analyses of the partitioning of absorbed energy between photosystems are needed for interpreting flux through linear electron flow, PSI cyclic electron flow, along with alternative electron sinks.

Long-term growth under elevated CO2 suppresses biotic stress genes in non-acclimated, but not cold-acclimated winter wheat

This study compared the photosynthetic performance and the global gene expression of the winter hardy wheat Triticum aestivum cv Norstar grown under non-acclimated (NA) or cold-acclimated (CA) conditions at either ambient CO2 or elevated CO2. CA Norstar maintained comparable light-saturated and CO2-saturated rates of photosynthesis but lower quantum requirements for PSII and non-photochemical quenching relative to NA plants even at elevated CO2. Neither NA nor CA plants were sensitive to feedback inhibition of photosynthesis at elevated CO2. Global gene expression using microarray combined with bioinformatics analysis revealed that genes affected by elevated CO2 were three times higher in NA (1,022 genes) compared with CA (372 genes) Norstar. The most striking effect was the down-regulation of genes involved in the plant defense responses in NA Norstar. In contrast, cold acclimation reversed this down-regulation due to the cold induction of genes involved in plant pathogenesis resistance; and cellular and chloroplast protection. These results suggest that elevated CO2 has less impact on plant performance and productivity in cold-adapted winter hardy plants in the northern climates compared with warmer environments. Selection for cereal cultivars with constitutively higher expression of biotic stress defense genes may be necessary under elevated CO2 during the warm growth period and in warmer climates.

Radiation hybrid QTL mapping of Tdes2 involved in the first meiotic division of wheat

Since the dawn of wheat cytogenetics, chromosome 3B has been known to harbor a gene(s) that, when removed, causes chromosome desynapsis and gametic sterility. The lack of natural genetic diversity for this gene(s) has prevented any attempt to fine map and further characterize it. Here, gamma radiation treatment was used to create artificial diversity for this locus. A total of 696 radiation hybrid lines were genotyped with a custom mini array of 140 DArT markers, selected to evenly span the whole 3B chromosome. The resulting map spanned 2,852 centi Ray with a calculated resolution of 0.384 Mb. Phenotyping for the occurrence of meiotic desynapsis was conducted by measuring the level of gametic sterility as seeds produced per spikelet and pollen viability at booting. Composite interval mapping revealed a single QTL with LOD of 16.2 and r (2) of 25.6 % between markers wmc326 and wPt-8983 on the long arm of chromosome 3B. By independent analysis, the location of the QTL was confirmed to be within the deletion bin 3BL7-0.63-1.00 and to correspond to a single gene located ~1.4 Mb away from wPt-8983. The meiotic behavior of lines lacking this gene was characterized cytogenetically to reveal striking similarities with mutants for the dy locus, located on the syntenic chromosome 3 of maize. This represents the first example to date of employing radiation hybrids for QTL analysis. The success achieved by this approach provides an ideal starting point for the final cloning of this interesting gene involved in meiosis of cereals.

Light saturated RuBP oxygenation by Rubisco is a robust predictor of light inhibition of respiration in Triticum aestivum L

Plant respiratory metabolism is complicated by the fact that the rate of non-photorespiratory mitochondrial CO2 release in the light (R light) may be lower than the rate of leaf respiration in the dark (R dark). A body of work on this topic implies a linkage between light inhibition of respiration and photorespiration, although the direction of effect and underlying mechanisms remain uncertain. In this study we used a variety of short- and long-term environmental manipulations to explicitly manipulate the rate of photorespiration (νo) and quantify the effect on the inhibition of mitochondrial respiration in the light (R light:R dark). We address the following three questions: (i) will the R light:R dark ratio increase or decrease with high CO2 or low O2 and at low temperatures; (ii) does νo correlate with R light:R dark, and if so, in what way; (iii) will suppression of respiration by light (the 'Kok effect') be seen to the same extent in Zea mays, a C4 plant, and in Triticum aestivum, a C3 plant? We found that Rlight :Rdark decreased under conditions that suppressed νo in wheat, and this resulted in a positive relationship between R light:R dark and νo. Inhibition of respiration by light in C4 maize did not respond to environmental treatment, and the fixed R light:R dark (0.46-0.72) was consistent with the wheat response, assuming a νo approaching zero. The most likely mechanism to explain this finding is that R light increases (or the inhibition of respiration by light decreases) when there is an increase in photorespiration and thus an increase in the demand for TCA cycle substrates associated with the recovery of photorespiratory cycle intermediates in the peroxisome. This work is significant because it combines a comparison of C3 and C4 metabolism with a range of environmental treatments to independently suppress νo.

Translocation of 125I, 75Se and 36Cl to wheat edible parts following wet foliar contamination under field conditions

Apart from radiocaesium and radiostrontium, there have been few studies on the foliar transfer of radionuclides in plants. Consequently, specific translocation factor (ftr) values for (129)I, (79)Se and (36)Cl are still missing from the IAEA reference databases. The translocation of short - lived isotopes, (125)I and (75)Se, and of (36)Cl to wheat grain were measured under field conditions following acute and chronic wet foliar contamination at various plant growth stages in the absence of leaching caused by rain. The translocation factors ranged from 0.02% to 1.1% for (125)I (a value similar to Sr), from 0.1% to 16.5% for (75)Se, and from 1% to 14.9% for (36)Cl. Both (36)Cl and (75)Se were as mobile as Cs. The phenomenological analysis showed that each element displayed a specific behavior. Iodide showed the lowest apparent mobility because of its preferential fixation in or on the leaves and a significant amount probably volatilized. Selenite internal transfer was significant and possibly utilized the sulphur metabolic pathway. However bio - methylation of selenite may have led to increased volatilization. Chloride was very mobile and quickly diffused throughout the plant. In addition, the analysis underlined the importance of plant growth responses to annual variations in weather conditions that can affect open field experiments because plant growth stage played a major role in ftr values dispersion. The chronic contamination results suggested that a series of acute contamination events had an additive effect on translocated elements. The highest translocation value obtained for an acute contamination event was shown to be a good conservative assessment of chronic contamination if data on chronic contamination translocation are lacking. The absence of rain leaching during the experiment meant that this investigation avoided potential radionuclide transfer by the roots, which also meant that radionuclide retention on or in the leaves was maximized. This study was therefore able to obtain accurate translocation factors, which are probably among the highest that could be recorded.

Will intra-specific differences in transpiration efficiency in wheat be maintained in a high CO₂ world? A FACE study

This study evaluates whether the target breeding trait of superior leaf level transpiration efficiency is still appropriate under increasing carbon dioxide levels of a future climate using a semi-arid cropping system as a model. Specifically, we investigated whether physiological traits governing leaf level transpiration efficiency, such as net assimilation rates (A(net)), stomatal conductance (g(s)) or stomatal sensitivity were affected differently between two Triticum aestivum L. cultivars differing in transpiration efficiency (cv. Drysdale, superior; cv. Hartog, low). Plants were grown under Free Air Carbon dioxide Enrichment (FACE, approximately 550 µmol mol⁻¹ or ambient CO₂ concentrations (approximately 390 µmol mol⁻¹). Mean A(net) (approximately 15% increase) and gs (approximately 25% decrease) were less affected by elevated [CO₂] than previously found in FACE-grown wheat (approximately 25% increase and approximately 32% decrease, respectively), potentially reflecting growth in a dry-land cropping system. In contrast to previous FACE studies, analyses of the Ball et al. model revealed an elevated [CO₂] effect on the slope of the linear regression by 12% indicating a decrease in stomatal sensitivity to the combination of [CO₂], photosynthesis rate and humidity. Differences between cultivars indicated greater transpiration efficiency for Drysdale with growth under elevated [CO₂] potentially increasing the response of this trait. This knowledge adds valuable information for crop germplasm improvement for future climates.

Effects of selenium on agronomical characters of winter wheat exposed to enhanced ultraviolet-B

Enhanced ultraviolet-B (UV-B) is one of the most important abiotic stress factors that can influence almost every aspect of plant. Selenium (Se) can increase the tolerance of plants to stressful environment. The paper mainly reported the effects of enhanced UV-B, Se supply and their combination on agronomical characters of winter wheat under field conditions. Enhanced UV-B caused a marked decrease in chlorophyll content, plant height, spike length, weight per spike, grain yield and protein content, grain nitrogen (N) and iron (Fe) concentration, and increased hydrogen peroxide (H2O2), malondialdehyde (MDA) and proline content, and grain zinc (Zn) and manganese (Mn) concentration under without supplemental Se supply. However, it also decreased plant height, spike length, weight per spike, grain yield and Fe concentration, and increased H2O2 content, grain potassium (K), Zn and Mn concentration under supplemental Se supply. On the other hand, Se supply induced an evident increase in chlorophyll content, spike length, weight per spike, grain yield, grain protein content, grain N, Fe, copper (Cu), and Se concentration under both UV-B levels. Moreover, significant UV-B×Se interaction was found on plant height, chlorophyll, MDA, H2O2 and proline content, and grain protein, N, K, Cu and Mn concentrations in wheat. The obtained results supported the hypothesis that Se supply increased the yield and improved the quality of winter wheat exposed to enhanced UV-B to some extent.

High irradiance improves ammonium tolerance in wheat plants by increasing N assimilation

Ammonium is a paradoxical nutrient ion. Despite being a common intermediate in plant metabolism whose oxidation state eliminates the need for its reduction in the plant cell, as occurs with nitrate, it can also result in toxicity symptoms. Several authors have reported that carbon enrichment in the root zone enhances the synthesis of carbon skeletons and, accordingly, increases the capacity for ammonium assimilation. In this work, we examined the hypothesis that increasing the photosynthetic photon flux density is a way to increase plant ammonium tolerance. Wheat plants were grown in a hydroponic system with two different N sources (10mM nitrate or 10mM ammonium) and with two different light intensity conditions (300 μmol photon m(-2)s(-1) and 700 μmol photon m(-2)s(-1)). The results show that, with respect to biomass yield, photosynthetic rate, shoot:root ratio and the root N isotopic signature, wheat behaves as a sensitive species to ammonium nutrition at the low light intensity, while at the high intensity, its tolerance is improved. This improvement is a consequence of a higher ammonium assimilation rate, as reflected by the higher amounts of amino acids and protein accumulated mainly in the roots, which was supported by higher tricarboxylic acid cycle activity. Glutamate dehydrogenase was a key root enzyme involved in the tolerance to ammonium, while glutamine synthetase activity was low and might not be enough for its assimilation.

Ingestion dose from 238U, 232Th, 226Ra, 40K and 137Cs in cereals, pulses and drinking water to adult population in a high background radiation area, Odisha, India

A natural high background radiation area is located in Chhatrapur, Odisha in the eastern part of India. The inhabitants of this area are exposed to external radiation levels higher than the global average background values, due to the presence of uranium, thorium and its decay products in the monazite sands bearing placer deposits in its beaches. The concentrations of (232)Th, (238)U, (226)Ra, (40)K and (137)Cs were determined in cereals (rice and wheat), pulses and drinking water consumed by the population residing around this region and the corresponding annual ingestion dose was calculated. The annual ingestion doses from cereals, pulses and drinking water varied in the range of 109.4-936.8, 10.2-307.5 and 0.5-2.8 µSv y(-1), respectively. The estimated total annual average effective dose due to the ingestion of these radionuclides in cereals, pulses and drinking water was 530 µSv y(-1). The ingestion dose from cereals was the highest mainly due to a high consumption rate. The highest contribution of dose was found to be from (226)Ra for cereals and drinking water and (40)K was the major dose contributor from the intake of pulses. The contribution of man-made radionuclide (137)Cs to the total dose was found to be minimum. (226)Ra was found to be the largest contributor to ingestion dose from all sources.

[Study of the effects of gamma-irradiation of common wheat F1 seeds using gliadins as genetic markers]

Effects of irradiation of dry F1 seeds with gamma rays in the dose of 200 Gy were studied. Hybrids between near-isogenic lines on the basis of the variety Bezostaya 1 served as the material of investigation. Irradiation markedly reduced productivity traits of F1 plants and did not affect the survival of F1 plants under the given growth conditions. A significant relative increase in the frequency of pollen grains with the 1BL/1RS translocation that formed F2 seeds in comparison with the control was one of the effects of irradiation of F1 seeds. Irradiation with gamma-rays induced mutations at gliadin loci with the frequency of 7,4 % (at 0,5 % in the control).

Dominance of a 675 nm chlorophyll(ide) form upon selective 632.8 or 654 nm laser illumination after partial protochlorophyllide phototransformation

The phototransformation pathways of protochlorophyllide forms were studied in 8-14-day-old leaves of dark-germinated wheat (Triticum aestivum L.) using white, 632.8 nm He-Ne laser and 654 nm laser diode light. The photon flux density (PFD) values (0.75-360 μmol photons m(-2) s(-1)), the illumination periods (20 ms-10 s) and the temperature of the leaves (between -60 °C and room temperature) were varied. The 77 K fluorescence spectra of partially phototransformed leaves showed gradual accumulation or even the dominance of the 675 nm emitting chlorophyllide or chlorophyll form at room temperature with 632.8 nm of PFD less than 200 μmol photons m(-2) s(-1) or with 654 nm of low PFD (7.5 μmol photons m(-2) s(-1)) up to 1 s. Longer wavelength (685 or 690 nm) emitting chlorophyllide forms appeared at illuminations under -25 °C with both laser lights or at room temperature when the PFD values were higher or the illumination period was longer than above. We concluded that the formation of the 675 nm emitting chlorophyllide form does not indicate the direct photoactivity of the 633 nm emitting protochlorophyllide form; it can derive from 644 and 657 nm forms via instantaneous disaggregation of the newly-produced chlorophyllide complexes. The disaggregation is strongly influenced by the molecular environment and the localization of the complex.

Acclimation of leaf nitrogen to vertical light gradient at anthesis in wheat is a whole-plant process that scales with the size of the canopy

Vertical leaf nitrogen (N) gradient within a canopy is classically considered as a key adaptation to the local light environment that would tend to maximize canopy photosynthesis. We studied the vertical leaf N gradient with respect to the light gradient for wheat (Triticum aestivum) canopies with the aims of quantifying its modulation by crop N status and genetic variability and analyzing its ecophysiological determinants. The vertical distribution of leaf N and light was analyzed at anthesis for 16 cultivars grown in the field in two consecutive seasons under two levels of N. The N extinction coefficient with respect to light (b) varied with N supply and cultivar. Interestingly, a scaling relationship was observed between b and the size of the canopy for all the cultivars in the different environmental conditions. The scaling coefficient of the b-green area index relationship differed among cultivars, suggesting that cultivars could be more or less adapted to low-productivity environments. We conclude that the acclimation of the leaf N gradient to the light gradient is a whole-plant process that depends on canopy size. This study demonstrates that modeling leaf N distribution and canopy expansion based on the assumption that leaf N distribution parallels that of the light is inappropriate. We provide a robust relationship accounting for vertical leaf N gradient with respect to vertical light gradient as a function of canopy size.

Achieving yield gains in wheat

Wheat provides 20% of calories and protein consumed by humans. Recent genetic gains are <1% per annum (p.a.), insufficient to meet future demand. The Wheat Yield Consortium brings expertise in photosynthesis, crop adaptation and genetics to a common breeding platform. Theory suggest radiation use efficiency (RUE) of wheat could be increased ~50%; strategies include modifying specificity, catalytic rate and regulation of Rubisco, up-regulating Calvin cycle enzymes, introducing chloroplast CO(2) concentrating mechanisms, optimizing light and N distribution of canopies while minimizing photoinhibition, and increasing spike photosynthesis. Maximum yield expression will also require dynamic optimization of source: sink so that dry matter partitioning to reproductive structures is not at the cost of the roots, stems and leaves needed to maintain physiological and structural integrity. Crop development should favour spike fertility to maximize harvest index so phenology must be tailored to different photoperiods, and sensitivity to unpredictable weather must be modulated to reduce conservative responses that reduce harvest index. Strategic crossing of complementary physiological traits will be augmented with wide crossing, while genome-wide selection and high throughput phenotyping and genotyping will increase efficiency of progeny screening. To ensure investment in breeding achieves agronomic impact, sustainable crop management must also be promoted through crop improvement networks.

Down-regulation of Glucan, Water-Dikinase activity in wheat endosperm increases vegetative biomass and yield

A novel mechanism for increasing vegetative biomass and grain yield has been identified in wheat (Triticum aestivum). RNAi-mediated down-regulation of Glucan, Water-Dikinase (GWD), the primary enzyme required for starch phosphorylation, under the control of an endosperm-specific promoter, resulted in a decrease in starch phosphate content and an increase in grain size. Unexpectedly, consistent increases in vegetative biomass and grain yield were observed in subsequent generations. In lines where GWD expression was decreased, germination rate was slightly reduced. However, significant increases in vegetative growth from the two leaf stage were observed. In glasshouse pot trials, down-regulation of GWD led to a 29% increase in grain yield while in glasshouse tub trials simulating field row spacing and canopy development, GWD down-regulation resulted in a grain yield increase of 26%. The enhanced yield resulted from a combination of increases in seed weight, tiller number, spikelets per head and seed number per spike. In field trials, all vegetative phenotypes were reproduced with the exception of increased tiller number. The expression of the transgene and suppression of endogenous GWD RNA levels were demonstrated to be grain specific. In addition to the direct effects of GWD down-regulation, an increased level of α-amylase activity was present in the aleurone layer during grain maturation. These findings provide a potentially important novel mechanism to increase biomass and grain yield in crop improvement programmes.

Damage repair effect of He-Ne laser on wheat exposed to enhanced ultraviolet-B radiation

We explored the use of He-Ne laser on alleviating the effects of ultraviolet-B (UV-B) light on winter wheat development. Triticum aestivum L. cv. Linyuan 077038 seeds were irradiated with either UV-B (10.08 kJ m(-2) d(-1)) (enhanced UV-B) or a combination of UV-B light and the He-Ne laser (5.43 mW mm(-2)). Plants also were exposed to the He-Ne laser alone. Our results showed that enhanced UV-B produced negative effects on seed germination and seedling development. Germination rate and shoot growth decreased compared with the control. Root development was inhibited, and root length was decreased. Chlorophyll content and expression of peroxidase (POD) isozymes and their activity decreased. Seedling height and shoot biomass dropped significantly compared to the control. Implementing the He-Ne laser partially alleviated the injury of enhanced UV-B radiation, because germination rate and shoot growth were enhanced together with root development. Chlorophyll content and POD expression and activity increased. Seedling height and shoot biomass were increased. Furthermore, the use of the He-Ne laser alone showed a favorable effect on seedling growth compared with the control.

Contrasting responses of salinity-stressed salt-tolerant and intolerant winter wheat (Triticum aestivum L.) cultivars to ozone pollution

Contrasting winter wheat cultivars, salt-tolerant DK961 and intolerant JN17, which sown in no salinity (-S) and salinity (+S) boxes were exposed to charcoal filtered air (CF) and elevated O(3) (+O(3)) in open top chambers (OTCs) for 30 days. In -S DK961 and JN17 plants, +O(3) DK961 and JN17 plants had significantly lower light-saturated net photosynthetic rates (A(sat), 26% and 24%), stomatal conductance (g(s), 20% and 32%) and chlorophyll contents (10% and 21%), while O(3) considerably increased foliar electrolyte leakage (13% and 39%), malondialdehyde content (9% and 23%), POD activity and ABA content. However, responses of these parameters to O(3) were significant in DK961 but not in JN17 in +S treatment. Correlation coefficient of DK961 reached significance level of 0.01, but it was not significant in JN17 under interaction of O(3) and salinity. O(3)-induced reductions were larger in shoot than in root in both cultivars. Results indicate that the salt-tolerant cultivar sustained less damage from salinity than did the intolerant cultivar but was severely injured by O(3) under +S condition. Therefore, selecting for greater salt tolerance may not lead to the expected gains in yield in areas of moderate (100 mM) salinity when O(3) is present in high concentrations. In contrast, salinity-induced stomatal closure effectively reduced sensitivity to O(3) in the salt-intolerant cultivar. Hence we suggest salt-tolerant winter wheat cultivars might be well adapted to areas of high (>100 mM) salinity and O(3) stress, while intolerant cultivars might be adaptable to areas of mild/moderate salinity but high O(3) pollution.

A microwave reactor for characterization of pyrolyzed biomass

A microwave reactor (MWR) was designed to investigate microwave-induced pyrolysis of biomass. Condensation of tars on the quartz reactor and the pipelines was prevented by an electric heating device, and a temperature control function allowed determination of product characteristics at constant temperatures. Temperature had an important influence on microwave pyrolysis; the yields of gas products increased from 17.69 wt.% to 22.27 wt.% and the ratio of combustible gas to total gas products increased from 67.21 vol.% to 77.14 vol.% as the temperature increased from 400 °C to 600 °C. A large number of volatiles was released as temperature increased, resulting in an increase in the number of pores of the coke and a uniform pore structure was obtained. The specific surface area of coke increased from 0.89 m(2)/g (400 °C) to 9.81m(2)/g (600 °C) and the pore volume increased from 0.006 cm(3)/g (400 °C) to 0.012 cm(3)/g (600 °C), but the average pore size decreased from 282.16 nm (400 °C) to 46.64 nm (600 °C).

60Co-γ radiation induces differential acetylation and phosphorylation of histones H3 and H4 in wheat

Histone modifications occur during DNA damage and repair in eukaryotes. These modifications were analysed in wheat seedlings exposed to (60) Co-γ radiation. Seedling height was not significantly affected in the first 2 days after irradiation up to 150 Gy. Subsequently, in the next 2 weeks, there was 30-40% reduction in seedling height, indicating that there were late effects of irradiation. The histones isolated from irradiated seedlings were analysed in the initial stages for modifications of H3 and H4 using antibodies. Global acetylation of H3 decreased and H4 increased in a dose-dependent manner till 100 Gy. The time course of individual modifications showed that for H3K4 and H3K9, acetylation decreased, whereas for H3S10 phosphorylation increased. There were fluctuations in acetylation of H4K5, H4K12 and H4K16, whereas H4K8 showed hyper-acetylation. The results indicate that γ radiation induced DNA damage and repair in wheat seedlings and initiated differential acetylation of H3 and H4. This is the first report in plants on site-specific H3 and H4 modifications in response to exposure to ionizing radiation.

The xanthophyll cycle and antioxidative defense system are enhanced in the wheat hybrid subjected to high light stress

Although the wheat hybrids have often shown higher grain yields, the physiological basis of the higher yields remains unknown. Previous studies suggest that tolerance to photoinhibition in the hybrid may be one of the physiological bases (Yang et al., 2006, Plant Sci 171:389-97). The objective of this study was to further investigate the possible mechanism responsible for tolerance to photoinhibition in the hybrid. Photosystem II (PSII) photochemistry, the xanthophyll cycle, and antioxidative defense system were compared between the hybrid and its parents subjected to high light stress (1500μmolm(-2)s(-1)). The analyses of oxygen-evolving activity, chlorophyll fluorescence, and protein blotting demonstrated that the higher tolerance in the hybrid than in its parents was associated with its higher tolerance of PSII to photoinhibition. High light induced an increase in non-photochemical quenching, and this increase was greater in the hybrid than in its parents. There were no differences in the pool size of the xanthophyll cycle between the hybrid and its parents. The content of violaxanthin decreased significantly, whereas the content of zeaxanthin+antherxanthin increased considerably during high light treatments. However, the decrease in violaxanthin content and the increase in zeaxanthin+antherxanthin content were greater in the hybrid than in its parents. High light resulted in a significant accumulation of H(2)O(2), O(2)(-) and catalytic Fe, and this accumulation was less in the hybrid than in its parents. High light induced a significant increase in the activities of superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase, dehydroascorbate reductase, and monodehydroascorbate reductase, and these increases were greater in the hybrid than its parents. These results suggest that the higher tolerance to photoinhibition in the hybrid may be associated with its higher capacity for antioxidative defense metabolism and the xanthophyll cycle.

Silicon improves the tolerance of wheat seedlings to ultraviolet-B stress

Enhanced ultraviolet-B (UV-B) irradiation is one of the most important abiotic stresses that could influence the growth and physiological traits of plants. In this work, we reported the effects of silicon on the growth and physiological characteristics of wheat seedlings (Triticum aestivum L. cv Hengmai5229) subject to UV-B stress. Treatments with silicon significantly increased total biomass and chlorophyll (a + b) content, and reduced malondialdehyde (MDA) content and the rate of superoxide radical (O(2) (-) ) production in wheat seedlings subjected to UV-B stress. Silicon treatments also induced an increased in soluble sugar, anthocyanins, and flavonoid content. Leaf silicon concentration increased with the increasing of silicon supply to soil. Positive correlations were found in leaf silicon concentration with total biomass, chlorophyll (a + b), proline, and soluble protein content, respectively. MDA content and the rate of O(2)(-) production were negatively correlated with leaf silicon concentration in seedlings. The results demonstrated that silicon alleviated the damage caused by UV-B on wheat seedlings to some extent by the increase in antioxidant compounds content and leaf silicon concentration.

Wheat floret survival as related to pre-anthesis spike growth

Further improvements to wheat yield potential will be essential to meet future food demand. As yield is related to the number of fertile florets and grains, an understanding of the basis of their generation is instrumental to raising yield. Based on (i) a strong positive association between the number of fertile florets or grains and spike dry weight at anthesis; and (ii) the finding that floret death occurs when spikes grow at maximum rate, it was always assumed that floret survival depends on the growth of the spike. However, this assumption was recently questioned, suggesting that assimilates diverted to the spike do not determine the number of florets and grains and that the onset of floret death may instead be a developmental process that is not associated with spike growth. In this study, the relationships between the fate of floret primordia and spike growth from six independent experiments that included different growing conditions (greenhouse/field experiments, growing seasons, photoperiod/shading treatments during the floret primordia phase) and diverse cultivar types (winter/spring, semi-dwarf/standard-height, photoperiod sensitive/insensitive) were re-analysed together. Onset of floret death was associated with the beginning of spike growth at the maximum rate in c. 80% of the cases analysed; and the rate of floret death (the main determinant of floret survival) showed a negative quantitative relationship with spike weight at anthesis. As floret death and survival were shown to be linked to pre-anthesis spike growth, the strategy of focusing on traits associated with pre-anthesis spike growth when breeding to increase wheat yield potential further is valuable.

Ttd1a promoter is involved in DNA-protein binding by salt and light stresses

Stress modulation of retrotransposons may play a role in generating host genetic plasticity in response to environmental stress. Transposable elements have been suggested to contribute to the evolution of genes, by providing cis-regulatory elements leading to changes in expression patterns. Indeed, their promoter elements are similar to those of plant defence genes and may bind similar defence-induced transcription factors. We previously isolated a new Ty1-copia retrontrasposon named Ttd1a and showed its activation and mobilization in salt and light stresses. Here, using a retard mobility assay in Triticum durum L. crude extracts, we showed that the CAAT motif present in the Ttd1a retrotransposon promoter, is involved in DNA-protein binding under salt and light stresses and therefore in the regulation of Ttd1a activity. Data presented in this paper suggest that nuclear proteins can interact with the CAAT motif either directly or indirectly and enhance Ttd1a by a specific ligand-dependent activation under stress.

[The chiral mutagens: cytogenetic effects on higher plants]

The paper covers investigation of cytogenetic activity of chiral mutagens and their specific effects on the plant cells chromosomes of soft winter wheat (Triticum aestivum L.). Comparative analysis of cytogenetic activity of chiral NEU: S(+)1-N-nitroso- 1-N-methyl-3-N-sec-buthylureas (S(+)NMsBU) and R(-)1-N-nitroso- 1N-methyl-3-Nsec-buthylureas (R(-)NMsBU) on winter wheat was performed. As it was shown by the frequency of chromosomal aberrations the S(+) stereoisomer was twice more active than R(-). In addition to typical anaphase aberrations (fragments, bridges, lagging chromosomes) the numerous mitosis pathologies were revealed - K-mitoses, hyperspiralization and despiralization of chromosomes, unequal allocation of chromosomes between the daughter nuclei, mass fragmentation, nondisjunction and chromosome adhesion, three-pole mitoses, etc. Neither of the mentioned pathologies was observed under the action of NEU and gamma-rays.

[Effects of reduced solar radiation on winter wheat flag leaf net photosynthetic rate]

Taking winter wheat Triticum aestivum L. (cv. Yangmai 13) as test material, a field experiment was conducted in Nanjing City to study the effects of simulated reduced solar radiation on the diurnal variation of winter wheat flag leaf photosynthetic rate and the main affecting factors. Five treatments were installed, i. e., 15% (T15), 20% (T20) , 40% (T40), 60% (T60), and 100% (CK) of total incident solar radiation. Reduced solar irradiance increased the chlorophyll and lutein contents significantly, but decreased the net photosynthetic rate (Pn). Under different solar irradiance, the diurnal variation of Pn had greater difference, and the daily maximum Pn was in the order of CK > T60 > T40 > T 20 > T15. In CK, the Pn exhibited a double peak diurnal curve; while in the other four treatments, the Pn showed a single peak curve, and the peak was lagged behind that of CK. Correlation analysis showed that reduced solar irradiance was the main factor affecting the diurnal variation of Pn, but the physiological parameters also played important roles in determining the diurnal variation of Pn. In treatments T60 and T40, the photosynthesis active radiation (PAR), leaf temperature (T1) , stomatal conductance (Gs) , and transpiration rate (Tr) were significantly positively correlated with Pn, suggesting their positive effects on Pn. The intercellular CO2 concentration (Ci) and stomatal limitation (Ls) had significant negative correlations with Pn in treatments T60 and T40 but significant positive correlations with Pn in treatments T20 and T15, implying that the Ci and Ls had negative (or positive) effects on Pn when the solar irradiance was higher (or lower) than 40% of incident solar irradiance.

Microwave pretreatment can enhance tolerance of wheat seedlings to CdCl2 stress

In order to determine the role of microwave in cadmium stress tolerance of wheat (Triticum aestivum L.), seeds were exposed to microwave radiation for 0, 5, 10 and 15 s (wavelength 125 mm, power density 126 mW cm(-2), 2450 MHz), and when the seedlings were 7 d old (with one fully expanded leaves), they were treated with 150 μM CdCl(2) solution for 10 d. Changes in a number of physiological and biochemical characteristics were measured and used as indicators of the protective capacity of microwave radiation in this experiment. Our results showed that 150 μM CdCl(2) treatment reduced plant height, root length, dry weight, AsA and GSH concentration and the activities of SOD, POD, CAT and APX, enhanced the concentration of MDA, H(2)O(2) and the production rate of O(2)- when compared with the control. However, seeds with microwave pretreatment 5 or 10 s conferred tolerance to cadmium stress in wheat seedlings by decreasing the concentration of MDA and H(2)O(2), the production rate of O(2)- and increasing the activities of SOD, POD, CAT, APX and AsA and GSH concentration. Therefore, antioxidative enzymes and antioxidative compounds may participate in tolerance of wheat seedlings to cadmium stress. The results also showed that the microwave radiation had a positive physiological effect on the growth and development of cadmium stressed seedlings. This is the first investigation reporting the use of microwave pretreatment to enhance cadmium stress tolerance of wheat.

Responses of wheat roots to exogenous selenium supply under enhanced ultraviolet-B

Effects of selenium (Se) on growth and some physiological traits of roots in wheat (Triticum aestivum L. cv Han NO.7086) seedlings exposed to enhanced ultraviolet-B (UV-B) stress are reported. Responses of roots were different depending on the Se concentration. Compared with the control, root weight of wheat seedlings treated with 1.0 and 2.0 mg Se kg(-1) soil increased by 39.47% and 16.28%, respectively. The lower amount Se (0.5 mg kg(-1)) and the higher amount Se treatments (3.0 mg kg(-1)) did not significantly affect on root weight. Se treatments significantly increased root activity, flavonoids and proline content, and activities of peroxidase and superoxide dismutase in wheat roots exposed to enhanced UV-B. In addition, the treatments with 0.5, 1.0, and 2.0 mg Se kg(-1) significantly reduced malondialdehyde content and the rate of superoxide radical (O2(-) ) production of roots, whereas the higher amount Se treatment only induced a decrease in the rate of O2(-) production. The results of this study demonstrated that optimal Se supply promoted roots growth of wheat seedlings, and that optimal Se supply could reduce oxidative stress in wheat roots under enhanced UV-B radiation.