Thigmomorphogenesis: Evidence for a translocatable thigmomorphogenetic factor induced by mechanical perturbation of beans (Phaseolus vulgaris)

Mechanical perturbation of bean (Phaseolus vulgaris L.) internodes results in reduced elongation and increased diameter of the internodes (thigmomorphogenesis). Perturbation of a single lower internode results in thigmorphogenesis in that internode and all of those internodes above it, the degree of which depends on the age (size) of the internodes and the frequency of perturbation. Application of ethephon to the internodes mimics mechanical perturbation. Early removal of the shoot tip or the cotyledons does not effect thigmomorphogenesis, indicating that those organs do not exert control over the response. Mechanical perturbation of one plant of a pair grafted together at the first internodes results in thigmomorphogenesis in both plants. This indicates the transport of some factor from the mechanically perturbed donor to the non-treated receiver. Evidence is presented to support the contention that ethylene is not this transportable factor.     

Thigmomorphogenesis: The Involvement of Auxin and Abscisic Acid in Growth Retardation Due to Mechanical Perturbation

When young bean plants are mechanically perturbed for up to10 days, they accumulate large amounts of an auxin-like substanceand increased amounts of ABA. Exogenous ethylene, applied inthe form of ethephon, produces the same result. Physiologicallymoderately high amounts of exogenously applied IAA or loweramounts of ABA cause the same sort of retardation of elongationthat is caused by either mechanical perturbation or exogenousethephon. Either mechanical perturbation or applied ethephonsignificantly retards the polar basipetal transport of ¹⁴C-IAAIt is proposed that mechanical perturbation of bean internodesinduces ethylene evolution which, in turn, induces the accumulationof high levels of IAA and the production of ABA, both of whichcontribute to the retardation of elongation of the internodes. (Received December 24, 1981; Accepted May 19, 1982)     

Author index volume 38 (1985)

Mechanical perturbation (MP, rubbing) of internodes of Pharbitis nil shoots initiates release of lateral buds (LB) from apical dominance within 48 h. Evidence is presented which suggests that MP promotion of LB outgrowth is mediated by ethylene-induced restriction of main shoot growth. Ethylene production in the internodes is stimulated by MP within 2 h. Effects of MP are mimicked by treatments with 1-aminocyclopropane-1-carboxylic acid (ACC) and are negated by the inhibitors of ethylene production or action, aminoethoxy vinylglycine (AVG) and AgNO₃. The fact that effects of MP, ACC and ethylene inhibitors are observed to occur on main shoot growth at least 24 h before they are observed to occur on LB growth suggests a possible cause and effect relationship. MP also causes an increase in internode diameter. MP stimulation of ethylene production appears to be mediated by ACC synthase. The results of this study and our previous studies suggest that apical dominance may be released by any mechanism which induces ethylene restriction of main shoot growth.     

Methyl jasmonate-induced ethylene production is responsible for conifer phloem defense responses and reprogramming of stem cambial zone for traumatic resin duct formation

Conifer stem pest resistance includes constitutive defenses that discourage invasion and inducible defenses, including phenolic and terpenoid resin synthesis. Recently, methyl jasmonate (MJ) was shown to induce conifer resin and phenolic defenses; however, it is not known if MJ is the direct effector or if there is a downstream signal. Exogenous applications of MJ, methyl salicylate, and ethylene were used to assess inducible defense signaling mechanisms in conifer stems. MJ and ethylene but not methyl salicylate caused enhanced phenolic synthesis in polyphenolic parenchyma cells, early sclereid lignification, and reprogramming of the cambial zone to form traumatic resin ducts in Pseudotsuga menziesii and Sequoiadendron giganteum. Similar responses in internodes above and below treated internodes indicate transport of a signal giving a systemic response. Studies focusing on P. menziesii showed MJ induced ethylene production earlier and 77-fold higher than wounding. Ethylene production was also induced in internodes above the MJ-treated internode. Pretreatment of P. menziesii stems with the ethylene response inhibitor 1-methylcyclopropene inhibited MJ and wound responses. Wounding increased 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase protein, but MJ treatment produced a higher and more rapid ACC oxidase increase. ACC oxidase was most abundant in ray parenchyma cells, followed by cambial zone cells and resin duct epithelia. The data show these MJ-induced defense responses are mediated by ethylene. The cambial zone xylem mother cells are reprogrammed to differentiate into resin-secreting epithelial cells by an MJ-induced ethylene burst, whereas polyphenolic parenchyma cells are activated to increase polyphenol production. The results also indicate a central role of ray parenchyma in ethylene-induced defense.     

Wound-induced Ethylene Formation in Albedo Tissue of Citrus Fruit

Excised albedo tissue of citrus fruit (Citrus unshiu and Citrus hassaku) produced ethylene at an increasing rate in response to wounding and aging. The application of 1-aminocyclopropane-1-carboxylic acid (ACC) enhanced ethylene production in both the fresh and aged tissues, but this increase was greater in the aged tissue than in the fresh tissue. ACC content was very low in fresh tissue but increased greatly in aging tissue, paralleling the rise in ethylene production. Aminoethoxyvinylglycine (AVG) strongly inhibited ethylene production in the aged tissue. In the presence of ACC, however, ethylene production was not inhibited by AVG. These results suggest that ACC is an intermediate in the pathway of ethylene biosynthesis in the albedo tissue and that both steps of ACC formation and ACC conversion to ethylene are enhanced by wounding and aging. Inhibitors of protein synthesis, cycloheximide and 2-(4-methyl-2,6-dinitroanilino)-N-methyl propionamide, strongly inhibited ethylene production in the albedo tissue, implying that protein synthesis is required to maintain the continuous evolution of ethylene. The stimulation of ethylene production by ACC was reduced by the addition of l-methionine, whereas d-methionine had very little inhibitory effect. Ethylene production in the albedo tissue was also inhibited by the addition of n-propyl gallate and 3,5-dibromo-4-hydroxybenzoic acid.     

Enhancement of wound-induced ethylene synthesis by ethylene in preclimacteric cantaloupe

Although intact fruits of unripe cantaloupe (Cucumis melo L.) produce very little ethylene, a massive increase in ethylene production occurred in response to excision. The evidence indicates that this wound ethylene is produced from methionine via 1-aminocyclopropanecarboxylic acid (ACC) as in ripening fruits. Excision induced an increase in both ACC synthase and the enzyme converting ACC to ethylene. Ethylene further increased the activity of the enzyme system converting ACC to ethylene. The induction by ethylene required a minimum exposure of 1 hour; longer exposure had increasingly larger effect. The response was saturated at approximately 3 microliters per liter ethylene and was inhibited by Ag⁺. Neither ethylene nor ACC had a promotive or inhibitory effect on ACC synthase beyond the effect attributable to wounding.     

伤处理和乙烯对桃ACC氧化酶基因表达的影响

桃果实不耐贮运,特别是溶质水蜜桃、珐I大11＿程技术的发展使番茄果实实现延熟保鲜'－'、人f［］也试图通过乙烯合成的关键酶的］i义HNA技术来延长桃果实的贮运期。：ICC氧化酶是乙烯生物合成的关键酶之一,ACC氧化酶4peJL从番茄'、矮牵牛。。。桃卜'、苹果、'等许多植物...     

Aluminum-induced ethylene production is associated with inhibition of root elongation in Lotus japonicus L

Inhibition of root elongation by toxic aluminum (Al(3+)) occurs rapidly and is one of the most distinct and earliest symptoms of Al toxicity. To elucidate mechanism underlying Al(3+)-induced inhibition of root elongation, we investigated the involvement of ethylene in Al(3+)-induced inhibition of root elongation using the legume model plants Lotus japonicus and Medicago truncatula. Root elongation of L. japonicus and M. truncatula was rapidly inhibited by exposure to AlCl(3). A similar rapid inhibition of root elongation by the ethylene-releasing substance, ethephon, and the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), was also observed. The Al(3+)-induced inhibition of root elongation was substantially ameliorated in the presence of antagonists of ethylene biosynthesis [Co(2+) and aminoethoxyvinylglycine (AVG)]. Al(3+) increased the activity of ACC oxidase (ACO), and induced a rapid evolution of ethylene from root apices and expression of genes of ACC synthase (ACS) and ACO. These findings suggest that induction of ethylene evolution resulting from up-regulation of ACS and ACO plays a critical role in Al(3+)-induced inhibition of root elongation.     

The role of ethylene in the growth response of submerged deep water rice

We investigated the effect of partial submergence on internode elongation in a Bangladesh variety of floating or deep water rice (Oryza sativa L., cv. Habiganj Aman II). In plants which were at least 21 days old, 7 days of submergence led to a 3- to 5-fold increase in internodal length. During submergence, the ethylene concentration in the internodes increased from about 0.02 to 1 microliters per liter. Treatment of nonsubmerged plants with ethylene also stimulated internode elongation. When ethylene synthesis in partially submerged plants was blocked with aminooxyacetic acid and aminoethoxyvinylglycine, internode elongation was inhibited. This growth inhibition was reversed when ethylene biosynthesis was restored with 1-aminocyclopropane-1-carboxylic acid (ACC). Radio-labeling studies showed that ethylene in floating rice was synthesized from methionine via ACC. Internodal tissue from submerged plants had a much higher capacity to form ethylene than did internodal tissue from nonsubmerged plants. This increase in ethylene synthesis appeared to be due to enhanced ACC formation rather than to increased conversion of ACC to ethylene. Our results indicate that ethylene produced during submergence is required for the stimulation of growth in submerged floating rice plants.     

Factors increasing ethylene production enhance the sensitivity of root growth to auxins

Light inhibits root elongation, increases ethylene production and enhances the inhibitory action of auxins on root elongation of pea ( Pisum sativum L. cv. Weibulls Marma) seedlings. To investigate the role of ethylene in the interaction between light and auxin, the level of ethylene production in darkness was increased to the level produced in light by supplying 1-aminocyclopropane-1-carboxylic acid (ACC) or benzylaminopurine (BAP). Ethylene production was measured in excised root tips after treatment of intact seedlings for 24 h, while root growth was measured after 48 h. Auxin, at a concentration causing a partial inhibition of root elongation, did not increase ethylene production significantly. A 4-fold increase in ethylene production, caused either by light, 0.1 μ M ACC or 0.1 μ M BAP, inhibited root elongation by 40–50%. The auxins 2,4-dichlorophenoxyacetic acid and indolebutyric acid applied at 0.1 μ M inhibited root elongation by 15–25% in darkness but by 50–60% in light. Supply of ACC or BAP in darkness enhanced the inhibitory effects of auxins to about the same extent as in light. The inhibition caused by the auxins as well as by the BAP was associated with swelling of the root tips. ACC and BAP treatment synergistically increased the swelling caused by auxins. We conclude that auxin and ethylene, when applied or produced in partially inhibitory concentrations, act synergistically to inhibit root elongation and increase root diameter. The effect of light on the response of the roots to auxins is mediated by a light-induced increase in ethylene production.     

Thigmomorphogenesis: Changes in Cell Division and Elongation in the Internodes of Mechanically-perturbed or Ethrel-treated Bean Plants

Examination of first internodes of young Phaseolus vulgarisL. plants which have been subjected to mechanical perturbationshows decreased elongation and increased radial growth. Thedecreased elongation can be attributed to both reduced cellelongation of epidermal and cortical cells and a reduced numberof cells in the vascular and pith tissues. The increased radialenlargement is due to increased cortical cell expansion andincreased secondary xylem production resulting from increasedcambial activity. All of these responses are observable withina few hours of a single mechanical perturbation. Treatment ofplants with ethrel mimics all of these effects of mechanicalperturbation. Phaseolus vulgarisL, Kidney bean, thigmomorphogenesis, mechanical perturbation, ethrel, (2-chloroethyl phosphonic acid), cell division, internode elongation     

Pithiness in plants: I. The effect of mechanical perturbation and the involvement of ethylene in petiole pithiness in celery

Mechanical perturbation (MP) applied to celery (Appium graveolens L. cv. Florida 683) leaf petioles or ethephon application to the plant did not induce thigmomorphogenesis (inhibition of elongation and increase in thickness of the petiole). However, the two treatments did cause the parenchyma breakdown which leads to pithiness or increased natural pithiness, mainly at the base of the petiole. Nevertheless, MP (but not ethephon) decreased the severity of drought-stress or GA3-induced pithiness. Although MP stimulates ethylene production, mainly at the middle part of the petiole, it seems that the protection by MP of the petiole may not be directly mediated by ethylene production. The exposure of the plant to drought stress brought about an increase in ethylene evolution. Upon reirrigating the plants, the first steps of pithiness were accompanied by a sharp decline in ethylene production. This decrease might be due to membrane disruption. The increase in ethylene production during drought stress may be one of the events which stimulate pithiness of the celery leaf petiole.     

Cobalt inhibition of thigmomorphogenesis in Bryonia dioica: possible role and mechanism of ethylene production

Rubbing-induced inhibition of elongation in Bryonia dioica was completely prevented by 10⁻⁷ M cobalt chloride. Cellular redistribution of peroxidases, mainly characterized by transiently enhanced membrane-binding of soluble peroxidases, occurred as an immediate consequence of rubbing and was not inhibited by Co²⁺. Ethylene synthesis and 1-aminocyclopropane-1-carboxylic acid (ACC) conversion readily increased upon rubbing and fell soon afterwards, but ACC conversion then increased again progressively. Co²⁺ did not drastically counteract these changes, except for the second rise in ACC conversion which was completely eliminated. The rubbing-induced rise in ethyiene production and ACC conversion was closely correlated to microsomal ACC conversion and peroxidase activity, but only during the first hours after rubbing. The presented approach enables us to correlate stress-induced ethylene production to membrane-binding of peroxidases. It is suggested that ACC conversion in Bryonia dioica is triggered by two different, sequentially ordered mechanisms. The difference in the effects of Co²⁺ on elongation and ethylene production is discussed with respect to the role of ethylene in thigmomorphogensis.     

Thigmomorphogenesis: the Effect of Mechanical Perturbation and Ethrel on Stem Pithiness in Tomato [Lycopersicon esculentum (Mill.) Plants]

The stems of ‘Y’-shaped (double stemmed) tomato(Lycopersicon esculentum Mill.) plants were mechanically perturbed(MP) by stroking for 6 successive days. The treatment reducedelongation of the two stems by 40 per cent. When only one branchof the pair was treated, its length was reduced to the sameextent as the two branches in the previous treatment, whilethe elongation of the untreated branch was increased by 60 percent over that of the control. Withholding irrigation induced stem pithiness due to droughtstress in non-MP-plants. However, in MP-pretreated plants, thenumber of pithy internodes was markedly less and the degreeof severity of the disorder was reduced. Ethrel applicationmimicked the effects of MP on pithiness. In some unknown way,the plants are hardened by MP or Ethrel. Lycopersicon esculentum Mill, tomato, drought stress, thigmomorphogenesis, ethylene, pithiness     

Thigmomorphogenesis: membrane lipid and protein changes in bean plants as affected by mechanical perturbation and Ethrel

When bean plants (Phaseolus vulgaris L. cv. Red Cherokee Bush) are mechanically perturbed by rubbing, their stem elongation is inhibited and the stem thickness increases. The decrease in cell elongation and the increase in lateral cell divisions, which are partially responsible for this syndrome, were correlated with a decrease in the tree fatty acids and in the phospholipids of the membranes of microsomal fractions of first and second internodes of mechanically stimulated plants. This was true even though only the first internode was mechanically stimulated. Of the microsomal free fatty acids, mechanical perturbation induced an increase in myristic acid and large decreases in stearic, oleic, linoleic and linolenic acids. It also reduced the unsaturated:saturated ratio of the fatty acids. It induced a decrease in phosphatidyl choline but an increase in phosphatidyl ethanolamine. When the fatty acids were cleaved from the microsomal phospholipids, mechanical perturbation caused only a slight decrease in the unsaturated:saturated ratio and no significant changes in the double bond index. Mechanical perturbation induced an increase in the total microsomal protein and of membrane-associated latent IDPase. However, the activity of membrane-associated KCN-insensitive NADPH cytochrome-c reductase was decreased by mechanical perturbation. Treatment of the first internode with exogenous Ethrel produced results that were very similar in all respects to those obtained by mechanical perturbation. The factors inducing hardening against frost and drought, as achieved by mechanical perturbation and Ethrel treatment, are not only related to sterols or the polar head-groups of phospholipids but may also be related to the protein components, and all may have an effect on the fluidity of a bilayer membrane model. These data support the hypothesis that ethylene mediates thigmomorphogenesis and that mechanical perturbation of the first internode results in the acropetal transport of a translocatable thigmomorphogenetic factor.     

Differential expression of antisense in regenerated tobacco plants transformed with an antisense version of a tomato ACC oxidase gene

Ethylene production was measured during vegetative and reproductive development in normal tobacco plants and in transgenic tobacco plants carrying antisense genes for tomato ACC oxidase driven by the 35S CaMV promoter (Hamilton et al., 1990). When expressed in three independently derived transgenic plants, the antisense ethylene gene failed to affect ethylene production in young/mature leaves or in stems but it did inhibit ethylene production in roots by 37–58%. Ethylene production in developing flowers (i.e. from small unopened flower buds up until open flowers at anthesis) was not affected in transgenic plants but ethylene production in fruits was inhibited by 35%. The most dramatic effect on ethylene production in transgenic plants was seen immediately after wounding leaf tissue, in which case the antisense gene inhibited wound ethylene production by 72%. Thus, the antisense gene composed of a 35S CaMV promoter driving a heterologous ACC oxidase sequence had differential effects on ethylene production in tobacco plants.     

Ethylene promotes ethylene biosynthesis during pea seed germination by positive feedback regulation of 1-aminocyclo-propane-1-carboxylic acid oxidase

 Increased ethylene evolution accompanies seed germination of many species including Pisum sativum L., but only a little is known about the regulation of the ethylene biosynthetic pathway in different seed tissues. Biosynthesis of the direct ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC), the expression of ACC oxidase (ACO), and ethylene production were investigated in the cotyledons and embryonic axis of germinating pea seeds. An early onset and sequential induction of ACC biosynthesis, accumulation of Ps-ACO1 mRNA and of ACO activity, and ethylene production were localized almost exclusively in the embryonic axis. Maximal levels of ACC, Ps-ACO1 mRNA, ACO enzyme activity and ethylene evolution were found when radicle emergence was just complete. Treatment of germinating seeds with ethylene alone or in combination with the inhibitor of ethylene action 2,5-norbornadiene showed that endogenous ethylene regulates its own biosynthesis through a positive feedback loop that enhances ACO expression. Accumulation of Ps-ACO1 mRNA and of ACO enzyme activity in the embryonic axis during the late phase of germination required ethylene, whereas Ps-ACS1 mRNA levels and overall ACC contents were not induced by ethylene treatment. Ethylene did not induce ACO in the embryonic axis during the early phase of germination. Ethylene-independent signalling pathways regulate the spatial and temporal pattern of ethylene biosynthesis, whereas the ethylene signalling pathway regulates high-level ACO expression in the embryonic axis, and thereby enhances ethylene evolution during seed germination. Received: 28 September 1999 / Accepted: 27 December 1999     

Ethylene as a possible mediator of light-induced inhibition of root growth

Eliasson, L. and Bollmark, M. 1988. Ethylene as a possible mediator of light-induced inhibition of root growth. - Physiol. Plant. 72: 605–609.
Pea seedlings ( Pisum sativum L. cv. Weibull's Marma) were used to investigate the possible role of ethylene in light-induced inhibition of root elongation. Illumination of the roots with white light inhibited root elongation by 40–50% and increased ethylene production by the roots about 4-fold. Our main approach was to use exogenous 1-aminocyclopropane-1-carboxylic acid (ACC), supplied in the growth solution, to monitor ethylene production of the roots independent of light treatment. Ethylene production of excised root tips increased with increasing ACC concentrations. The rate of ethylene production in dark-grown roots treated with 0.1 μ M ACC was similar to that caused by illumination. Low ACC concentrations (0.01–0.1 μ M ) decreased the rate of root elongation, especially in seedlings grown in the dark, and 0.1 μ M ACC inhibited elongation to about the same extent as light. In light the roots curved and grew partly plagiogravitropically. This effect was also simulated by the 0.1 μ M ACC treatment. At 1 μ M and higher concentrations, ACC inhibited root growth almost completely and caused conspicuous curvatures of the root tips both in light and darkness. Inhibitors of ethylene synthesis and action partially counteracted the inhibition of root elongation caused by light. These observations suggest that the increase in ethylene production caused by light is at least partly responsible for the decreased growth of light-exposed roots.     

Rapidly induced ethylene formation after wounding is controlled by the regulation of 1-aminocyclopropane-1-carboxylic acid synthesis

Bean leaves from Phaseolus vulgaris L. var. Pinto 111 react to mechanical wounding with the formation of ethylene. The substrate for wound ethylene is 1-aminocyclopropane-1-carboxylic acid (ACC). It is not set free by decompartmentation but is newly synthesized. ACC synthesis starts 8 to 10 min after wounding at 28°C, and 15 to 20 min after wounding at 20°C. Aminoethoxyvinylglycine (AVG), a potent inhibitor of ethylene formation from methionine via ACC, inhibits wound ethylene synthesis by about 95% when applied directly after wounding (incubations at 20°C). AVG also inhibits the accumulation of ACC in wounded tissue. AVG does not inhibit conversion of ACC to ethylene. Wound ethylene production is also inhibited by cycloheximide, n-propyl gallate, and ethylenediaminetetraacetic acid.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AVG ammoethoxyvinylglycine - EDTA ethylenediaminetetraacetic acid