Effects of ethylene on tuberization in radish (Raphanus sativus)

The effects of ethylene on the elongation of radish hypocotyls and on dry matter partitioning between tubers and shoots were analysed in order to gain insight into the possible role of ethylene in the regulation of tuberization. Treatment of very young seedlings with ethylene results in heavier tubers (Vreugdenhil et al. 1984). Here we report that addition of ethylene or ethephon two days after germination inhibited the elongation of the hypocotyl; trapping of endogenously produced ethylene had a stimulative effect on elongation. Ethephon, sprayed at a later stage, changed the partitioning of assimilates between tubers and shoots, resulting in lower tuber weights. It is concluded that ethylene had a dual effect on tuberization in radish: at a very early stage of development it inhibited elongation of the hypocotyl, resulting in earlier tuber formation and heavier tubers. At a later stage, it had a negative effect on tuber weight by changing dry matter partitioning.     

Light‐induced stabilization of ACS contributes to hypocotyl elongation during the dark‐to‐light transition in Arabidopsis seedlings

Hypocotyl growth during seedling emergence is a crucial developmental transition influenced by light and phytohormones such as ethylene. Ethylene and light antagonistically control hypocotyl growth in either continuous light or darkness. However, how ethylene and light regulate hypocotyl growth, including seedling emergence, during the dark‐to‐light transition remains elusive. Here, we show that ethylene and light cooperatively stimulate a transient increase in hypocotyl growth during the dark‐to‐light transition via the light‐mediated stabilization of 1‐aminocyclopropane‐1‐carboxylic acid (ACC) synthases (ACSs), the rate‐limiting enzymes in ethylene biosynthesis. We found that, in contrast to the known inhibitory role of light in hypocotyl growth, light treatment transiently increases hypocotyl growth in wild‐type etiolated seedlings. Moreover, ACC, the direct precursor of ethylene, accentuates the effects of light on hypocotyl elongation during the dark‐to‐light transition. We determined that light leads to the transient elongation of hypocotyls by stabilizing the ACS5 protein during the dark‐to‐light transition. Furthermore, biochemical analysis of an ACS5 mutant protein bearing an alteration in the C‐terminus indicated that light stabilizes ACS5 by inhibiting the degradation mechanism that acts through the C‐terminus of ACS5. Our study reveals that plants regulate hypocotyl elongation during seedling establishment by coordinating light‐induced ethylene biosynthesis at the post‐translational level. Moreover, the stimulatory role of light on hypocotyl growth during the dark‐to‐light transition provides additional insights into the known inhibitory role of light in hypocotyl development.     

Lithium,aminoethoxyvinylglycine and cobalt reversal of the cotyledonary pricking-induced growth inhibition in the hypocotyl of Bidens pilosus in relation to ethylene and peroxidases

Pretreatment of young Bidens pilosus plants with lithium (Li), aminoethoxyvinylglycine (AVG) or cobalt (Co) prevents the cotyledonary pricking-induced growth inhibition of the hypocotyl. The effect is correlated with parallel prevention of the pricking-induced enhancement of peroxidase and ethylene production in the hypocotyl. Only Co prevents the increased capacity of hypocotyl segments or microsomes to convert aminocyclopropane carboxylic acid to ethylene. Li, AVG, and Co do not interfere with peroxidase and ethylene metabolism in pricked cotyledons. Although Li, AVG as well as Co are known to interfere with ethylene biosynthesis and action, they could well remove the wounding effect by different modes of action.     

Galactose-induced Ethylene Evolution in Mung Bean Hypocotyls: A Possible Mechanism for Galactose Retardation of Plant Growth

Galactose has long been known to inhibit growth in certain plant systems and more recently to promote abscission. These same systems are similarly affected by ethylene. The mung bean (Phaseolus aureus Roxb.) hypocotyl system was employed to ascertain whether the inhibitory effects of galactose might be regulated through ethylene. Galactose alone (at 10 and 100 mM) of the many carbohydrates tested elicited high rates of ethylene evolution (1.5–4.0 nl/g fresh weight x h) as determined by gas chroma-tography. Hook opening, pigment formation, and hypocotyl elongation were inhibited by this resultant ethylene. Galactose and auxin were found to act synergistically with respect to ethylene induction. Use of an auxin antagonist and auxin transport inhibitor revealed that galactose-induced ethylene formation is auxin dependent. Time course studies indicate that this effect may be auxin-sparing. Methionine appears to be the substrate of galactose-induced ethylene. since a methionine antagonist [L-2-amino-4-(2′-amino ethoxy)-trans-3-butenoic acid] abolished the induction. Potential interrelationships between galactose and ethylene synthesis are discussed.     

Comparison of the effects of white light and the growth retardant paclobutrazol on the ethylene production in bean hypocotyls

At a concentration of 17 µmol·L^–1, paclobutrazol (PP), a triazole plant growth retardant, effectively reduced the elongation and increased the thickness of hypocotyls in 6-day-old Phaseolus vulgaris L. cv. Juliska seedlings, both in the light and in the dark. PP treatment did not increase the cell number in transverse sections of hypocotyls. The diameter of hypocotyls was uniform from the zone of intensive elongation along the whole hypocotyl in etiolated plants, but those grown in the light exhibited an additional lateral expansion at the base. Ethylene evolution was not reduced by PP in etiolated hypocotyls, and did not differ significantly in the elongating apical and fully grown basal zones. PP reduced the ethylene release by the growing zones in green hypocotyls, but not in the basal parts, which resulted in an increasing ethylene gradient towards the hypocotyl base. The level of 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of ethylene, was much higher in retardant-treated hypocotyls than in the controls, which was due in part to the reduced malonylation. The swelling of the hypocotyl bases could be eliminated by inhibitors of ethylene biosynthesis or action, or could be induced by 10 µmol·L^–1ACC in control plants in the light. None of these treatments had a significant effect on the lateral expansion of hypocotyls in etiolated seedlings. PP treatment induced a similar effect to that of white light in etiolated seedlings, and amplified the effect of light in green plants with respect to the ACC distribution, and consequently, the ethylene production in the hypocotyls of 6-day-old bean seedlings. It can be concluded that the lateral expansion of hypocotyl bases in PP-treated green plants is controlled by ethylene.     

Ethylene‐triggered abscisic acid: A principle in plant growth regulation?

The application of auxins to sensitive plant species or their overproduction in transgenic plants stimulates ethylene biosynthesis via induction of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase. Recent studies with auxin herbicides and indole-3-acetic acid (IAA) have revealed that auxin-stimulated ethylene triggers an increase in the biosynthesis of abscisic acid (ABA), which then functions as a second messenger, leading to growth inhibition and senescence. This raises the question of whether ethylene-triggered ABA is restricted to the action of auxin herbicides or whether it is a widespread phenomenon in the normal plant growth regulation. Our own results and a reappraisal of the literature indicate that ethylene-induced ABA may, indeed, play a role in natural physiological phenomena, such as root gravireaction and suppression of lateral bud growth in apical dominance. In addition, it would be worthwhile to investigate whether ethylene-triggered ABA is involved in other processes which coincide with a strong stimulation of ethylene biosynthesis, such as growth inhibition induced by cytokinins and senescence elicited under stress conditions.     

Narrow-band light regulation of ethylene and gibberellin levels in hydroponically-grown <Emphasis Type="Italic">Helianthus annuus</Emphasis> hypocotyls and roots

Both hypocotyl and root growth of sunflower (Helianthus annuus) were examined in response to a range of narrow-band width light treatments. Changes in two growth-regulating hormones, ethylene and gibberellins (GAs) were followed in an attempt to better understand the interaction of light and hormonal signaling in the growth of these two important plant organs. Hydroponically-grown 6-day-old sunflower seedlings had significantly elongated hypocotyls and primary roots when grown under far-red (FR) light produced by light emitting diodes (LEDs), compared to narrow-band red (R) and blue (B) light. However, hypocotyl and primary root lengths of seedlings given FR light were still shorter than was seen for dark-grown seedlings. Light treatment in general (compared to dark) increased lateral root formation and FR light induced massive lateral root formation, relative to treatment with R or B light. Levels of ethylene evolution (roots and hypocotyls) and concentrations of endogenous GAs (hypocotyls) were assessed from both 6-day-old sunflower plants either grown in the dark, or treated with FR, R or B light. Both R and B light had similar effects on hypocotyl and root growth as well as on ethylene and on hypocotyl GA levels. Dark treatment resulted in the highest ethylene levels, whereas FR treatment significantly reduced ethylene evolution for both hypocotyls and roots. R- and B-light treatments elevated ethylene evolution relative to FR light. Endogenous GA₅₃ and GA₁₉ levels in hypocotyls were significantly higher and GA₄₄, GA₂₀ and GA₁ levels significantly lower, for dark and FR light treatments compared to R and B light-treatments. The patterns seen for changes in GA concentrations indicate FR-, R- and B-light-mediated effects [differences] in the metabolism of the early C₂₀ GAs, GA₅₃ → GA₄₄ → GA_19. Surprisingly, GA₂₀, GA₁ and GA₈ levels in hypocotyls were very much reduced by treatment of the plants with FR light, relative to B and R-light treatments, e.g. the increased hypocotyl elongation induced by FR light was correlated with reduced levels of all three of the downstream C₁₉ GAs. The best explanation, albeit speculative, is that a more rapid metabolism, i.e. GA₂₀ → GA₁ → GA₈ → GA₈ conjugates occurs under FR light. Although this study provided no evidence that elevated ethylene evolution by roots or hypocotyls of sunflower is controlling growth via endogenous GA biosynthesis, there are differences between soil-grown and hydroponically-grown sunflower seedlings with regard to trends seen for hypocotyl GA concentrations and both root and hypocotyl ethylene evolution in response to narrow band width R and FR light signaling.     

激素对水生植物生理生态的影响及其应用

激素代谢是植物传导信号和调节生长发育的重要途径.陆地植物五大类激素在水生植物中也有分布,尽管近年来环境污染导致水生植物衰退的问题日益得到重视,但水生植物激素的研究和应用却远滞后于陆生植物.在总结了近年来激素类物质在水生植物中的研究成果,分别从激素的种类、激素的生理生态作用、激素生物合成的途径及作用的部位和机制、激素之间的相互作用.激素类物质在实验和实践上的应用等进行了全面阐述,指出了水生植物激素生理生态学研究的发展方向,从利用激素类物质诱导水生植物抗性的表达,提高抗逆性,恢复水生植被,以及研究和开发适于水生植物生产和管理的生长调节剂等方面,就水生植物激素的进一步研究和应用进行了探讨.     

The interaction of light irradiance with ethylene in regulating growth of Helianthus annuus shoot tissues

Shade light found in ecological niches where plants are growing under a canopy or in proximity of taller neighbouring vegetation consist mainly of two separate light signals: low red to far-red ratio and low photosynthetically active radiation (PAR). The effect of the latter on the growth of 7-day old sunflower shoots was examined by assessing hypocotyl, cotyledon and leaf tissue growth under three varying PAR levels: near-normal of 1,000 μmol m^?2 s^?1, low of 100 μmol m^?2 s^?1 and very low of 10 μmol m^?2 s^?1. Then, the possible interaction between PAR signaling and ethylene in regulating growth of these sunflower tissues was investigated. The results showed that gradual decrease in PAR level increases hypocotyl elongation and decreases ethylene evolution. However, gradual decrease in PAR level decreases cotyledon and leaf growth and increases ethylene evolution. Thus it seems possible that PAR regulation of shoot growth is mediated by changes in ethylene evolution in tissue specific manner. This hypothesis was supported by experiments with the ethylene releasing factor, ethephon, and the ethylene biosynthesis inhibitor, AVG, as well as by transfer experiments where sunflower seedlings were transferred from one PAR regime to another with subsequent growth and ethylene measurements.     

Effects of ethylene on the tuberization of potato (Solanum tuberosum) cuttings

Ethylene, applied as ethephon, inhibited the elongation of etiolated, axillary potato shoots cultured in vitro and it stimulated radial growth along the whole length of these shoots. The same phenomena were observed when ACC, the precursor of ethylene, was added to the medium, whereas silver ions reversed these effects. However, tuber formation in vitro was suppressed by ethephon. This indicates a dual role of ethylene in the induction of tuber formation in potatoes: it had a positive effect by blocking the elongation of stolons and it suppressed tuber initiation.     

Isolation of a novel SUMO protein from tomato that suppresses EIX-induced cell death

Challenging tomato or tobacco varieties with ethylene-inducing xylanase (EIX) from the fungus Trichoderma viride causes rapid induction of plant defence responses leading to programmed cell death. Using the yeast two-hybrid system, we isolated a novel protein, tomato small ubiquitin-related modifier protein (T-SUMO), which specifically interacts with EIX. T-SUMO, a cytoplasmic protein, is a member of the ubiquitin-like protein family. It shows homology to human protein sentrin/SUMO1, which suppresses tumour necrosis factor-induced cell death. Transgenic plants that express T-SUMO in the sense orientation suppress EIX induction of ethylene biosynthesis and cell death, while in the antisense orientation they enhance EIX-induced ethylene biosynthesis. These results indicate that T-SUMO is involved in mediating the signal generated by EIX that leads to induction of plant defence responses.     

Role of Ethylene in Induction of Flooding Damage in Sunflower

The possibility that symptoms of flooding damage in plants are primarily caused by an accumulation of ethylene was investigated using pot-grown sunflower (Helianthus annuus) plants. When plants were flooded to the basal pairs of leaves, ethylene in roots and stems below the water line began to increase. This coincided with the start of hypocotyl hypertrophy and new root formation in hypocotyls, which continued for 14-16 days. There were highly significant correlations between ethylene concentration and number of roots and hypocotyl diameter. After approximately 4 days of flooding, ethylene concentrations in stems between nodes for the 1st and 3rd basal pairs of leaves started to increase, coinciding with initiation of chlorophyll breakdown and epinasty of the 2nd basal pairs of leaves. Thus, there were correlations between ethylene concentration and chlorophyll breakdown and epinasty. The lower the leaves, the more chlorophyll breakdown among 1st, 2nd, 3rd, and 4th basal pairs of leaves. The longer the flooding, the more severe the flooding damage; and even when returned to normal condition, plants flooded longer than 3 days were not able to recover from flooding damage. A gas chromatographic study revealed that Ethephon was absorbed by roots and decomposed to ethylene in the plant. Damage symptoms caused by soil application of Ethephon, such as reduced stem height, chlorophyll breakdown, epinasty of the 2nd basal pairs of leaves, and hypocotyl hypertrophy, were almost identical with those caused by soil flooding treatment. Microscopic studies revealed that radially enlarged cells and increased intercellular spaces in the cortex were the major contribution to the increased hypocotyl diameter in both flooded and Ethephon-treated plants. It is concluded that the increase in ethylene concentration in flooded plants is largely, although not exclusively, responsible for flooding damage symptoms.     

The Diageotropica Gene Differentially Affects Auxin and Cytokinin Responses throughout Development in Tomato

The interactions between the plant hormones auxin and cytokinin throughout plant development are complex, and genetic investigations of the interdependency of auxin and cytokinin signaling have been limited. We have characterized the cytokinin sensitivity of the auxin-resistant diageotropica (dgt) mutant of tomato (Lycopersicon esculentum Mill.) in a range of auxin- and cytokinin-regulated responses. Intact, etiolated dgt seedlings showed cross-resistance to cytokinin with respect to root elongation, but cytokinin effects on hypocotyl growth and ethylene synthesis in these seedlings were not impaired by the dgt mutation. Seven-week-old, green wild-type and dgt plants were also equally sensitive to cytokinin with respect to shoot growth and hypocotyl and internode elongation. The effects of cytokinin and the dgt mutation on these processes appeared additive. In tissue culture organ regeneration from dgt hypocotyl explants showed reduced sensitivity to auxin but normal sensitivity to cytokinin, and the effects of cytokinin and the mutation were again additive. However, although callus induction from dgt hypocotyl explants required auxin and cytokinin, dgt calli did not show the typical concentration-dependent stimulation of growth by either auxin or cytokinin observed in wild-type calli. Cross-resistance of the dgt mutant to cytokinin thus was found to be limited to a small subset of auxin- and cytokinin-regulated growth processes affected by the dgt mutation, indicating that auxin and cytokinin regulate plant growth through both shared and separate signaling pathways.     

Growth and stomata development of Arabidopsis hypocotyls are controlled by gibberellins and modulated by ethylene and auxins

The plant hormones gibberellin (GA), ethylene and auxin can promote hypocotyl elongation of Arabidopsis seedlings grown in the light on a low nutrient medium (LNM). In this study, we used hypocotyl elongation as a system to investigate interactions between GA and ethylene or auxin and analysed their influence on the development of stomata in the hypocotyl. When applied together, GA and ethylene or auxin exerted a synergistic effect on hypocotyl elongation. Stimulated cell elongation is the main cause of hypocotyl elongation. Furthermore, hypocotyls treated with GA plus either ethylene or auxin show an increased endoreduplication. In addition, a small but significant increase in cell number was observed in the cortical cell files of hypocotyls treated with ethylene and GA together. However, studies with transgenic seedlings expressing CycB1::uidA genes revealed that cell division in the hypocotyl occurs only in the epidermis and mainly to form stomata, a process strictly regulated by hormones. Stomata formation in the hypocotyl is induced by the treatment with either GA or ethylene. The effect of GA could be strongly enhanced by the simultaneous addition of ethylene or auxin to the growth medium. Gibberellin is the main signal inducing stomata formation in the hypocotyl. In addition, this signal regulates hypocotyl elongation and is modulated by ethylene and auxin. The implication of these three hormones in relation to cell division and stomata formation is discussed.     

外源赤霉素对心里美萝卜幼苗花青素的影响

花青素是植物体内广泛存在的一类天然色素,具有重要的生理功能。花青素合成途径可受多种因素调控,其中植物生长激素赤霉素（gibberellic acid,GA）对其的调控作用报道较少。本文用不同浓度的赤霉素处理心里美萝卜幼苗,以探讨它对花青素含量的影响。结果表明,外源GA3处理显著增加了萝卜幼苗的下胚轴长度,并提高了下胚轴中α-淀粉酶活性;显著降低下胚轴中花青素的含量。1 μmol/L GA3处理效果较好;处理后第3 d和第5 d,花青素合成的关键酶查尔酮合酶、查尔酮异构酶和花青素还原酶编码基因的表达水平均低于对照组。同时,外源GA3显著诱导过氧化物酶活性的升高。上述结果表明,外源赤霉素可能通过下调花青素合成基因的表达,提高过氧化物酶活性和促进下胚轴伸长生长降低花青素的水平。     

Of light and length: regulation of hypocotyl growth in Arabidopsis

At all stages, plant development results from a complex integration of multiple endogenous and environmental signals. The sedentary nature of plants strongly enhances the impact of the environment on plant development as compared to animal development. The embryonic and postembryonic seedling stem, called the hypocotyl, of the model species Arabidopsis (thale cress) has proved to be an excellent system for studying such signal interplay in the regulation of growth and developmental responses. The extension of the hypocotyl, which is regulated by a network of interacting factors, including light and plant hormones, is such a process. These regulatory factors often reciprocally regulate their biosynthesis and/or signalling. Here we present the current state of knowledge about the regulation of hypocotyl growth by a large repertoire of internal and external cues.     

Phosphorylation of 1-aminocyclopropane-1-carboxylic acid synthase by MPK6, a stress-responsive mitogen-activated protein kinase, induces ethylene biosynthesis in Arabidopsis

Mitogen-activated protein kinases (MAPKs) are implicated in regulating plant growth, development, and response to the environment. However, the underlying mechanisms are unknown because of the lack of information about their substrates. Using a conditional gain-of-function transgenic system, we demonstrated that the activation of SIPK, a tobacco (Nicotiana tabacum) stress-responsive MAPK, induces the biosynthesis of ethylene. Here, we report that MPK6, the Arabidopsis thaliana ortholog of tobacco SIPK, is required for ethylene induction in this transgenic system. Furthermore, we found that selected isoforms of 1-aminocyclopropane-1-carboxylic acid synthase (ACS), the rate-limiting enzyme of ethylene biosynthesis, are substrates of MPK6. Phosphorylation of ACS2 and ACS6 by MPK6 leads to the accumulation of ACS protein and, thus, elevated levels of cellular ACS activity and ethylene production. Expression of ACS6(DDD), a gain-of-function ACS6 mutant that mimics the phosphorylated form of ACS6, confers constitutive ethylene production and ethylene-induced phenotypes. Increasing numbers of stress stimuli have been shown to activate Arabidopsis MPK6 or its orthologs in other plant species. The identification of the first plant MAPK substrate in this report reveals one mechanism by which MPK6/SIPK regulates plant stress responses. Equally important, this study uncovers a signaling pathway that modulates the biosynthesis of ethylene, an important plant hormone, in plants under stress.