Pleiotropic Effects of sym-17 : A Mutation in Pisum sativum L. cv Sparkle Causes Decreased Nodulation, Altered Root and Shoot Growth, and Increased Ethylene Production

R82 (sym-17), a stable mutant of Pisum sativum L. cv Sparkle, is described. The shoot growth of the mutant was less than that of its parent under light or dark growth conditions. Gibberellic acid treatment did not normalize the shoot growth of R82. The mutant had thick and short roots. It formed few nodules, but the specific nitrogenase activity was not affected. R82 produced and contained more ethylene than Sparkle. It also contained more free 1-amino-cyclopropane-1-carboxylic acid than did its parent in both the shoot and the root. The root tip of R82 had a lower activity of ethylene-forming enzyme than that of Sparkle, whereas the whole shoot of R82 had a similar activity. The sensitivity of R82 to exogenous ethylene was not more than that of Sparkle. Exogenous ethylene treatments did not make Sparkle mimic R82, and inhibitors of ethylene biosynthesis or action did not normalize the phenotype of R82. The data suggest that the primary effect of sym-17 is not the enhanced ethylene production.     

Ethylene as a Possible Mediator of Light- and Nitrate-Induced Inhibition of Nodulation of Pisum sativum L. cv Sparkle

R82 (sym-17), a stable mutant of Pisum sativum L. cv Sparkle, is described. The shoot growth of the mutant was less than that of its parent under light or dark growth conditions. Gibberellic acid treatment did not normalize the shoot growth of R82. The mutant had thick and short roots. It formed few nodules, but the specific nitrogenase activity was not affected. R82 produced and contained more ethylene than Sparkle. It also contained more free 1-amino-cyclopropane-1-carboxylic acid than did its parent in both the shoot and the root. The root tip of R82 had a lower activity of ethylene-forming enzyme than that of Sparkle, whereas the whole shoot of R82 had a similar activity. The sensitivity of R82 to exogenous ethylene was not more than that of Sparkle. Exogenous ethylene treatments did not make Sparkle mimic R82, and inhibitors of ethylene biosynthesis or action did not normalize the phenotype of R82. The data suggest that the primary effect of sym-17 is not the enhanced ethylene production.     

Burst of Ethylene upon Horizontal Placement of Tomato Seedlings

Seedlings of Lycopersicon esculentum Mill. cv Rutgers emit a pulse of ethylene during the first 2 to 4 minutes following horizontal placement. Because this burst appears too rapid and brief to be mediated by increase in net activity of 1-aminocyclopropane-1-carboxylic acid synthase, it might result from accelerated transformation of vacuolar 1-aminocyclopropane-1-carboxylic acid to ethylene.     

Effect of Inhibitors and Stimulators of Ethylene Production on Gall Development in Meloidogyne javanica-Infected Tomato Roots

Excised tomato roots infected with Meloidogyne javanica produced ethylene at 3-6 times the rate of noninfected roots. This increase in ethylene production started 5 days after inoculation. Gall growth and ethylene production in infected roots were accelerated by 1-aminocyclopropane-1-carboxylic acid (ACC), indole acetic acid (IAA), and ethrel known as ethylene production stimulators. When inhibitors of ethylene production, like aminoethoxyvinylglycine (AVG) or aminoxyacetic acid (AOA), or inhibitors of ethylene action like silver thiosulfate (STS), were applied, gall growth and ethylene production were inhibited. Enhanced expansion of parenchymatous cells was observed in sections from nematode-induced galls and ethylene-treated roots. Lignification of xylem elements and fibers in the vascular cylinder was markedly inhibited in the gall, compared with noninfected root tissue. Because ethylene is known to induce cell expansion and to inhibit lignification, it is suggested that this plant hormone plays a major role in the development of M. javanica-induced galls. Ethylene affects gall size by enhancing parenchymatous tissue development and allows expansion of giant cells and the nematode body by reducing tissue lignification.     

Ethylene synthesis in petunia stigma tissues governs the growth of pollen tubes in progamic phase of fertilization

In the pollen-pistil system of petunia (Petunia hybrida L.) self-compatible and self-incompatible clones within 7 h after self-pollination, we determined the content of ACC (1-aminocyclopropane-1-carboxylic acid), the activity of two enzymes (ACC synthase and ACC oxidase), and the rate of ethylene production. Depending on the type of pollination, germination of pollen on the stigma surface and the pollen tube growth in the tissues of style were accompanied by different levels of ACC and ethylene release. The pollen-pistil system of the self-compatible clone contained twice more ACC than in the self-incompatible clone, whereas the pollen-pistil system in the self-incompatible clone produced 4–5 times more ethylene than in the self-compatible clone. For both types of pollination, ACC and ethylene were predominantly produced in the stigma tissues. The rate of ethylene production therein was 50 times greater than in the styles and ovaries, and the content of ACC was 100 times higher than in the styles and ovaries. Germination of male gametophyte after both types of pollination was accompanied by elevated ACC synthase activity (especially in the case of compatible pollination), whereas notable increase in ACC oxidase activity was manifested in growing pollen tubes after self-incompatible pollination     

Ethylene formation from 1-aminocyclopropane-1-carboxylic acid by microsomal membranes from senescing carnation flowers

Isolated membranes from the petals of senescing carnation flowers (Dianthus caryophyllus L. cv. White-Sim) catalyze the conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene. A microsomal membrane fraction obtained by centrifugation at 131,000 g for 1 h proved to be more active than the membrane pellet isolated by centrifugation at 10,000 g for 20 min. The ethylene-producing activity of the microsomal membranes is oxygen-dependent, heat-denaturable, sensitive to n-propyl gallate, and saturable with ACC. Corresponding cytosol fractions from the petals are incapable of converting ACC to ethylene. Moreover, the addition of soluble fraction back to the membrane fraction strongly inhibits the ACC to ethylene conversion activity of the membranes. The efficiency with which isolated membranes convert ACC to ethylene is lower than that exhibited by intact flowers based on the relative yield of membranes per flower. This may be due to the presence of the endogenous soluble inhibitor of the reaction, for residual soluble fraction inevitably remains trapped in membrane vesicles isolated from a homogenate.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AOA aminoxyacetic acid - AVG aminoethoxyvinylglycine - EPPS N-2-hydroxyethylpiperazine propane sulfonic acid     

Ethylene production and metabolism of 1-aminocyclopropane-1-carboxylic acid in a long-day plant,Chenopodium murale L., as influenced by photoperiodic flower induction

Chenopodium murale plants, induced to flower by 5 days of continuous light, produced 43% more ethylene than vegetative plants kept under short days (16 h darkness, 8 h light). The 1-aminocyclopropane-1-carboxylic acid (ACC)-induced ethylene production, using saturating ACC concentration (10 mol·m⁻³) was also 55% higher in induced plants. Their ACC and N-malonyl-ACC (MACC) levels were also higher, the former increasing by 56% in both shoots and roots, the latter by 288% and 108% in shoots and roots, respectively. Administration of labeled [2,3-¹⁴C]ACC produced a very similar relative content of ACC and MACC in both treatments. The only process influenced by flower induction was ACC conversion to ethylene. Induced plants converted 66% more ACC than the vegetative ones. The effects of photoperiod on ethylene formation and metabolism in a long-day plant (LDP)C. murale and a short-day plant (SDP)C. rubrum are compared. Ethylene formation seems to be under photoperiodic control in both species, but its role in flower induction remains obscure.     

Ethylene and auxin-ethylene interaction in adventitious root formation in mung bean (Vigna radiata) cuttings

The role of ethylene in adventitious root formation and its involvement in auxin-induced rooting were investigated in cuttings ofVigna radiata (L.). Treatment with 30 M indole-3-acetic acid (IAA) for 24 h slightly inhibited rooting, whereas the same concentration of indole-3-butyric acid (IBA) significantly stimulated it. Ethylene derived from 1-aminocyclopropane-1-carboxylic acid (ACC) increased the number of adventitious roots but inhibited their emergence and elongation. Endogenous levels of ethylene, ACC, and malonyl-ACC (MACC) were initially higher in cuttings treated with IAA. This trend was quickly reversed, and cuttings, particularly hypocotyls, treated with IBA produced higher levels of ethylene and had more ACC and MACC during most of the rooting process. Aminoethoxyvinylglycine significantly inhibited rooting, but its inhibitory effect could not be reversed by ACC. The data suggest that the stimulating effect of IBA on rooting is closely associated with its induction of ACC and ethylene biosynthesis.     

Ethylene precursors and antagonists increase embryogenesis of Hordeum vulgare L. anther culture

The role of ethylene in microspore embryogenesis and regeneration was analyzed by studying the effects of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) and the ethylene antagonists silver nitrate and silver thiosulphate on the androgenic response of in vitro cultured anthers of seven genotypes of barley. Incorporation of either ACC or silver salts in the culture medium lead to a significant increase in callus induction for five of the seven genotypes tested. The treatment that increased callus induction depended upon genotype. Only anthers cultured on 1 mg l^–1 silver thiosulphate gave rise to fertile plants in all seven genotypes tested.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - IAA indole acetic acid - PAA phenyl acetic acid - STS silver thiosulphate - ACC 1-aminocyclopropane-1-carboxylic acid     

Stimulation of ethylene production and gas-space (aerenchyma) formation in adventitious roots of Zea mays L. by small partial pressures of oxygen

Adventitious roots of two to four-weekold intact plants of Zea mays L. (cv. LG11) were shorter but less dense after extending into stagnant, non-aerated nutrient solution than into solution continuously aerated with air. Dissolved oxygen in the non-aerated solutions decreased from 21 kPa to 3–9 kPa within 24 h. When oxygen partial pressures similar to those found in non-aerated solutions (3, 5 and 12 kPa) were applied for 7 d to root systems growing in vigorously bubbled solutions, the volume of gas-space in the cortex (aerenchyma) was increased several fold. This stimulation of aerenchyma was associated with faster ethylene production by 45-mm-long apical root segments. When ethylene production by roots exposed to 5 kPa oxygen was inhibited by aminoethoxyvinylglycine (AVG) dissolved in the nutrient solution, aerenchyma formation was also retarded. The effect of AVG was reversible by concomitant applications of 1-aminocyclopropane-1-carboxylic acid, an immediate precursor of ethylene. Addition of silver nitrate, an inhibitor of ethylene action, to the nutrient solution also prevented the development of aerenchyma in roots given 5 kPa oxygen. Treating roots with only 1 kPa oxygen stimulated ethylene production but failed to promote gas-space formation. These severely oxygen-deficient roots seemed insensitive to the ethylene produced since a supplement of exogeneous ethylene that promoted aerenchyma development in nutrient solution aerated with air (21 kPa oxygen) failed to do so in nutrient solution supplied with 1 kPa oxygen. Both ethylene production and aerenchyma formation were almost completely halted when roots were exposed to nutrient solutions devoid of oxygen. Thus both processes require oxygen and are stimulated by oxygen-deficient surroundings in the 3-to 12-kPa range of oxygen partial pressures when compared with rates observed in air (21 kPa oxygen).Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AVG aminoethoxyvinylglycine     

The Effect of the Ethylene Action Inhibitor 1-Cyclopropenylmethyl Butyl Ether on Early Plant Growth

Increased levels of ethylene in plants are responsible for many deleterious effects such as early senescence, fruit deterioration and inhibition of root elongation. Several cyclopropene derivatives have previously been studied as inhibitors of ethylene action in plants. This study focuses on one such compound, 1-cyclopropenylmethyl butyl ether and its effect on the growth of roots and shoots of canola plants as well as rooting of mung bean seedlings 1-cyclopropenylmethyl butyl ether increased root length in canola plants, but had no significant effect on shoot length. In rooting studies, mung bean seedlings treated with 1-cyclopropenylmethyl butyl ether prior to root excision had fewer numbers of roots than control plants that were not treated with the ethylene action inhibitor. The same rooting study, when repeated in the presence of 1-aminocyclopropane-1-carboxylic acid (ACC), demonstrated an overall increase in the number of roots of inibitor-treated and non-treated plants, however, the inhibitor was still effective in decreasing the number of roots, compared to its non-treated conterpart. Online publication: 7 April 2005     

The Role of Ethylene in the Inhibition of Rooting under Low Oxygen Tensions

A 60-fold increase in ethylene content was observed in stem cuttings of chrysanthemum (Chrysanthemum × morifolium Ramat.) held in aero-hydroponics under anoxic conditions during the 8 to 12 days necessary for adventitious root formation. Ethylene, 1-aminocyclopropane-1-carboxylic acid, and 10-(malonylamino) cyclopropane-1-carboxylic acid contents were highest in the immersed portion of the cuttings, but there was substantial ethylene produced by the anoxic, misted portions of the cutting above the liquid. Application of ethylene (10 microliters per liter) to chrysanthemum cuttings stimulated root development in cuttings held in high dissolved oxygen concentrations (8.0 milligrams per liter). Since the application of ethylene did not inhibit rooting in cuttings held at low dissolved oxygen concentrations (2.0 milligrams per liter), the inhibition of rooting under low oxygen concentrations is not mediated by the observed increase in endogenous ethylene content.     

Changes in 1-Aminocyclopropane-1-carboxylic Acid Content and Ethylene Production in Hiproly Barley Callus during Differentiation

During differentiation after auxin withdrawal, the change in the ethylene production of Hiproly barley callus paralleled the change in 1-aminocyclopropane-1-carboxylic acid (ACC) content. The levels of ACC and ethylene production decreased rapidly, and then increased in Hiproly barley callus.

Aminooxyacetic acid (AOA) prevented the ACC and ethylene production of the callus. Moreover, aminoisobutyric acid (AIB) also inhibited the ethylene production, but did not prevent the ACC synthesis of the callus. On the other hand, methylglyoxal-bis(guanylhydrazone) (MGBG) greatly enhanced the ACC and ethylene production. Formation of adventitious roots in Hiproly barley callus was enhanced by the cultivation in the medium containing AIB or AOA. However, differentiation of the callus was strongly inhibited by MGBG.

Thus, prevention of ethylene production may be significant for differentiation of Hiproly barley callus.     

Root Formation in Ethylene-Insensitive Plants

Experiments with ethylene-insensitive tomato (Lycopersicon esculentum) and petunia (Petunia x hybrida) plants were conducted to determine if normal or adventitious root formation is affected by ethylene insensitivity. Ethylene-insensitive Never ripe (NR) tomato plants produced more below-ground root mass but fewer above-ground adventitious roots than wild-type Pearson plants. Applied auxin (indole-3-butyric acid) increased adventitious root formation on vegetative stem cuttings of wild-type plants but had little or no effect on rooting of NR plants. Reduced adventitious root formation was also observed in ethylene-insensitive transgenic petunia plants. Applied 1-aminocyclopropane-1-carboxylic acid increased adventitious root formation on vegetative stem cuttings from NR and wild-type plants, but NR cuttings produced fewer adventitious roots than wild-type cuttings. These data suggest that the promotive effect of auxin on adventitious rooting is influenced by ethylene responsiveness. Seedling root growth of tomato in response to mechanical impedance was also influenced by ethylene sensitivity. Ninety-six percent of wild-type seedlings germinated and grown on sand for 7 d grew normal roots into the medium, whereas 47% of NR seedlings displayed elongated tap-roots, shortened hypocotyls, and did not penetrate the medium. These data indicate that ethylene has a critical role in various responses of roots to environmental stimuli.     

Ethylene formation in Pisum sativum and Vicia faba protoplasts

Protoplasts isolated from leaves of peas (Pisum sativum L.) and of Vicia faba L. produced 1-aminocyclopropane-1-carboxylic acid (ACC) from endogenous substrate. Synthesis of ACC and conversion of ACC to ethylene was promoted by light and inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea and carbonyl cyanide m-chlorophenylhydrazone. Aminoethoxyvinylglycine inhibited ethylene synthesis to a minor extent when given during incubation of the protoplasts but was very effective when added both to the medium in which the protoplasts were isolated and to the incubation medium as well. Radioactivity from [U-¹⁴C]methionine was incorporated into ACC and ethylene. However, the specific radioactivity of the C-2 and C-3 atoms of ACC, from which ethylene is formed, increased much faster than the specific radioactivity of ethylene. It appears that ACC and ethylene are synthesized in different compartments of the cell and that protoplasts constitute a suitable system to study this compartmentation.Abbreviations ACC 1-Aminocyclopropane-1-carboxylic acid - AVG aminoethoxyvinylglycine - CCCP carbonyl cyanide m-chlorophenylhydrazone - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea     

Manipulation of Ethylene Synthesis in Roots Through Bacterial ACC Deaminase for Improving Nodulation in Legumes

Symbiotic association between rhizobia and legumes results in the development of unique structures on roots, called nodules. Nodulation is a very complex process involving a variety of genes that control NOD factors (bacterial signaling molecules), which are essential for the establishment, maintenance and regulation of this process and development of root nodules. Ethylene is an established potent plant hormone that is also known for its negative role in nodulation. Ethylene is produced endogenously in all plant tissues, particularly in response to both biotic and abiotic stresses. Exogenous application of ethylene and ethylene-releasing compounds are known to inhibit the formation and functioning of nodules. While inhibitors of ethylene synthesis or its physiological action enhance nodulation in legumes, some rhizobial strains also nodulate the host plant intensively, most likely by lowering endogenous ethylene levels in roots through their 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity. Co-inoculation with ACC deaminase containing plant growth promoting rhizobacteria plus rhizobia has been shown to further promote nodulation compared to rhizobia alone. Transgenic rhizobia or legume plants with expression of bacterial ACC deaminase could be another viable option to alleviate the negative effects of ethylene on nodulation. Several studies have well documented the role of ethylene and bacterial ACC deaminase in development of nodules on legume roots and will be the primary focus of this critical review.     

Ethylene induced shikonin biosynthesis in shoot culture of Lithospermum erythrorhizon.

Lithospermum erythrorhizon shoots, cultured on phytohormone-free Murashige and Skoog solid medium, produced shikonin derivatives, whereas shoots cultured in well-ventilated petri dishes, produced small amount. Analysis by gas chromatography revealed the presence of ethylene in non-ventilated petri dishes where the shoots, producing shikonin derivatives, were cultured. Therefore, the possible involvement of ethylene in shikonin biosynthesis of shoot cultures was investigated. Treatment of ethylene or the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid, resulted in increasing shikonin derivatives contents in cultured shoots. Silver ion, an ethylene-response inhibitor, or aminoethoxyvinylglycine, an ethylene biosynthesis inhibitor, decreased production of shikonin derivatives in cultured shoots. Our results indicate that ethylene is one of the regulatory elements of shikonin biosynthesis in L. erythrorhizon shoot culture.     

Stress-induced Ethylene Production in the Ethylene-requiring Tomato Mutant Diageotropica

Ethylene synthesis in vegetative tissues is thought to be controlled by indoleacetic acid (IAA). However, ethylene synthesis in the diageotropica (dgt) mutant of tomato (Lycopersicon esculentum Mill.) was much less sensitive to IAA than in the normal variety (VFN8). Yet, mechanical wounding stimulated ethylene production by the mutant. The dgt tomato provides an opportunity to study the regulation of stress ethylene independent of IAA effects. Waterlogging (i.e. anaerobic stress) stimulated production of the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), in the roots. The ACC was transported to the shoot where it was converted to ethylene. The dgt mutant efficiently utilized ACC for ethylene synthesis under aerobic conditions. The results confirm that the genetic lesion in dgt is located at a step prior to the formation of ACC. Furthermore, induction of ethylene synthesis by anaerobic or mechanical stresses in this mutant is independent of IAA action.     

Ethylene production and metabolism of 1-aminocyclopropane-1-carboxylic acid inChenopodium rubrum L. as influenced by photoperiodic flower induction

Chenopodium rubrum plants, induced to flower by three cycles of 12 h darkness and 12 h light, produced 42% less ethylene than vegetative plants kept under continuous light. Plants that had each dark cycle broken by 2 h light in the middle did not flower and produced almost as much ethylene as the vegetative plants. Shoots and roots of plants of all three experimental treatments had a similar content of 1-aminocyclopropane-1-carboxylic acid (ACC), the mean amounting to about 2 nmol · g^–1 dry weight. Also the content of N-malonyl-ACC (MACC) was similar in shoots of all three treatments. MACC content in roots was shown to be much higher, especially in the treatments with three dark periods (about 85 nmol · g^–1 dry weight). When labeled [2,3-¹⁴C] ACC was administered, the relative contents of ACC and MACC were very similar among all three treatments. The only process influenced by flower induction was ACC conversion to ethylene. Induced plants converted 36% less ACC than the vegetative ones. Plants subjected to night-break converted almost as much ACC to ethylene as vegetative plants. It is concluded that flower induction in the short-day plantChenopodium rubrum decreases ethylene production by decreasing their capability of converting ACC to ethylene.     

Ethylene and in vitro rooting of rose shoots

Effects of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC), ethylene biosynthesis inhibitor, (CoCl₂), and inhibitor of ethylene binding to receptors, 1-methylcyclopropene (1-MCP), on ethylene production and rooting in shoot culture of Rosa hybrida L. cv. Alba meidiland were studied. Additionally, effect of ethylene removal by KMnO₄ and HgClO₄ on rooting was tested. ACC increased ethylene production and delayed root formation, decreased the number of roots per shoot and inhibited root growth. In contrast, inhibition of ethylene production by CoCl₂ accelerated root emergence, and increased the number of roots per shoot. Likewise, removing ethylene from the ambient atmosphere improved root emergence and, increased root number of per shoot and markedly inhibited root growth. Blocking the ethylene receptors by 1-MCP increased ethylene level in the ambient atmosphere and increased both emergence and root formation. Both ethylene biosynthesis and action are involved in the control of rooting. Ethylene concentration in glass jars was too high for root emergence and formation, but was appropriate for root growth. CoCl₂ or 1-MPC can be recommended for regulation of rooting in rose shoot culture, since both emergence and number of roots were improved but root growth was not inhibited.