Ethylene in Plant Growth

Activity of arginine decarboxylase in etiolated pea seedlings appears 24 hours after seed imbibition, reaches its highest level on the 4th day, and levels off until the 7th day. This activity was found in the apical and subapical tissue of the roots and shoots where intensive DNA synthesis occurs. Exposure of the seedlings to ethylene greatly reduced the specific activity of this enzyme. The inhibition was observed within 30 min of the hormone application, and maximal effect-90% inhibition-after 18 hours. Ethylene at physiological concentrations affected the enzyme activity; 50% inhibitory rate was recorded at 0.12 microliters per liter ethylene and maximal response at 1.2 microliters per liter. Ethylene provoked a 5-fold increase in the K,," of arginine decarboxylase for its substrate and reduced the V.w by 10-fold. However, the enzyme recovered from the inhibition and regained control activity 7 hours after transferral of the seedlings to ethylene-free atmosphere. Reducing the endogenous level of ethylene in the tissue by hypobaric pressure, or by exposure to light, as well as interfering with ethylene action by treatment with silver thiosulfate or 2,5-norbornadiene, caused a gradual increase in the specific activity of arginine decarboxylase in the apical tissue of the etiolated seedlings. On the basis of these findings, the possible control of arginine decarboxylase activity by endogenous ethylene, and its implication for the hormone effect on plant growth, are discussed.arises from the study of Bagni (5), who first reported that growth ofdormant Helianthus tuberosus was initiated when either auxin or one of the polyamines was added to the medium and that growth was accompanied by an increase in polyamine titer. There are now recorded instances of increased polyamine biosynthesis and titer in plants following application of each of the growthpromoting plant hormones: auxin (6), GA3 (13), and cytokinin (28). On the other hand, retardation ofgrowth by ABA has been shown to be accompanied by decreased polyamine biosynthesis (28). Consequently, the role of 'second messenger' mediating the effect of plant hormones has been proposed for polyamines (14).Ethylene has been shown to inhibit cell division, DNA synthesis, and growth in meristems of roots, shoots, and axillary buds of etiolated pea seedlings (1). In the shoot apex, cell division was almost completely annulled by ethylene and only 60% inhibition was observed in the root apex (1). The gas inhibits cell division by blocking a stage before prophase (1). In the subapical regions of the seedling, the hormone inhibited cell expansion and DNA synthesis (2). In the various parts of the seedling, a qualitative relationship was found between the inhibition of DNA synthesis, cell division, and growth caused by ethylene (1).In view of the above, a study was undertaken to pursue a possible involvement of polyamines in the effects of ethylene on plant growth. In this communication, we show that ethylene provokes a pronounced and reversible inhibition of ADC2 ac...

Section: Resultsmentioning

confidence: 99%

Control by Ethylene of Arginine Decarboxylase Activity in Pea Seedlings and Its Implication for Hormonal Regulation of Plant Growth

Apelbaum¹,

Goldlust²,

Icekson³

1985

“…The increased acid-induced transverse extension is correlated with the deposition of randomly oriented cellulose microfibrils on the inner quarter of the wall (24,25). (2,12,17). Warner and Leopold (30) were able to detect an inhibition of elongation in decapitated seedlings in as little as 6 min.…”

Section: Discussionmentioning

confidence: 99%

“…Such kinetics can hardly be caused by reoriented cellulose microfibrils, even though it is not clear whether the kinetics of lateral expansion exactly parallel the inhibition of elongation. Burg (2) has reported that ethylene can prevent gravitropic curvature of excised pea internode segments within 15 min, probably due to an inhibition of auxin transport. Ethylene did not alter the rate of cell expansion during this time.…”

Section: Discussionmentioning

confidence: 99%

Ethylene-Induced Lateral Expansion in Etiolated Pea Stems

Taiz¹,

Rayle²,

Eisinger³

1983

Ethylene-induced inhibition of elongation and promotion of lateral expansion in the stems of etiolated pea (Pisum sativum L. var Alaska) seedlings is not associated with any alteration of auxin-stimulated proton extrusion. Indeed, lateral expansion in response to ethylene apparently requires an acidified wall since it is prevented by strong neutral buffers and by the ATPase inhibitor orthovanadate. Ethylene treatment reduces the capacity of live and frozen-thawed sections to extend in the longitudinal direction in response to acid. The effect of ethylene on lateral acid growth capacity is more complicated. Ethylene-treated internodes do not exhibit acid-induced lateral expansion. Ethylene-treated segments which have been frozen-thawed do show an enhanced capacity to extend in the transverse direction at acid pH, but only when the inner tissues have been removed by coring. We conclude that two of the factors which control the directionality of expansion during ethylene treatment are a decrease in the sensitivity of the walls to acid longitudinally and an increase in the sensitivity of the outer cortical parenchyma walls to acid in the transverse direction.Although the effect of ethylene on the reorientation of the cellulose microfibrils in pea stems has been well established (1,3,9,13,17, 22,27), there is scant and contradictory information available on the changes in wall extension capacity associated with the shift to longitudinal microfibrils. Ridge (22) using a plasmometric method demonstrated a 50% reduction in the longitudinal extensibility of pea stem sections which had been previously treated 3 h with ethylene. In contrast, two extensibility studies on methanol-extracted walls using an Instron (16, 18) failed to detect a significant difference between ethylene-treated and control stems after 3 h, although Osborne (18) 2 To whom reprint requests should be addressed.the directionality of acid-induced extension in ethylene-treated and control tissues.The possible importance ofwall acidification and acid-induced wall loosening for ethylene-promoted lateral growth is suggested by the data of Demichelis and Lado (6). These authors present data showing that ethylene does not block auxin and fusicoccininitiated medium acidification and that both agents enhance transverse growth in the presence of ethylene. A plausible explanation of these data is that the relevant cell wall property in determining the directionality of growth (i.e. longitudinal extension versus lateral expansion) is the capacity of the wall to respond to acid. MATERIALS AND METHODSPisum sativum L. (var Alaska) seeds were soaked for 6 h in tap water and planted in moist vermiculite. Seedlings were grown for 7 d at 20°C in darkness at which time the third internode was 1 to 2 cm in length. Harvested third internodes were manually abraded, to facilitate the measurement of proton extrusion, with a slurry of emery powder (Emery No. 305, Edmund Scientific Co.), cut to 1 cm, and incubated in media as previously described (7). Control experiment...

“…If ethylene is removed during the period of intermediate inhibition, the tissue continues to respond at this level (16). The effects of ethylene on elongation are irreversible after a 4-h treatment (16 (2,21,24), but the inhibition of excised segments has been largely overlooked (4). In intact seedlings, the dramatic inhibition of total cell expansion during the first 24 h is probably related to changes in the matrix components and not the newly deposited longitudinal cellulose microfibrils.…”

Section: Kinetics Of Ethylene-induced Lateral Expansionmentioning

confidence: 99%

“…Ethylene inhibits elongation and induces lateral expansion of etiolated pea internode tissue (2,3). Ethylene is thought to affect the mode of growth by altering microtubule and cellulose microfibril orientation (1,9,12,21,26).…”

mentioning

confidence: 99%

Ethylene-Induced Lateral Expansion in Etiolated Pea Stems

Eisinger

Croner²,

Taiz³

1983

Treatment of etiolated pea (Pisum sativum L.) internode tissue with ethylene gas inhibits elongation and induces lateral expansion. Precise kinetics of the induction of this altered mode of gro4vth of excised internode segments were recorded using a double laser optical monitoring device. Inhibition of elongation and promotion of lateral expansion began after about 1 hour of treatment and achieved a maximum by 3 hours. Similar induction kinetics were observed after treating internodes with coichicine and 2,6-dichlorobenzonitrile, an inhibitor of cellulose synthesis. In sealed flask experiments, ethylene had no detectable effect on incorporation of label from '4Cqglucose into any of the classical pectin, hemicellulose, or cellulose wall fractions. Ethylene inhibited fresh weight increase (total cell expansion) of both excised internode segments (in sealed flasks) and intact seedlings. Ethylene treatment resulted in an increase in cell sap osmolality in those tissues (intact and excised) which are inhibited by the ps. A model for ethylene-induced inhibition of elonption and induction of lateral expansion is presented.Ethylene inhibits elongation and induces lateral expansion of etiolated pea internode tissue (2, 3). Ethylene is thought to affect the mode of growth by altering microtubule and cellulose microfibril orientation (1,9,12,21,26). Colchicine and other agents which affect microtubule and microfibril orientation also inhibit elongation and induce lateral expansion (6). DCB3, a specific inhibitor of cellulose synthesis (14), induces lateral expansion in soybean tissue (30). Coumarin, a less specific inhibitor of cellulose synthesis, has been shown to induce lateral expansion in several kinds of tissues (7,10).Although the inhibition kinetics of elongation with ethylene treatment have been studied in detail (16) MATERIALS AND METHODSSeeds of Pisum sativum L. (var Alaska) were soaked in tap water for 6 h, planted in vermiculite moistened with 0.1 mM CaCl2 in deionized H20, and grown for 7 d in darkness at 22C. For experiments using excised internode segments, a 1-cm section of third internode tissue was cut immediately below the apical hook. Unless otherwise stated, all excised tissues were incubated, 10 pieces/lot, in sealed 125-ml flasks with 10 ml of medium with or without 10 gl/l ethylene. The medium contained 5 mM K-phosphate (pH 6.8), 2% sucrose (w/v), 5 AM CoC12, and 1 gM IAA. Growth ofsegments in length and width was measured using the LOLA described by Taiz and Metraux (27). The measuring system was calibrated with a micrometer and the magnifications (x 118 for length and 598 for diameter) were found to be constant within the range used for these experiments. The SD among replicate experiments averaged less than 10% of the increase in growth of the segments. The tissue chamber and the mechanical lever system of the LOLA were enclosed in a sealed Plexiglas box with a volume of approximately 300 L. The atmosphere within this box was constantly circulated. The tissue segment in the LOLA chamber...