Reactivation of meristem activity and sprout growth in potato tubers require both cytokinin and gibberellin

Reactivation of dormant meristems is of central importance for plant fitness and survival. Due to their large meristem size, potato (Solanum tuberosum) tubers serve as a model system to study the underlying molecular processes. The phytohormones cytokinins (CK) and gibberellins (GA) play important roles in releasing potato tuber dormancy and promoting sprouting, but their mode of action in these processes is still obscure. Here, we established an in vitro assay using excised tuber buds to study the dormancy-releasing capacity of GA and CK and show that application of gibberellic acid (GA(3)) is sufficient to induce sprouting. In contrast, treatment with 6-benzylaminopurine induced bud break but did not support further sprout growth unless GA(3) was administered additionally. Transgenic potato plants expressing Arabidopsis (Arabidopsis thaliana) GA 20-oxidase or GA 2-oxidase to modify endogenous GA levels showed the expected phenotypical changes as well as slight effects on tuber sprouting. The isopentenyltransferase (IPT) from Agrobacterium tumefaciens and the Arabidopsis cytokinin oxidase/dehydrogenase1 (CKX) were exploited to modify the amounts of CK in transgenic potato plants. IPT expression promoted earlier sprouting in vitro. Strikingly, CKX-expressing tubers exhibited a prolonged dormancy period and did not respond to GA(3). This supports an essential role of CK in terminating tuber dormancy and indicates that GA is not sufficient to break dormancy in the absence of CK. GA(3)-treated wild-type and CKX-expressing tuber buds were subjected to a transcriptome analysis that revealed transcriptional changes in several functional groups, including cell wall metabolism, cell cycle, and auxin and ethylene signaling, denoting events associated with the reactivation of dormant meristems.

Induction of systemic resistance in different varieties of Solanum tuberosum by pure and crude elicitor treatment

A 10 kD elicitor protein (infestin) produced by Phytopthora infestans was purified and its efficacy for induction of systemic resistance in resistant and susceptible varieties of Solanum tuberosum was studied. Culture filtrates from P. infestans with and without purified elicitor (infestin) were used as elicitors to understand the effect of purified elicitor (infestin) on development of systemic resistance. Culture filtrate and purified elicitor (infestin) were found to induce hypersensitive reaction on the leaves of resistant varieties, but not on susceptible varieties after 48 h. Culture filtrate devoid of purified elicitor (infestin) did not induce any necrotic spots even on resistant variety. Purified elicitor (infestin) was found to induce glucose oxidase, NADPH oxidase, superoxide dismutase, glutathione reductase, catalase and peroxidase enzymes in resistant S. tuberosum plants, however the induction of these enzymes was low in susceptible varieties. The oxidative enzymes were found to induce earlier than antioxidative enzymes and there was negative correlation between these two groups of enzymes. Levels of salicylic acid, phenylalanine ammonia lyase (PAL), beta-1, 3 glucanase and chitinase activities were also found higher in resistant than in susceptible varieties. It was observed that purified elicitor (infestin) was superior to crude culture filtrate, but was not capable of inducing systemic resistance in susceptible varieties.

Expression of StMYB1R-1, a novel potato single MYB-like domain transcription factor, increases drought tolerance

Potato (Solanum tuberosum) is relatively vulnerable to abiotic stress conditions such as drought, but the tolerance mechanisms for such stresses in potato are largely unknown. To identify stress-related factors in potato, we previously carried out a genetic screen of potato plants exposed to abiotic environmental stress conditions using reverse northern-blot analysis. A cDNA encoding a putative R1-type MYB-like transcription factor (StMYB1R-1) was identified as a putative stress-response gene. Here, the transcript levels of StMYB1R-1 were enhanced in response to several environmental stresses in addition to drought but were unaffected by biotic stresses. The results of intracellular targeting and quadruple 9-mer protein-binding microarray analysis indicated that StMYB1R-1 localizes to the nucleus and binds to the DNA sequence (G)/(A)GATAA. Overexpression of a StMYB1R-1 transgene in potato plants improved plant tolerance to drought stress while having no significant effects on other agricultural traits. Transgenic plants exhibited reduced rates of water loss and more rapid stomatal closing than wild-type plants under drought stress conditions. In addition, overexpression of StMYB1R-1 enhanced the expression of drought-regulated genes such as AtHB-7, RD28, ALDH22a1, and ERD1-like. Thus, the expression of StMYB1R-1 in potato enhanced drought tolerance via regulation of water loss. These results indicated that StMYB1R-1 functions as a transcription factor involved in the activation of drought-related genes.

Selection of stress-tolerant yeasts for simultaneous saccharification and fermentation (SSF) of very high gravity (VHG) potato mash to ethanol

Highly concentrated bioethanol production requires less volume in fermentation tanks and conserves distillery energy. We screened osmotolerant yeasts from a collection of 1699 yeast strains at our institute and found that three strains, NFRI3062, NFRI3213, and NFRI3225, were candidates for use in bioethanol production. All of these strains belonged to Saccharomyces cerevisiae. NFRI3062 produced 15.0% (w/v) of ethanol from YPD medium containing 35% glucose cultivated at 30 degrees C for 60 h, while S. cerevisiae NBRC0224, which has previously been reported suitable for ethanol production, only produced 13.0% (w/v). The thermotolerances of NFRI3213 and NFRI3225 were also superior to those of NBRC0224 and NFRI3062. We also demonstrated the simultaneous saccharification and fermentation (SSF) of very high gravity (VHG) potato mash and sweet-potato mash. NFRI3225 produced ethanol from potato mash at the fastest rate and in the highest volume (13.7% (w/v)) among the tested strains. The maximum productivity and ethanol yields were 9.1g/L/h and 92.3%, respectively. Although the potato mash was not sterilized, bacterial contamination was not observed. This may have been due to the growth inhibition of bacteria by the rapid glucose consumption and ethanol production of NFRI3225 during the VHG-SSF process.

Ozone-induced reductions in below-ground biomass: an anatomical approach in potato

Potato plants were grown in open-top chambers under three ozone concentrations during two complete cropping seasons (93 and 77 d in 2004 and 2005, respectively). The effects of chronic exposure to ozone on leaf anatomy, cell ultrastructure and crop yield were studied. Severe cell damage was found, even at ambient ozone levels, mainly affecting the spongy parenchyma and areas near the stomata. Damage to the cell wall caused loss of cell contact, and loss of turgor pressure due to tonoplast disintegration, contributed to cell collapse. Phloem sieve plates were obstructed by callose accumulation, and damaged mesophyll cells increased their starch stores. Tuber yield fell sharply (24-44%), due to the biggest tubers becoming smaller, which affected commercial yield. These anatomical findings show the mechanisms of ozone effect on assimilate partitioning, and thus crop yield decrease, in potato. Further implications of ozone causing reductions in below-ground biomass are also discussed.

Mint essential oil can induce or inhibit potato sprouting by differential alteration of apical meristem

Sprouting of potatoes during storage, due to tuber dormancy release, is associated with weight loss and softening. Sprout-preventing chemicals, such as chlorpropham (CIPC), can negatively impact the environment and human health. Monthly thermal fogging with mint (Mentha spicata L.) essential oil (MEO) inhibited sprouting in eight potato cultivars during large-volume 6-month storage: the tubers remained firm with 38% lower weight loss after 140 days of storage. The sprout-inhibitory action may be nullified: treated tubers washed with water resumed sprouting within days, with reduced apical dominance. MEO application caused local necrosis of the bud meristem, and a few weeks later, axillary bud (AX) growth was induced in the same sprouting eye. MEO components analysis showed that 73% of its content is the monoterpene R-carvone. Tubers treated with synthetic R-carvone in equivalent dose, 4.5 microl l(-1), showed an inhibitory effect similar to that of MEO. Surprisingly, 0.5 microl l(-1) of MEO or synthetic R-carvone catalyzed AX sprouting in the tuber. To the best of our knowledge, this is the first report of an essential oil vapor inducing early sprouting of potato tubers. R-carvone caused visible damage to the meristem membrane at sprout-inhibiting, but not sprout-inducing doses, suggesting different underlying mechanisms. After 5 days' exposure to R-carvone, its derivatives transcarveol and neo-dihydrocarveol were found in buds of tubers treated with the inhibitory dose, suggesting biodegradation. These experiments demonstrate the potential of MEO vapor as an environmentally friendly alternative to CIPC in stored potatoes and as a research tool for the control of sprouting in plants.

DL-beta-aminobutyric acid-induced resistance of potato against Phytophthora infestans requires salicylic acid but not oxylipins

Inducing systemic resistance responses in crop plants is a promising alternative way of disease management. To understand the underlying signaling events leading to induced resistance, functional analyses of plants defective in defined signaling pathway steps are required. We used potato, one of the economically most-important crop plants worldwide, to examine systemic resistance against the devastating late blight pathogen Phytophthora infestans, induced by treatment with dl-beta-aminobutyric acid (BABA). Transgenic plants impaired in either the 9-lipoxygenase pathway, which produces defense-related compounds, or the 13-lipoxygenase pathway, which generates jasmonic acid-derived signals, expressed wild-type levels of BABA-induced resistance. Plants incapable of accumulating salicylic acid (SA), on the other hand, failed to mount this type of induced resistance. Consistently, treatment of these plants with the SA analog 2,6-dichloroisonicotinic acid restored BABA-induced resistance. Together, these results demonstrate the indispensability of a functional SA pathway for systemic resistance in potato induced by BABA.

The effect of essential oil formulations for potato sprout suppression

The concerns over safety and environmental impact of synthetic pesticides such as chlorpropham (CIPC) has stimulated interest in finding environmentally benign, natural sprout suppressants, including essential oils. The effects of Chenopodium ambrosioides and Lippia multiflora essential oils on sprout growth and decay of stored potatoes has been investigated. Formulations of essential oils with alumina, bentonite, or kaolin, both with and without Triton X-100 additive, were tested. These formulations have been compared to the pulverized plant materials themselves as well as wick-volatilized essential oils. The results showed that the tested oils possess compositions that make them suitable for application as sprout suppressants. Additionally, the formulation seems to be able to reduce the volatility of the essential oil and artificially extend dormancy of stored potatoes.

[Interference of phytohormones and synthetic growth regulator melafen in the control of Ca2+ translocation across the plasma membrane of potato (Solanum tuberosum L) tuber cells]

Interference of phytohormones (jasmonic, gibberellic, and abscisic acids) and synthetic growth regulator melafen on Ca2+ translocation across the membrane of plasma membrane vesicles prepared from dormant potato (Solanum tuberosum L.) tubers was studied. The activity of plasma membrane Ca2+, Mg(2+)-ATPase was stimulated by melafen and jasmonic and gibberellic acids and suppressed by abscisic acid. These agents did not change the passive membrane permeability for Ca2+. The pattern of the effect of melafen on the activity of Ca2+, Mg(2+)-ATPase depended on the presence of phytohormones in incubation medium. When melafen and each phytohormone were simultaneously added to incubation medium, their effects were not additive, which indicates that the effects of the tested compounds on the Ca2+ uptake into the plasma membrane vesicles are interdependent. Apparently, the interaction between the phytohormones and plasma membrane components modulates the response to melafen.

Potato (Solanum tuberosum) greenhouse tuber production as an assay for asexual reproduction effects from herbicides

The present study determined whether young potato plants can be used as an assay to indicate potential effects of pesticides on asexual reproduction. Solanum tuberosum (Russet Burbank) plants were grown from seed pieces in a mineral soil in pots under greenhouse conditions. Plants were treated with herbicides (cloransulam, dicamba, glyphosate, imazapyr, primsulfuron, sulfometuron, or tribenuron) at simulated drift levels [</=0.1 x standard field application rates (f.a.r.)], approximately 14 d after emergence (DAE). Plant height was measured approximately 14 d after treatment (DAT). Production of small tubers and shoot dry weight were determined at approximately 28 DAT. Imazapyr, sulfometuron, and tribenuron caused significant reductions in tuber fresh weight, with the effective concentrations producing a 25% potato tuber fresh weight (EC25) of 0.00038, 0.0016, and 0.0021 x f.a.r. of 1,124, 52, and 9 g active ingredient hectare(-1) (g a.i. HA(-1)), respectively. Primisulfuron, dicamba, and cloransulam also significantly reduced tuber fresh weight, but with higher EC25 values of 0.011, 0.07, and 0.010 to 0.2 x f.a.r. of 40, 558, and 18 g a.i. HA(-1), respectively. Glyphosate had little effect on tuber fresh weight, with a significant reduction in only one experiment. Sulfometuron reduced tuber fresh weight at an EC25 value lower than the EC25 values for shoot dry weight or plant height. For other herbicides, the reduction in tuber fresh weight occurred within the range of EC25 values for other responses. Although additional experiments are required to develop further a phytotoxicity test, these results indicated that tuber production in young potato plants (harvested approximately 42 DAE) may be an effective assay for below-ground asexual reproductive responses to herbicides, especially acetolactate synthase inhibitors.

Monitoring gene expression of potato under salinity using cDNA microarrays

The molecular response to salt exposure was studied in the leaves of a Solanum tuberosum clone using cDNA microarray. Differentially expressed genes were classified according to their known or predicted function and their expression ratio as compared to the control. The major changes upon a 150 mM NaCl exposure in potato leaves occurred in the photosystem apparatus and Calvin cycle: many transcripts coding for proteins belonging to photosystems I and II and chlorophyll synthesis were repressed. On the other hand, we observed the induction of various kinds of transcription factors implicated in osmotic stress response via ABA-dependent or ABA-independent pathways but also in plant defense pathways. This revealed a crosstalk between abiotic and biotic stress responses during salt exposure, which activated several adaptation mechanisms including heat shock proteins, late embryogenesis abundant, dehydrins and PR proteins. Gene expression changes related to carbohydrate and amino acid metabolism were also observed, pointing at putative modifications at the metabolic level.

Oxidative stress is an early symptom triggered by aluminum in Al-sensitive potato plantlets

The objective of this study was to evaluate whether the oxidative stress caused by aluminum (Al) toxicity is an early symptom that can trigger root growth inhibition in Macaca (Al-sensitive) and SMIC148-A (Al-tolerant) potato clones. Plantlets were grown in a nutrient solution (pH 4.00) with 0, 100 and 200mg Al L(-1). At 24, 72, 120 and 168h after Al addition, root length and biochemical parameters were determined. Regardless of exposure time, root length of the Macaca clone was significantly lower at 200mg Al L(-1). For the SMIC148-A clone, root length did not decrease with any Al treatments. Al supply caused lipid peroxidation only in Macaca, in both roots (at 24, 72, 120 and 168h) and shoot (at 120 and 168h). In roots of the Macaca, catalase (CAT) and ascorbate peroxidase (APX) activity decreased at 72 and 120h, and at 24, 72 and 120h, respectively. At 168h, both activities increased upon addition of Al. In roots of the SMIC148-A, CAT activity increased at 72 and 168h, whereas APX activity decreased at 72h and increased at 24, 12 and 168h. The Macaca showed lower root non-protein thiol group (NPSH) concentration at 200mg Al L(-1) in all evaluations, but the SMIC148-A either did not demonstrate any alterations at 24 and 72h or presented higher levels at 120h. This pattern was also observed in root ascorbic acid (AsA) concentration at 24 and 120h. The cellular redox status of these potato clones seems to be affected by Al. Therefore, oxidative stress may be an important mechanism for Al toxicity, mainly in the Al-sensitive Macaca clone.

Scenario approach for assessing the utility of dispersal information in decision support for aerially spread plant pathogens, applied to Phytophthora infestans

Opportunities exist to improve decision support systems through the use of dispersal information gained from epidemiological research. However, dispersal and demographic information is often fragmentary in plant pathology, and this uncertainty creates a risk of inappropriate action whenever such information is used as a basis for decision making. In this article, a scenario-based simulation approach is used to evaluate crop and economic risks and benefits in the use of dispersal information for decision making using the potato late blight pathosystem (Phytophthora infestans-Solanum tuberosum) as a case study. A recently validated spatiotemporal potato late blight model was coupled to submodels for crop growth, tuber dry matter production, and fungicide efficacy. The yield response of a range of management scenarios to a single influx of primary inoculum (the initial spore load) was calculated. Damage curves (relative yield loss versus initial spore load) from a range of combinations of varietal susceptibility and fungicide treatments were used to classify the various management scenarios as either sensitive to initial spore load or tolerant to initial spore load, thus identifying where a high degree of accuracy would be required in dispersal information for appropriate decision making, and where a greater degree of uncertainty could be tolerated. General epidemics, resulting from spatially homogeneous initial spore loads, responded more strongly to the size of the initial spore load than focal epidemics, resulting from an initial spot infection. Susceptible cultivars responded with sizeable yield losses even at low levels of initial spore load, regardless of the fungicide management regime used. These results indicated that, for susceptible cultivars (late cultivars in particular), the degree of accuracy that would be required in dispersal information for appropriate decision making is unlikely to be practically attainable. The results also indicated that, contrary to "folk wisdom," spore loads of a few hundred spores per square meter do not lead to appreciable crop loss in resistant cultivars and are therefore acceptable. We conclude that scope exists for including dispersal information in decision making for potato late blight with resistant potato cultivars but not for susceptible cultivars. The modeling framework used in this study can be extended to investigate the scope for inclusion of dispersal information in decision support for other aerially transmitted pathogens.

Glycosides of arylnaphthalene lignans from Acanthus mollis having axial chirality

Glycosides of arylnaphthalene lignans having axial chirality were isolated from Acanthus mollis. Owing to the axial chirality, their structure, including absolute configuration, was determined by means of extensive spectroscopic data such as UV, IR, MS, 1D and 2D NMR spectra, and computational chiroptical methods. A compound, 2',4-dihydroxyretrohelioxanthin (2'-hydroxy-justirumalin), has a structure containing two aromatic moieties with substituents hindering rotation about the biaryl axis. The aglycone was connected to a saccharide moiety linked at C-4 or C-2' and made up of one or four sugars (rhamnose or quinovose, and tetrasaccharide 4-O-beta-D-xylopyranosyl-(1'''''-6'')-O-[beta-D-rhamnopyranosyl-(1''''-3'')]-O-beta-D-apiofuranosyl-(1''''-2'')-O-beta-D-glucopyranoside and quinovose). Two mono- and one tetraglycoside gave positive results in the sea urchin eggs test (Paracentrotus lividus) of cytotoxicity and in a crown gall tumor on potato disks test (Agrobacterium tumefaciens).

[Antitumor activity of some complex preparations in the culture of potato cells transformed by Agrobacterium tumefaciens]

Antitumor and antibacterial activity of complex preparations consisting of yeast mannan, diacetile-2,4-dioxohexahidro-1,3,5-triasine, cianohyanidine, alcansulfonic acids (emulsifier E-30), and microbial metabolites was studied. The investigation was carrying out on explants of tuber potato parenchyma infected by Agrobacterium tumefaciens. We found that preparations have the antitumor activity. The most activity was exhibited by addition of preparations to the cultural medium and treatment of explants before of infection.

Comparative cDNA-AFLP analysis reveals that DL-beta-amino-butyric acid induces resistance through early activation of the host-defense genes in potato

DL-beta-amino-butyric acid (BABA) has been found to protect potato plants against late blight caused by Phytophthora infestans. This paper compares gene expression profiles of a potato clone harboring horizontal resistance to P. infestans in response to BABA and the pathogen by using cDNA-amplified fragment length polymorphism (cDNA-AFLP), aiming at fudermental elucidation of molecular mechanisms of BABA induced resistance (BABA-IR). In total, 101 transcript derived fragments (TDFs) showed significant differential expression among the treated and their respective control samples. About half of differentially expressed fragments (49) were overlapped in both BABA and P. infestans induction systems, and homology analysis showed that these TDFs in common involved in signaling, cell wall strengthening and synthesis of antimicrobial compounds, reflecting both BABA-IR and the natural resistance shared similar defense mechanisms to a great extent. Analysis of the transcription profiles demonstrated that an early activation of plant basal defense system could be crucial for BABA-IR. Some differentially expressed TDFs homologous to genes encoding proteins related to jasmonic acid-and salicylic acid-dependent signaling pathways, were up-regulated by BABA. Similar genes associated with these pathways were also identified in the pathogen inoculated samples, reinforcing that the extensive cross-talk between BABA-IR and horizontal resistance may be important to coordinate the genes responsible for P. infestans infection in potato.

Activation of the pathogen-inducible Gst1 promoter of potato after elicitation by Venturia inaequalis and Erwinia amylovora in transgenic apple (Malus x domestica)

Rather than using a constitutive promoter to drive transgenes for resistance against fungal and bacterial diseases in genetic engineering of apple (Malus x domestica) cultivars, a promoter induced only after infection was preferred. The ability of the Pgst1 promoter from potato (Solanum tuberosum L.) to drive expression of the gusA reporter gene was determined in two genotypes of apple: the fruit cultivar Royal Gala and the M.26 rootstock. beta-Glucuronidase activity in the transgenic lines grown in a growth chamber was determined quantitatively using fluorometric assays and compared to the activity in Cauliflower Mosaic Virus (CaMV) 35S promoter-driven transgenic lines. In both apple genotypes, the Pgst1 promoter exhibited a low level of expression after bacterial and fungal inoculation compared to the level obtained with the PCaMV35S promoter (15% and 8% respectively). The Pgst1 promoter was systematically activated in apple at the site of infection with a fungal pathogen. It was also activated after treatment with salicylic acid, but not after wounding. Taken together, these data show that, although the Pgst1 promoter is less active than the PCaMV35S promoter in apple, its pathogen responsiveness could be useful in driving the expression of transgenes to promote bacterial and fungal disease resistance.

Phenanthrene sorption by fruit cuticles and potato periderm with different compositional characteristics

Phenanthrene sorption by fruit cuticles (tomato, apple, and grape), potato tuber periderm, and their fractions were investigated to elucidate effects of compositional characteristics on affinity of plant cuticle (above-ground) and periderm (below-ground) with hydrophobic organic contaminants (HOCs). The distinct roles of the extractable lipids (waxes), the depolymerizable lipids (cutin/suberin), the nonsaponifiable lipids (cutan/suberan) and polysaccharide are discussed. The cutin/suberin rather than waxes dominates the sorption properties of bulk cuticle/periderm, but the sorption coefficient (K(d)) is linearly correlated with the total lipid contents. Polysaccharide plays a negative role in HOC sorption due to its obviously poor affinity with HOCs and restriction effect on the other powerful sorptive regions in cuticle/periderm. The significantly lower sorption of periderm than cuticle is attributed to the former having higher polysaccharide and lower depolymerizable lipids. The linear correlation of K(d) of bulk cuticle/periderm with polysaccharide content is observed for a potential prediction of plant uptake.

Ethylene contributes to potato aphid susceptibility in a compatible tomato host

Resistance to potato aphid (Macrosiphum euphorbiae) in tomato (Solanum lycopersicum) is conferred by Mi-1. Early during both compatible and incompatible interactions, potato aphid feeding induces the expression of ethylene (ET) biosynthetic genes. Here, we used genetic and pharmacologic approaches to investigate the role of ET signaling in basal defense and Mi-1-mediated resistance to potato aphid in tomato. The effect of potato aphid infestation on ET biosynthesis in susceptible and resistant plants was assessed. Aphid bioassays were performed using plants impaired in ET biosynthesis or perception using virus-induced gene silencing, the Never ripe (Nr) mutant, and 1-methylcyclopropene (MCP) treatment. A burst of ET was observed after aphid feeding in both resistant and susceptible plants, correlated with an increase in the expression of ET biosynthetic genes. However, impairing ET signaling or biosynthesis did not compromise Mi-1-mediated resistance but it did decrease susceptibility to potato aphid in a compatible host. ET may not play a significant role in Mi-1-mediated resistance to potato aphids in tomato but modulates the host basal defense, enhancing its susceptibility to the aphid.

Inhibition of 2-oxoglutarate dehydrogenase in potato tuber suggests the enzyme is limiting for respiration and confirms its importance in nitrogen assimilation,

The 2-oxoglutarate dehydrogenase complex constitutes a mitochondrially localized tricarboxylic acid cycle multienzyme system responsible for the conversion of 2-oxoglutarate to succinyl-coenzyme A concomitant with NAD(+) reduction. Although regulatory mechanisms of plant enzyme complexes have been characterized in vitro, little is known concerning their role in plant metabolism in situ. This issue has recently been addressed at the cellular level in nonplant systems via the use of specific phosphonate inhibitors of the enzyme. Here, we describe the application of these inhibitors for the functional analysis of the potato (Solanum tuberosum) tuber 2-oxoglutarate dehydrogenase complex. In vitro experiments revealed that succinyl phosphonate (SP) and a carboxy ethyl ester of SP are slow-binding inhibitors of the 2-oxoglutarate dehydrogenase complex, displaying greater inhibitory effects than a diethyl ester of SP, a phosphono ethyl ester of SP, or a triethyl ester of SP. Incubation of potato tuber slices with the inhibitors revealed that they were adequately taken up by the tissue and produced the anticipated effects on the in situ enzyme activity. In order to assess the metabolic consequences of the 2-oxoglutarate dehydrogenase complex inhibition, we evaluated the levels of a broad range of primary metabolites using an established gas chromatography-mass spectrometry method. We additionally analyzed the rate of respiration in both tuber discs and isolated mitochondria. Finally, we evaluated the metabolic fate of radiolabeled acetate, 2-oxoglutarate or glucose, and (13)C-labeled pyruvate and glutamate following incubation of tuber discs in the presence or absence of either SP or the carboxy ethyl ester of SP. The data obtained are discussed in the context of the roles of the 2-oxoglutarate dehydrogenase complex in respiration and carbon-nitrogen interactions.

Morphological and molecular characterization of a spontaneously tuberizing potato mutant: an insight into the regulatory mechanisms of tuber induction

BACKGROUND

Tuberization in potato (Solanum tuberosum L.) represents a morphogenetic transition of stolon growth to tuber formation, which is under complex environmental and endogenous regulation. In the present work, we studied the regulatory mechanisms and the role of different morphogenetic factors in a newly isolated potato mutant, which exhibited spontaneous tuberization (ST). The ST mutant was characterized in detail at morphological, physiological and biochemical levels.

RESULTS

Tuberization of the ST mutant grown in the soil was photoperiod-insensitive; predominantly sessile tubers formed directly from axillary buds even under continuous light. Single-node cuttings of the ST mutant cultured in vitro frequently formed tubers or basal tuber-like swellings instead of normal shoots under conditions routinely used for shoot propagation. The tuberization response of ST cuttings under light was dependent on sucrose, the concentration of which had to exceed certain threshold that inversely correlated with irradiance. Gibberellic acid prevented tuberization of ST cuttings, but failed to restore normal shoot phenotype and caused severe malformations. Carbohydrate analysis showed increased levels of both soluble sugars and starch in ST plants, with altered carbohydrate partitioning and metabolism. Comparative proteomic analysis revealed only a few differences between ST- and wild-type plants, primary amongst which seemed to be the absence of an isoform of manganese-stabilizing protein, a key subunit of photosystem II.

CONCLUSION

ST mutant exhibits complex developmental and phenotypic modifications, with features that are typical for plants strongly induced to tuberize. These changes are likely to be related to altered regulation of photosynthesis and carbohydrate metabolism rather than impaired transduction of inhibitory gibberellin or photoperiod-based signals. The effect of gibberellins on tuberization of ST mutant suggests that gibberellins inhibit tuberization downstream of the inductive effects of sucrose and other positive factors.

Effects of low concentrations of herbicides on full-season, field-grown potatoes

Current phytotoxicity plant test protocols for US pesticide registration require testing for effects on seedling emergence and early growth without regard to other important factors, such as plant reproduction. Yield and quality reduction can have significant economic and ecological effects. Therefore, field trials were conducted to determine if potato (Solanum tubersum L.) vegetative growth and tuber yield and quality were affected by herbicides at below recommended field rates. Potatoes were grown in fields at the Oregon State University Horticulture Farm with herbicides applied at below recommended field application rates 14 d after emergence (DAE) or at 28 DAE. Plant height was measured before and 14 d after application. Visual foliar injury was rated 14 d after application, and tuber yield and quality parameters were measured at harvest (120 DAE). Some tubers were grown in the greenhouse the following year to determine if there were carry-over effects. Potato vegetation and tuber yield quality were generally more affected by herbicides applied at 14 DAE than at 28 DAE. Tuber yield and quality parameters were more affected by lower herbicide rates than were plant height or injury. There were significant yield losses caused by low rates of sulfometuron methyl and imazapyr and, to a lesser extent, with glyphosate and cloransulam-methyl. Bromoxynil and MCPA ((4-chloro-2-methylphenoxy)acetic) acid had little effect on the plants. Vegetative responses did not accurately predict yield and quality responses of tubers; therefore, reproductive responses should be considered in phytotoxicity test protocols for pesticide registration in the USA.

Influence of alternating temperature preculture on cryopreservation results for potato shoot tips

Cryopreservation is the most suitable long-term storage method for genetic resources of vegetatively maintained crops like potato. In the Leibniz Institute of Plant Genetics and Crop Plant Research (IPK) the DMSO droplet method is applied, and so far more than 1000 accessions are cryopreserved with an average regeneration rate of 58%. New experiments with four potato accessions using alternating temperatures (22/8 degrees C day/night temperature, 8 h photoperiod, 7 d) prior to cryopreservation showed improved regeneration. The influence of this preculture on the shoot tips was studied for two wild, frost resistant species Solanum acaule and S. demissum and for two cultivated, frost sensitive potatoes S. tuberosum 'Désirée' and 'King Edward'. Comparison of liquid and solid media after cryopreservation showed improved regeneration on solid media with higher regeneration percentages, less callus formation and better plantlet structure. In comparative analyses biochemical factors like soluble sugars, starch, and amino acid concentrations were measured. Shoot tips after constant and after alternating temperature preculture were analyzed. Total concentrations of soluble sugars (glucose, fructose, and sucrose) were higher for all accessions after the alternating temperature preculture, which could be the reason for improved cryopreservation results.

Effects of different plant density and nitrogen application rate on nitrogen use efficiency of potato tuber

In order to investigate the plant density and nitrogen level on nitrogen use efficiency components (agronomical, physiological, apparent recovery and nitrogen use efficiency), the amount of nitrogen uptake by plant, yield and yield components of potato (Solanum tuberosum L.) Agria cultivars' tuber, a factorial experiment based on randomized complete block design was conducted in Ardabil, Iran, in 2006 with three replications. Factors were adjusted for the nitrogen level (0, 80, 160 and 200 kg ha(-1) net nitrogen) and plant density (5.5, 7.5 and 11 plant m(-2)). Results showed that with increasing the nitrogen levels and plant densities agronomical nitrogen use efficiency, physiological nitrogen efficiency and nitrogen use efficiency were decreased and apparent recovery nitrogen efficiency was increased. The most nitrogen uptake in plant was observed at the 200 kg ha(-1) net nitrogen. The most yield and number of tuber per unit area were gained at the 80 and 160 kg ha(-1) net nitrogen. Increasing the plant density resulted in increasing in the tuber yield per unit area and the rate of nitrogen up to the 160 kg ha(-1) net nitrogen. So, application of the 80 kg ha(-1) net nitrogen and plant density of 11 plant m(-2) is recommended to get highest yield with the most nitrogen use efficiency.