Occurrence of hydroxylated jasmonic acids in leaflets of Solanum demissum plants grown under long- and short-day conditions

Under short-day (SD) conditions both 11-OH-jasmonic acid (11-OH-JA) and a smaller quantity of 12-OH-JA occurred in leaflets of Solanum demissum Lindl. Plants which had formed tubers. This is the first time that 11-OH-JA has been detected as a native substance in higher plants. Under long-day (LD) conditions no tubers were formed and none of these compounds were detectable. A positive correlation was found between the occurrence of 11-OH-JA and 12-OH-JA in leaflets of S. demissum and tuber formation, but a causal relation has yet to be proved. The (-)-JA content in leaflets was not significantly different under short and long days. Mild stress applied to detached SD and LD leaflets caused a rapid accumulation of JA in these leaflets. Upon this treatment an increase in the levels of hydroxylated JAs was detected in SD leaflets only.
JA was a potent promotor of tuber formation in vitro in S. demissum explants. Lipoxygenase (LOX: EC 1.13.11.12) is involved in the biosynthesis of JA. Under SD conditions, application of salicylhydroxamic acid (SHAM), an inhibitor of LOX activity, to the roots did not prevent tuber formation in vivo. It is suggested that daylength controls the hydroxylation of JA. The enzyme(s), responsible for the hydroxylation of JA, would only be effective under SD conditions.     

Growth rate of potato tubers and endogenous contents of indolylacetic acid and abscisic acid

Potato plants ( Solanum tuberosum L. ev. Ostara) were grown in water culture and the growth rate of individual tubers was measured daily or at two day intervals. Tubers of different growth rate and/or different age (days after tuberization) were harvested and analysed for indolylacetic acid (IAA) and abscisic acid (ABA). Within individual tubers the IAA content decreases from the apical to the basal part of the tuber. Tuber age and corresponding fresh weight are negatively correlated with the endogenous IAA content. If, however, individual tubers of comparable age but different growth rates are compared, a significant positive correlation between growth rate and IAA content is revealed, while ABA showed a significant negative correlation with growth rate. Removal of all fast-growing tubers from individual plants causes an increase in the growth rate of the remaining tubers within 3–4 days. This coincides with a particularly steep increase in IAA content. The data support the idea that endogenous IAA content may be one factor responsible for controlling the growth rate ("sink-activity ") of individual tubers.     

Morphogenesis of potato plants in vitro. I. Effect of light quality and hormones

Stem cuttings of potato plants (Solanum tuberosum L., cv. Miranda) were cultured in vitro on MS medium with sucrose either without or with addition of indole-3-acetic acid (IAA) or kinetin (K) under red light (R) or blue light (B). Plants on medium without hormones under R were thin, long, with very small leaves, and produced no or only a few microtubers (after longer-lasting cultivations). In B, plants remained short, thick, with large, wellde-veloped leaves and produced a significant amount of microtubers. Darkening of both roots and shoots strongly promoted tuber formation; the tubers were formed on the darkened part of the plant. IAA had no pronounced effect on plant development in B except for slight lengthening of the stem, and, in longer cultivations, slightly enhanced tuber formation as well. In R, IAA brought about several significant effects: stem reduction and induction of tuber formation being the most significant. Kinetin in R increased tuber formation slightly. In B, kinetin not only strongly stimulated tuber formation, but also increased the total fresh weight and root (+ stolons)/shoot ratio. Results are discussed with regard to the possible role of auxins and/or cytokinins in mediating the morphogenetic effects of light.     

Abscisic acid involvement in the induction of summer‐dormancy in Poa bulbosa, a grass geophyte

Summer‐dormancy occurs in geophytes that inhabit regions with a Mediterranean climate (mild, rainy winters and hot, dry summers). The environmental control of summer‐dormancy and the involvement of phytohormones in its induction have been little studied. Poa bulbosa L. is a perennial grass geophyte in which summer‐dormancy is induced by long days and by high temperature. Prolonged treatment with ABA (0.1‐1.0 m M ) under non‐inductive 8‐h short days (SD) resulted in cessation of leaf and tiller production and in the development of typical features of dormancy: bulbing at the base of the tillers and leaf senescence. Short‐term applications of ABA had similar effects but dormancy was transient, i.e. after a short while, leaf growth from the formed bulbs was resumed. ABA treatment of plants growing under an inductive 16‐h photoperiod (LD) enhanced the onset of dormancy. Endogenous levels of ABA in leaf blades and at the tiller base (where the bulb develops) increased markedly after the plants were transferred from SD to LD. This increase was greater in the tiller base, and concomitant with bulb maturation. High temperature (27/22 vs 22/17°C) accelerated both bulb development and ABA accumulation in leaf blades.
These results suggest that ABA plays a key role in the photoperiodic induction and development of summer‐dormancy in P. bulbosa .     

Morphogenesis of potato plants in vitro. II. Endogenous levels,distribution, and metabolism of IAA and cytokinins

The levels of endogenous IAA and cytokinins (zeatin, zeatin riboside, isopentenyladenine, and isopentenyladenosine) were determined in potato plants cultured in vitro under red light (R) and blue light (B) on medium with or without hormones. On medium without hormones in B, plants contained much higher cytokinin levels, particularly in leaves and roots, and also slightly elevated IAA levels. Kinetin in the medium in B changed the distribution of cytokinins and significantly increased IAA level in roots. In R, the presence of kinetin led to an increased cytokinin level in the whole plant, while the IAA level was slightly lower. IAA in the medium in B decreased cytokinin level in all plant parts, while the IAA level did not change significantly. In R, the presence of IAA in the medium led to a moderate increase of CK level and to a significant increase in IAA level, especially in roots. Uptake of 1-¹⁴C-IAA and of ³H-zeatin was generally higher in B than in R. Higher percentage of IAA taken up in B was converted to conjugates in the roots. Metabolism of ³H-zeatin was similar in R and B with only slight differences in metabolite amounts.Thus, in all experimental situations in which tuber formation was stimulated, IAA level in roots and stolons rose significantly, stressing the importance of an IAA gradient for tuber formation.     

Effect of Zinc Sulfate and Boric Acid on the Hormonal Status of Potato Plants in Relation to Tuberization

Potato (Solanum tuberosum L.) plants were grown in a greenhouse using zinc- and boron-deficient soil. The effects of seed-tuber treatment with 3 mM zinc sulfate and 8 mM boric acid on the content and ratio of phytohormones in the leaves and mature tubers, the indices of photosynthetic activity, the rate and NaF-sensitivity of respiration, and the tuber growth were studied. Zinc-sulfate treatment shifted the hormonal balance toward a substantial increase in the cytokinin content and the cytokinin/ABA ratio, as well as a decrease in the IAA/cytokinin ratio. Boric-acid treatment resulted in an increase in the IAA content and IAA/cytokinin ratio. Zinc-sulfate treatment abolished the apical dominance and increased the tuber weight due to their increased number and the number of phellem (cork) cell layers. Boric-acid treatment increased cell diameter in the tuber perimedullary zone; an increase in tuber weight per plant was related to tuber growth. A relationship between changes in the plant hormonal status induced by zinc-sulfate and boric-acid treatments and the activity of physiological processes is discussed.     

Endogenous hormonal levels and growth of dark-incubated shoots of Catasetum fimbriatum

Apical shoots and Lateral buds of the epiphytic orchid Catasetum fimbriatum give rise to rootless etiolated stolons, when cultured in the presence of light and then transferred to the dark. The stolons are characterized by fast and continuous apical longitudinal growth. Measurements of four endogenous cytokinin, indole-3-acetic acid (IAA) and abscisic acid (ABA) levels in etiolated shoots and light-grown plants were low. However, after transfer of green plants to the dark, cytokinin Levels increased 3- and 7-fold by 10 and 30 days of incubation, respectively. IAA levels also increased significantly, but the increase was not as great as for cytokinins. A similar trend was observed in the roots. A close relationship seems to exist between both cytokinin accumulation and the formation of etiolated stolons. Variations in ABA levels were practically inconspicuous. The presence of paclobutrazol in the medium, a potent inhibitor of gibberellin synthesis, strongly inhibited etiolated and non-etiolated longitudinal shoot growth, although no apparent effect was observed on apical meristem activity.     

Changes in Tuberization and Assimilate Partitioning in Potato (Solanum tuberosum) During the First 18 Days of Photoperiod Treatment

Potato (Solanum tuberosum L.) plants were equilibrated under18-h days (LD) before a subset of the plants was transferredto 10-h photosynthetic periods with either a dark night (SD)or an 8-h dim photoperiod extension with incandescent lamps(DE). Plants were harvested at regular intervals for growthanalysis during the 18 d after transfer. Leaf area increasedrapidly under SD and LD but was inhibited under DE. Internodeelongation was similar under SD and LD, but much higher underDE. Stem d. wts were lowest under SD. Axillary branching wasgenerally greatest under LD. Total shoot weights were greatestunder LD. Total shoot weights were similar under SD to thoseunder DE, even though within 18 d of transfer as much as one-thirdof the biomass of SD plants was in tubers. Tuber initiationwas later under LD than under SD, and was delayed even moreby DE. High temperature increased the delay in tuberizationfrom LD. The early tuber initiation under SD was concurrentwith a rapid increase in leaf area under SD, not with an earlycessation of leaf growth. This was contrary to assumptions basedupon studies of long-term effects of photoperiod. The resultanthigh sink strength under SD contributed to the greater efficiencyof biomass production. Potato, Solanum tuberosum L. cv. Norchip, photoperiod, temperature, morphology, tuberization, growth analysis, biomass partitioning, sink strength, leaf area, short term effects     

Occurrence of jasmonic acid in organs of Solanum tuberosum L. and its effect on tuberization

The aims of this study were to demonstrate the endogenous presence of jasmonic acid (JA) in roots, stolons and periderm of new formed tubers, by means of bioassays, ELISA and GC-MS, and to test a microdrop bioassay using the leaflets of potato cuttings cultured in vitro. Our results confirm the existence of JA by bioassays and GC-MS in foliage, stolons, roots and tuber periderm.Abbreviations DW dry weight - GC-MS gas chromatography-mass spectrometry - JA jasmonic acid - MeOH methanol - SD short day     

Genomic and functional characterization of StCDPK1

StCDPK1 is a calcium dependent protein kinase expressed in tuberizing potato stolons and in sprouting tubers. StCDPK1 genomic sequence contains eight exons and seven introns, the gene structure is similar to Arabidopsis, rice and wheat CDPKs belonging to subgroup IIa. There is one copy of the gene per genome and it is located in the distal portion of chromosome 12. Western blot and immunolocalization assays (using confocal and transmission electron microscopy) performed with a specific antibody against StCDPK1 indicate that this kinase is mainly located in the plasma membrane of swelling stolons and sprouting tubers. Sucrose (4–8%) increased StCDPK1 protein content in non-induced stolons, however the amount detected in swelling stolons was higher. Transgenic lines with reduced expression of StCDPK1 (β7) did not differ from controls when cultured under multiplication conditions, but when grown under tuber inducing conditions some significant differences were observed: the β7 line tuberized earlier than controls without the addition of CCC (GA inhibitor), developed more tubers than wild type plants in the presence of hormones that promote tuberization in potato (ABA and BAP) and was more insensitive to GA action (stolons were significantly shorter than those of control plants). StCDPK1 expression was induced by GA, ABA and BAP. Our results suggest that StCDPK1 plays a role in GA-signalling and that this kinase could be a converging point for the inhibitory and promoting signals that influence the onset of potato tuberization.     

Starch Accumulation in Leaves of Potato (Solanum tuberosum L.) during the First 18 Days of Photoperiod Treatment

Potato (Solanum tuberosum L.) plants were grown under long days(LD) of 18 h before a subset of the plants was transferred to10-h photosynthetic periods with either a dark night (SD) oran 8-h dim photoperiod extension with incandescent lamps (DE).Temperature was constant at 21 °C. Leaves were sampled atthe beginning and end of the high density light period for starchanalyses. Potato leaves accumulated starch more rapidly underSD than under LD; and this difference continued after a secondmajor sink, the tuber, began to develop. Starch accumulationover 10 h in SD leaves was three times higher than in LD leaves,even after 17 d of treatment. By this time SD gave higher wholeplant relative growth rates than LD, and the tuber mass of SDplants exceeded 30% of their total plant biomass. The DE treatmentresulted in starch accumulation intermediate to the LD and SDtreatments. Genotypes likewise differed: the earlier genotype,more strongly induced to tuberize, had higher leaf starch accumulationthan the later genotype. The effects of photoperiod and genotypewere also present when potatoes were grown at 27 °C, a temperatureunfavourable for tuberization under LD. Thus the formation ofa strong tuber sink was consistently associated with more rapidleaf starch accumulation. Potato, Solanum tuberosum L., cv. Norchip, photoperiod, temperature, genotype, starch accumulation, partitionin     

Involvement of abscisic acid (ABA) in bulb dormancy of Allium wakegi Araki I. Endogenous levels of ABA in relation to bulb dormancy and effects of exogenous ABA and fluridone

Allium wakegi plants exposed to long days (LD, 14 h-photoperiod) developed bulbs, which were dormant from the 30th to the 125th day of LD, but those grown under natural short days (SD) did not develop bulbs. The contents of abscisic acid (ABA) in both whole bulbs and buds of the bulbs increased in LD, reaching a maximum at the 60th day of LD and decreasing thereafter, but those in basal leaf sheaths (this part corresponds to a bulb after bulb development) and buds did not increase in SD. The ABA content was related to the depth of bulb dormancy. Application of 500 M ABA to bulbs for 24 h significantly delayed sprouting, but that of 5 or 50 M ABA had little or no effect. Application of 25 or 125 M fluridone to the soil just before exposure to LD bleached new expanding leaves and reduced bulb size, but had no effect on the development of bulb scales that characterize bulb formation. The bulbs formed under such conditions sprouted earlier than those of control plants. The levels of endogenous ABA in bulbs, buds of the bulbs, leaf blades, and roots were reduced by fluridone application. These results indicate that ABA plays an important role in bulb dormancy of Allium wakegi.     

Causes of Flowering of Long-Day Potato Species under Short-Day and Cold-Night Conditions

Flowering and tuber formation in high-mountain potato species Solanum sparsipilum Bitt., S. acaule Bitt., S. punae Juz., S. demissum Lindl., and a tuber crop Ullucus tuberosus Caldas. were investigated. All these species are characterized by absolute requirement of long day-length for flowering and short day-length for tuberization. Plants were grown under the following conditions: natural day-length with a photoperiod of 17 h or longer (treatment 1), short days with a photoperiod of 12 h and warm nights (15–20°C) (treatment 2), and short days with cold nights (5–6°C) (treatment 3). In the first treatment, plants produced flowers but no tubers. In the second treatment, plants produced tubers but no flowers. In the third treatment, plants produced both flowers and tubers. In leaves of S. acaule and U. tuberosus, the levels of gibberellins and ABA were determined. A high activity of gibberellins in the third treatment was similar to that in the first treatment, whereas high ABA activity in the third treatment was similar to that in the second treatment. It is supposed that cold nights retard the destruction of GA in plants during the dark period of diurnal cycle and ensure a permanently high level of gibberellins, which facilitates flowering of long-day species under short-day conditions. The high level of ABA is considered a plant response to short-day conditions, which is favorable for tuberization.     

Changes in cytokinins during initiation and development of potato tubers

Cytokinin-like activity was assayed in stolons and tubers of Solanum tuberosum L. ssp. andigena (Juz. et Buk.) Hawkes cv. 165 grown in pots under controlled environment conditions. The plants were allowed to tuberise without the application of environmental or other external stimuli. The soluble sugar and starch contents of stolon tips and tubers were measured. Starch accumulation was a precise indicator of tuber initiation. Cytokinin-like activity began to increase in tubers with a diameter greater than 7.5 mm and, as assessed on a per tuber basis, was greatest in the largest size-category analysed. However, expressed as a function of fresh and dry weight, activity was greatest in tubers of 15–20 mm in diameter. Increases in cytokinin-like activity occurred subsequent to tuber formation, indicating that the tuberisation stimulus is unlikely to be cytokinin-like in nature.     

Assessing potato tuber diel growth by means of X‐ray computed tomography

The formation and development of belowground organs is difficult to study. X‐ray computed tomography (CT) provides the possibility to analyse and interpret subtle volumetric changes of belowground organs such as tubers, storage roots and nodules. Here, we report on the establishment of a method based on a voxel dimension of 240 μm and precision (standard deviation) of 30 μL that allows interpreting growth differences among potato tubers happening within 3 h. Plants were not stressed by the application of X‐ray radiation, which was shown both by morphological comparison with control plants and by analysis of lipid peroxidation as a measure of oxidative stress. Diel (24 h) tuber growth fluctuations of three potato genotypes were monitored in soil‐filled pots of 10 L. In contrast to the results from previous reports, most tubers grew at similar rates during day and night. Tuber growth was not related to the developmental stage of plants and tubers. Pronounced differences were observed between average growth rates in different tubers within a plant. These results are discussed in the context of restrictions of past methods to study tuber growth and in the context of their potential for the characterization of the formation and development of other belowground plant organs.     

The Role of Gibberellin, Abscisic Acid, and Sucrose in the Regulation of Potato Tuber Formation in Vitro

The effects of plant hormones and sucrose (Suc) on potato (Solanum tuberosum L.) tuberization were studied using in vitro cultured single-node cuttings. Tuber-inducing (high Suc) and -noninducing (low Suc or high Suc plus gibberellin [GA]) media were tested. Tuberization frequencies, tuber widths, and stolon lengths were measured during successive stages of development. Endogenous GAs and abscisic acid (ABA) were identified and quantified by high-performance liquid chromatography and gas chromatography-mass spectrometry. Exogenous GA_4/7 promoted stolon elongation and inhibited tuber formation, whereas exogenous ABA stimulated tuberization and reduced stolon length. Indoleacetic acid-containing media severely inhibited elongation of stolons and smaller sessile tubers were formed. Exogenous cytokinins did not affect stolon elongation and tuber formation. Endogenous GA₁ level was high during stolon elongation and decreased when stolon tips started to swell under inducing conditions, whereas it remained high under noninducing conditions. GA₁ levels were negatively correlated with Suc concentration in the medium. We conclude that GA₁ is likely to be the active GA during tuber formation. Endogenous ABA levels decreased during stolon and tuber development, and ABA levels were similar under inducing and noninducing conditions. Our results indicate that GA is a dominant regulator in tuber formation: ABA stimulates tuberization by counteracting GA, and Suc regulates tuber formation by influencing GA levels.     

Water stress,CO2 and photoperiod influence hormone levels in wheat

'Super Dwarf' wheat (Triticum aestivum L.) plants have been grown from seed to maturity in the Mir space station where they were periodically exposed, because of microgravity and other constraints, to water deficit, waterlogging, high CO2 levels, and low light intensities. The plants produced many tillers, but none of them produced viable seed. Studies have been initiated to determine why the plants responded in these ways. In the present study, effects of the listed stresses on abscisic acid (ABA), indole-3-acetic acid (IAA) and isopentenyl adenosine ([9R]iP) levels in roots and leaves of plants grown under otherwise near optimal conditions on earth were measured. Hormones were extracted, purified by HPLC, and quantified by noncompetitive indirect ELISA. In response to water deficit, ABA levels increased in roots and leaves, IAA levels decreased in roots and leaves, and [9R]iP levels increased in leaves but decreased in roots. In response to waterlogging, ABA, IAA and [9R]iP levels briefly increased in roots and leaves and then decreased. When portions of the root system were exposed to waterlogging and/or water deficit, ABA levels in leaves increased while [9R]iP and IAA levels decreased. These responses were correlated with the percentage of the root system stressed. At a low photosynthetic photon flux (100 micromoles m-2 s-1), plants grown in continuous light had higher leaf ABA levels than plants grown using an 18 or 21 h photoperiod.     

Infection of potato tubers with soft rot bacteria

Stolons attached to developing potato tubers were inoculated with the soft rot bacterium Erwinia carotovora var. atroseptica. Almost all the stolons rotted, but soft rots developed in less than 10% of new tubers; the bacterium was isolated later from these tubers. No rots developed in the other tubers but the bacterium was later isolated from about half of them. It could not be isolated from tubers attached to inoculated stolons where the rot on them did not extend to the tuber or from tubers attached to stolons that were not inoculated though many of these rotted. The bacterium was reisolated from almost all arrested lesions in tubers inoculated 8 month earlier with E. carotovora var. atroseptica. Blackleg did not develop from plants grown fom these tubers under various soil conditions. It did develop in a large proportion of plants from tubers inoculated shortly before planting and grown in cool, wet soil. Less than 1% blackleg developed in plants grown from tubers from plants with blackleg or from plants immediately adjacent. The presence of pectolytic bacteria and E. caratovora var. atroseptica in seed and new tubers was investigated during June, July and August. Although E. caratovora var. atroseptica was obtained from c. 40% tubers, only c. 0·3% of c. 8400 plants developed blackleg. The bacterium was isolated from only three of 160 new tubers sampled during the summer.     

Changes in jasmonate and gibberellin levels during development of potato plants (Solanum tuberosum)

Among the multiple environmental signals and hormonal factors regulatingpotato plant morphogenesis and controlling tuber induction, jasmonates (JAs)andgibberellins (GAs) are important components of the signalling pathways in theseprocesses. In the present study, with Solanum tuberosum L.cv. Spunta, we followed the endogenous changes of JAs and GAs during thedevelopmental stages of soil-grown potato plants. Foliage at initial growthshowed the highest jasmonic acid (JA) concentration, while in roots the highestcontent was observed in the stage of tuber set. In stolons at the developmentalstage of tuber set an important increase of JA was found; however, in tubersthere was no change in this compound during tuber set and subsequent growth.Methyl jasmonate (Me-JA) in foliage did not show the same pattern as JA; Me-JAdecreased during the developmental stages in which it was monitored, meanwhileJA increased during those stages. The highest total amount of JAs expressed asJA+Me-JA was found at tuber set. A very important peak ofJA in roots was coincident with that observed in stolons at tuber set. Also, aprogressive increase of this compound in roots was shown during the transitionof stolons to tubers. Of the two GAs monitored, gibberellic acid(GA₃) was the most abundant in all the organs. While GA₁and GA₃ were also found in stolons at the time of tuber set, noothermeasurements of GAs were obtained for stolons at previous stages of plantdevelopment. Our results indicate that high levels of JA and GAs are found indifferent tissues, especially during stolon growth and tuber set.     

Effect of gibberellic acid on growth and carbohydrate metabolism of developing tubers of potato (Solanum tuberosum)

Potato plants (Solanum tuberosum L. cv. Ostara) were grown in aerated water culture in a controlled environment. When the tubers had reached a diameter of 1–3 cm. ¹⁴C-labelled or unlabelled gibberellic acid (GA₃) was applied to the surface of the stolons at points approximately 1 crn from the developing tubers, and treatment continued for 10 days. - Significant quantities of GA₃ moved into tuber tissue within 2–4 days of hormone application. This influx of GA₃ was accompanied by a marked reduction in both the activity of ADPG-pyrophospharylase and the ratio ADPG-pyrophosphorylase/starch phosphorylase and an increase in the activity of UDPG-pyrophosphorylase. Starch phosphorylase activity initially increased slightly but then fell, whereas the activity of starch synthase remained constant throughout the experiment. The soluble sugar composition of the tubers changed qualitatively towards a pattern characteristic of growing stolon tips prior to tuber initiation, but there was no clear evidence of net starch degradation. Changes in the activities of the enzymes were observed prior to noticeable effects of the hormone on tuber growth rate or the development of new stolons at the tuber eyes. - GA₃- treated tubers imported more ¹⁴C from labelled photosynthate than expected on the basis of growth rate. However, the capacity to convert solub#e-¹⁴C to ethaTiol-insoluble-¹⁴C (predominantly starch) was reduced in comparison with non-treated tubers. - The observed changes in carbohydrate composition and enzyme activities indicate that GA₃ induces a drastic change in potato tuber metabolism towards a pattern characteristic for the termination of the storage process.