Involvement of hydrogen peroxide in the regulation of senescence in pear

Assessing of growth, antioxidant enzymes, and phytohormone regulation in Cucurbita pepo under cadmium stress

One of the major problems worldwide is soil pollution by trace metal elements, which limits plant productivity and threatens human health. In this work, we have studied the effect of different concentrations of cadmium on Cucurbita pepo plants, evaluating different physiological and biochemical parameters: hormone signaling, metabolite concentration (malondialdehyde and hydrogen peroxide) and, in addition, the antioxidant enzyme activities of catalase and superoxide dismutase were evaluated. The production of biomass decreased under the Cd-stress. The results showed that C. pepo accumulates higher amounts of Cd2+ in roots than in shoots and fruits. Cd2+ differently affected the content of endogenous phytohormones. Furthermore, data suggest an essential involvement of roots in the regulation of tolerance to trace elements. As a result, indole acetic acid content increased in roots of treated plants, indicating that this phytohormone can stimulate root promotion and growth under Cd-stress. Similarly, salicylic acid content in roots and shoots increased in response to Cd2+, as well as abscisic acid levels in roots and fruits. In roots, the rambling accumulation pattern observed for jasmonic acid and salicylic acid suggests the lack of a specific regulation role against trace element toxicity. The activity of catalase and superoxide dismutase decreased, disrupted by the metal stress. However, the proline, malondialdehyde and hydrogen peroxide content significantly increased in Cd2+in all the analyzed tissues of the stressed plants. All these data suggest that C. pepo plants are equipped with an effective antioxidant mechanism against oxidative stress induced by cadmium up to a concentration of 500 μM.

Glycinebetaine mitigated the photoinhibition of photosystem II at high temperature in transgenic tomato plants

Photosystem II (PSII), especially the D1 protein, is highly sensitive to the detrimental impact of heat stress. Photoinhibition always occurs when the rate of photodamage exceeds the rate of D1 protein repair. Here, genetically engineered codA-tomato with the capability to accumulate glycinebetaine (GB) was established. After photoinhibition treatment at high temperature, the transgenic lines displayed more thermotolerance to heat-induced photoinhibition than the control line. GB maintained high expression of LeFtsHs and LeDegs and degraded the damaged D1 protein in time. Meanwhile, the increased transcription of synthesis-related genes accelerated the de novo synthesis of D1 protein. Low ROS accumulation reduced the inhibition of D1 protein translation in the transgenic plants, thereby reducing protein damage. The increased D1 protein content and decreased phosphorylated D1 protein (pD1) in the transgenic plants compared with control plants imply that GB may minimize photodamage and maximize D1 protein stability. As D1 protein exhibits a high turnover, PSII maybe repaired rapidly and efficiently in transgenic plants under photoinhibition treatment at high temperature, with the resultant mitigation of photoinhibition of PSII.

Dynamic Responses of Ascorbate Pool and Metabolism in Lettuce to Light Intensity at Night Time under Continuous Light Provided by Red and Blue LEDs

To understand the dynamic changes of hydroponic lettuce growth, ascorbate (AsA) pool and metabolism under two different dark period light intensities (LL, 20 μmol·m-2·s-1; CL, 200 μmol·m-2·s-1) of continuous light and normal light (NL, 0 μmol·m-2·s-1) provided by red (R) and blue (B) LEDs, the chlorophyll fluorescence parameters, ascorbate pool size, AsA metabolism-related enzyme activities, and H2O2 contents of lettuce were measured at 0, 8, 16, 24, 32, 40, 48, 56, 64, and 72 h after light treatment and the lettuce growth parameters were measured on the 9th day after light treatment. The results showed that compared with the NL, CL treatment for 9 days significantly increased the biomass, dry matter content, and specific leaf weight of lettuce, but had no significant effect on the leaf area and root-to-shoot ratio; LL had no significant effect on lettuce biomass, but it would reduce the root-shoot ratio. Compared with the NL, the AsA content of CL increased significantly within 8 h after light treatment (at the end of first dark period), and then maintained at a relatively stable level with a slight increase; there was no significant difference in AsA contents between NL and LL showing the same circadian rhythm characteristics. Overall, the activities of L-galactono-1,4-lactone dehydrogenase (GalLDH), ascorbate peroxidase(APX), monodehydroascorbate reductase (MDHAR), and glutathione reductase (GR) under CL were the highest among the three treatments, and the differences with the other two treatments reached significant levels at several time points; there was almost no significant difference in the activities of GalLDH, APX, MDHAR, and GR between NL and LL; there was no significant difference in the activities of dehydroascorbate reductase (DHAR) under different treatments. Compared with the NL, CL caused a sharp decrease of PSⅡ maximal photochemical efficiency (Fv/Fm) in lettuce within 0-8 h after treatment, which then stabilized at a relatively stable level; the Fv/Fm value under the LL was almost the same as the NL. Except for 32 h, the H2O2 content of lettuce under CL was the highest among the three treatments during the entire experimental period, and was significantly higher than that of NL at several time points; the H2O2 content of LL was almost the same as NL. In summary, lettuce biomass, AsA contents, AsA metabolism-related enzyme activities, chlorophyll fluorescence parameters, and H2O2 contents were regulated by the dark period light intensities of continuous light rather than continuous light signals.

Involvement of the Mitochondrial Protein Tyrosine Phosphatase PTPM1 in the Promotion of Conidiation, Development, and Pathogenicity in Colletotrichum graminicola

The phosphorylation status of proteins, which is determined by protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs), governs many cellular actions. In fungal pathogens, phosphorylation-mediated signal transduction has been considered to be one of the most important mechanisms in pathogenicity. Colletotrichum graminicola is an economically important corn pathogen. However, whether phosphorylation is involved in its pathogenicity is unknown. A mitochondrial protein tyrosine phosphatase gene, designated CgPTPM1, was deduced in C. graminicola through the use of bioinformatics and confirmed by enzyme activity assays and observation of its subcellular localization. We then created a CgPTPM1 deletion mutant (ΔCgPTPM1) to analyze its biological function. The results indicated that the loss of CgPTPM1 dramatically affected the formation of conidia and the development and differentiation into appressoria. However, the colony growth and conidial morphology of the ΔCgPTPM1 strains were unaffected. Importantly, the ΔCgPTPM1 mutant strains exhibited an obvious reduction of virulence, and the delayed infected hyphae failed to expand in the host cells. In comparison with the wild-type, ΔCgPTPM1 accumulated a larger amount of H2O2 and was sensitive to exogenous H2O2. Interestingly, the host cells infected by the mutant also exhibited an increased accumulation of H2O2 around the infection sites. Since the expression of the CgHYR1, CgGST1, CgGLR1, CgGSH1 and CgPAP1 genes was upregulated with the H2O2 treatment, our results suggest that the mitochondrial protein tyrosine phosphatase PTPM1 plays an essential role in promoting the pathogenicity of C. graminicola by regulating the excessive in vivo and in vitro production of H2O2.

Reticine A, a new potent natural elicitor: isolation from the fruit peel of Citrus reticulate and induction of systemic resistance against tobacco mosaic virus and other plant fungal diseases

BACKGROUND

Systemic acquired resistance (SAR) induced by elicitors is a highly satisfying form of resistance that protects plants against invading pathogens. Exploration and development of new elicitors is a promising alternative to conventional biocides in resistant pest management. In our previous broad screening, fruit peel extract of Citrus reticulata Blanco exhibited the ability to induce SAR in tobacco.

RESULT

A new potent elicitor reticine A was isolated from the fruit peel extract of industrial crop C. reticulate and its structure was well elucidated. In vivo assays showed that reticine A had considerable control efficacies at 100 and 500 μg mL-1 , being superior to commercial elicitor benzothiadiazole (BTH) (100 μg mL-1 ). Reticine A had no significant impact on the virulence of tobacco mosaic virus (TMV) particles under in vitro conditions. Application of reticine A induced a local hypersensitive reaction (HR), systemic accumulation of H2 O2 and salicylic acid (SA), systemic increase in defensive enzyme activities and systemic upregulated expression of pathogenesis-related (PR) proteins, suggesting its induction of SAR in tobacco. The expression of NPR1 and SA biosynthesis genes ICS and PAL were systemically upregulated.

CONCLUSION

SAR induced by reticine A against TMV in tobacco was demonstrated and the mechanism might be attributed to activating the expression of several defensive genes mediated by an SA signal. This study highlights the potential of reticine A which is recommended to be applied directly or as an active ingredient in the crude extract formulation ahead of time in the field, as well as being a potential lead compound for further optimization.

Disentangling the photosynthesis performance in japonica rice during natural leaf senescence using OJIP fluorescence transient analysis

Rice undergoes leaf senescence accompanied with grain filling when the plants reach the end of their temporal niche, and a delay in leaf senescence ultimately improves the yield and quality of grain. To estimate the decline in photosynthesis during leaf senescence and to find an efficient and useful tool to identify rice genotypes with a longer duration of active photosynthesis, we examined PSII photosynthetic activity in the flag leaves of japonica rice Shennong265 (SN265) and Beigeng3 (BG3) during leaf senescence using chlorophyll a fluorescence kinetics. The results show that inhibition occurred in the electron transport chains, but the energetic connectivity of PSII units was not affected as dramatically during leaf senescence. PSII reaction centres (RCs) were transformed into 'silent RCs,' and the chlorophyll content decreased during leaf senescence. However the size of the 'economic' antennae increased. Further, the percentage of variation of the specific energy flux parameters can rationally be used to indicate leaf senescence from the perspective of energy balance. Although the performance indices were more sensitive than other functional and structural JIP-test parameters, they still did not serve as an indicator of crop yield.

Integration of subcellular partitioning and chemical forms to understand silver nanoparticles toxicity to lettuce (Lactuca sativa L.) under different exposure pathways

The current understanding of the biological impacts of silver nanoparticles (AgNPs) is restricted to the direct interactions of the particles with biota. Very little is known about their intracellular fate and subsequent toxic consequences. In this research we investigated the uptake, internal fate (i,e., Ag subcellular partitioning and chemical forms), and phytotoxicity of AgNPs in lettuce following foliar versus root exposure. At the same AgNP exposure concentrations, root exposure led to more deleterious effects than foliar exposure as evidenced by a larger extent of reduced plant biomass, elevated oxidative damage, as well as a higher amount of ultrastructural injuries, despite foliar exposure leading to 2.6-7.6 times more Ag bioaccumulation. Both Ag subcellular partitioning and chemical forms present within the plant appeared to elucidate this difference in toxicity. Following foliar exposure, high Ag in biologically detoxified metals pool (29.2-53.0% by foliar exposure vs. 12.8-45.4% by root exposure) and low Ag proportion in inorganic form (6.1-11.9% vs. 14.1-19.8%) potentially associated with AgNPs tolerance. Silver-containing NPs (24.8-38.6 nm, 1.5-2.3 times larger than the initial size) were detected in lettuce plants exposed to NPs and to dissolved Ag+, suggesting possible transformation and/or aggregation of AgNPs in the plants. Our observations show that the exposure pathway significantly affects the uptake and internal fate of AgNPs, and thus the associated phytotoxicity. The results are an important contribution to improve risk assessment of NPs, and will be critical to ensure food security.

The effect of low ascorbic acid content on tomato fruit ripening

The oxidant/antioxidant balance affects the ripening time of tomato fruit. Ripening of tomato fruit is associated with several modifications such as loss of cell wall firmness and transformation of chloroplasts to chromoplasts. Besides a peak in H₂O₂, reactive oxygen species (ROS) are observed at the transition stage. However, the role of different components of oxidative stress metabolism in fruit ripening has been scarcely addressed. Two GDP-L-galactose phosphorylase (GGP) Solanum lycopersicum L. cv Micro-Tom mutants which have fruit with low ascorbic acid content (30% of wild type) were used in this work to unravel the participation of ascorbic acid and H₂O₂ in fruit maturation. Both GGP mutants show delayed fruit maturation with no peak of H₂O₂; treatment with ascorbic acid increases its own concentration and accelerates ripening only in mutants to become like wild type plants. Unexpectedly, the treatment with ascorbic acid increases H₂O₂ synthesis in both mutants resembling what is observed in wild type fruit. Exogenous supplementation with H₂O₂ decreases its own synthesis delaying fruit maturation in plants with low ascorbic acid content. The site of ROS production is localized in the chloroplasts of fruit of all genotypes as determined by confocal microscopy analysis. The results presented here demonstrate that both ascorbic acid and H₂O₂ actively participate in tomato fruit ripening.

Diversification of petal monoterpene profiles during floral development and senescence in wild roses: relationships among geraniol content, petal colour, and floral lifespan

Wild roses store and emit a large array of fragrant monoterpenes from their petals. Maximisation of fragrance coincides with floral maturation in many angiosperms, which enhances pollination efficiency, reduces floral predation, and improves plant fitness. We hypothesized that petal monoterpenes serve additional lifelong functions such as limiting metabolic damage from reactive oxygen species (ROS), and altering isoprenoid hormonal abundance to increase floral lifespan. Petal monoterpenes were quantified at three floral life-stages (unopened bud, open mature, and senescent) in 57 rose species and 16 subspecies originating from Asia, America, and Europe, and relationships among monoterpene richness, petal colour, ROS, hormones, and floral lifespan were analysed within a phylogenetic context. Three distinct types of petal monoterpene profiles, revealing significant developmental and functional differences, were identified: Type A, species where monoterpene abundance peaked in open mature flowers depleting thereafter; Type B, where monoterpenes peaked in senescing flowers increasing from bud stage, and a rare Type C (8 species) where monoterpenes depleted from bud stage to senescence. Cyclic monoterpenes peaked during early floral development, whereas acyclic monoterpenes (dominated by geraniol and its derivatives, often 100-fold more abundant than other monoterpenes) peaked during floral maturation in Type A and B roses. Early-diverging roses were geraniol-poor (often Type C) and white-petalled. Lifetime changes in hydrogen peroxide (H₂O₂) revealed a significant negative regression with the levels of petal geraniol at all floral life-stages. Geraniol-poor Type C roses also showed higher cytokinins (in buds) and abscisic acid (in mature petals), and significantly shorter floral lifespan compared with geraniol-rich Type A and B roses. We conclude that geraniol enrichment, intensification of petal colour, and lower potential for H₂O₂-related oxidative damage characterise and likely contribute to longer floral lifespan in monoterpene-rich wild roses.

Biochemical Profile of the Soybean Seed Embryonic Axis and Its Changes during Accelerated Aging

Seed deterioration is an important topic in plant science, as the majority of cultivated species use seeds as their means of propagation; however, due to its complexity, the process of seed deterioration has not yet been completely elucidated. Three soybean cultivars (BMX Raio, BMX Zeus, and DM 53i54) exposed to four distinct periods of accelerated aging (0, 3, 6 and 9 days) in a fully randomized experimental design. Initially, vigor and germination tests were performed. The activity of superoxide dismutase, catalase, ascorbate peroxidase enzymes, hydrogen peroxide, malonaldehyde, DNA oxidation, macromolecules and mineral content, and Maillard reactions were quantified in the embryonic axis. Results showed that DNA did not suffer degradation or oxidation. In terms of consumption of reserves, only sugars were consumed, while levels of protein, starch, and triglycerides were maintained. The Maillard reaction did show potential as an indicator of buffer capacity of protein to ROS. Additionally, levels of catalase and ascorbate peroxidase decreased during the aging process. Moreover, nutrient analysis showed that a high magnesium level in the cultivar bestowed greater resilience to deterioration, which can indicate a potential function of magnesium in the cell structure via reflex in seed aging through seed respiration.

A novel plant protein-disulfide isomerase participates in resistance response against the TYLCV in tomato

Overexpression or silencing of the SlPDI could increase plants resistance or sensitivity to TYLCV through enhancing or reducing the plant's antioxidant capacity. Tomato yellow leaf curl virus (TYLCV), a plant virus that could infect a variety of crops, is particularly destructive to tomato growth. Protein disulfide isomerase (PDI) is a member of the thioredoxin (Trx) superfamily, is capable of catalyzing the formation and heterogeneity of protein disulfide bonds and inhibiting the aggregation of misfolded proteins. Studies have shown that PDI plays important roles in plant response to abiotic stress, there is no research report on the function of PDI in response to biotic stress, especially TYLCV infection. Here, we identified a tomato PDI gene, SlPDI, was involved in regulating tomato plants resistance to TYLCV. Subcellular localization results showed that SlPDI was located at the endoplasmic reticulum (ER), and its location remained unchanged after infection with TYLCV virus. Overexpression or silencing of SlPDI could increase plants resistance or sensitivity to TYLCV. Transgenic plants that overexpressing SlPDI exhibit enhanced antioxidant activity evidenced by lower hydrogen peroxide (H₂O₂) level and higher activity of superoxide dismutase (SOD) and peroxidase (POD) in comparison with WT plants, after infected by TYLCV. Moreover, the SlPDI-silencing plants showed opposite results. The promoter analyzes result showed that SlPDI was involved in response to salicylic acid (SA), and our experimental results also showed that the expression level of SlPDI was induced by SA. Taken together, our results indicated that SlPDI could regulate plant resistance to TYLCV through enhancing the protein folding function of ER and promoting the synthesis and conformation of antioxidant-related proteins.

Assessment of ZnO-NPs toxicity in maize: An integrative microRNAomic approach

Rapid expansion of nanotechnology and indiscriminate discharge of metal oxide nanoparticles (NPs) into the environment pose a serious hazard to the ecological receptors including plants. To better understand the role of miRNAs in ZnO-NPs stress adaptation, two small RNA libraries were prepared from control and ZnO-NPs (800 ppm, <50 nm particle size) stressed maize leaves. Meager performance of ZnO-NPs treated seedlings was associated with elevated tissue zinc accumulation, enhanced ROS generation, loss of root cell viability, increased foliar MDA content, decrease in chlorophyll and carotenoids contents. Deep sequencing identified 3 (2 known and 1 novel) up- and 77 (73 known and 4 novel) down-regulated miRNAs from ZnO-NPs challenged leaves. GO analysis reveals that potential targets of ZnO-NPs responsive miRNAs regulate diverse biological processes viz. plant growth and development (miR159f-3p, zma_18), ROS homeostasis (miR156b, miR166l), heavy metal transport and detoxification (miR444a, miR167c-3p), photosynthesis (miR171b) etc. Up-regulation of SCARECROW 6 in ZnO-NPs treated leaves might be responsible for suppression of chlorophyll biosynthesis leading to yellowing of leaves. miR156b.1 mediated up-regulation of CALLOSE SYNTHASE also does not give much protection against ZnO-NPs treatment. Taken together, the findings shed light on the miRNA-guided stress regulatory networks involved in plant adaptive responses to ZnO-NPs stress.

Regulation of Ascorbate Accumulation and Metabolism in Lettuce by the Red:Blue Ratio of Continuous Light Using LEDs

Ascorbate (AsA), an antioxidant that cannot be synthesized and stored by the human body, plays an essential role in the proper functioning of both plants and humans. With the goal of increasing the AsA level in lettuce, the effects of different ratios of red (R) to blue (B) light (75R:25B, 50R:50B, and 25R:75B) on AsA pool sizes as well as the transcript levels and activities of key enzymes involved in AsA metabolism were constantly monitored for 12 days under continuous light (200 μmol⋅m^-2⋅s^-1) from LEDs. The results showed that lettuce biomass was positively correlated with the ratio of red light, while the AsA pool size had a positive correlation with the ratio of blue light during the whole experiment. The 25R:75B treatment increased the expression of genes involved in AsA biosynthesis (GMP, GME, GGP, GPP, GLDH) and regeneration (APX, MDHAR, DHAR, and GR) on day 3 but only significantly elevated the activities of enzymes involved in AsA regeneration (APX, MDHAR, DHAR, and GR) subsequently. AsA regeneration enzymes (MDHAR, DHAR and GR) had greater correlations with the AsA level than the AsA synthesis enzyme (GLDH). Thus, it is concluded that a high ratio of blue light elevated the AsA level mainly by promoting AsA regeneration rather than biosynthesis. Taken together, altering the red:blue ratio of continuous light from high to low before harvest is recommended for lettuce cultivation to achieve both high yield and high quality.

Acid invertase confers heat tolerance in rice plants by maintaining energy homoeostasis of spikelets

Heat stress impairs both pollen germination and pollen tube elongation, resulting in pollination failure caused by energy imbalance. Invertase plays a critical role in the maintenance of energy homoeostasis; however, few studies investigated this during heat stress. Two rice cultivars with different heat tolerance, namely, TLY83 (heat tolerant) and LLY722 (heat susceptible), were subjected to heat stress. At anthesis, heat stress significantly decreased spikelet fertility, accompanied by notable reductions in pollen germination on stigma and pollen tube elongation in ovule, especially in LLY722. Acid invertase (INV), rather than sucrose synthase, contributed to sucrose metabolism, which explains the different tolerances of both cultivars. Under heat stress, larger enhancements in NAD(H), ATP, and antioxidant capacity were found in TLY83 compared with LLY722, whereas a sharp reduction in poly(ADP-ribose) polymerase (PARP) activity was found in the former compared with the latter. Importantly, exogenous INV, 3-aminobenzamide (a PARP inhibitor), sucrose, glucose, and fructose significantly increased spikelet fertility under heat stress, where INV activity was enhanced and PARP activity was inhibited. Therefore, INV can balance the energy production and consumption to provide sufficient energy for pollen germination and pollen tube growth under heat stress.

Epiphytic fungi induced pathogen resistance of invasive plant Ipomoea cairica against Colletotrichum gloeosporioides

Background

Ipomoea cairica (L.) Sweet is a destructive invasive weed in South China but rarely infected with pathogens in nature. Its pathogen resistance mechanism is largely unknown at present. Some non-pathogenic isolates of Fusarium oxysporum and Fusarium fujikuroi are prevalent on many plant species and function as pathogen resistance inducers of host plants. The objective of the present research is to investigate whether the symbiosis between the both fungi and I. cairica is present, and thereby induces pathogen resistance of I. cairica.

Methods

Through field investigation, we explored the occurrence rates of F. oxysporum and F. fujikuroi on leaf surfaces of I. cairica plants in natural habitats and compared their abundance between healthy leaves and leaves infected with Colletotrichum gloeosporioides, a natural pathogen. With artificial inoculation, we assessed their pathogenicity to I. cairica and studied their contribution of pathogen resistance to I. cairica against C. gloeosporioides.

Results

We found that F. oxysporum and F. fujikuroi were widely epiphytic on healthy leaf surfaces of I. cairica in sunny non-saline, shady non-saline and sunny saline habitats. Their occurrence rates reached up to 100%. Moreover, we found that the abundance of F. oxysporum and F. fujikuroi on leaves infected with C. gloeosporioides were significantly lower than that of healthy leaves. With artificial inoculation, we empirically confirmed that F. oxysporum and F. fujikuroi were non-pathogenic to I. cairica. It was interesting that colonization by F. fujikuroi, F. oxysporum alone and a mixture of both fungi resulted in a reduction of C. gloeosporioides infection to I. cairica accompanied by lower lesion area to leaf surface area ratio, increased hydrogen peroxide (H₂O₂) concentration and salicylic acid (SA) level relative to the control. However, NPR1 expression, chitinase and β-1,3-glucanase activities as well as stem length and biomass of I. cairica plant only could be significantly improved by F. oxysporum and a mixture of both fungi but not by F. fujikuroi. In addition, as compared to colonization by F. oxysporum and a mixture of both fungi, F. fujikuroi induced significantly higher jasmonic acid (JA) level but significantly lower β-1,3-glucanase activity in leaves of I. cairica plants. Thus, our findings indicated the symbiosis of epiphytic fungiF. fujikuroi and F. oxysporum induced systemic resistance of I. cairica against C. gloeosporioides. F. oxysporum played a dominant role in inducing pathogen resistance of I. cairica. Its presence alleviated the antagonism of the JA signaling on SA-dependent β-1,3-glucanase activity and enabled I. cairica plants to maintain relatively higher level of resistance against C. gloeosporioides.

ATP Hydrolysis Determines Cold Tolerance by Regulating Available Energy for Glutathione Synthesis in Rice Seedling Plants

BACKGROUND

Glutathione (GSH) is important for plants to resist abiotic stress, and a large amount of energy is required in the process. However, it is not clear how the energy status affects the accumulation of GSH in plants under cold stress.

RESULTS

Two rice pure lines, Zhongzao39 (ZZ39) and its recombinant inbred line 82 (RIL82) were subjected to cold stress for 48 h. Under cold stress, RIL82 suffered more damages than ZZ39 plants, in which higher increases in APX activity and GSH content were showed in the latter than the former compared with their respective controls. This indicated that GSH was mainly responsible for the different cold tolerance between these two rice plants. Interestingly, under cold stress, greater increases in contents of carbohydrate, NAD(H), NADP(H) and ATP as well as the expression levels of GSH1 and GSH2 were showed in RIL82 than ZZ39 plants. In contrast, ATPase content in RIL82 plants was adversely inhibited by cold stress while it increased significantly in ZZ39 plants. This indicated that cold stress reduced the accumulation of GSH in RIL82 plants mainly due to the inhibition on ATP hydrolysis rather than energy deficit.

CONCLUSION

We inferred that the energy status determined by ATP hydrolysis involved in regulating the cold tolerance of plants by controlling GSH synthesis.

Non-Photochemical Quenching Involved in the Regulation of Photosynthesis of Rice Leaves under High Nitrogen Conditions

Excess and deficient nitrogen (N) inhibit photosynthesis in the leaves of rice plants, but the underlying mechanism is still unclear. N can improve the chlorophyll content and thus affect photon absorption, but the photosynthetic rate does not increase accordingly. To investigate this mechanism, three concentrations of N treatments were applied to two rice varieties, Zhefu802 and Fgl. The results indicated increased chlorophyll content of leaves with an increased N supply. Little discrepancy was detected in Rubisco enzyme activity and Non-photochemical quenching (NPQ) in the high nitrogen (HN) and moderate nitrogen (MN) treatments. The model that photoinhibition occurs in Zhefu802 due to a lack of balance of light absorption and utilization is supported by the higher malondialdehyde (MDA) content, higher H₂O₂ content, and photoinhibitory quenching (qI) in HN treatment compared with MN treatment. A lower proportion of N in leaf was used to synthesize chlorophyll for Fgl compared with Zhefu802, reducing the likelihood of photoinhibition under HN treatment. In conclusion, HN supply does not allow ideal photosynthetic rate and increases the likelihood of photoinhibition because it does not sustain the balance of light absorption and utilization. Apart from Rubisco enzyme activity, NPQ mainly contributes to the unbalance. These results of this study will provide reference for the effective N management of rice.

Abscisic Acid Negatively Modulates Heat Tolerance in Rolled Leaf Rice by Increasing Leaf Temperature and Regulating Energy Homeostasis

BACKGROUND

Abscisic acid (ABA) acts as a signaling hormone in plants against abiotic stress, but its function in energy homeostasis under heat stress is unclear.

RESULTS

Two rice genotypes, Nipponbare (wild-type, WT) with flat leaves and its mutant high temperature susceptibility (hts) plant with semi-rolled leaves, were subjected to heat stress. We found significantly higher tissue temperature, respiration rate, and ABA and H2O2 contents in leaves as well as a lower transpiration rate and stomatal conductance in hts than WT plants. Additionally, increased expression of HSP71.1 and HSP24.1 as well as greater increases in carbohydrate content, ATP, NAD (H), and dry matter weight, were detected in WT than hts plants under heat stress. More importantly, exogenous ABA significantly decreased heat tolerance of hts plants, but clearly enhanced heat resistance of WT plants. The increases in carbohydrates, ATP, NAD (H), and heat shock proteins in WT plants were enhanced by ABA under heat stress, whereas these increases were reduced in hts plants.

CONCLUSION

It was concluded that ABA is a negative regulator of heat tolerance in hts plants with semi-rolled leaves by modulating energy homeostasis.

The effects of exogenous malic acid in relieving aluminum toxicity in Pinus massoniana

Two different genotypes of Pinus massoniana seedlings (aluminum-resistant FJ5 and aluminum-sensitive GD20) were used, the effects of different exogenous malic acid (0.00, 0.01, 0.02, 0.04, 0.08, 0.16 mmol·L^-1) on the growth attributes of P. massoniana seedlings treated by the Al³⁺ concentration of 0.8 mmol·L^-1 were studied, to provide a basis for the growth in acidified soil. In our experiment, the seedling growth was inhibited by Al³⁺ treatment. After treatment with a low concentration of exogenous malic acid, the activities of antioxidant enzymes in leaves were enhanced, the concentrations of hydrogen peroxide (H₂O₂), superoxide (O₂^-·), malondialdehyde (MDA) and osmotic adjustment substances were reduced accordingly. GD20 exhibited more severe changes compared with FJ5. The larger ones of the contribution rates of the indices in principal component analysis were H₂O₂, Glutathione Reductase (GR). These results indicated that Al³⁺ with high concentration inhibits the growth of P. massoniana. Malic acid could effectively alleviate the toxicity, and the mitigation effect on the aluminum-sensitive species, which genotype is more sensitive to the response of Al³⁺ toxicity, was more effective than that on the aluminum-resistant. How to select and cultivate more resistant species, by using the main parameter (H₂O₂ and GR), is worthy in further study.

Pathogenesis strategies and regulation of ginsenosides by two species of Ilyonectria in Panax ginseng: power of speciation

BACKGROUND

The valuable medicinal plant Panax ginseng has high pharmaceutical efficacy because it produces ginsenosides. However, its yields decline because of a root-rot disease caused by Ilyonectria mors-panacis. Because species within Ilyonectria showed variable aggressiveness by altering ginsenoside concentrations in inoculated plants, we investigated how such infections might regulate the biosynthesis of ginsenosides and their related signaling molecules.

METHODS

Two-year-old ginseng seedlings were treated with I. mors-panacis and I. robusta. Roots from infected and pathogen-free plants were harvested at 4 and 16 days after inoculation. We then examined levels or/and expression of genes of ginsenosides, salicylic acid (SA), jasmonic acid (JA), and reactive oxygen species (ROS). We also checked the susceptibility of those pathogens to ROS.

RESULTS

Ginsenoside biosynthesis was significantly suppressed and increased in response to infection by I. mors-panacis and I. robusta, respectively. Regulation of JA was significantly higher in I. robusta-infected roots, while levels of SA and ROS were significantly higher in I. mors-panacis-infected roots. Catalase activity was significantly higher in I. robusta-infected roots followed in order by mock roots and those infected by I. mors-panacis. Moreover, I. mors-panacis was resistant to ROS compared with I. robusta.

CONCLUSION

Infection by the weakly aggressive I. robusta led to the upregulation of ginsenoside production and biosynthesis, probably because only a low level of ROS was induced. In contrast, the more aggressive I. mors-panacis suppressed ginsenoside biosynthesis, probably because of higher ROS levels and subsequent induction of programmed cell death pathways. Furthermore, I. mors-panacis may have increased its virulence by resisting the cytotoxicity of ROS.

Strengthened antioxidant capacity improves photosynthesis by regulating stomatal aperture and ribulose-1,5-bisphosphate carboxylase/oxygenase activity

ABA is important for plant growth and development; however, it also inhibits photosynthesis by regulating the stomatal aperture and ribulose-1,5-bisphosphate carboxylase/oxygenase activity. Noteworthy, this negative effect can be alleviated by antioxidants including ascorbic acid (AsA) and catalase (CAT), but the underlying mechanism remains unclear. Two rice cultivars, Zhefu802 (recurrent parent) and its near-isogenic line, fgl were selected and planted in a greenhouse with 30/24 °C (day/night) under natural sunlight conditions. Compared to fgl, Zhefu802 had significantly lower net photosynthetic rate (PN) and stomatal conductance (Cond) as well as significantly higher ABA and H₂O₂ contents. However, AsA and CAT increased PN, Cond, and stomatal aperture, which decreased H₂O₂ and malondialdehyde (MDA) levels. In this process, AsA and CAT significantly increased the ribulose-1,5-bisphosphate carboxylase activity, while they strongly decreased the ribulose-1,5-bisphosphate oxygenase activity, and finally caused an obvious decrease in the ratio of photorespiration (Pr) to PN. Additionally, AsA and CAT significantly increased the expression levels of RbcS and RbcL genes of leaves, while H₂O₂ significantly decreased them, especially the RbcS gene. In summary, the removal of H₂O₂ by AsA and CAT can improve the leaf photosynthesis by alleviating the inhibition on the stomatal conductance and ribulose-1,5-bisphosphate carboxylase capacity caused by ABA.

SODs involved in the hormone mediated regulation of H2O2 content in Kandelia obovata root tissues under cadmium stress

Cadmium (Cd) pollution in mangrove wetlands has received increasing attention as urbanization expands rapidly. As a dominant mangrove species, Kandelia obovata is highly tolerant to Cd toxicity. Plant hormones and superoxide dismutase (SODs) play critical roles in the response to heavy metal stress in K. obovata roots. Although theirs important influence have been reported, the regulation mechanism between SODs and plant hormones in Cd detoxification by K. obovata roots remains limited. Here, we investigated relationships among SOD, plant hormones, and Cd tolerance in K. obovata roots exposed to Cd. We found that Cd was retained in the epidermis and exodermis of roots, and the epidermis and exodermis had highest hydrogen peroxide (H₂O₂) content and SOD activity. Similarly, SOD isozymes also exhibited distinct activity in the different parts of root. Overexpressed KoCSD3 and KoFSD2 individually in Nicotiana benthamiana revealed that different SOD members contributed to H₂O₂ content regulation by promote the activity of downstream antioxidant enzymes under Cd treatment. In addition, assays on the effects of hormones showed that increased endogenous indole-3-acetic acid (IAA) was observed in the cortex and stele, whereas the abscisic acid (ABA) content was enhanced in the epidermis and exodermis in roots during Cd treatment. The results of exogenous hormones treatment indicated that KoFSD2 upregulated under ABA and IAA treatment, but KoCSD3 only induced by ABA stimulation. Taken together, our results reveal the relationship between SODs and plant hormones, which expands the knowledge base regarding KoSODs response to plant hormones and mediating H₂O₂ concentration under Cd stress.

CaDHN4, a Salt and Cold Stress-Responsive Dehydrin Gene from Pepper Decreases Abscisic Acid Sensitivity in Arabidopsis

Dehydrins play an important role in improving plant resistance to abiotic stresses. In this study, we isolated a dehydrin gene from pepper (Capsicum annuum L.) leaves, designated as CaDHN4. Sub-cellular localization of CaDHN4 was to be found in the nucleus and membrane. To authenticate the function of CaDHN4 in cold- and salt-stress responses and abscisic acid (ABA) sensitivity, we reduced the CaDHN4 expression using virus-induced gene silencing (VIGS), and overexpressed the CaDHN4 in Arabidopsis. We found that silencing of CaDHN4 reduced the growth of pepper seedlings and CaDHN4-silenced plants exhibited more serious wilting, higher electrolyte leakage, and more accumulation of ROS in the leaves compared to pTRV2:00 plants after cold stress, and lower chlorophyll contents and higher electrolyte leakage compared to pTRV2:00 plants under salt stress. However, CaDHN4-overexpressing Arabidopsis plants had higher seed germination rates and post-germination primary root growth, compared to WT plants under salt stress. In response to cold and salt stresses, the CaDHN4-overexpressed Arabidopsis exhibited lower MDA content, and lower relative electrolyte leakage compared to the WT plants. Under ABA treatments, the fresh weight and germination rates of transgenic plants were higher than WT plants. The transgenic Arabidopsis expressing a CaDHN4 promoter displayed a more intense GUS staining than the normal growth conditions under treatment with hormones including ABA, methyl jasmonate (MeJA), and salicylic acid (SA). Our results suggest that CaDHN4 can protect against cold and salt stresses and decrease ABA sensitivity in Arabidopsis.

Comparative phosphoproteomic analysis of blast resistant and susceptible rice cultivars in response to salicylic acid

BACKGROUND

Salicylic acid (SA) is a significant signaling molecule that induces rice resistance against pathogen invasion. Protein phosphorylation carries out an important regulatory function in plant defense responses, while the global phosphoproteome changes in rice response to SA-mediated defense response has not been reported. In this study, a comparative phosphoproteomic profiling was conducted by two-dimensional gel electrophoresis (2-DE) and mass spectrometry (MS) analysis, with two near-isogenic rice cultivars after SA treatment.

RESULTS

Thirty-seven phosphoprotein spots were differentially expressed after SA treatment, twenty-nine of which were identified by MALDI-TOF/TOF MS, belonging to nine functional categories. Phosphoproteins involved in photosynthesis, antioxidative enzymes, molecular chaperones were similarly expressed in the two cultivars, suggesting SA might alleviate decreases in plant photosynthesis, regulate the antioxidant defense activities, thus improving basal resistance response in both cultivars. Meanwhile, phosphoproteins related to defense, carbohydrate metabolism, protein synthesis and degradation were differentially expressed, suggesting phosphorylation regulation mediated by SA may coordinate complex cellular activities in the two cultivars. Furthermore, the phosphorylation sites of four identified phosphoproteins were verified by NanoLC-MS/MS, and phosphorylated regulation of three enzymes (cinnamoyl-CoA reductase, phosphoglycerate mutase and ascorbate peroxidase) was validated by activity determination.

CONCLUSIONS

Our study suggested that phosphorylation regulation mediated by SA may contribute to the different resistance response of the two cultivars. To our knowledge, this is the first report to measure rice phosphoproteomic changes in response to SA, which provides new insights into molecular mechanisms of SA-induced rice defense.

Enhanced Tolerance to Methyl Viologen-Mediated Oxidative Stress via AtGR2 Expression From Chloroplast Genome

Owing to their sessile life habit, plants are continuously subjected to a broad range of environmental stresses. During periods of (a)biotic stresses, reactive oxygen species (ROS) levels can rise excessively, leading to oxidative stress. Glutathione reductase (GR) plays an important role in scavenging the ROS and maintenance of redox potential of the cell during oxidative stress. To enhance ROS scavenging capacity, and hence stress tolerance, the Arabidopsis thalianaGR2 (AtGR2) gene was expressed from the tobacco plastid (chloroplast) genome, the main source of ROS production in plant photosynthetic tissues, in this study. Leaves of transplastomic tobacco plants had about seven times GR activity and 1.5 times total glutathione levels compared to wild type. These transplastomic tobacco plants showed no discernible phenotype and exhibited more tolerance to methyl viologen-induced oxidative stress than wild-type control plants. The results indicate that introducing AtGR2 in chloroplasts is an efficient approach to increase stress tolerance. This study also provides evidence that increasing antioxidant enzyme via plastid genome engineering is an alternative to enhance plant's tolerance to stressful conditions.

Enterobacter asburiae Reduces Cadmium Toxicity in Maize Plants by Repressing Iron Uptake-Associated Pathways

Soil microbes have recently been utilized to improve cadmium (Cd) tolerance and lower its accumulation in plants. Nevertheless, whether rhizobacteria can prevent Cd uptake by graminaceous plants and the underlying mechanisms remain elusive. In this study, inoculation with Enterobacter asburiae NC16 reduced transpiration rates and the expression of some iron (Fe) uptake-related genes including ZmFer, ZmYS1, ZmZIP, and ZmNAS2 in maize (Zea mays) plants, which contributed to mitigation of Cd toxicity. However, the inoculation with NC16 failed to suppress the transpiration rates and transcription of these Fe uptake-related genes in plants treated with fluridone, an abscisic acid (ABA) biosynthetic inhibitor, indicating that the impacts of NC16-inoculation observed were dependent on the actions of ABA. We found that NC16 increased the host ABA levels by mediating the metabolism of ABA rather than its synthesis. Moreover, the capacity of NC16 to inhibit plant uptake of Cd was greatly weakened in plants overexpressing ZmZIP, encoding a zinc/iron transporter. Collectively, our findings indicated that E. asburiae NC16 reduced Cd toxicity in maize plants at least partially by hampering the Fe uptake-associated pathways.

OsCAF1, a CRM Domain Containing Protein, Influences Chloroplast Development

The chloroplast RNA splicing and ribosome maturation (CRM) domain proteins are involved in the splicing of chloroplast gene introns. Numerous CRM domain proteins have been reported to play key roles in chloroplast development in several plant species. However, the functions of CRM domain proteins in chloroplast development in rice remain poorly understood. In the study, we generated oscaf1 albino mutants, which eventually died at the seedling stage, through the editing of OsCAF1 with two CRM domains using CRISPR/Cas9 technology. The mesophyll cells in oscaf1 mutant had decreased chloroplast numbers and damaged chloroplast structures. OsCAF1 was located in the chloroplast, and transcripts revealed high levels in green tissues. In addition, the OsCAF1 promoted the splicing of group IIA and group IIB introns, unlike orthologous proteins of AtCAF1 and ZmCAF1, which only affected the splicing of subgroup IIB introns. We also observed that the C-terminal of OsCAF1 interacts with OsCRS2, and OsCAF1–OsCRS2 complex may participate in the splicing of group IIA and group IIB introns in rice chloroplasts. OsCAF1 regulates chloroplast development by influencing the splicing of group II introns.

Brassinosteroids function in spikelet differentiation and degeneration in rice

Brassinosteroids (BRs) play crucial roles in many aspects of plant development. However, their function in spikelet differentiation and degeneration in rice (Oryza sativa L.) remains unclear. Here, we investigated the roles of these phytohormones in spikelet development in field-grown rice subjected to five different nitrogen (N) fertilization treatments during panicle differentiation. BR levels and expression of genes involved in BR biosynthesis and signal transduction were measured in spikelets. Pollen fertility and the number of differentiated spikelets were closely associated with 24-epicastasterone (24-epiCS) and 28-homobrassinolide (28-homoBL) levels in spikelets. Enhanced BR biosynthesis and signal transduction, in response to N treatment, enhanced spikelet differentiation, reduced spikelet degeneration, and increased grain yield. Increases in proton-pumping ATPase activity, ATP concentration, energy charge, and antioxidant system (AOS) levels were consistent with 24-epiCS and 28-homoBL concentrations. Exogenous application of 24-epiCS or 28-homoBL on young panicles induced a marked increase in endogenous 24-epiCS or 28-homoBL levels, energy charge, AOS levels, spikelet differentiation, and panicle weight. The opposite effects were observed following treatment with a BR biosynthesis inhibitor. Our findings indicate that, in rice, BRs mediate the effects of N fertilization on spikelet development and play a role in promoting spikelet development through increasing AOS levels and energy charge during panicle development.

Plant-microbiome assisted and biochar-amended remediation of heavy metals and polyaromatic compounds ─ a microcosmic study

The study has been carried out to develop a plant-microbes assisted remediation technology to accelerate polyaromatic hydrocarbons (PAHs) degradation and heavy metals (HMs) removal in a microcosmic experiment. The quaternary mixture of PAHs (phenanthrene, anthracene, pyrene, and benzo[a] pyrene) and metals (Cr, Ni, and Pb) spiked the soil, constructing a microcosm; the microcosms were bioaugmented with newly developed plant bacterial consortia (Cpm₁ and Cpm₂). The microcosms were amended with biochar (sieved particle size 0.5-2 mm) as redox regulators to reduce oxidative stress of plant-microbe systems. To formulate the two plant-bacterial consortia, plant species were collected and bacteria were isolated from oil spill soil. The bacterial strains used in two formulated consortia includes ─ Cpm₁ (Enterobacter cloacae HS32, Brevibacillus reuszeri HS37, and Stenotrophomonas sp. HS16) and Cpm₂ (Acinetobacter junii HS29, Enterobacter aerogenes HS39 and Enterobacter asburiae HS22). The PAHs degradation and metal removal efficacy of the consortia (Cpm₁ and Cpm₂) were studied after 24 weeks of trial. The physicochemical properties of microcosm's soil (M₂ and M₃) were assessed after experimentation, which resulted in the finding that the soil exhibits dropped in pH from basic to neutral after application of the plant microbe's consortium. The electrical conductivity was lower in M₂ and M₃ soils, with a range between 1.60 and 1.80 mS/cm after the treatment. The Gas Chromatography/Mass Spectrometry (GC/MS) results illustrate how metabolites with the different molecular weight (M.W) were found in M₂ and M₃ soils (184─446), as a result of the plant-microbes mediated rhizodegradation of four spiked PAHs. The metals in microcosm's soil are very low in concentration after 24 weeks of trial when compared to control(M₁). The Cr, Ni and Pb removal percentages were found in 45.79, 42.19 and 44.85 in M₂. However, the removal percentages were found to be 45.41, 41.47 and 44.25 respectively for these same HMs in M₃ soil. Both the consortia that were newly developed showed similar trends of metals removal and PAHs degradation. This study provides a breakthrough in the area of rhizosphere engineering with the goal of maintaining a sustainable application of plant-microbes in ecosystem services.

Partial and full root-zone drought stresses account for differentiate root-sourced signal and yield formation in primitive wheat

BACKGROUND

Partial and full root-zone drought stresses are two widely used methods to induce soil drying in plant container-culture experiments. Two methods might lead to different observational results in plant water relation, such as non-hydraulic root-sourced signal (nHRS). We compared partial and full stress methods to induce nHRS in two diploids (MO1 and MO4) and two tetraploids (DM 22 and DM 31) wheat varieties under pot-culture conditions. Partial root-zone stress (PS) was performed using split-root alternative water supply method (one half wetting and the other drying) to induce the continuous operation of nHRS, and full root-zone stress (FS) was exposed to whole soil block to induce periodic operation of nHRS since jointing stage.

RESULTS

We tested the two drought methods whether it influenced the nHRS mediated signalling and yield formation in primitive wheat species. Results showed that partial root-zone stress caused more increase in abscisic acid (ABA) production and decline in stomatal closure than full root-zone stress method. The incline in ABA was closely related to triggering reactive oxygen species (ROS) generation, and reducing cytokinin synthesis which, thereby, led to crosstalk with other signalling molecules. Furthermore, PS up-regulated the antioxidant defense system and proline content. Water use efficiency and harvest index was significantly increased in PS, suggesting that PS was more likely to simulate the occurrence of nHRS by increasing the adaptive strategies of plants and closer to natural status of soil drying than FS.

CONCLUSION

These findings lead us to conclude that partial root-zone stress method is more feasible method to induce nHRS which has great capacity to reduce water consumption and enhance plant adaptation to constantly changing environment. These observations also suggest that different root-zone planting methods can be considered to improve the plant phenotypic plasticity and tolerance in water-limited rainfed environments.

Differential activity of the antioxidant defence system and alterations in the accumulation of osmolyte and reactive oxygen species under drought stress and recovery in rice (Oryza sativa L.) tillering

The objective of this study was to investigate the effects of drought stress on the activity of antioxidant enzymes and osmotic adjustment substance content in the tillering period of drought-sensitive and drought-tolerant rice cultivars. The results showed that the superoxide dismutase (SOD), peroxidase (POD), catalase activity (CAT), hydrogen peroxide content, soluble protein content and soluble sugar content increased with the accumulation of time and intensity of drought stress. Compared with the drought-sensitive cultivar, drought-resistant cultivar had a smaller photosynthetic affected area, longer CAT enzyme activity duration, and lower H2O2 accumulation. Unlike POD and CAT enzymes, which maintain the ability to scavenge hydrogen peroxide under long drought conditions, ascorbate peroxidase (APX) enzymes seem to be a rapid response mechanism to scavenge hydrogen peroxide under drought stress. Under a -10 kPa water potential, using soluble sugars on the osmotic adjustment ability of the drought-resistant cultivars was more efficient; under -40 kPa water potential, drought-resistant cultivars can maintain relative high levels of ascorbate (ASA) content in the short term. After the restoration of irrigation, the indices gradually returned to control levels. The ASA content showed faster accumulation ability in drought-resistant cultivars and faster recovery. The soluble protein content recovered more slowly in drought-sensitive cultivars under the -40 kPa treatment. Drought-resistant cultivars showed stronger resistance to drought in the -10 kPa treatment and obtained similar yield to the control, while the drought-sensitive cultivars were more obviously affected by the drought stress.

Enhanced Resistance to Leaf Fall Disease Caused by Phytophthora palmivora in Rubber Tree Seedling by Sargassum polycystum Extract

The brown seaweed (Sargassum polycystum C. Agardh-Sargassaceae) extract was examined for its bioelicitor properties in the rubber tree seedling (Hevea brasiliensis (Willd. ex A.Juss.) Müll.Arg. - Euphorbiaceae) and its application to reduce the leaf fall disease caused by Phytophthora palmivora (Edwin John) Butler, 1917 (Peronosporaceae). The major purpose of this study was to apply this seaweed extract (SWE) to improve the disease resistance in rubber tree seedling compared to a chemical fungicide (1% metalaxyl). After foliar spraying of SWE solution, two antioxidant enzymes, catalase (CAT) and peroxidase (POD) and systemic acquired resistance (SAR)-triggered enzyme, β-1,3-glucanase (GLU), were analyzed. Both secondary metabolites, a phytoalexin scopoletin (Scp) and a signaling molecule salicylic acid (SA) were measured by high performance liquid chromatography (HPLC). Both SWE- and metalaxyl-treated plants had a close disease index (DI)-score which were 16.90 ± 1.93 and 15.54 ± 1.25, respectively, while the positive control sprayed with P. palmivora showed DI-score of 29.27 ± 1.89 which was much higher than those treated with SWE or fungicide. CAT, POD, and GLU were increased in rubber tree leaves treated with SWE solution. Furthermore, Scp and SA were significantly increased in SWE-treated leaves. Enhanced systemic acquired resistance induction, 2.09 folds of SA accumulation, was observed in the distal area comparing to the local area of SWE application. In conclusion, the positive effects of SWE elicitation from these studies revealed that SWE could be used as an alternative biocontrol agent for foliar spraying to enhance the defense responses in rubber tree seedling against P. palmivora.

Physiological and biochemical responses of two spring wheat genotypes to non-hydraulic root-to-shoot signalling of partial and full root-zone drought stress

Non-hydraulic root-sourced signal (nHRS) is so far affirmed to be a unique positive early-warning response to drying soil, however its physiological and agronomic implications are still unclear. We designed two contrast methods to induce nHRS in two wheat (Triticum aestivum L.) genotypes released in different decades under pot-culture conditions. Partial root-zone stress (PS) was performed using the method of split-root alternative water supply (one half wetting and the other drying) to induce the continuous operation of nHRS, and full root-zone stress (FS) was subjected to whole root system to periodic operation of nHRS. nHRS-mediated signalling increased abscisic acid (ABA) production and triggered ROS (reactive oxygen species) generation, which, thereby, led to up-regulation of antioxidant defense system. Cytokinin synthesis reduced during drought stress while proline and malodialdehyde (MDA) content were increased. Regardless of drought treatment methods and wheat genotype, a significant decrease in grain yield, root biomass and above-ground biomass (p < 0.05) was observed, without significant changes in root-to-shoot ratio. Harvest index was increased, proposing that more energy was allocated to reproductive organs during the action of nHRS. Moreover, higher water use efficiency was witnessed in PS. The data suggest that nHRS triggered ABA accumulation, thereby closing stomata, and reducing water use and also decreases the production of ROS and improves the antioxidant defence enzymes, thus enhancing drought tolerance. This survey of different-decade genotypes suggests that advances in grain yield and drought tolerance would be made by targeted selection for a wheat genetic resource.

Nickel oxide nanoparticles cause substantial physiological, phytochemical, and molecular-level changes in Chinese cabbage seedlings

Nickel oxide nanoparticles (NiO NPs) are utilized in various industries and their release into the environment may lead to the pollution of agricultural areas. However, assessing the toxicity of NiO NPs in major food crops is difficult due to the limited information available on their toxicity. The present investigation was carried out to evaluate how NiO NPs affect plant growth, photosynthetic efficiency, and phytochemical content, as well as changes at the transcriptional level of these phytochemicals in Chinese cabbage seedlings. Chlorophyll, carotenoid, and sugar contents were reduced, while proline and the anthocyanins were significantly upregulated in NiO NPs-treated seedlings. The levels of malondialdehyde, hydrogen peroxide, and reactive oxygen species, as well as peroxidase (POD) enzyme activity, were all enhanced in seedlings exposed to NiO NPs. The levels of glucosinolates and phenolic compounds were also significantly increased in NiO NPs-treated seedlings compared to control seedlings. The expression of genes related to oxidative stress (CAT, POD, and GST), MYB transcription factors (BrMYB28, BrMYB29, BrMYB34, and BrMYB51), and phenolic compounds (ANS, PAP1, and PAL) were significantly upregulated. We suggest that NiO NPs application stimulates toxic effects and enhances the levels of phytochemicals (glucosinolates and phenolic compounds) in Chinese cabbage seedlings.

Regulation of antioxidant mechanisms by AtDREB1A improves soil-moisture deficit stress tolerance in transgenic peanut (Arachis hypogaea L.)

The present study evaluated the soil-moisture deficit stress tolerance of AtDREB1A transgenic peanut lines during reproductive stages using lysimetric system under controlled glasshouse conditions. The antioxidant activities of AtDREB1A transgenic lines were measured by biochemical assays. The transgenic peanut lines recorded significantly lower accumulation of malondialdehyde and hydrogen peroxide than the wild-type. Whereas, specific activity of catalase, guaiacol peroxidase, ascorbate peroxidase, glutathione reductase and ascorbic acid were found to be significantly higher in transgenic lines than in the wild-type line under drought stress. The results showed that the transgenic lines expressed lower oxidative damage than wild-type and could protect themselves from the elevated levels of reactive oxygen species under drought stress. This could be attributed to the regulation of various stress-inducible genes by AtDREB1A transcription factor. Improved photosynthetic and growth parameters were also recorded in transgenic lines over wild-type under drought stress. Improved physio-biochemical mechanisms in transgenic peanut lines might have resulted in improved growth-related traits as significant correlations were observed between physio-biochemical parameters and growth-related traits under drought stress. The potential target genes of AtDREB1A transcription factor in transgenic peanut lines during drought stress were identified, which helped in understanding the molecular mechanisms of DREB-regulated stress responses. The transgenic line D6 reported the best physio-biochemical mechanisms and growth-related parameters under drought stress over other transgenic lines and wild-type, suggesting it may be used to develop high yielding and terminal drought-tolerant peanut varieties.

UMP Kinase Regulates Chloroplast Development and Cold Response in Rice

Pyrimidine nucleotides are important metabolites that are building blocks of nucleic acids, which participate in various aspects of plant development. Only a few genes involved in pyrimidine metabolism have been identified in rice and the majority of their functions remain unclear. In this study, we used a map-based cloning strategy to isolate a UMPK gene in rice, encoding the UMP kinase that phosphorylates UMP to form UDP, from a recessive mutant with pale-green leaves. In the mutant, UDP content always decreased, while UTP content fluctuated with the development of leaves. Mutation of UMPK reduced chlorophyll contents and decreased photosynthetic capacity. In the mutant, transcription of plastid-encoded RNA polymerase-dependent genes, including psaA, psbB, psbC and petB, was significantly reduced, whereas transcription of nuclear-encoded RNA polymerase-dependent genes, including rpoA, rpoB, rpoC1, and rpl23, was elevated. The expression of UMPK was significantly induced by various stresses, including cold, heat, and drought. Increased sensitivity to cold stress was observed in the mutant, based on the survival rate and malondialdehyde content. High accumulation of hydrogen peroxide was found in the mutant, which was enhanced by cold treatment. Our results indicate that the UMP kinase gene plays important roles in regulating chloroplast development and stress response in rice.

The miRNA-Mediated Post-Transcriptional Regulation of Maize in Response to High Temperature

High temperature (HT) has recently become one of the most important abiotic stresses restricting crop production worldwide. MicroRNAs (miRNAs) are important regulators in plant development and stress responses. However, knowledge of miRNAs of maize in response to HT is limited. In this study, we simultaneously adopted miRNA sequencing and transcriptome profiling to analyze the differential expression of miRNAs and mRNAs in maize during exposure to HT stress. Our analysis revealed 61 known miRNAs belonging to 26 miRNA families and 42 novel miRNAs showing significant differential expression, with the majority being downregulated. Meanwhile, the expression of 5450 mRNAs was significantly altered in the same stressed tissues. Differentially expressed transcripts were most significantly associated with response to stress, photosynthesis, biosynthesis of secondary metabolites, and signal transduction pathways. In addition, we discovered 129 miRNA–mRNA pairs that were regulated antagonistically, and further depiction of the targeted mRNAs indicated that several transcription factors, protein kinases, and receptor-like-protein-related transmembrane transport and signaling transduction were profoundly affected. This study has identified potential key regulators of HT-stress response in maize and the subset of genes that are likely to be post-transcriptionally regulated by miRNAs under HT stress.

Amelioration of the Oxidative Stress Generated by Simple or Combined Abiotic Stress through the K⁺ and Ca2+ Supplementation in Tomato Plants

Abiotic stressors such as drought, heat, or salinity are major causes of yield loss worldwide due to the oxidative burst generated under these conditions. Recent studies have revealed that plant response to a combination of different environmental stressors is unique and cannot be deduced from the response developed to each stress when applied individually. Some studies have demonstrated that a different management of some nutrients in the irrigation solution may provide an advantage to the plants against abiotic stressors. Thus, the aim of this study was to investigate if an increase in potassium (K⁺) and calcium (Ca2+) concentration in the nutrient solution may have a positive effect on the amelioration of oxidative stress which occurs under the combination of salinity and heat in tomato plants. Our results indicated that plants irrigated with an increase in K⁺ and Ca2+ concentrations in the irrigation solution from 7mM (K⁺) to 9.8 mM and from 4 mM (Ca2+) to 5.6 mM, respectively, induced a recovery of the biomass production compared to the plants treated with salinity or salinity + heat, and subsequently irrigated with the regular Hoagland solution. This was correlated with a better performance of all the photosynthetic parameters, a reduction in the foliar concentration of H₂O₂ and a lower lipid peroxidation rate, and with a better performance of the antioxidant enzymes ascorbate peroxidase ascorbate peroxidase (APX), dehydroascorbate reductactase (DHAR), glutathione reductase (GR), and NADPH oxidase. Our results showed that these enzymes were differentially regulated at the transcriptional level, showing a higher reactive oxygen species (ROS) detoxification efficiency under salinity and under the combination of salinity and heat, as compared to those plants irrigated with common Hoagland. An increase in K⁺ and Ca2+ in the irrigation solution also induced a lower Na+ accumulation in leaves and a higher K⁺/Na⁺ ratio. Thus, our study highlights the importance of the right management of the plant nutritional status and fertilization in order to counteract the deleterious effects of abiotic stress in plants.

Abscisic acid prevents pollen abortion under high-temperature stress by mediating sugar metabolism in rice spikelets

Heat stress at the pollen mother cell (PMC) meiotic stage leads to pollen sterility in rice, in which the reactive oxygen species (ROS) and sugar homeostasis are always adversely affected. This damage is reversed by abscisic acid (ABA), but the mechanisms underlying the interactions among the ABA, sugar metabolism, ROS and heat shock proteins in rice spikelets under heat stress are unclear. Two rice genotypes, Zhefu802 (a recurrent parent) and fgl (its near-isogenic line) were subjected to heat stress of 40°C after pre-foliage sprayed with ABA and its biosynthetic inhibitor fluridone at the meiotic stage of PMC. The results revealed that exogenous application of ABA reduced pollen sterility caused by heat stress. This was achieved through various means, including: increased levels of soluble sugars, starch and non-structural carbohydrates, markedly higher relative expression levels of heat shock proteins (HSP24.1 and HSP71.1) and genes related to sugar metabolism and transport, such as sucrose transporters (SUT) genes, sucrose synthase (SUS) genes and invertase (INV) genes as well as increased antioxidant activities and increased content of adenosine triphosphate and endogenous ABA in spikelets. In short, exogenous application of ABA prior to heat stress enhanced sucrose transport and accelerated sucrose metabolism to maintain the carbon balance and energy homeostasis, thus ABA contributed to heat tolerance in rice.

1-Methylcyclopropene Modulates Physiological, Biochemical, and Antioxidant Responses of Rice to Different Salt Stress Levels

Salt stress in soil is a critical constraint that affects the production of rice. Salt stress hinders plant growth through osmotic stress, ionic stress, and a hormonal imbalance (especially ethylene), therefore, thoughtful efforts are needed to devise salt tolerance management strategies. 1-Methylcyclopropene (1-MCP) is an ethylene action inhibitor, which could significantly reduce ethylene production in crops and fruits. However, 1-MCPs response to the physiological, biochemical and antioxidant features of rice under salt stress, are not clear. The present study analyzed whether 1-MCP could modulate salt tolerance for different rice cultivars. Pot culture experiments were conducted in a greenhouse in 2016-2017. Two rice cultivars, Nipponbare (NPBA) and Liangyoupeijiu (LYP9) were used in this trial. The salt stress included four salt levels, 0 g NaCl/kg dry soil (control, CK), 1.5 g NaCl/ kg dry soil (Low Salt stress, LS), 4.5 g NaCl/kg dry soil (Medium Salt stress, MS), and 7.5 g NaCl/kg dry soil (Heavy Salt stress, HS). Two 1-MCP levels, 0 g (CT) and 0.04 g/pot (1-MCP) were applied at the rice booting stage in 2016 and 2017. The results showed that applying 1-MCP significantly reduced ethylene production in rice spikelets from LYP9 and NPBA by 40.2 and 23.9% (CK), 44.3 and 28.6% (LS), 28 and 25.9% (MS), respectively. Rice seedlings for NPBA died under the HS level, while application of 1-MCP reduced the ethylene production in spikelets for LYP9 by 27.4% compared with those that received no 1-MCP treatment. Applying 1-MCP improved the photosynthesis rate and SPAD value in rice leaves for both cultivars. 1-MCP enhanced the superoxide dismutase production, protein synthesis, chlorophyll contents (chl a, b, carotenoids), and decreased malondialdehyde, H2O2, and proline accumulation in rice leaves. Application of 1-MCP also modulated the aboveground biomass, and grain yield for LYP9 and NPBA by 19.4 and 15.1% (CK), 30.3 and 24% (LS), 26.4 and 55.4% (MS), respectively, and 34.5% (HS) for LYP9 compared with those that received no 1-MCP treatment. However, LYP9 displayed a better tolerance than NPBA. The results revealed that 1-MCP could be employed to modulate physiology, biochemical, and antioxidant activities in rice plants, at different levels of salt stress, as a salt stress remedy.

Vitamin C Content in Fruits: Biosynthesis and Regulation

Throughout evolution, a number of animals including humans have lost the ability to synthesize ascorbic acid (ascorbate, vitamin C), an essential molecule in the physiology of animals and plants. In addition to its main role as an antioxidant and cofactor in redox reactions, recent reports have shown an important role of ascorbate in the activation of epigenetic mechanisms controlling cell differentiation, dysregulation of which can lead to the development of certain types of cancer. Although fruits and vegetables constitute the main source of ascorbate in the human diet, rising its content has not been a major breeding goal, despite the large inter- and intraspecific variation in ascorbate content in fruit crops. Nowadays, there is an increasing interest to boost ascorbate content, not only to improve fruit quality but also to generate crops with elevated stress tolerance. Several attempts to increase ascorbate in fruits have achieved fairly good results but, in some cases, detrimental effects in fruit development also occur, likely due to the interaction between the biosynthesis of ascorbate and components of the cell wall. Plants synthesize ascorbate de novo mainly through the Smirnoff-Wheeler pathway, the dominant pathway in photosynthetic tissues. Two intermediates of the Smirnoff-Wheeler pathway, GDP-D-mannose and GDP-L-galactose, are also precursors of the non-cellulosic components of the plant cell wall. Therefore, a better understanding of ascorbate biosynthesis and regulation is essential for generation of improved fruits without developmental side effects. This is likely to involve a yet unknown tight regulation enabling plant growth and development, without impairing the cell redox state modulated by ascorbate pool. In certain fruits and developmental conditions, an alternative pathway from D-galacturonate might be also relevant. We here review the regulation of ascorbate synthesis, its close connection with the cell wall, as well as different strategies to increase its content in plants, with a special focus on fruits.

Genetic Transformation of Cotton with the Harpin-Encoding Gene hpaXoo of Xanthomonas oryzae pv. oryzae and Evaluation of Resistance Against Verticillium Wilt

The soilborne fungal pathogen Verticillium dahliae Kleb causes Verticillium wilt in a wide range of crops including cotton (Gossypium hirsutum). To date, most upland cotton varieties are susceptible to V. dahliae, and the breeding for cotton varieties with the resistance to Verticillium wilt has not been successful. Hpa1Xoo is a harpin protein from Xanthomonas oryzae pv. oryzae which induces the hypersensitive cell death in plants. When hpa1Xoo was transformed into the susceptible cotton line Z35 through Agrobacterium-mediated transformation, the transgenic cotton line (T-34) with an improved resistance to Verticillium dahliae was obtained. Here, we describe the related research approach, such as Western blot, Southern blot, immuno-gold labeling, evaluation of resistance to Verticillium dahliae, and how to detect the micro-hypersensitive response and oxidative burst elicited by harpin_Xoo in plant tissue.

Transcriptomic view of survival during early seedling growth of the extremophyte Haloxylon ammodendron

Seedling establishment in an extreme environment requires an integrated genomic and physiological response to survive multiple abiotic stresses. The extremophyte, Haloxylon ammodendron is a pioneer species capable of colonizing temperate desert sand dunes. We investigated the induced and basal transcriptomes in H. ammodendron under water-deficit stress during early seedling establishment. We find that not only drought-responsive genes, but multiple genes in pathways associated with salt, osmotic, cold, UV, and high-light stresses were induced, suggesting an altered regulatory stress response system. Additionally, H. ammodendron exhibited enhanced biotic stress tolerance by down-regulation of genes that were generally up-regulated during pathogen entry in susceptible plants. By comparing the H. ammodendron basal transcriptome to six closely related transcriptomes in Amaranthaceae, we detected enriched basal level transcripts in H. ammodendron that shows preadaptation to abiotic stress and pathogens. We found transcripts that were generally maintained at low levels and some induced only under abiotic stress in the stress-sensitive model, Arabidopsis thaliana to be highly expressed under basal conditions in the Amaranthaceae transcriptomes including H. ammodendron. H. ammodendron shows coordinated expression of genes that regulate stress tolerance and seedling development resource allocation to support survival against multiple stresses in a sand dune dominated temperate desert environment.

Salicylic acid reverses pollen abortion of rice caused by heat stress

BACKGROUND

Extremely high temperatures are becoming an increasingly severe threat to crop yields. It is well documented that salicylic acid (SA) can enhance the stress tolerance of plants; however, its effect on the reproductive organs of rice plants has not been described before. To investigate the mechanism underlying the SA-mediated alleviation of the heat stress damage to rice pollen viability, a susceptible cultivar (Changyou1) was treated with SA at the pollen mother cell (PMC) meiosis stage and then subjected to heat stress of 40 °C for 10 d until 1d before flowering.

RESULTS

Under control conditions, no significant difference was found in pollen viability and seed-setting rate in SA treatments. However, under heat stress conditions, SA decreased the accumulation of reactive oxygen species (ROS) in anthers to prevent tapetum programmed cell death (PCD) and degradation. The genes related to tapetum development, such as EAT1 (Eternal Tapetum 1), MIL2 (Microsporeless 2), and DTM1 (Defective Tapetum and Meiocytese 1), were found to be involved in this process. When rice plants were exogenously sprayed with SA or paclobutrazol (PAC, a SA inhibitor) + H2O2 under heat stress, a significantly higher pollen viability was found compared to plants sprayed with H2O, PAC, or SA + dimethylthiourea (DMTU, an H2O2 and OH· scavenger). Additionally, a sharp increase in H2O2 was observed in the SA or PAC+ H2O2 treatment groups compared to other treatments.

CONCLUSION

We suggest that H2O2 may play an important role in mediating SA to prevent pollen abortion caused by heat stress through inhibiting the tapetum PCD.