Senescence, Abscission and Cellulase Activity in Phaseolus vulgaris

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: 99%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

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

Beyer¹

1975

“…However, a sensitive tissue implies that a change has taken place. Whether such a change is biochemical (2,14,16,27) or biophysical (6,13,17,20,(25)(26)(27) remains to be elucidated.…”

Section: Methodsmentioning

confidence: 99%

Physiology of Oil Seeds

Ketring

Morgan

1970

The germination and ethylene production by dormant Virginia-type peanut seeds were observed in relation to phytohormone treatments that could conceivably release the dormancy of these seeds. A comparison was made between the effects of these treatments on the less dormant apical seeds and the more dormant basal seeds. Indole-3-acetic acid did not stimulate ethylene production by, or germination of, the dormant seeds to any extent. Gibberellic acid at 5 X 104 M stimulated ethylene production by apical seeds to 17 millimicroliters per hour and germination to only 40% above the control. The more dormant basal seeds were affected even less by gibberellic acid than the seeds. Ethylene gas at 8 microliters per liter stimulated germination to 85% above the control for both apical and basal seeds. At this ethylene concentration the physiology of the more dormant basal seeds was altered, so that they behaved in a manner similar to the inherently less dormant apical seeds. 2-Chloroethylphosphonic acid at 103 and 5 X 10-M provided results similar to ethylene gas. Both apical and basal seeds germinated 100% at 48 hours. Among the phytohormones tested in this study, ethylene gas produced the greatest germination at low concentrations, and it appears must directly related to initiating the reactions required for converting the quiescent cells to an active state of growth.Some varieties of Virginia-type peanut seeds exhibit a "primary" inherent dormancy at harvest. Neither the mechanism nor convenient methods of breaking the dormancy are known. The first method for breaking the "primary" postharvest dormancy of Virginia-type peanut seeds was heating at 40 to 45 C for about 15 days (5). Leaching and treatments with natural aromatic compounds were only partially successful in breaking this dormancy (30).Shibuya (29) reported that indole-3-acetic in lanolin (0.1 g of IAA/g of lanolin) applied to the exposed radical end of dormant peanut seeds stimulated germination. However pods under natural conditions for 1 week and determining germination at the end of 2 weeks. With the exception of ethylene, other phytohormones have not, to our knowledge, been used in attempts to break the dormancy of peanut seeds.The seed coats provide either a diffusion or permeability barrier, since removal of the coats can increase germination of dormant peanut seeds, but this removal appears to be secondary to subsequent conditions or seed treatments (30).Five per cent CO2 in air is capable of stimulating germination of dormant peanut seeds, and in either darkness or continuous fluorescent light, 100 ,ul/liter C2H4 induced nearly 100% germination (30). The results with CO2 were discussed in a previous report by Ketring and Morgan (18) in relation to the discovery that as little as 3.5 ,ul/liter of ethylene would effectively break the dormancy of NC-13 Virginia-type peanut seeds. In contrast, lettuce seed germination is stimulated by ethylene although it is apparently without effect on dormant lettuce seeds (3).Thus far the only two effective mea...

“…These include hormonally induced growth responses (6,10), abscission of leaves (1,2,14,19), pollen tube growth (16,31), and softening of fruits as they ripen (7,12,33). However, little is known about the nature of cellulase from higher plants despite the probable physiological importance of cellulase in growth and development.…”

mentioning

confidence: 99%

Partial Characterization of C_x Cellulase and Cellobiase from Ripening Tomato Fruits

Pharr¹,

Dickinson²

1973

Cellulolytic enzymes were studied in extracts from the locular contents of ripening fruits of Lycopersicon esculentum var. KC-146. When acting on carboxymethyl cellulose, the enzyme preparations were capable of decreasing the viscosity of the reaction mixture and generating reducing groups, oligosaccharides, and glucose. Cellobiose celiotriose, celiotetrose, and cellopentose also served as substrates for glucose production.