Effects of gibberellin and auxin on the synthesis of abscisic acid and ethylene in buds of dormant and sprouting potato tubers

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

Carbon Dioxide, Oxygen and Ethylene Effects on Potato Tuber Dormancy Release and Sprout Growth

The possible roles of oxygen and carbon dioxide treatments inthe presence or absence of ethylene on tuber dormancy releasein potato (Solanum tuberosumL.) were examined. Using two gascompositions (I: 60% CO₂–20% O₂–20% N₂and II: 20%CO₂–40% O₂–40% N₂), the phase of tuber dormancyand previous storage temperature were demonstrated to be importantparameters for dormancy release by these gas mixtures. Gas Icaused decreased abscisic acid (ABA) levels within 24 h regardlessof previous storage temperature, although this effect was reversible.Exogenous C₂H₄, an effective dormancy release agent, also causeddecreased ABA levels within 24 h. It also enhanced dormancyrelease and further promoted ABA losses by gas I. Gas II treatmentled to slight reductions in ABA levels that were further decreasedby C₂H₄. Sprout length was modelled successfully by multipleregression analysis in terms of glucose and ABA levels withinthe apical eye tissues of Russet Burbank tubers immediatelyafter, and regardless of, previous gas treatments or storagetemperatures. Solanum tuberosum,potato, abscisic acid, ethylene, carbon dioxide, oxygen, dormancy.     

Effect of growth regulators on proton transport through cytoplasmic membrane of potato tuber cells

Effects of the growth regulators epibrassinolide-694 (EB), gibberellic acid (GA), and abscisic acid (ABA) on the ATP-dependent translocation of H+ through the membranes of plasma membrane vesicles of potato (Solanum tuberosum L.) tuber cells were studied. The ATP-dependent accumulation of H+ in the plasma membrane vesicles from dormant tubers was inhibited by EB and ABA and stimulated by GA. After the break of dormancy, the stimulatory effect of GA increased, the inhibitory effect of ABA decreased, and EB stimulated the accumulation of H+ in the vesicles. The data suggest that the plasma membrane H+ ATPase is a target of phytohormones that regulate the dormancy of potato tubers.     

Effects of Growth Regulators on H+Translocation across the Membranes of Plasma Membrane Vesicles from Potato Tuber Cells

Effects of the growth regulators epibrassinolide-694 (EB), gibberellic acid (GA), and abscisic acid (ABA) on the ATP-dependent translocation of H⁺through the membranes of plasma membrane vesicles of potato (Solanum tuberosumL.) tuber cells were studied. The ATP-dependent accumulation of H⁺in the plasma membrane vesicles from dormant tubers was inhibited by EB and ABA and stimulated by GA. After the break of dormancy, the stimulatory effect of GA increased, the inhibitory effect of ABA decreased, and EB stimulated the accumulation of H⁺in the vesicles. The data suggest that the plasma membrane H⁺ATPase is a target of phytohormones that regulate the dormancy of potato tubers.     

Brassinolide Effect on Growth of Apical Meristems, Ethylene Production, and Abscisic Acid Content in Potato Tubers

Treatment of intact potato (Solanum tuberosum L., cv. Nevskii) tubers with 24-epibrassinolide (EB) resulted in prolonged deep dormancy, increased production of ethylene and higher contents of free and bound abscisic acid (ABA) in buds. EB at the most efficient concentration 0.021 mg dm^–3, applied immediately after tuber harvest, inhibited sprouting by 36 – 38 d, increased ethylene formation after 1 and 7 d of storage by almost 300 and 150%, respectively, and increased the content of both free and bound ABA during the whole period of storage (on average by about 80%). Electron microscopic and morphometric studies showed that EB brings about a decrease in cell volume in tunica and all types of meristems and an increase in the number of vacuoles, accompanied by a decrease in their volume.     

Hormonal Regulation of Organic and Phosphoric Acid Release by Barley Aleurone Layers and Scutella

The release of acid from the aleurone layer and scutellum of barley (Hordeum vulgare L. cv Himalaya) was investigated. Aleurone layers isolated from mature barley grains acidify the external medium by releasing organic and phosphoric acids. Gibberellic acid and abscisic acid stimulate acid release 2-fold over control tissue incubated in 10 mM CACl2. Gibberellic acid causes medium acidification by stimulating the release of phosphoric and citric acids, whereas abscisic acid stimulates the release of malic acid. The accumulation of these acids in the incubation medium buffers the medium against changes in pH, particularly between pH 4 and 5. The amounts of amino acids that accumulate in the medium are low (2-12 nmol/layer) compared to other organic and phosphoric acids (100-500 nmol/layer). The scutellum does not play a major role in medium acidification but participates in the uptake of organic acids. The organic acid composition of the starchy endosperm changes after 3 d of imbibition; malic, succinic, and lactic acids decrease, whereas citric and phosphoric acids remain unchanged or increase. These results indicate that during postgerminative growth, the acidity of the starchy endosperm is maintained by acid production by the aleurone layer.     

拟南芥突变体种子休眠与萌发的研究进展

种子的休眠和萌发是一个复杂的过程, 至今尚未能清楚阐明其调控机制。目前已从拟南芥突变体中鉴定了一些与种子萌发和休眠相关的基因, 有助于阐明种子休眠和萌发的分子机制。本文综述了拟南芥突变体种子休眠与萌发方面的研究进展。赤霉素是促进种子萌发的主要因素之一, RGL、SPY、GCR、SLY和GAR等基因的表达参与赤霉素对种子萌发的调控。脱落酸与种子休眠有关, ABI1、ABI2、ABI3、ABI4、ABI5、FUS3、LEC、MARD和CIPK等基因参与了脱落酸的调控过程。对3类乙烯反应的突变体 (ein、etr和ctr) 以及油菜素内酯突变体 (det和bri) 的研究表明乙烯和油菜素内酯是通过拮抗脱落酸而促进种子萌发的。光对种子萌发的调节, 是通过具有Ser/Thr蛋白激酶活性的光敏色素PhyA、PhyB、 PhyC、PhyD和PhyE, 以磷酸化/去磷酸化方式调节其它与萌发相关基因的表达。含氮化合物对种子萌发的促进, 可能是以一种依赖一氧化氮的方式解除种子休眠。     

Physiology of oil seeds: I. Regulation of dormancy in virginia-type peanut seeds

The germination and ethylene production by dormant Virginia-type peanut seeds were observed in relation to phytohormone treatments that could conceivably release the dormancy of these seeds. A comparison was made between the effects of these treatments on the less dormant apical seeds and the more dormant basal seeds. Indole-3-acetic acid did not stimulate ethylene production by, or germination of, the dormant seeds to any extent. Gibberellic acid at 5 × 10⁻⁴ M stimulated ethylene production by apical seeds to 17 millimicroliters per hour and germination to only 40% above the control. The more dormant basal seeds were affected even less by gibberellic acid than the seeds. Ethylene gas at 8 microliters per liter stimulated germination to 85% above the control for both apical and basal seeds. At this ethylene concentration the physiology of the more dormant basal seeds was altered, so that they behaved in a manner similar to the inherently less dormant apical seeds. 2-Chloroethylphosphonic acid at 10⁻³ and 5 × 10⁻⁴ M provided results similar to ethylene gas. Both apical and basal seeds germinated 100% at 48 hours. Among the phytohormones tested in this study, ethylene gas produced the greatest germination at low concentrations, and it appears must directly related to initiating the reactions required for converting the quiescent cells to an active state of growth.     

拟南芥突变体种子休眠与萌发的研究进展

种子的休眠和萌发是一个复杂的过程,至今尚未能清楚阐明其调控机制。目前已从拟南芥突变体中鉴定了一些与种子萌发和休眠相关的基因,有助于阐明种子休眠和萌发的分子机制。本文综述了拟南芥突变体种子休眠与萌发方面的研究进展。赤霉素是促进种子萌发的主要因素之一,RGL、SPY、GCR、SLY和GAR等基因的表达参与赤霉素对种子萌发的调控。脱落酸与种子休眠有关,ABI1、ABI2、ABI3、ABI4、ABI5、FUS3、LEC、MARD和CIPK等基因参与了脱落酸的调控过程。对3类乙烯反应的突变体（ein、etr和ctr）以及油菜素内酯突变体（det和bri）的研究表明乙烯和油菜素内酯是通过拮抗脱落酸而促进种子萌发的。光对种子萌发的调节,是通过具有Ser／Thr蛋白激酶活性的光敏色素PhyA、PhyB、PhyC、PhyD和PhyE,以磷酸化／去磷酸化方式调节其它与萌发相关基因的表达。含氮化合物对种子萌发的促进,可能是以一种依赖一氧化氮的方式解除种子休眠。     

The control of bud dormancy in potato tubers

Potato (Solanum tuberosum L.) tuber buds normally remain dormant through the growing season until several weeks after harvest. In the cultivar Majestic, this innate dormancy persisted for 9 to 12 weeks in storage at 10° C, but only 3 to 4 weeks when the tubers were stored at 2° C. At certain stages, supplying cytokinins to tubers with innately dormant buds induced sprout growth within 2 d. The growth rate was comparable to that of buds whose innate dormancy had been lost naturally. Cytokinin-treatment did not accelerate the rates of cell division and cell expansion in buds whose innate dormancy had already broken naturally. Gibberellic acid did not induce sprout growth in buds with innate dormancy. We conclude that cytokinins may well be the primary factor in the switch from innate dormancy to the non-dormant state in potato tuber buds, but probably do not control the subsequent sprout growth.Abbreviations tio ⁶ade 6-(4-hydroxy-3-methylbut-trans-2-enyl amino)purine, zeatin - tio⁶ado 6-(4-hydroxy-3-methylbut-trans-2-enyl amino)-9--D-ribofuranosyl purine, zeatin riboside     

Physiology of Oil Seeds: IV. Role of Endogenous Ethylene and Inhibitory Regulators during Natural and Induced Afterripening of Dormant Virginia-type Peanut Seeds

To further elucidate the regulation of dormancy release, we followed the natural afterripening of Virginia-type peanut (Arachis hypogaea L.) seeds from about the 5th to 40th week after harvest. Seeds were kept at low temperature (3 ± 2 C) until just prior to testing for germination, ethylene production, and internal ethylene concentration. Germination tended to fluctuate but did not increase significantly during the first 30 weeks; internal ethylene concentrations and ethylene production remained comparatively low during this time. When the seeds were placed at room temperature during the 30th to 40th weeks after harvest, there was a large increase in germination, 49% and 47% for apical and basal seeds, respectively. The data confirm our previous suggestion that production rates of 2.0 to 3.0 nanoliters per gram fresh weight per hour are necessary to provide internal ethylene concentrations at activation levels which cause a substantial increase of germination. Activation levels internally must be more than 0.4 microliter per liter and 0.9 microliter per liter for some apical and basal seeds, respectively, since dormant-imbibed seeds containing these concentrations did not germinate. Abscisic acid inhibited germination and ethylene production of afterripened seeds. Kinetin reversed the effects of ABA and this was correlated with its ability to stimulate ethylene production by the seeds. Ethylene also reversed the effects of abscisic acid. Carbon dioxide did not compete with ethylene action in this system. The data indicate that ethylene and an inhibitor, possibly abscisic acid, interact to control dormant peanut seed germination. The inability of CO₂ to inhibit competitively the action of ethylene on dormancy release, as it does other ethylene effects, suggests that the primary site of action of ethylene in peanut seeds is different from the site for other plant responses to ethylene.     

Effect of elicitors on accumulation of protease inhibitors in injured potato tubers

The time course of accumulation and the composition of proteinase-inhibiting proteins in diffusates from potato tubers treated with elicitors such as salicylic, jasmonic, and arachidonic acids were studied. The 40-kDa reserve protein patatin and the chymotrypsin inhibitors, among which proteins of 24.6, 22.0, and 16.0 kDa were prevalent, accumulated in diffusates from potato tubers. Jasmonic and arachidonic acids activated the accumulation of the chymotrypsin inhibitors in tubers in response to the injury stress, whereas salicylic acid inhibited this process. The effects of jasmonic and arachidonic acids increased when their concentrations decreased to 10(-6) M. The data suggest an important role of the lipoxygenase metabolism in signal transduction of the anti-injury defense system in the dormant potato tubers.     

Dual effects of ethylene on potato dormancy and sprout growth

Dormant potato tubers (Solanum tuberosum L.) of two cultivars were treated with various concentrations of ethylene gas for various exposure periods. As has been shown by others, ethylene caused a rapid but transient increase in respiration rate, which appeared to be independent of any effects on dormancy. All concentrations tested caused accelerated sprouting, 2 microliters per liter being the most effective. Ethylene exerts a dual effect on potato tubers: it markedly shortens the duration of rest, but it inhibits elongation of the sprouts during extended treatment. Comparing these results with published work on seeds, bulbs, and corms suggests that ethylene must have a significant but as yet unexplained role in rest and dormancy. However, since the most effective ethylene treatment did not equal the response elicited by treatment with ethylene chlorhydrin, other factors must also contribute to termination of rest.     

Studies on the role of abscisic acid in the initiation of bud dormancy in Alnus glutinosa and Betula pubescens

Summary The effects of leaf-applied (+-)-abscisic acid on the growth and dormancy of Betula pubescens Ehrh. and Alnus glutinosa Gaertn. growing under long days provide no evidence that leaf-applied abscisic acid induces or promotes the formation of resting buds in these species. Radiotracer studies show that a small percentage of the radioactivity applied as [2-¹⁴C]abscisic acid to the leaves accumulates in the apical region of the shoot. Of the radioactivity that was recovered from this region after 8 days, less than 10% was chromatographically similar to [2-¹⁴C]abscisic acid. The significance of these results with respect to the role of abscisic acid in regulating the induction of bud dormancy is discussed.Abbreviation ABA abscisic acid     

Ethanol breaks dormancy of the potato tuber apical bud

Growing potato tubers or freshly harvested mature tubers have a dormant apical bud. Normally, this dormancy is spontaneously broken after a period of maturation of the tuber, resulting in the growth of a new sprout. Here it is shown that in in vitro-cultured growing and maturing tubers, ethanol can rapidly break this dormancy and re-induce growth of the apical bud. The in vivo promoter activity of selected genes during this secondary growth of the apical bud was monitored, using luciferase as a reporter. In response to ethanol, the expression of carbohydrate-storage, protein-storage, and cell division-related genes are rapidly down-regulated in tuber tissue. It was shown that dormancy was broken by primary but not by secondary alcohols, and the effect of ethanol on sprouting and gene expression in tuber tissue was blocked by an inhibitor of alcohol dehydrogenase. By contrast, products derived from alcohol dehydrogenase activity (acetaldehyde and acetic acid) did not induce sprouting, nor did they affect luciferase reporter gene activity in the tuber tissue. Application of an inhibitor of gibberellin biosynthesis had no effect on ethanol-induced sprouting. It is suggested that ethanol-induced sprouting may be related to an alcohol dehydrogenase-mediated increase in the catabolic redox charge [NADH/(NADH+NAD+)].     

Starch-related enzymes during potato tuber dormancy and sprouting

Activities of enzymes presumably involved in starch biosynthesis (ADP-glucose pyrophosphorylase, AGPase) and/or breakdown (starch phosphorylase, STP; amylases) were determined during potato (Solanum tuberosum L.) tuber dormancy and sprouting. Overall activities of all these enzymes decreased during the first stage of tuber dormancy. No clear changes were detected at the time of dormancy breaking and sprouting. However, when AGPase activity was monitored by in situ staining during the entire dormancy period, a clear decrease during the dormant period and a large increase before visible sprouting could be observed. This increase was especially evident near the vascular tissue and at the apical bud, which showed a very intensive staining. In situ staining of STP activity in sprouting tubers showed that the tissue distribution of STP was the same as for AGPase. As a possible explanation, direct starch cycling is suggested: STP produces glucose-1-phosphate during starch breakdown, which can be directly used as a substrate by AGPase for starch synthesis. Gene expression studies with the AGPaseS promoter coupled to the firefly luciferase reporter gene also clearly showed a higher activity in sprouting tubers as compared to dormant tubers, with the highest expression levels observed around the apical buds. The presence of amylase activity at dormancy initiation and AGPase activity persistent at the sprouting stage suggest that starch was cycling throughout the entire dormancy period. According to the in situ studies, the AGPase activity increased well before visible sprout growth and could therefore be one of the first physiological determinants of dormancy breakage.     

Influence of Plant Hormones on Ethylene Production in Apple, Tomato, and Avocado Slices during Maturation and Senescence

Ethylene production by tissue slices from preclimacteric, climacteric, and postclimacteric apples was significantly reduced by isopentenyl adenosine (IPA), and by mixtures of IPA and indoleacetic acid, and of IPA, indoleacetic acid, and gibberellic acid after 4 hours of incubation. Ethylene production by apple (Pyrus malus L.) slices in abscisic acid was increased in preclimacteric tissues, decreased in climacteric peak tissues, and little affected in postclimacteric tissues. Indoleacetic acid suppressed ethylene production in tissues from preclimacteric apples but stimulated ethylene production in late climacteric rise, climacteric, and postclimacteric tissue slices. Gibberellic acid had less influence in suppressing ethylene production in preclimacteric peak tissue, and little influenced the production in late climacteric rise, climacteric peak, and postclimacteric tissues. IPA also suppressed ethylene production in pre- and postclimacteric tissue of tomatoes (Lycopersicon esculentum) and avocados (Persea gratissima). If ethylene production in tissue slices of ripening fruits is an index of aging, then IPA would appear to retard aging in ripening fruit, just as other cytokinins appear to retard aging in senescent leaf tissue.     

Regulation of Bud Rest in Tubers of Potato, Solanum tuberosum L: VIII. Early Effects of Gibberellin A(3) and Abscisic Acid on Ultrastructure

Using the electron microscope, we compared the effects of abscisic acid and gibberellin A₃ on excised buds from resting potato (Solanum tuberosum L.) tubers. Cells of abscisic acid-treated buds became progressively more vacuolated during a 12-hour time course study as compared with control (water) and gibberellin A₃-treated buds. Concentric configurations of endoplasmic reticulum were present in apical cells of freshly excised buds. After about 6 hours these configurations began to open and disperse, and after 12 hours, intact concentric configurations were no longer evident. Both abscisic acid and gibberellin A₃ induced opening and dispersal of the concentric configurations, sometimes as early as 0.5 hour after excision and treatment with hormones.