Enhanced production of antimicrobial sesquiterpenes and lipoxygenase metabolites in elicitor-treated hairy root cultures of Solanum tuberosum

Potato (Solanum tuberosum) hairy root cultures, established by infecting potato tuber discs with Agrobacterium rhizogenes, were used as a model system for the production of antimicrobial sesquiterpenes and lipoxygenase (LOX) metabolites. Of the four sesquiterpene phytoalexins (rishitin, lubimin, phytuberin and phytuberol) detected in elicitor-treated hairy root cultures, rishitin (213 micrograms g-1 dry wt) was the most predominant followed by lubimin (171 micrograms g-1 dry wt). The elicitors also induced LOX activity (25-fold increase) and LOX metabolites, mainly 9-hydroxyoctadecadienoic acid and 9-hydroxyoctadecatrienoic acid, in potato hairy root cultures. The combination of fungal elicitor plus cyclodextrin was the most effective elicitor treatment, followed by methyl jasmonate plus cyclodextrin in inducing sesquiterpenes and LOX metabolites.

Reactive oxygen species production in association with suberization: evidence for an NADPH-dependent oxidase

In response to wounding, potato tubers generate reactive oxygen species (ROS) in association with suberization. Immediately following wounding, an initial burst of ROS occurs, reaching a maximum within 30 to 60 min. In addition to this initial oxidative burst, at least three other massive bursts occur at 42, 63 and 100 h post-wounding. These latter bursts are associated with wound healing and are probably involved in the oxidative cross-linking of suberin poly(phenolics). The source of ROS is likely to be a plasma membrane NADPH-dependent oxidase immunorelated to the human phagocyte plasma membrane oxidase. The initial oxidative burst does not appear to be dependent on new protein synthesis, but the subsequent bursts are associated with an increase in oxidase protein components. Oxidase activity is enhanced in vitro by hydroxycinnamic acids and conjugates associated with the wound healing response in potato.

[Effect of ambiol and 2-chloroethylphosphonic acid on the content of phytohormones in potato leaves and tubers]

The effects of the antioxidant Ambiol and 2-chlorethylphosphonic acid (2-CEPA) on individual concentrations and concentration ratios of phytohormones, photosynthesis and photophosphorylation rates, sucrose and starch content in tubers, and plant productivity were studied in potato (Solanum tuberosum L). Ambiol increased the ratio of indoleacetic acid (IAA) to abscisic acid (ABA), IAA/ABA, and that of zeatin (Z) and zeatin riboside (ZR) to ABA, (Z + ZR)/ABA. These effects were underlain by an increase in the content of auxins and cytokinins and a decrease in ABA. Unlike Ambiol, 2-CEPA increased the level of ABA, the effect being the most pronounced in the tubers. Ambiol increased the rates of photosynthesis and noncyclic photophosphorylation in chloroplasts isolated from potato leaves. The relation of this phenomenon to auxin and cytokinin accumulation, Ambiol- and 2-CEPA-induced changes in the hormonal balance of potato tubers, carbon metabolism, and plant productivity is discussed.

Potato disc tumor induction assay: a multiple mode of drug action assay

The study reported herein utilized the Agrobacterium tumefaciens-induced potato disc tumor assay. The objective was to verify the detection of antineoplastic activity in the potato disc tumor induction assay, regardless of the mode of antineoplastic drug action. Camptothecin, paclitaxel, podophyllin, vinblastine and vincristine were tested, each with a different mode of action. All drugs tested inhibited tumor induction. The order of activity was: camptothecin = paclitaxel = vinblastine < podophyllin = vincristine. No effect on the viability of the bacterium was detected. The A. tumefaciens-induced potato disc tumor assay was an effective indicator of antitumor activity regardless of the mechanism of drug action. Thus, this assay would be acceptable as a primary general screen for antineoplastic activity of various crude extracts, as well as for purified fractions, regardless of mode of inhibitory action on tumor formation.

In plants the alc gene expression system responds more rapidly following induction with acetaldehyde than with ethanol

It has recently been proposed that acetaldehyde is the physiological inducer of the alc gene system and hence indirectly the activator of the AlcA promoter in Aspergillus nidulans. Here we show that this chemical induces expression of a GUS (beta-D-glucuronidase) reporter under the control of the alc gene system in transgenic potato tubers more rapidly than ethanol allowing tighter control of transgene expression. Furthermore by analysis of metabolite levels we demonstrate that the application of inducer has few effects on metabolism. We propose that this system is therefore ideal for the temporal regulation of important metabolic enzyme activities.

Investigation of the effect of soil herbicides on the growth and nutrient uptake of potato

In our experiments the effect of three preemergent herbicides was examined on potato varieties. The experiments were carried out under greenhouse conditions in pots with six Hungarian potato varieties. The following herbicides were applied: PATORAN 50 WP (metobromuron), SENCOR 70 WG (metribuzin) and COMMAND 48 EC (chlomazon). The results indicate that the variety Góliát showed the slowest growth. In the case of Lilla fresh and dry shoot weight was decreased by the application of PATORAN 50 WP and SENCOR 70 WG. Tuber weight showed a decrease with the application of SENCOR 70 WG in all varieties. The least tuber weight appeared with the varieties Kánkán and Szózszorszép. Nutrient concentration of potato and N, P and K uptake by potato were examined. In the case of White Lady, Százszorszép and Kánkán N concentration and uptake increase significantly because of SENCOR 70 WG. There was a significant increase in phosphorus concentration and uptake in White Lady, Hópehely and Kánkán varieties in all herbicide treatments. Potassium concentration increased in the case of all the six varieties because of herbicide treatments. Based on these experiments all varieties showed susceptibility against the used herbicides. The results show that important differences occur in the sensitivity and tolerance of varieties against herbicides, which are consequently significant for practical crop protection.

The heterogeneity of sprout inhibitor application with chlorpropham

The CIPC or chlorpropham is used on potatoes as "sprouting inhibitor". These lasts years, some set of belgian potatoes treated by CIPC exceeded the Maximum Residue Limit (MRL), fixed at 5 mg/kg. The heterogeneity of sprout inhibitor application would be one of the causes of over-dosage. In order to estimate the distribution of CIPC between potatoes, according to the formulation used (DP, EC and HN), a research project financed by "le fond budgétaire des matières premieres" has been set up. In order to evaluate the distribution of CIPC into the pile of potatoes, the efficiency of the different formulations as well as the residues caused by their application on tubers, some tests have been placed in the storage hall. These tests consist in taking off some samples at different places into the pile of potatoes during storage and destocking. The content of CIPC is analysed by capillary gas chromatography with detection by mass spectrometry detection (GC-MS) or nitrogen specific detection (GC-NPD). To estimate the efficiency, the sprouting are observed every month and samples of potatoes are taken off on the top of the pile to control the evolution of CIPC content. Considering the results of the tests, the inhibitor treatment with the formulation DP+HN seems to be the more efficient. As for the residues, the formulation DP leads to a higher content of CIPC than HN, that has a very low concentration. After treatment, the quantity really applied on tubers depends on the formulation used. In fact, 50% of CIPC applied by DP formulation are found on tubers but hardly 10%, after gas application.

[Morphogenetic changes in ambiol-treated regenerates of parent and transgenic potato plants]

The effects of ambiol, a new growth regulator, on the formation of leaves and roots in parent and defensin gene-transformed regenerants of potato Solanum tuberosum L. (cultivar Desire). Various concentrations of ambiol induced differences in morphogenetic parameters between parent and transgenic plants. In some cases, ambiol caused the formation of shoots without leaves or with rudimentary leaves. The data suggest that features of root and leaves formation in parent and transgenic regenerants induced by ambiol are due to changes in hormone balance in transgenic plants caused by expression of the defensin gene and the effect of ambiol on the plant hormonal balance.

The production of transgenic potato plants expressing human alpha-interferon using lipofectin-mediated transformation

The lipofectin system was used to transform potato protoplasts with plasmid DNA (pIG3031), which contains human alpha-interferon cDNA and codes for the selectable neomycin phosphotransferase II gene (NPT II). Both genes are under the control of the bi-directional plant active transcriptional promoter from Agrobacterium tumefaciens T-DNA. The criteria of phenotype stability after selective pressure removal, in vitro activity assay of NPT II, the biological analysis of alpha-interferon activity, Southern blot analysis and RNA slot blot were used to confirm the mitotic stability of the foreign gene and its expression and stable integration into the host genome. These studies demonstrate that human alpha-interferon cDNA can be correctly expressed in potato cells.

Ethanol vapor is an efficient inducer of the alc gene expression system in model and crop plant species

We have demonstrated that low concentrations of ethanol vapor efficiently induce the alc gene expression system in tobacco (Nicotiana tabacum cv Samsun NN), potato (Solanum tuberosum cv Solara), and oilseed rape (Brassica napus cv Westar). For many situations, this may be the preferred method of induction because it avoids direct application of comparatively high concentrations of an ethanol solution. Although induction was seen with less than 0.4 microM ethanol vapor, maximal induction of the chloramphenicol acetyl transferase gene was achieved after 48 h in leaves of tobacco plants enclosed with 4.5 microM ethanol vapor. In the absence of ethanol, there is no detectable gene expression. Treatment of potato tubers with ethanol vapor results in uniform beta-glucoronidase (GUS) expression. Vapor treatment of a single oilseed rape leaf resulted in induction of GUS in the treated leaf only and (14)C-ethanol labeling in tobacco confirmed that the inducer was not translocated. In contrast, enclosure of the roots, aerial parts, or whole plant with ethanol vapor resulted in induction of GUS activity in leaves and roots. The data reported here broaden the utility of the alc system for research and crop biotechnology.

Differential sensitivities of plant and animal mitochondria to the herbicide paraquat

Paraquat herbicide is toxic to animals, including humans, via putative toxicity mechanisms associated to microsomal and mitochondrial redox systems. It is also believed to act in plants by generating highly reactive oxygen free radicals from electrons of photosystem I on exposure to light. Paraquat also acts on non-chlorophyllous plant tissues, where mitochondria are candidate targets, as in animal tissues. Therefore, we compared the interaction of paraquat with the mitochondrial bioenergetics of potato tuber, using rat liver mitochondria as a reference. Paraquat depressed succinate-dependent mitochondrial Delta(psi), with simultaneous stimulation of state 4 O2 consumption. It also induced a slow time-dependent effect for respiration of succinate, exogenous NADH, and N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD)/ascorbate, which was more pronounced in rat than in potato mitochondria. However, with potato tuber mitochondria, the Delta(psi) promoted by complex-I-dependent respiration is insensitive to this effect, indicating a protection against paraquat radical afforded by complex I redox activity, which was just the reverse of to the findings for rat liver mitochondria. The experimental set up with the tetraphenyl phosphonium (TPP+)-electrode also indicated production of the paraquat radical in mitochondria, also suggesting its accessibility to the outside space. The different activities of protective antioxidant agents can contribute to explain the different sensitivities of both kinds of mitochondria. Values of SOD activity and alpha-tocopherol detected in potato mitochondria were significantly higher than in rat mitochondria, which, in turn, revealed higher values of lipid peroxidation induced by paraquat.

Impact of elevated CO(2) and O(3) on gas exchange parameters and epidermal characteristics in potato (Solanum tuberosum L.)

Potato plants (Solanum tuberosum L. cv. Bintje) were grown in open-top chambers (OTCs) under three CO(2) levels (ambient and 24 h d(-1) seasonal mean concentrations of 550 and 680 micromol mol(-1)) and two O(3) levels (ambient and a seasonal mean 8 h d(-1) concentration of 50 nmol mol(-1)). The objectives were to determine the effects of season-long exposure to these key climate change gases on gas exchange, leaf thickness and epidermal characteristics. The experimental design also provided an ideal opportunity to examine within-leaf variation in epidermal characteristics at the whole-leaf level. Stomatal and epidermal cell density and stomatal index were measured at specific locations on the youngest fully expanded leaf (centre of lamina, mid-way between tip and base) and representative whole leaves from each treatment. Effects on leaf conductance, assimilation rate and instantaneous transpiration efficiency were determined by infrared gas analysis, while anatomical characteristics were examined using a combination of leaf impressions and thin sections. Exposure to elevated CO(2) or O(3) generally increased leaf thickness, leaf area, stomatal density, and assimilation rate, but reduced leaf conductance. The irregular stomatal distribution within leaves resulted from a combination of uneven differentiation and expansion of the epidermal cells. The results are discussed with reference to sampling protocols and the need to account for within-leaf variation when examining the impact of climate change or other environmental factors on epidermal characteristics.

Prevention of browning in potato with a heat-treated onion extract

The inhibitory effect of an onion extract on browning of potato was investigated. The addition of the heated onion extract to potato exhibited a marked inhibitory effect on potato polyphenol oxidase and the formation of a brown color. The inhibitory effect of the onion extract was dependent upon its heating temperature. The addition of both glycine and glucose increased the inhibitory effect of the onion extract toward potato polyphenol oxidase.

[Effect of ambiol on stem growth in regenerants of source and transgenic potato plants]

The effects of ambiol, a new growth regulator, on stem growth and morphological features of stem development have been compared in regenerants of potato (Solanum tuberosum L., var. Desire) plants transgenic for a defensin gene and in original potato plants. The original and transgenic plants exhibited differences in shoot development, which were observed both in control settings (no ambiol) and in the presence of various ambiol concentrations. In addition to normal plants of both forms, plant regenerants with morphological deviations were present in ambiol-treated groups. It is suggested that the abnormal shoot development observed in original and transgenic potato plants treated with ambiol is associated with (a) hormonal changes caused by expression of the defensin gene in the transgenic plants and (b) effects of ambiol on the hormonal balance of the plants.

The effect of exogenous sugars on the control of flux by adenosine 5'-diphosphoglucose pyrophosphorylase in potato tuber discs

The aim of this work was to investigate the effect of exogenous sugars on the extent to which starch synthesis in potato ( Solanum tuberosum L.) is controlled by adenosine 5'-diphosphoglucose pyrophosphorylase (EC 2.7.7.27; AGPase). Tuber discs were incubated in the presence of a range of concentrations of glucose and sucrose, and metabolic fluxes measured following the supply of [U-14C]glucose and measurement of the specific radioactivity of the hexose phosphate pool. In the presence of glucose there was a marked increase in the flux through glucose-phosphorylating hexokinase, and at high concentrations of external glucose this led to a stimulation of the rate of starch and sucrose synthesis relative to those measured in the presence of sucrose. In the presence of glucose the ratio of the rate of starch synthesis to the rate of glycolysis was higher than in the presence of sucrose. Similar effects of glucose were observed at two stages of tuber development. We conclude that the presence of glucose perturbs the carbohydrate metabolism of tuber discs so that starch synthesis is favoured. In order to determine the extent to which AGPase controls flux, we measured fluxes in wild-type plants and transgenic plants with reduced AGPase activity as a result of the expression of a cDNA encoding the B subunit in the antisense orientation. In the presence of sucrose a reduction in AGPase activity had a greater impact on the rate of starch synthesis than in the presence of glucose. The flux control coefficient of AGPase over starch synthesis was higher in the presence of sucrose (0.7-0.9) than in the presence of glucose (0.4-0.6). Conversely, the impact of reduced AGPase activity on the rate of sucrose synthesis was lower in the presence of sucrose than glucose. In the presence of 200 mM sucrose the flux control coefficient of AGPase over the rate of sucrose synthesis was not significantly different from zero. This demonstrates that the nature of the sugar supplied to potato tuber discs can have a major influence on the distribution of control within metabolism. These data were also used to investigate the relationship between demand for ATP and the rate of hexose phosphate entry into glycolysis. A very strong correlation between ATP demand and glycolytic flux was demonstrated.

A leaf-specific 27 kDa protein of potato Kunitz-type proteinase inhibitor is induced in response to abscisic acid, ethylene, methyl jasmonate, and water deficit

The 22 kDa Kunitz-type potato proteinase inhibitor (22 kDa KPPI) was induced in tubers. However, the 27 kDa protein, which is immunologically related to the 22 kDa KPPI, was induced in leaves by wounding, hormones, and environmental stresses. The leaf-specific 27 kDa protein was induced in leaves that were treated with exogenous abscisic acid (ABA), ethephon, methyl jasmonate (MeJA), and water deficit. These results indicate that the 27 kDa protein in leaves could function as a defense protein against mechanical damages by herbivorous animals and abiotic environmental stresses that could induce plant hormones.

[The influence of genotype on the effects of impact damage and light exposure on the accumulation of glycoalkaloids in potato tubers]

The experiment was carried out in 1999 with 24 Polish and 23 West European cultivars of potato tubers. The tubers were analysed for TGA content after 3 months of dark storage conditions in store-house (8 degrees C). 20 tubers of every cultivar were damaged and placed for a week to dark and under 15 W fluorescent lamps--13 mumol m-2 sec(-1)--equivalent to light in supermarkets. Glycoalkaloids content was determined with Bergers (1980) method. Tubers which had been damaged and exposed for a week to fluorescent light had two fold higher levels of TGA, than undamaged tubers stored at dark. It was found that content of glycoalkaloids in potato tubers and the increase of TGA content due to damage and light exposure depended on genotype. It was higher in varieties with higher level of these compounds, for example: Peppo, Albatros, Columbus and Santana (above 200 mg/kg fresh weight)--tab. I. The smaller increase occurred in tubers of varieties with low content of TGA: Polish--Irga, Grot, Baszta, Tokaj and West European--Satina, Ditta Gloria, Victoria--tab. I, II. Therefore it is important to breed new cultivars with low content of TGA.

Utilization of potatoes for life support systems in space. IV. Effect of CO2 enrichment

Potatoes (Solanum tuberosum L.) cvs. Norland and Russet Burbank were grown in solid stands in separate controlled environment rooms at two CO2 levels, 365 micromoles mol-1 (ppm) and 1000 micromoles mol-1. Rooms were maintained under continuous fluorescent light (450 micromoles s-1 m-2 PPF), 16 C and 70% relative humidity. Norland plants were grown for 110 days and Russet Burbank plants for 126 days. CO2 assimilation rates (net photosynthetic rates) of exposed, upper canopy leaves were measured at weekly intervals beginning at 21-days-age for Norland and 28-days-age for Russet Burbank. Elevation of CO2 increased CO2 assimilation rates of Norland leaves by approximately 24%, but decreased rates of Russet Burbank leaves by approximately 12%. Assimilation rates of Norland leaves under the high CO2 decreased as plants matured so that their rates were similar to rates under the low CO2 levels after 70-days-age. Assimilation rates of Russet Burbank leaves under high CO2 remained depressed in comparison to low CO2 plants throughout the period of measurements. Yield data showed only marginal benefits from CO2 enrichment: tuber dry weight increased 2% for Norland and 12% for Russet Burbank, total plant dry weight was increased 6% for Norland and 4% for Russet Burbank. The best productivity obtained in this study (21.9 g tuber dry wt m-2 day-1 from Norland at 1000 micromoles mol-1 of CO2) indicates that the dietary energy needs of one human in space could be supplied from 34 m2 of potatoes.

Potato growth and yield using nutrient film technique (NFT)

Potato plants, cvs Denali and Norland, were grown in polyvinyl chloride (PVC) trays using a continuous flowing nutrient film technique (NFT) to study tuber yield for NASA's Controlled Ecological Life Support Systems (CELSS) program. Nutrient solution pH was controlled automatically using 0.39M (2.5% (v/v) nitric acid (HNO3), while water and nutrients were replenished manually each day and twice each week, respectively. Plants were spaced either one or two per tray, allotting 0.2 or 0.4 m2 per plant. All plants were harvested after 112 days. Denali plants yielded 2850 and 2800 g tuber fresh weight from the one- and two-plant trays, respectively, while Norland plants yielded 1800 and 2400 g tuber fresh weight from the one- and two-plant trays. Many tubers of both cultivars showed injury to the periderm tissue, possibly caused by salt accumulation from the nutrient solution on the surface. Total system water usage throughout the study for all the plants equaled 709 liters (L), or approximately 2 L m-2 d-1. Total system acid usage throughout the study (for nutrient solution pH control) equaled 6.60 L, or 18.4 ml m-2 d-1 (7.2 mmol m-2 d-1). The results demonstrate that continuous flowing nutrient film technique can be used for tuber production with acceptable yields for the CELSS program.

Involvement of reactive oxygen species in the induction of (S)-N-p-coumaroyloctopamine accumulation by beta-1,3-glucooligosaccharide elicitors in potato tuber tissues

Treatment of potato tuber tissues with beta-1,3-glucooligosaccharide induces accumulation of (S)-N-p-coumaroyloctopamine (p-CO). We examined the role of reactive oxygen species (ROS) and nitric oxide (NO) in the signal transduction leading to p-CO accumulation. Induction was suppressed by an NADPH-oxidase inhibitor, diphenyleneiodonium chloride, and oxygen radical scavengers. H2O2 was generated in the tuber tissue within a few minutes of treatment with beta-1,3-glucooligosaccharide. On the other hand, treatment with NO specific scavenger, nitric oxide synthase inhibitor, and serine protease inhibitor did not inhibit p-CO induction. Our findings suggest that ROS generated by the action of NADPH-oxidase play an important role in this system, while NO and serine protease are unlikely to be involved in this process.

Gibberellins signal nuclear import of PHOR1, a photoperiod-responsive protein with homology to Drosophila armadillo

S. tuberosum ssp. andigena potato plants require short days (SD) for tuberization. We have isolated PHOR1 (photoperiod-responsive 1), which shows upregulated expression in induced leaves (SD). PHOR1 encodes an arm repeat protein with homology to the Drosophila segment polarity protein armadillo. Antisense inhibition of PHOR1 produces a semidwarf phenotype similar to that of GA-deficient plants, and the antisense lines show reduced GA responsiveness combined with a higher endogenous GA content than wild-type plants. Feedback regulation of GA biosynthetic genes is also altered in these lines. Conversely, transgenic lines overexpressing PHOR1 show an enhanced response to GA. GA application induces rapid migration of PHOR1-GFP protein to the nucleus. Thus, PHOR1 appears to be a general component of GA signaling pathways that relocalizes to the nucleus in the presence of GA.

Expression of two subtypes of human IFN-alpha in transgenic potato plants

Plant expression systems have advantages over other in vitro expression systems in terms of low production costs and low risk of contamination by animal viruses or bacterial endotoxins. In this study, cDNA encoding two subtypes of human interferon-alpha2b and 8 (HuIFN-alpha2b and HuIFN-alpha8) were introduced into potato plants (Solanum tuberosum) using Agrobacterium-mediated transformation. Transcription and translation of the inserted HuIFN-alpha cDNA were confirmed by Northern blot analysis and ELISA, respectively. Bioactivity of the products was assayed by inhibition of vesicular stomatitis virus (VSV) replication on a human amniotic cell line. However, because of the presence of substances in potato tissue extracts that were toxic to animal cells, successful demonstration of IFN bioactivity in the transformants was achieved only after removal of such substances by dialysis. The maximum level of IFN activity in plant extracts was 560 IU/g of tissue. These results indicated that the HuIFN-alpha gene introduced into the potato plant was correctly translated and transcribed in plant cells. This report for the first time shows that biologically active animal cytokines with potential pharmaceutical applications could be expressed in transgenic potato plants.

Sustainable soil management practices and quality of potato grown on erodible lands

Land productivity can decline when top soil is lost. In Kentucky, limited resource farmers often produce vegetable crops on erodible lands. The objectives of this study were 1) to quantify the impact of three soil management practices (SMPs) on quantity of potato produced on erodible land, 2) to evaluate the impact of pyrethrin and azadirachtin insecticides on potato tuber quality, and 3) to assess the impact of yard waste compost on the chemical composition (ascorbic acid, free sugars, phenol contents) of potato tubers. Potatoes (Solanum tuberosum L. cv. Kennebec) were grown in a silty loam soil of 10% slope. Plots (n= 18) were 3.7 m wide and 22 m long (10% slope), with metal borders of 20 cm above ground level. Two botanical insecticides, Multi-Purpose Insecticide (containing pyrethrin 0.2%) and Neemix 4EC (containing 0.25% azadirachtin) were sprayed twice on potato foliage during each of two growing seasons (1997 and 1999) at the recommended rates of 6 lbs and 2 gallons.acre(-1), respectively. The SMPs were tall fescue strips (FS) intercropped between each two potato rows, soil mixed with yard waste compost (COM) and no-mulch (NM) treatment (roto-tilled bare soil). The experimental designwas a 2 x 3 x 3 factorial with main factors of two insecticides and three SMPs replicated three times. Average potato yield was lowest in NM and FS and highest in COM treatments. Yield obtained from the bottom of the plots was greater than that obtained from the top of plots. Tuber defects (rot, scab, sun green, hollow heart, necrosis, and vascular discoloration) were significantly different between the two growing seasons. The two insecticidal treatments did not have much influence on potato yield or tuber defects. Tubers obtained from tall fescue treatments had low levels of ascorbic acid and reducing sugars compared to compost treatments.

[Effect of arachidonic acid on potato tubers during storage]

Potato (Solanum tuberosum L.) tubers were treated with various concentrations (10(-9) to 10(-4) M) of the biogenic elicitor arachidonic acid during the period of storage (from October to July). The data showed that the resistance-inducing concentration of arachidonic acid was 10(-6) M in autumn and 10(-9) M in spring. Possible causes of the change in the immunizing concentration of arachidonic acid during storage of potato tubers are discussed.

Increased levels of adenine nucleotides modify the interaction between starch synthesis and respiration when adenine is supplied to discs from growing potato tubers

To investigate the importance of the overall size of the total adenine nucleotide pool for the regulation of primary metabolism in growing potato tubers, freshly cut discs were provided with zero or 2 mM adenine in the presence of 1 or 100 mM [U-14C]glucose or 100 mM [U-14C]sucrose in the presence and absence of 20 mM orthophosphate (Pi). Adenine led to a 150-250% increase of the total adenine nucleotide pool, which included an increase of ADP, a larger increase of ATP and an increase of the ATP:ADP ratio. There was a 50-100% increase of ADP-glucose (ADPGlc), and starch synthesis was stimulated. Respiratory oxygen uptake was stimulated, and the levels of glycerate-3-phosphate, phosphoenolpyruvate and alpha-ketoglutarate decreased. The response to adenine was not modified by Pi. It is proposed that increased ATP stimulates ADPGlc pyrophosphorylase, leading to a higher rate of starch synthesis. The impact on starch synthesis is constrained, however, because increased ADP can lead to a stimulation of respiration and decline of glycerate-3-phosphate, which will inhibit ADPGlc pyrophosphorylase. The quantitative impact depends on the conditions. In the presence of 1 mM glucose, the levels of phosphorylated intermediates and the rate of starch synthesis were low. Adenine led to a relatively large stimulation of respiration, but only a small stimulation of starch synthesis. In the presence of 100 mM glucose, discs contained high levels of phosphorylated intermediates, low ATP:ADP ratios (< 3) and low rates of starch synthesis (< 20% of the metabolised glucose). Adenine led to marked increase of ATP and 2- to 4-fold stimulation of starch synthesis. Discs incubated with 100 mM sucrose already had high ATP:ADP ratios (> 8) and high rates of starch synthesis (> 50% of the metabolised sucrose). Adenine led to a further increase, but the stimulation was less marked than in high glucose. These results have implications for the function of nucleotide cofactors in segregating sucrose mobilisation and respiration, and the need for energy conservation during sugar-starch conversions.

The sucrose analog palatinose leads to a stimulation of sucrose degradation and starch synthesis when supplied to discs of growing potato tubers

In the present paper we investigated the effect of the sucrose (Suc) analog palatinose on potato (Solanum tuberosum) tuber metabolism. In freshly cut discs of growing potato tubers, addition of 5 mM palatinose altered the metabolism of exogenously supplied [U-14C]Suc. There was slight inhibition of the rate of 14C-Suc uptake, a 1.5-fold increase in the rate at which 14C-Suc was subsequently metabolized, and a shift in the allocation of the metabolized label in favor of starch synthesis. The sum result of these changes was a 2-fold increase in the absolute rate of starch synthesis. The increased rate of starch synthesis was accompanied by a 3-fold increase in inorganic pyrophosphate, a 2-fold increase in UDP, decreased UTP/UDP, ATP/ADP, and ATP/AMP ratios, and decreased adenylate energy charge, whereas glycolytic and Krebs cycle intermediates were unchanged. In addition, feeding palatinose to potato discs also stimulated the metabolism of exogenous 14C-glucose in favor of starch synthesis. In vitro studies revealed that palatinose is not metabolized by Suc synthases or invertases within potato tuber extracts. Enzyme kinetics revealed different effects of palatinose on Suc synthase and invertase activities, implicating palatinose as an allosteric effector leading to an inhibition of Suc synthase and (surprisingly) to an activation of invertase in vitro. However, measurement of tissue palatinose levels revealed that these were too low to have significant effects on Suc degrading activities in vivo. These results suggest that supplying palatinose to potato tubers represents a novel way to increase starch synthesis.

Occurrence of 11-hydroxyjasmonic acid glucoside in leaflets of potato plants (Solanum tuberosum L.)

In order to examine the occurrence of 11-hydroxyjasmonic acid glucoside in potato plants, a synthesis of 11-hydroxyjasmonic acid was accomplished, and the synthetic compound was employed as a standard for an LC-SIM analysis. The existence of 11-hydroxyjasmonic acid glucoside was proved by the LC-SIM analysis.

Increase of membrane permeability of mitochondria isolated from water stress adapted potato cells

In order to gain some insight into mitochondria permeability under water stress, intact coupled mitochondria were isolated from water stress adapted potato cells and investigations were made of certain transport processes including the succinate/malate and ADP/ATP exchanges, the plant mitochondrial ATP-sensitive potassium channel (PmitoKATP) and the plant uncoupling mitochondrial protein (PUMP). The Vmax values measured for succinate/malate and ADP/ATP carriers, as photometrically investigated, as well as the same values for the PmitoK(ATP) and the PUMP were found to increase; this suggested that mitochondria adaptation to water stress can cause an increase in the membrane permeability.

Effects of elevated carbon dioxide and ozone on the growth and yield of potatoes (Solanum tuberosum) grown in open-top chambers

Potato (Solanum tuberosum cv. Bintje) was grown in open-top chambers under three carbon dioxide (ambient and seasonal mean concentrations of 550 and 680 mumol mol-1 CO2) and two ozone concentrations (ambient and an 8 h day-1 seasonal mean of 50 nmol mol-1 O3) between emergence and final harvest. Periodic non-destructive measurements were made and destructive harvests were carried out at three key developmental stages (24, 49 and 101 days after emergence) to establish effects on growth and tuber yield. Season-long exposure to elevated O3 reduced above-ground dry weight at final harvest by 8.4% (P < 0.05), but did not affect tuber yields. There was no significant interaction between CO2 and O3 for any of the growth and yield variables examined. Non-destructive analyses revealed no significant effect of elevated CO2 on plant height, leaf number or green leaf area ratio. However, destructive harvests at tuber initiation and 500 degrees Cd after emergence showed that above-ground dry weight (8 and 7% respectively) and tuber yield (88 and 44%) were significantly increased (P < 0.05) in the 550 mumol mol-1 CO2 treatment. Responses to 550 and 680 mumol mol-1 CO2 were not significantly different for most parameters examined, suggesting the existence of an upper limit to the beneficial influence of CO2 enrichment. Significant effects on above-ground dry weight and tuber yield were no longer apparent at final harvest, although tuber numbers were increased (P < 0.05) under elevated CO2, particularly in the smaller size categories. The results show that the O3 treatment imposed was insufficient to reduce tuber yields and that, although elevated CO2 enhanced crop growth during the early stages of the season, this beneficial effect was not sustained to maturity.

Synthesis and potato cell expansion-inducing activity of the stereochemically restricted bicyclic analogue of 7-epi-jasmonic acid

The stereochemically restricted bicyclic analogue of 7-epi-jasmonic acid was synthesized from a known bicyclo[3.3.0]octane derivative. The enol triflate derived from the bicyclic compound was subjected to palladium-catalyzed coupling with allyltributyltin to give the desired carbon skeleton. Selective catalytic hydrogenation and subsequent acidic hydrolysis gave a new bicyclic analogue of 7-epi-jasmonic acid. The ACC conjugate of the bicyclic analogue was also synthesized. This ACC conjugate exhibited only slightly weaker potato cell expansion-inducing activity than that of the JA standard.

Extremely rapid effects of polyunsaturated fatty acids and N-acetylglucosamine on free-radical metabolism in cultured potato plant cells

The effects of arachidonic and linoleic acids, separately and in co-operation with N-acetylglucosamine oligomers, on Solanum tuberosum plant suspension cell cultures were investigated in terms of the fluorescent oxygen-activated-species-sensitive dye 2',7'-dichlorofluorescin diacetate. The inductors used triggered extremely rapid (within 2-10 min) generation of H(2)O(2) in the cells; the majority was expressed in cultures treated with combined polyunsaturated fatty acid and N-acetylglucosamine oligomers. The stimulation of free-radical generation may be related to defensive mechanisms modulating a plant-pathogenic-micro-organism interaction.

The cytotoxic lipid peroxidation product, 4-hydroxy-2-nonenal, specifically inhibits decarboxylating dehydrogenases in the matrix of plant mitochondria

4-Hydroxy-2-nonenal (HNE), a cytotoxic product of lipid peroxidation, inhibits O(2) consumption by potato tuber mitochondria. 2-Oxoglutarate dehydrogenase (OGDC), pyruvate dehydrogenase complex (PDC) (both 80% inhibited) and NAD-malic enzyme (50% inhibited) are its major targets. Mitochondrial proteins identified by reaction with antibodies raised to lipoic acid lost this antigenicity following HNE treatment. These proteins were identified as acetyltransferases of PDC (78 kDa and 55 kDa), succinyltransferases of OGDC (50 kDa and 48 kDa) and glycine decarboxylase H protein (17 kDa). The significance of the effect of these inhibitions on the impact of lipid peroxidation and plant respiratory functions is discussed.

[Effect of gibberellin and auxin on the synthesis of abscisic acid and ethylyne in buds of dormant and sprouting potato tuber]

Gibberellic and beta-indolylacetic acids at concentrations of 10(-7)-10(-5) M were shown to change the hormonal status and duration of dormancy in potato tubers. Gibberellic acid shortened the dormancy and decreased the contents of abscisic acid and ethylene in apical meristems. beta-Indolylacetic acid elongated the dormancy, decreased abscisic acid production, but caused a more than tenfold increase in the production of ethylene by apical tissues. The data suggest that beta-indolylacetic acid and ethylene, as well as gibberellic and abscisic acids, are involved in the regulation of dormancy in potato tubers.

PBF-2 is a novel single-stranded DNA binding factor implicated in PR-10a gene activation in potato

Elicitor-induced activation of the potato pathogenesis-related gene PR-10a requires a 30-bp promoter sequence termed the ERE (elicitor response element) that is bound by the nuclear factor PBF-2 (PR-10a binding factor 2). In this study, PBF-2 has been purified to near homogeneity from elicited tubers through a combination of anion-exchange and DNA affinity chromatography. Evidence demonstrates that inactive PBF-2 is stored in the nuclei of fresh tubers and becomes available for binding to the ERE upon elicitation. A protein with an apparent molecular mass of 24 kD (p24) is a DNA binding component of PBF-2. A cDNA encoding p24 has been cloned and encodes a novel protein with a potential transcriptional activation domain that could also act as a single-stranded DNA binding domain. Both PBF-2 and the cDNA-encoded protein bind with high affinity to the single-stranded form of the ERE in a sequence-specific manner. The inverted repeat sequence of the ERE, TGACAnnnnTGTCA, is critical for binding of this factor in vitro and for PR-10a expression in vivo, supporting the role of PBF-2 as a transcriptional regulator.

Inositol hexakisphosphate is a physiological signal regulating the K+-inward rectifying conductance in guard cells

(RS)-2-cis, 4-trans-abscisic acid (ABA), a naturally occurring plant stress hormone, elicited rapid agonist-specific changes in myo-inositol hexakisphosphate (InsP(6)) measured in intact guard cells of Solanum tuberosum (n = 5); these changes were not reproduced by (RS)-2-trans, 4-trans-abscisic acid, an inactive stereoisomer of ABA (n = 4). The electrophysiological effects of InsP(6) were assessed on both S. tuberosum (n = 14) and Vicia faba (n = 6) guard cell protoplasts. In both species, submicromolar concentrations of InsP(6), delivered through the patch electrode, mimicked the inhibitory effects of ABA and internal calcium (Ca(i)(2+)) on the inward rectifying K(+) current, I(K,in), in a dose-dependent manner. Steady state block of I(K,in) by InsP(6) was reached much more quickly in Vicia (3 min at approximately 1 microM) than Solanum (20-30 min). The effects of InsP(6) on I(K,in) were specific to the myo-inositol isomer and were not elicited by other conformers of InsP(6) (e.g., scyllo- or neo-). Chelation of Ca(2+) by inclusion of 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid or EGTA in the patch pipette together with InsP(6) prevented the inhibition of I(K,in), suggesting that the effect is Ca(2+) dependent. InsP(6) was approximately 100-fold more potent than Ins(1,4,5)P(3) in modulating I(K,in). Thus ABA increases InsP(6) in guard cells, and InsP(6) is a potent Ca(2+)-dependent inhibitor of I(K,in). Taken together, these results suggest that InsP(6) may play a major role in the physiological response of guard cells to ABA.

[Mathematical modeling of the effects of chemical pollutants on the quality of agricultural crops]

Detergents, lead, and nitrogen fertilizers were tested for their effects on the level of sugar in the beets and that of starch in the potatoes. Models were developed for estimating the quality of potatoes and beets grown under irrigation and soil nitrogen fertilization. Lead made the greatest contribution to the lowering sugar in the beets and starch in the potatoes.

Potato micro-tuber inducing hydroxylasiodiplodins from Lasiodiplodia theobromae

Three hydroxylasiodiplodins were isolated from the mycelium extracts of Lasiodiplodia theobromae IFO 31059; and their structures were identified as (3R),(4S)-4-hydroxylasiodiplodin, (3R),(6R)-6-hydroxy-de-O-methyllasiodiplodin and (3R),(5R)-5-hydroxy-de-O-methyllasiodiplodin. All showed potato micro-tuber inducing activity.

Chemical characterization and biological activity of Macfadyena unguis-cati (Bignoniaceae)

Macfadyena unguis-cati (L.) has been widely used in folk medicine as an anti-inflammatory, antimalarial and antivenereal. The purpose of this study was to chemically characterize the main plant components, and to evaluate the biological properties of some of the fractions derived from leaves (MACb) and liana (MACa) of this plant. Chemical characterization allowed the identification of the compounds corymboside, vicenin-2, quercitrin, chlorogenic acid, isochlorogenic acid, lupeol, beta-sitosterol, beta-sitosterylglucoside, allantoin and lapachol. The biological screening of fractions and/or purified substances derived from fractions revealed antitumoral and antitrypanosomal activities in fractions MACa/lapachol and MACb/MACb21, respectively. The anti-lipoxygenase and anti-cyclooxygenase effect seen in fractions MACa and MACb showed a partial correlation with the anti-inflammatory property attributed to this plant.

Nitric oxide protects against cellular damage produced by methylviologen herbicides in potato plants

Methylviologen compounds are normally used in agronomy as herbicides. They cause an overproduction of reactive oxygen species (ROS) within chloroplasts, subjecting the plant to a severe oxidative stress. Since nitric oxide (NO) is a bioactive ROS scavenger, we analyzed its effect over some toxic processes caused by the methylviologens diquat and paraquat in potato leaves (Solanum tuberosum L. cv. Pampeana). Three NO donors, (i) sodium nitroprusside (SNP), (ii) S-nitroso-N-acetylpenicillamine, and (iii) a mixed solution of ascorbic acid and NaNO2, were able to prevent chlorophyll loss. Residual products from NO generation and decomposition failed to prevent chlorophyll decline and a specific NO scavenger, carboxy-PTIO, arrested NO-mediated chlorophyll protection. Dichlorophenyldimethylurea, an inhibitor of chloroplastic electron transport, mimicked NO-mediated chlorophyll protection. During oxidative stress, cell ion leakage to intercellular compartments occurs as an early step, leading to a special kind of programmed cell death. NO proved to specifically decrease the extent of ion leakage originated by diquat, since the protection originated by 100 microM SNP was completely arrested by carboxy-PTIO. These results suggest that NO can strongly protect plants from methylviologen damage and strengthen the evidence in favor of NO as a potent antioxidant in some situations.

A distinct member of the basic (class I) chitinase gene family in potato is specifically expressed in epidermal cells

We have isolated cDNA clones encoding class I chitinase (ChtC) from potato leaves which share a high degree of nucleotide and amino acid sequence similarity to other, previously described basic (class I) chitinases (ChtB) from potato. Despite this similarity, characteristic features distinguish ChtC from ChtB, including an extended proline-rich linker region between the hevein and catalytic domains and presence of a potential glycosylation site (NDT) in the deduced protein. These differences are in accordance with the properties of purified chitinase C which is glycosylated and hence has a higher molecular mass in comparison to chitinase B. In contrast to the coding sequences, the 3'-untranslated regions of ChtC and ChtB exhibited a low degree of similarity, which allowed us to generate gene-specific probes to study the genomic organization and expression of both types of gene. Genomic DNA blots suggest that ChtC and ChtB are each encoded by one or two genes per haploid genome. RNA blot analysis showed that in healthy potato plants ChtC mRNA is most abundant in young leaves, the organs which also contain high levels of chitinase C. By contrast, ChtB mRNA abundance is highest in old leaves, which accumulate chitinase B. By in situ RNA hybridization with gene-specific probes we could demonstrate that ChtC mRNA in leaves is restricted to epidermal cells, whereas ChtB mRNA showed no distinct pattern of cell-type-specific localization. Infection of potato leaves with Phytophthora infestans, or treatment with fungal elicitor, ethylene, or wounding resulted in accumulation of both ChtC and ChtB mRNAs; however, for ChtC, in contrast to ChtB, no corresponding accumulation of the encoded protein could be detected, suggesting a post-transcriptional mechanism of regulation. Salicylic acid treatment did not induce accumulation of either mRNA. The possible functional implications of these findings for pathogen defence and developmental processes are discussed.

Effects of CO2 on stomatal conductance: do stomata open at very high CO2 concentrations?

Potato and wheat plants were grown for 50 d at 400, 1000 and 10000 micromoles mol-1 carbon dioxide (CO2). and sweetpotato and soybean were grown at 1000 micromoles mol-1 CO2 in controlled environment chambers to study stomatal conductance and plant water use. Lighting was provided with fluorescent lamps as a 12 h photoperiod with 300 micromoles m-2 s-1 PAR. Mid-day stomatal conductances for potato were greatest at 400 and 10000 micromoles mol-1 and least at 1000 micromoles mol-1 CO2. Mid-day conductances for wheat were greatest at 400 micromoles mol-1 and least at 1000 and 10000 micromoles mol-1 CO2. Mid-dark period conductances for potato were significantly greater at 10000 micromoles mol-1 than at 400 or 1000 micromoles mol-1, whereas dark conductance for wheat was similar in all CO2 treatments. Temporarily changing the CO2 concentration from the native 1000 micromoles mol-1 to 400 micromoles mol-1 increased mid-day conductance for all species, while temporarily changing from 1000 to 10000 micromoles mol-1 also increased conductance for potato and sweetpotato. Temporarily changing the dark period CO2 from 1000 to 10000 micromoles mol-1 increased conductance for potato, soybean and sweetpotato. In all cases, the stomatal responses were reversible, i.e. conductances returned to original rates following temporary changes in CO2 concentration. Canopy water use for potato was greatest at 10000, intermediate at 400, and least at 1000 micromoles mol-1 CO2, whereas canopy water use for wheat was greatest at 400 and similar at 1000 and 10000 micromoles mol-1 CO2. Elevated CO2 treatments (i.e. 1000 and 10000 micromoles mol-1) resulted in increased plant biomass for both wheat and potato relative to 400 micromoles mol-1, and no injurious effects were apparent from the 10000 micromoles mol-1 treatment. Results indicate that super-elevated CO2 (i.e. 10000 micromoles mol-1) can increase stomatal conductance in some species, particularly during the dark period, resulting in increased water use and decreased water use efficiency.

Synthesis and kinetic evaluation of 4-deoxymaltopentaose and 4-deoxymaltohexaose as inhibitors of muscle and potato alpha-glucan phosphorylases

alpha-Glucan phosphorylases degrade linear or branched oligosaccharides via a glycosyl transfer reaction, occurring with retention of configuration, to generate alpha-glucose-1-phosphate (G1P). We report here the chemoenzymic synthesis of two incompetent oligosaccharide substrate analogues, 4-deoxymaltohexaose (4DG6) and 4-deoxymaltopentaose (4DG5), for use in probing this mechanism. A kinetic analysis of the interactions of 4DG5 and 4DG6 with both muscle and potato phosphorylases was completed to provide insight into the nature of the binding mode of oligosaccharide to phosphorylase. The 4-deoxy-oligosaccharides bind competitively with maltopentaose and non-competitively with respect to orthophosphate or G1P in each case, indicating binding in the oligosaccharide binding site. Further, 4DG5 and 4DG6 were found to bind to potato and muscle phosphorylases some 10-40-fold tighter than does maltopentaose. Similar increases in affinity as a consequence of 4-deoxygenation were observed previously for the binding of polymeric glycogen analogues to rabbit muscle phosphorylase [Withers (1990) Carbohydr. Res. 196, 61-73].

Characterization of the wound-induced metallocarboxypeptidase inhibitor from potato. cDNA sequence, induction of gene expression, subcellular immunolocalization and potential roles of the C-terminal propeptide

A partial cDNA clone for the potato wound-inducible metallocarboxypeptidase inhibitor (PCI) was isolated from a cDNA library constructed from mRNA of abscisic acid (ABA)-treated potato leaves. The full 5' region of the cDNA was obtained through a RACE-PCR protocol. PCI mRNA encodes a precursor polypeptide which comprises a 29 residue N-terminal signal peptide, a 27 residue N-terminal pro-region, the 39 residue mature PCI protein, and a 7 residue C-terminal extension. Northern blot analysis demonstrates that the PCI gene is transcriptionally activated by wounding, and wound signaling can be induced by ABA and jasmonic acid. Subcellular localization of the protein was investigated by immunocytochemistry and electron microscopy, showing that PCI accumulates within the vacuole. A partial PCI precursor form, comprising the mature protein and the C-terminal extension, has been expressed in Escherichia coli and characterized. Its inability to inhibit carboxypeptidases, and stability to carboxypeptidase digestion, suggest that the C-terminal pro-domain may have, besides a probable vacuolar sorting function, a role in modulation of the inhibitory activity of PCI.

Shelf life of sliced raw potatoes of various cultivar varieties--substitution of bisulfites

The effects of potato variety (Van Gogh, Bintje and Fambo), washing with browning prevention chemicals in place of sodium bisulfite, percentages of CO2, O2, and N2 in the package headspace, and storage time (1, 4, and 7 days) on the sensory and microbiological quality of potato slices were examined. Citric acid and ascorbic acid (at 0.1% each and at 0.5% each) were used as browning prevention chemicals. In the packaging atmosphere the percentage of N2 was 75 or 80%, the percentage of O2 was 5 or 0%, and the percentage of CO2 was 20% at the beginning of storage. Packed potato slices were stored in the dark at 5 degrees C. Darkening was the most important factor limiting the sensory quality of raw potato slices. Darkening occurred quickly with Fambo slices; it seems that Fambo is not a suitable potato variety if slices are to be stored. Water-washed and cooked Van Gogh slices were still acceptable for retailing after a storage period of 7 days. After 7 days of storage the best sensory quality of both raw and cooked Bintje slices was obtained with washing solutions containing 0.1 to 0.5% citric and ascorbic acids and with the gas mixture containing 20% CO2 and 80% N2. The number of microorganisms was higher in samples stored in the atmosphere containing 5% O2 than samples stored in the atmosphere containing 0% O2. Washing of potato slices with browning prevention chemicals decreased the number of microorganisms compared to potato slices not washed or potato slices washed with water after 7 days of storage.

Fatty acid-mediated uncoupling of potato tuber mitochondria

The present work examined whether the ATP/ADP carrier, other than the plant uncoupling mitochondrial protein, participates in free fatty acid-mediated uncoupling of potato tuber mitochondria. The basal respiration rate of succinate-energized mitochondria was stimulated by a low concentration of palmitate (20 microM). This uncoupling was reversed by 10 microM carboxyatractyloside and by the subsequent addition of 0.1% bovine serum albumin. The decrease in membrane potential caused by palmitate was suppressed by carboxyatractyloside (1 microM) and, to a lesser degree, by bongkrekate (20 microM). GTP could also reversed this decrease via a carboxyatractyloside-independent mechanism. These results indicate that the ATP/ADP carrier, along with the plant uncoupling mitochondrial protein, participates in the protonophoric action of palmitate in potato tuber mitochondria.

The role of ethylene in the development of constant-light injury of potato and tomato

The role of ethylene in the development of constant-light injury of potato (Solanum tuberosum L.) and tomato (Lycopersicon esculentum Mill.) was investigated. In one study, silver thiosulfate (STS) was applied to the foliage of four potato cultivars growing under constant light. Leaf area and shoot dry mass of 'Kennebec' and 'Superior', cultivars normally injured by constant light, were greater (P < 0.05) than those of control plants given foliar applications of distilled water. Examination of STS-treated 'Kennebec' leaflets revealed significantly less injury (necrotic spotting and reduced starch content) than the water-treated controls. 'Norland' and 'Denali', cultivars tolerant of constant light, exhibited no differences in growth between treatments. In a second study, injury (necrotic spotting and reduced starch content) was induced in leaflets of 'Denali' when exposed to spray applications of 0.5 mmol L-1 ethephon or air containing 0.5 to 0.8 microL L-1 ethylene. In a third study, three genotypes of 'Ailsa Craig' tomato were grown under constant light. Leaves of the normal 'Ailsa Craig' exhibited epinasty, reduced chlorophyll concentration, and reduced starch content. Leaves of a mutant 'Ailsa Craig', containing the Never ripe mutation, did not exhibit epinasty but exhibited the same amount of reduced chlorophyll concentration and starch content as normal plants. Leaves of a transgenic 'Ailsa Craig', containing an antisense gene of 1-aminocyclopropane 1-carboxylate (ACC) oxidase, were epinastic, but chlorophyll concentration and starch content were greater than in leaves of normal and mutant plants. These results suggest that transgenic plants were more tolerant of constant light than the other genotypes. Evidence from these studies indicates that ethylene, combined with constant light, has an important role in the development of constant-light injury.

Response of potatoes to nitrogen concentrations differ with nitrogen forms

Two separate experiments were conducted to investigate plant growth and mineral composition of potatoes (Solanum tuberosum L.) at varied solution concentrations of nitrate (NO3-) and ammonium (NH4+). Each experiment evaluated five nitrogen (N) concentrations of 0.5, 2, 4, 8, and 12 mM, which were maintained with a non-recirculating nutrient film system in controlled environment. Plants were harvested on day 42 with NO3-; and day 35 with NH4+ after transplanting of tissue culture plantlets, and growth measurements were taken as leaf area, tuber number, and dry weights of different parts. With NO3-, plant growth was greatest and similar at 2, 4, and 8 mM of N whereas with NH4+, plant growth was best only at 2 and 4 mM of N. At 12 mM of N, plants exhibited interveinal ammonium toxicity with NH4+ nutrition, but healthy growth appearance with NO3- nutrition. With either N form, total N concentrations in tissues tended to increase with increased N concentrations, and tissue phosphorus (P) concentrations were reduced at 0.5 and 2 mM of N. Tissue concentrations of calcium (Ca), magnesium (Mg), and sulfur (S) changed only slightly at particular N concentrations, yet changed substantially with different N forms. The data indicate that the optimal ranges of N concentrations in both solution and tissues are wider and higher with NO3- than with NH4+ nutrition, and thus a careful control of NH4+ concentrations is necessary to minimize possible ammonium toxicity to potato plants.

Primary structure and expression of acidic (class II) chitinase in potato

Infection of potato (Solanum tuberosum) leaves by the late blight fungus Phytophthora infestans or treatment with fungal elicitor leads to a strong increase in chitinase activity. We isolated cDNAs encoding acidic (class II) chitinases (ChtA) from potato leaves and determined their structures and expression patterns in healthy and stressed plants. From the total number of cDNAs and the complexity of genomic DNA blots we conclude that acidic chitinase in potato is encoded by a gene family which is considerably smaller than that encoding basic (class I) chitinase (ChtB). The deduced amino acid sequences show 78 to 96% identity to class II chitinases from related plant species tomato, tobacco) whereas the identity to basic chitinases of potato is in the range of 60%. RNA blot analysis revealed that both acidic and basic chitinases were strongly induced by infection or elicitor treatment and that the induction occurred both locally at the site of infection and systemically in upper uninfected leaves. In contrast, a differential response to other types of stress was observed. Acidic chitinase mRNA was strongly induced by salicylic acid, whereas basic chitinase mRNA was induced by ethylene or wounding. In healthy, untreated plants, acidic chitinase mRNA accumulated also in an organ-, cell-type- and development-specific manner as revealed by RNA blot analysis and in situ RNA hybridization. Relatively high transcript levels were observed in old leaves and young internodes as well as in vascular tissue and cells constituting the stomatal complex in leaves and petioles. Lower, but appreciable mRNA levels were also detectable in roots and various flower organs, particularly in sepals and stamens. The possible implications of these findings in pathogen defense, development and growth processes are discussed.

Specific interaction of cytokinins and their analogs with rotenone-sensitive internal NADH dehydrogenase in potato tuber mitochondria

Effects of cytokinins were studied on rotenone-sensitive NADH dehydrogenase in mitochondria from fresh potato tubers (Solanum tuberosum), in consideration of the operation of external and rotenone-insensitive internal NADH dehydrogenases that has not been fully accounted for in previous studies. In submitochondrial particles (smp), zeatin was only weakly active, and zeatin riboside (ZR) was inactive. Inhibition rates at 400 microns of isopentenyladenine (iP) and isopentenyladenosine (iPA) were 45% and 30%, respectively, and that of BA (BA) was 64%. In intact mitochondria, the inhibition by iP and BA significantly increased, I50 being 50 and 250 microM, respectively, but that by zeatin and iPA decreased. A structure-activity study showed that hydrophobic and steric factors are important for the activity. Cytokinins inhibited the electron flow via natural quinone more strongly than that via synthetic quinone. These results suggest that among the cytokinins the species that can regulate the electron transport is iP rather than its riboside or zeatin.