Tuberosum Cv Research Articles

Interaction between arbuscular mycorrhizal fungi and the nematicide aldicarb on hatch and development of the potato cyst nematode, Globodera pallida, and yield of potatoes

Abstract The effects of inoculation of roots of the potato (Solanum tuberosum) cv. Golden Wonder with the mixed-isolate arbuscular mycorrhizal fungus (AMF) inoculum Vaminoc, or with three single-isolates AMF inocula (Glomus intraradices, G. mosseae and G. dussii; components of Vaminoc), on the potato cyst nematode (PCN) Globodera pallida were assessed in a pot experiment in the presence or absence of the nematicide aldicarb (Temik 10G). Mycorrhization of potato roots stimulated an 11% overall mean increase in the hatch of G. pallida within the first 2-4 weeks from planting. In the presence of aldicarb, AMF-inoculated plants exhibited only 57% of the PCN population size (viable eggs (g soil)−1) of the non-inoculated plants; in the absence of aldicarb the respective value was 42%. Root length colonisation by AMF was unaffected by the application of aldicarb. Roots of PCN-infested plants exhibited reduced levels of mycorrhizal colonisation (41%) compared to non-PCN-infested plants (45%). The AMF isolates used differed in their ability to produce a plant growth response (expressed as root dry weight, shoot dry weight or total dry biomass) and to affect tuber yield. In this regard, the single Glomus isolates enhanced plant growth (36% increase in total dry biomass) and improved fresh tuber yield by 22% on average, while Vaminoc had, in most cases, no effect. It was concluded that AMF have potential to reduce G. pallida multiplication via a dual mechanism involving stimulation of nematode hatch and inhibition of root invasion. Field experimentation will be required to take this research forward and assess the feasibility of including AMF in G. pallida integrated management strategies.

The effects of IAA and tetcyclacis on tuberization in potato (Solanum tuberosum L.) shoot cultures in vitro

Potato (Solanum tuberosum cv. Desiree) shoots grown in vitro in continuous darkness or in long days (LDs), were used to investigate indole-3-acetic acid (IAA) effects on stolon initiation and tuber formation, combining IAA with increased or decreased gibberellin levels. An increased gibberellin (GA) level was achieved by the applying 1 μM GA3, while decreased gibberellin level was presumably realized by the adding 3 μM tetcyclacis (Tc). About 15% of potato shoots developed stolons both in LDs and in darkness. Stolon initiation was stimulated by GA3 in darkness and by Tc in LDs. Tuber formation was strongly inhibited in LDs and by GA3 both in light and darkness, but stimulated in darkness at low GA level. Exceptionally, tuber formation occurred in LDs at the highest Tc concentrations, in about 25% of explants. Indole-3-acetic acid alone stimulated stolon formation in LDs, both in the presence or absence of GA3. IAA alone also stimulated tuber formation in dark-grown shoots, but could not overcome the inhibitory effect of LDs. Indications that, depending on their concentration ratio, IAA may interact with GA3 in different tuberization phases, have been discussed.

Heavy metal soil contamination delays the appearance of virus-induced symptoms on potato but favours virus accumulation

Here we report on the investigation of virus infection development in plants undergoing simultaneous heavy metal stress. We carried out small-scale field experiments using model system Potato virus X (PVX) – Solanum tuberosum cv. Povin' (potato) plants. Heavy metals zinc (Zn), copper (Cu) and lead (Pb) were added to the soil separately (monometal contamination) at a range of concentrations. Our results show that heavy metal stress significantly delays the appearance and potentiates severity of virus-specific symptoms on infected potato plants. We also demonstrate that PVX content in plants may increase tremendously in response to this abiotic stressor. Finally, we provide links to the possible consequences in the context of virus epidemiology.

Plant Hormones Isolated from “Katahdin” Potato Plant Tissues and the Influence of Photoperiod and Temperature on Their Levels in Relation to Tuber Induction

Qualitative and quantitative analyses were carried out on vegetative tissues of potato (Solanum tuberosum cv. “Katahdin”) in search of natural products thought to play a role in tuber induction. Tissues were obtained from plants initially grown in a growth chamber under noninducing conditions (30°C day and 28°C night with an 18-h photoperiod), and then half of the plants were moved to inducing chambers (28°C day and 13°C night with a 10-h photoperiod) for 10 days prior to tissue harvest. Plants from each chamber were then harvested at 2-day intervals for 10 days, separated into above- and belowground portions, and the lyophilized tissues were extracted and subjected to rigorous purification and separation using high-performance liquid chromatography. This was followed by identification and quantification using combined gas chromatography-mass spectrometry. Compounds isolated and identified included gibberellic acid; cytokinins cis-zeatin riboside, trans-zeatin, trans-zeatin riboside, and isopentenyladenine; and jasmonates jasmonic acid, tuberonic acid and its methyl ester, methyl 7-isocucurbate, and 9,10-dihydromethyljasmonate. Methyl 7-isocucurbate and 9,10-dihydromethyljasmonate were detected for the first time in potato tissue as endogenous compounds. Cytokinin and jasmonate levels generally increased under inducing conditions, whereas gibberellic acid levels declined progressively during the 10-day sampling period. Only gibberellic acid, jasmonic acid, and cis-zeatin riboside levels were significantly influenced by induction.

Interspecific potato somatic hybrids between Solanum berthaultii and Solanum tuberosum L. showed recombinant plastome and improved tolerance to salinity

In this study three somatic hybrid lines originating from protoplast fusion between Solanum tuberosum cv. BF15 and Solanum berthaultii were subjected to a detailed molecular analysis using the I-SSR-PCR technique based on 5′-anchored microsatellite primers. The data obtained revealed a polymorphism between the different lines, suggesting that they correspond to symmetric hybrids. The analysis of chloroplast genome of these hybrids showed that they are resulting from a recombination between parental plastomes. When transferred to a greenhouse, these hybrid lines displayed an improved vigour compared to the cultivated potato BF15 parent. Indeed, an important growth rate and high tuber yield and weight were obtained for these hybrids compared to the parent. Some of these hybrids showed also an improved ion homeostasis control and they seem to display a better tolerance to salt stress compared to the potato BF15 parent.

Potato aucuba mosaic virus in Potato in New York State

Solanum tuberosum cv. Elmer's Blue is one of a number of heritage potato accessions maintained at Cornell University that exhibit virus-like symptoms of stunting and a leaf yellowing or a mottle mosaic. Testing of this cultivar by double-antibody sandwich (DAS)-ELISA revealed that it was infected with Potato virus S (PVS) but none of the other common potato viruses screened for in North American potato certification programs (3). Mechanical inoculation of sap from potato cv. Elmer's Blue onto Nicotiana debneyii, N. megalosiphon, N. occidentalis, and N. tabacum produced a range of yellowing and mosaic symptoms (symptomless on N. tabacum), indicating the presence of a transmissible agent, but all these hosts tested negative for PVS. To identify possible viruses, reverse transcription (RT)-PCR assays involving generic primers for different groups of viruses were performed on the potato and the Nicotiana spp. Degenerate primers specific to members of the genus Potexvirus (4) amplified a 600-bp region from the symptomatic potato and N. debneyii. Nucleotide sequencing of the RT-PCR amplified product from potato cv. Elmer's Blue (Genbank Accession No. EF609120) and comparisons with GenBank sequences revealed the amplified sequence as having 91% identity with the genomic sequence of Potato aucuba mosaic virus (PAMV; Accession No. S73580). The presence of this virus in potato cv. Elmer's Blue and N. debneyii was confirmed by PAMV-specific antibodies (Agdia, Inc., Elkhart, IN) in a DAS-ELISA format. PAMV is reported to occur worldwide, but uncommonly, with most descriptive work from Europe (2). While this virus has been studied in North America (1,2), these reports employed virus stocks from Europe under experimental conditions or virus in tubers obtained directly from Europe; to our knowledge, there are no unambiguous reports of PAMV in naturally infected North American potato cultivars. By contrast, the PAMV-infected cultivar in this report is a selection originally from a Canadian grower, and although not grown commercially, it is maintained in garden and field plots in New York and other states.

Use of a stress inducible promoter to drive ectopic AtCBF expression improves potato freezing tolerance while minimizing negative effects on tuber yield

Solanum tuberosum is a frost-sensitive species incapable of cold acclimation. A brief exposure to frost can significantly reduce its yields, while hard frosts can completely destroy entire crops. Thus, gains in freezing tolerance of even a few degrees would be of considerable benefit relative to frost damage. The S. tuberosum cv. Umatilla was transformed with three Arabidopsis CBF genes (AtCBF1-3) driven by either a constitutive CaMV35S or a stress-inducible Arabidopsis rd29A promoter. AtCBF1 and AtCBF3 over-expression via the 35S promoter increased freezing tolerance about 2 degrees C, whereas AtCBF2 over-expression failed to increase freezing tolerance. Transgenic plants of AtCBF1 and AtCBF3 driven by the rd29A promoter reached the same level of freezing tolerance as the 35S versions within a few hours of exposure to low but non-freezing temperatures. Constitutive expression of AtCBF genes was associated with negative phenotypes, including smaller leaves, stunted plants, delayed flowering, and reduction or lack of tuber production. While imparting the same degree of freezing tolerance, control of AtCBF expression via the stress-inducible promoter ameliorated these negative phenotypic effects and restored tuber production to levels similar to wild-type plants. These results suggest that use of a stress-inducible promoter to direct CBF transgene expression can yield significant gains in freezing tolerance without negatively impacting agronomically important traits in potato.

Changes in the antioxidant status in leaves of Solanum species in response to elicitor from Phytophthora infestans

Three Solanum genotypes with various polygenic resistance levels to the oomycete pathogen Phytophthora infestans (Mont.) De Bary were studied for their antioxidant response to the pathogen culture filtrate (CF). Detached plant leaves were treated with CF for 6, 18 and 30 h, and assayed for changes in hydrogen peroxide content, total ascorbate and glutathione pools and redox ratios (reduced form to total pool), as well as for changes in activities of ascorbate peroxidase, glutathione reductase and glutathione-S-transferase. In CF treated leaves of non-host resistant S. nigrum var. gigantea and field resistant S. tuberosum cv Bzura, the H(2)O(2) content did not change in comparison to water treated control leaves, whereas in the susceptible S. tuberosum clone H-8105 it decreased below the control level. In CF treated leaves of all genotypes, the total ascorbate pools were relatively unaltered and their redox ratio changed only transiently. In Bzura leaves the total glutathione content increased earlier than in the two other genotypes. The glutathione redox ratio remained rather stable, except for the susceptible clone H-8105, where it decreased transiently by about 42%. The relative increases in activity of all the studied enzymes were the highest in the susceptible clone H-8105. The results are discussed in the light of oxidative processes occurring in CF treated leaves. We conclude that stringent control of pro- and anti-oxidant reactions bringing the H(2)O(2) and/or cellular redox state to the threshold level is decisive for deployment of an effective defense strategy.

Modeling expansion of individual leaves in the potato canopy

A model to simulate expansion of individual leaves in potato ( Solanum tuberosum cv. Kennebec) was developed by modifying a growth simulation routine from the model POTATO. Data for model development and testing were obtained from three soil–plant–atmosphere-research (SPAR) chamber experiments. The first experiment (D1) used six SPAR chambers with treatments of 14/10, 17/12, 20/15, 23/18, 28/23, or 34/29 °C day/night temperatures (16 h thermoperiod) at an elevated atmospheric carbon dioxide concentration ([CO 2]) of 740 μmol mol −1. Experiment D2 used two SPAR chambers at 23/18 °C at 740 μmol mol −1 [CO 2]. Experiment D3 duplicated the temperature treatments of D1 but at ambient [CO 2] (370 μmol mol −1). Potato leaf area expansion was sensitive to air temperature and [CO 2]. Maximum individual leaf area values were highest at cooler temperatures and elevated [CO 2]. Growth duration, defined as the time interval between leaf appearance and when 99% of final area was attained, was negatively correlated with increasing temperature. Growth duration increased by about 4 days at 14/10 and 34/29 °C at ambient [CO 2]. Temperature response and leaf physiological aging functions were developed from D1 and used to modify the existing growth model. D2 and D3 data were used to evaluate the modified model simulations during conditions of non-limited and limited carbohydrate availability. By varying an input to the model that simulates the effect of plant carbohydrate status on leaf expansion, the model was shown to be capable of reproducing leaf growth curves within 8% of the measured final area. The modified leaf expansion model is suitable for integration with existing potato models that simulate canopy leaf appearance. The expansion model provides an approach for coupling plant assimilate, water, and nutrient status with canopy expansion and the new response functions in the model can potentially be modified for use in different crop models.

Production of high‐starch, low‐glucose potatoes through over‐expression of the metabolic regulator SnRK1

Transgenic potato (Solanum tuberosum cv. Prairie) lines were produced over-expressing a sucrose non-fermenting-1-related protein kinase-1 gene (SnRK1) under the control of a patatin (tuber-specific) promoter. SnRK1 activity in the tubers of three independent transgenic lines was increased by 55%-167% compared with that in the wild-type. Glucose levels were decreased, at 17%-56% of the levels of the wild-type, and the starch content showed an increase of 23%-30%. Sucrose and fructose levels in the tubers of the transgenic plants did not show a significant change. Northern analyses of genes encoding sucrose synthase and ADP-glucose pyrophosphorylase, two key enzymes involved in the biosynthetic pathway from sucrose to starch, showed that the expression of both was increased in tubers of the transgenic lines compared with the wild-type. In contrast, the expression of genes encoding two other enzymes of carbohydrate metabolism, alpha-amylase and sucrose phosphate synthase, showed no change. The activity of sucrose synthase and ADP-glucose pyrophosphorylase was also increased, by approximately 20%-60% and three- to five-fold, respectively, whereas the activity of hexokinase was unchanged. The results are consistent with a role for SnRK1 in regulating carbon flux through the storage pathway to starch biosynthesis. They emphasize the importance of SnRK1 in the regulation of carbohydrate metabolism and resource partitioning, and indicate a specific role for SnRK1 in the control of starch accumulation in potato tubers.

Growth modulation of transgenic potato plants by heterologous expression of bacterial carbohydrate-binding module

Transgenic potato plants (Solanum tuberosum cv. Desiree) expressing the bacterial carbohydrate-binding module (CBM) family III, which is part of the Clostridium cellulovorans CBPA, under control of the CaMV 35S promoter were employed to investigate the influence of this protein on plant development. Eleven independent transgenic plants were found to express the cbm gene, at levels varying from one to four copies. Relative to non-transgenic controls, CBM-expressing plants were characterized by significantly more rapid elongation of the main stem. In addition, under both greenhouse and field conditions, the emergence rate of these plants was higher than in the controls, and their leaf area at early stages of development was larger, resulting in faster accumulation of fresh and dry weight than in control plants. Determination of cell size indicated that epidermal cells in young tissue were significantly larger in CBM-expressing than in control potato plants. These findings suggest that the CBM influence at the cellular level my cause significant alterations in plant growth both in tissue culture and in vivo under field conditions.

Impact of iron stress on biomass, yield, metabolism and quality of potato ( Solanum tuberosum L.)

In order to study the influence of variable iron on biomass, economic yield and role of iron in potato ( Solanum tuberosum) cv. Chandramukhi metabolism, plants were grown in refined sand at variable iron ranging from 0.001 to 2.0 mM. Exposure of potato plants to Fe stress (i.e. a Fe concentration different from 0.1 mM) shows retarded growth, decreased chlorophyll concentration and Hill reaction activity, induced changes in enzyme activities and concentration of Fe and Mn. The visible symptoms of iron deficiency appeared on day 15 at 0.001 mM Fe as chlorosis of young leaves. The excess of iron (at >0.1 mM Fe) appeared later, after 25 days and the chlorosis was observed on older leaves. Both deficiency (0.001 mM) and excess (>0.1 mM) of iron reduced the tuber yield, deteriorating its quality by lowering the concentration of sugars, starch and protein nitrogen and increasing the accumulation of non-protein nitrogen and phenols in tubers.

The Free NADH Concentration Is Kept Constant in Plant Mitochondria under Different Metabolic Conditions

The reduced coenzyme NADH plays a central role in mitochondrial respiratory metabolism. However, reports on the amount of free NADH in mitochondria are sparse and contradictory. We first determined the emission spectrum of NADH bound to proteins using isothermal titration calorimetry combined with fluorescence spectroscopy. The NADH content of actively respiring mitochondria (from potato tubers [Solanum tuberosum cv Bintje]) in different metabolic states was then measured by spectral decomposition analysis of fluorescence emission spectra. Most of the mitochondrial NADH is bound to proteins, and the amount is low in state 3 (substrate + ADP present) and high in state 2 (only substrate present) and state 4 (substrate + ATP). By contrast, the amount of free NADH is low but relatively constant, even increasing a little in state 3. Using modeling, we show that these results can be explained by a 2.5- to 3-fold weaker average binding of NADH to mitochondrial protein in state 3 compared with state 4. This indicates that there is a specific mechanism for free NADH homeostasis and that the concentration of free NADH in the mitochondrial matrix per se does not play a regulatory role in mitochondrial metabolism. These findings have far-reaching consequences for the interpretation of cellular metabolism.

Characterization and functional analysis of a pollen-specific gene st901 in Solanum tuberosum

A pollen-specific gene, sb401, which was isolated from a cDNA library of in vitro geminated pollen of the diploid potato species Solanum berthaultii, belongs to the class of genes expressed late during pollen development. Using sb401 as a probe, a pollen-specific gene st901 was isolated from the genomic library of a potato species Solanum tuberosum cv. Desiree. Sequencing and RT-PCR analysis showed that the st901 genomic gene is 2,889 bp long, contains three exons and two introns, and encodes a putative polypeptide of 217 residues. The predicted protein sequence contains four imperfect repeated motifs of V-V-E-K-K-N/E-E; the core sequence of the repeats (K-K-N/E-E) resembles a microtubule-binding domain of the microtubule-associated protein MAP1B from mouse. The examination of a promoter-reporter construct in transgenic potato plants revealed that the st901 is expressed exclusively in mature pollen grains, which is consistent with the results of Northern blot and RT-PCR. For analysis of the function of st901, transgenic plants harboring antisense copies of st901 cDNA driven by a native st901 promoter were generated. Suppression of st901 gene in potato resulted in aberrant pollen at maturation and pollen viability of transgenic plants ranged from 4.4 to 14.8%, while that of control plants were more than 90%. These results strongly suggest that st901 has an essential role in pollen development.

Antisense reduction of serine hydroxymethyltransferase results in diurnal displacement of NH4+ assimilation in leaves of Solanum tuberosum

Serine hydroxymethyltransferase (SHMT) is part of the mitochondrial enzyme complex catalysing the photorespiratory production of serine, ammonium and CO(2) from glycine. Potato plants (Solanum tuberosum cv. Solara) with antisensed SHMT were generated to investigate whether photorespiratory intermediates accumulated during light lead to nocturnal activation of the nitrogen-assimilating enzymes glutamine synthetase (GS) and glutamate synthase (GOGAT). The transformant lines contained 70-90% less SHMT protein, and exhibited a corresponding decrease in mitochondrial SHMT activity. SHMT antisense plants displayed lower photosynthetic capacity and accumulated glycine in light. Glycine was converted to serine in the second half of the light period, while serine, ammonium and glutamine showed an inverse diurnal rhythm and reached highest values in darkness. GS/GOGAT protein levels and activities in the transgenics also reached maximum levels in darkness. The diurnal displacement of NH(4)(+) assimilation was accompanied by a change in the subunit composition of GS(2), but not GS(1). It is concluded that internal accumulation of post-photorespiratory ammonium is leading to nocturnal activation of GS/GOGAT, and that the time shift in ammonia assimilation can constitute part of a strategy to survive photorespiratory impairment.

한국 분리주 감자 잎말림 바이러스 (PLRV) 외피 단백질 유전자의 클로닝 및 감자 내 도입

한국 분리주 감자잎말림바이러스 (PLRV)로부터 627bp 크기의 외피단백질 유전자의 ORF (AF296280)를 분리하여 장려품종 감자인 '수미'를 형질전환 하였다. 17계통의 형질전환체를 선발하여 온실과 포장에서 5세대를 증식하면서 PLRV에 대한 저항성이 큰 5계통을 선발 하였다. 도입된 유전자들의 유전적인 안정성을 확인하기위해 PCR, Southern, 그리고 northern blot 분석을 수행하였다. 또한 클론으로 증식된 형질전환 감자들의 특성과 저항성도 검정하였다. 형질전환된 감자들에서 PLRV의 외피단백질 유전자는 안전적으로 발현되며 저항성을 유지하였으며, 유사도가 비교적 낮은 감자 바이러스 Y (PVY)에는 저항성을 나타내지 않았다. 따라서 이러한 저항성은 도입된 유전자와 유사성도가 높은 바이러스에 저항성을 나타내는 homology dependent gene silencing으로 판단되었다. 유망계통 형질전환 감자 계통들의 포장평가를 통해 PLRV에 대한 저항성을 제외한 주요한 농업적 특성과 식물학적 특성은 형질전환 되지 않은 감자와 큰 차이를 보이지 않았다. The coat protein gene (AF296280) of the Korean isolate Potato leafroll virus (PLRV) was cloned and the open reading frame (627 bp) was transformed into potato (Solanum tuberosum cv. Superior). Out of seventeen individual transgenic lines, five lines were identified to confer resistance to PLRV through the five generation's selection program in the greenhouse as well as isolated trial field. Successful introduction and genetic stability of coat protein gene in the genome of potato were confirmed by polymerase chain reaction (PCR), Southern blot hybridization and northern blot hybridization. Some of the transgenic lines were highly resistant to PLRV but did not show any resistance to less homologous Potato virus Y (PVY). Our results suggest that the resistance to PLRV is due to homology dependent gene silencing by sense strand coat protein gene. In addition, the results of field test through five generations showed that there were no significant differences comparing to nontransgenic potatoes in the morphological aspect of shoot as well as tuber, Ho remarkable differences were also observed in the major agronomic characters and yields except for the resistance to PLRV.

Kunitz-Type Serine Protease Inhibitor from Potato (Solanum tuberosum L. cv. Jopung)

An antifungal protein, AFP-J, was purified from tubers of the potato (Solanum tuberosum cv. L Jopung) by various chromatographic columns. AFP-J strongly inhibited yeast fungal strains, including Candida albicans, Trichosporon beigelii, and Saccharomyces cerevisiae, whereas it exhibited no activity against crop fungal pathogens. Automated Edman degradation determined the partial N-terminal sequence of AFP-J to be NH2-Leu-Pro-Ser-Asp-Ala-Thr-Leu-Val-Leu-Asp-Gln-Thr-Gly-Lys-G lu-Leu-Asp-Ala-Arg-Leu-. The partially sequence had 83% homology with a serine protease inhibitor belonging to the Kunitz family, and the protein inhibited chymotrypsin, pepsin, and trypsin. Mass spectrometry showed that its molecular mass was 13 500.5 Da. This protease inhibitor suppressed over 50% the proteolytic activity at 400 microg/mL. These results suggest that AFP-J is an excellent candidate as a lead compound for the development of novel antiinfective agents.

Expression of a fungal endo-α-1,5- l-arabinanase during stolon differentiation in potato inhibits tuber formation and results in accumulation of starch and tuber-specific transcripts in the stem

Potato ( Solanum tuberosum cv. Posmo) was transformed with a fungal endo-α-1,5- l-arabinanase gene (E.C. 3.2.1.99) and the enzyme secreted to the apoplast. Using promoters that are known to be sucrose inducible in potato—the granule bound starch synthase promoter and the promoter of the patatin storage protein gene—strong expression of the arabinanase was observed in developing sinks, notably the meristems giving rise to tubers, stolons and side shoots. Expression of the arabinanase interfered with normal meristem function and depending on the promoter used, different phenotypes were obtained devoid of tubers or both tubers, stolons and side shoots. The altered ratio of source to sink tissues in the transformants was used to study the regulation of photoassimilate allocation to different tissues. Tuberless transformants were unable to fully balance supply with demand and excess photoassimilates were deposited as starch granules with the structure of tuber starch in above ground tissues, notably in the stem pith. Transcripts normally associated with tuber development were detected in the starch accumulating tissues and the tuberlike transcript profile was not limited to transcripts that are directly sucrose inducible. These observations are discussed in relation to organ identity and source–sink regulation in potato.

Hydroxylated jasmonate levels during stolon to tuber transition inSolarium tuberosum L

Various octadecanoids and derived compounds have been identified in potato leaves. However, information regarding jasmonate hydroxylated forms in stolons or tubers is scarce. We investigated endogenous jasmonates in stolon material ofSolarium tuberosum cv. Spunta. Stolons and incipient tubers were collected from 8 weeks old plants. The material was cut into apical regions and stolons. We identified jasmonic acid (JA), methyl jasmonate, 11-OH-JA, 12-OH-JA, 12-oxo-phytodienoic acid (OPDA) and a conjugate. The content of JA and 12OH-JA decreased in the apical region but remained high in stolons during tuberization. Thus the apical region might be a site of JAs-utilization or metabolization and stolons might supply JAs to that region. The content of 12-OH-JA was higher than that of 11-OH-JA in all stages analyzed, both in apical regions and stolons. However, these compounds showed a different time-course in the apical region: while 11-OH-JA increased, 12-OH-JA decreased. Thus, JA from leaves or roots could be transported as 12-OH-JA to the apical region, stimulating tuber formation.

Characterization of tryptophan-overproducing potato transgenic for a mutant rice anthranilate synthase α-subunit gene (OASA1D)

Potato plants (Solanum tuberosum cv. May Queen) transgenic for OASA1D, which encodes a point mutant of an alpha-subunit of rice (Oryza sativa) anthranilate synthase (AS, EC 4.1.3.27), were generated in order to determine the effects of the mutant gene on levels of free tryptophan (Trp) and AS activity in this important crop. Expression of OASA1D in potato induced a 2- to 20-fold increase in the amount of free Trp. This increase was likely due to a reduction in the sensitivity of AS containing the mutant alpha-subunit to feedback inhibition by Trp. Nontargeted metabolite profiling by high-performance liquid chromatography coupled with ultraviolet photodiode array detection as well as targeted profiling by liquid chromatography coupled with mass spectrometry revealed no marked changes in the levels of other metabolites, with the exception of indole-3-acetic acid (IAA), in the transgenic plants. The level of IAA in the upper part of the shoot was increased by a factor of 8.3-39, depending on the transgenic lines, with no detectable effect on plant growth or development. The effects of transformation thus appeared limited to the biosynthesis of Trp and IAA, with the overall metabolic network in potato being virtually unaffected. These results suggest that transformation with OASA1D may prove effective for the breeding of crops with an increased level of free Trp.