Abscission

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The leaf blade of cotton (Gossy-piu7n hirsutum L. cv. Stoneville 213) was investigated as the initial site of ethylene action in abscission. Ethylene applied at 14 ul/l to intact 3-week-old plants caused abscission of the third true leaf within 3 days. However, keeping only the leaf blade of this leaf in air during ethylene treatment of the rest of the plant completely prevented its abscission for up to 7 days. This inhibition of abscission was apparently the result of continued auxin production in the blade since (a) the application of an auxin transport inhibitor to the petiole of the air-treated leaf blade restored ethylene sensitivity to the leaf in terms of abscission; (b) repeated applications of naphthaleneacetic acid to the leaf blade of the third true leaf, when the entire plant was exposed to ethylene, had the same preventive effect on abscission of this leaf as keeping its leaf blade in air; and (c) the inhibitory effect of ethylene on auxin transport in the petiole, which is reduced by auxin treatment, was also reduced by placing the leaf blade in air.The reverse treatment of exposing only the leaf blade of the third true leaf to 14 ,l/l of ethylene, while the rest of the plant was kept in air, also did not cause abscission for up to 5 days. Auxin transport in the petioles of these leaves, however, was inhibited over 80% within 2 days and this effect presumably accounted for their increased sensitivity to ethylene during the subsequent exposures of the whole leaf to the gas.These results suggest that an initial and essential function of applied ethylene in abscission is to reduce the amount of auxin transported out of the leaf blade. This reduction together with the inhibitory effect of ethylene on auxin transport in the petiole reduces the auxin level at the abscission zone to a point where the cells in this region become responsive to the more direct action of the gas (e.g., enzyme induction and secretion). This sequence of events accounts for the lack of abscission unless ethylene is applied to both the leaf blade and the abscission zone.

Section: Resultsmentioning

confidence: 72%

Section: Resultsmentioning

confidence: 85%

Section: Resultsmentioning

confidence: 99%

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Abscission: The Initial Effect of Ethylene Is in the Leaf Blade

Beyer¹

1975

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“…First, three appropriate species were tested. Both beans and cotton produce ethylene which regulates, at least in part, natural leaf abscission (7,20). Both species demonstrated the common acceleration of ethylene release from detached leaves when they are air dried ( Fig.…”

Section: Discussionmentioning

confidence: 99%

Does Water Deficit Stress Promote Ethylene Synthesis by Intact Plants?

Morgan¹,

He²,

Greef³

et al. 1990

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120

The effect of plant water deficit on ethylene production by intact plants was tested in three species, beans (Phaseolus vulgaris L.), cotton (Gossypium hirsutum L.) and miniature rose (Rosa hybrida L., cv Bluesette). Compressed air was passed through glass, plant-containing cuvettes, ethylene collected on chilled columns, and subsequently assayed by gas chromatography. The usual result was that low water potential did not promote ethylene production. When plants were subjected to cessation of irrigation, ethylene production decreased on a per plant or dry weight basis of calculation. No significant promotion of ethylene production above control levels was detected when water deficit-treated bean or cotton plants were rewatered. The one exception to this was for cotton subjected to a range of water deficits, plants subjected to deficits of -1.4 to -1.6 MPa exhibited a transient increase of ethylene production of 40 to 50% above control levels at 24 or 48 hours. Ethylene was collected from intact leaves while plants developed a water deficit stress of -2.9 megapascals after rewatering, and no significant promotion of ethylene production was detected. The shoots of fruited, flowering cotton plants produced less ethylene when subjected to cessation of irrigation. In contrast, the ability of bench drying of detached leaves to increase ethylene production several-fold was verified for both beans and cotton. The data indicate that detached leaves react differently to rapid drying than intact plants react to drying of the soil with regard to ethylene production. This result suggests the need for additional attention to ethylene as a complicating factor in experiments employing excised plant parts and the need to verify the relevance of shock stresses in model systems.interest because the ethylene could be responsible for senescence and abscission induced by water deficits (13,25,26).Although the promotion of ethylene synthesis by water deficits appears firmly established, there are a number of concerns. First, to have a convenient experimental system, water deficits have often been imposed rapidly by drying detached leaves or fruits (3-6, 16, 18, 24, 31). In contrast, under natural drought the soil water is depleted slowly and plants progress through a series of drying cycles during which #w3 falls during the day and rises at night as plants recover due to reduced evaporative demand (30). Second, the experimental measurement of ethylene has usually required that detached plant parts be concentrated in a sealed container from which air samples are withdrawn and analyzed for ethylene. The air supply in these containers has often been static which is of some concern because oxygen is needed for the conversion of ACC to ethylene (2) and CO2 can either promote or reduce the production of ethylene (33). Finally, there are a few reports in the literature where investigators failed to observe a promotion of ethylene release with water deficit treatment of intact plants (6,9,13,19).With the development of flowing air sys...

“…Additionally, metabolic acclimation to low oxygen improves the tolerance of roots to anoxia (29). ' The gaseous plant hormone, ethylene, is associated with a wide variety of responses in higher plant cells (3). In earlier reports we showed that aerenchyma formation in adventitious (nodal) roots of maize by cell lysis is induced by a partial oxygen deficiency (hypoxia) and is closely related to enhanced endogenous concentrations of ethylene (1 1).…”

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confidence: 99%

Decreased Ethylene Biosynthesis, and Induction of Aerenchyma, by Nitrogen- or Phosphate-Starvation in Adventitious Roots of Zea mays L.

Drew¹,

He²,

Morgan³

1989

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162

129

Plants of Zea mays L. cv TX5855 were grown in a complete, well oxygenated nutrient solution then subjected to nutrient starvation by omitting either nitrate and ammonium or phosphate from the solution. These treatments induced the formation of aerenchyma close to the apex of the adventitious roots that subsequently emerged from the base of the shoot, a response similar to that shown earlier to be induced by hypoxia. Compared with control plants supplied with all nutrients throughout, N-or Pstarvation consistently depressed the rates of ethylene release by excised, 25 mm apical segments of adventitious roots. Some enzymes and substrates of the ethylene biosynthetic pathway were examined. The content of 1-amino cyclopropane-1-carboxylic acid (ACC) paralleled the differences in ethylene production rates, being depressed by N or P deficiency, while malonyl-ACC showed a similar trend. Activity of ACC synthase and of ethylene forming enzyme (g-1 fresh weight) was also greater in control roots than in nutrient starved ones. These results indicate that much of the ethylene biosynthetic pathway is slowed under conditions of N-or P-starvation. Thus, by contrast to the effects of hypoxia, the induction of aerenchyma in roots of Zea mays by nutrient starvation is not related to an enhanced biosynthesis and/or accumulation of ethylene in the root tips.Many dryland species are exposed to temporary periods of oxygen deficiency during their growth following heavy rain, irrigation, or flooding, when the soil becomes water saturated (10,17). Some species respond to this situation by forming roots with continuous, gas-filled channels in the roots (19). These channels improve the internal supply of oxygen, the oxygen originating from the atmosphere or photosynthesis and passing from leaves to roots down a concentration gradient (1). The flooding resistance of a wide range of monocot and dicotyledonous species, both herbaceous and woody, is often associated, in part, with the capacity to develop such aerenchymatous roots (8,9,16,17,19,23 The gaseous plant hormone, ethylene, is associated with a wide variety of responses in higher plant cells (3). In earlier reports we showed that aerenchyma formation in adventitious (nodal) roots of maize by cell lysis is induced by a partial oxygen deficiency (hypoxia) and is closely related to enhanced endogenous concentrations of ethylene (1 1). Hypoxia clearly stimulates the biosynthesis of ethylene in growing maize roots (2,11,12,20) as in other responsive plant tissues (4, 5, 7). Low exogenous concentrations of ethylene under aerobic conditions (1-5 uL L-' in air) induce aerenchyma (18) that is structurally indistinguishable from that induced by hypoxia (1 1, 12); furthermore, hypoxically induced aerenchyma formation in the apices of growing roots is blocked by inhibitors of ethylene biosynthesis or ethylene action (12,18,20).However, Konings and Verschuren (21) showed that formation of aerenchyma in the seminal roots of maize was stimulated under fully aerobic conditions by omission o...