Abscission and its Control

Carns, H. R.

doi:10.1146/annurev.pp.17.060166.001455

Cited by 40 publications

(22 citation statements)

References 33 publications

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“…It is a well established fact that the application of high concentrations of IAA to the distal zone delays abscission ' (8). Recently, this was also shown to be true in citrus explants (16,20).…”

Section: Resultsmentioning

confidence: 92%

Activity of Pectin Esterase and Cellulase in the Abscission Zone of Citrus Leaf Explants

1969

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Abstract. The activity of pectin esterase and cellulase in abscission of citrus explants was studied. No relation was established between pectin esterase and abscission, while cellulase activity was markedly increased before absoission and for a certain period after excision. IAA and cycloheximide delay abscission and cellulase activity, while ethylene and, to a lesser extent, GA. acoelerate them. Application of cycloheximide during the lag period and before cellulase activity can be measured, inhibits to a certain extent the formation of 'cellulase An escape from the inhibitory effect of cycloheximide is detected when inhibitor is supplied at the end of the -lag period. Osiborne (21) claimed that pectin esterase (PE) participates in the abscission process of bean leaves. In a later report Horton and Osborne (12) mention that cellulase is also active in the albscission zone of bean leaves. While studying the role of PE in the abscission zone of citrus explants we found that cellulase rather than PE is responsible for the separation process.Very recently, Abeles (5) published a parallel study, showing the role of cellulase in the abscission zone of bean, cotton, and coleus explants which were aged for 20 hr and then transferred into ethylene environment. He concludes that the mechanism of ethylene action during cell separation induces protein synthesis which is essential for cell separation by the production of essgential enzymes for the physiological processes of abscission. The present work was carried out independently although simultaneously with that of Abeles (5). The objective was to define the time relationship which exists between the ajbscission mechanism and cellulase activity in citrus leaves. Petioles of 10 explants were tied to a glass-slide and kept for the desired period in a humidified Petri dish, 9 cm in diameter, in the dark and at 250. At the end of each experiment the percent of abscission was determined by counting the distal sections which had already abscised and those which albscised due to a gentle touch administered by forceps (7).Pectin Esterase (PE) Assay. The method employed was that of Kertez (14) with the modification of Rouse and Atkins '(25). Two sections of 2 mm were cut from 20 explants, from each side of the abscission-layer over a 8 mm wide section from the proximal to the distal end (21). Twenty similar sections, representing the same portion with respect to the abscission line, were pooled, weighed, and homogenized in 20 ml of 0.2 N NaCl in a mortar. The homogenate was transferred into 50 ml of 1 % 1717 www.plantphysiol.org on May 12, 2018 -Published by Downloaded from

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Section: Resultsmentioning

confidence: 92%

Activity of Pectin Esterase and Cellulase in the Abscission Zone of Citrus Leaf Explants

1969

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“…Ethylene appears to play multiple roles in leaf abscission resulting in a reduction in auxin transport to the abscission zone (4,5,7), and by the induction of hydrolytic enzyme synthesis (1,2,10,13,16,17,19,21) Plant Materials. Cotton seedlings (Gossypium hirsutum L. cv Stoneville 213) were grown in a controlled environment chamber in a mixture of sand, peat, and vermiculite (3:2:1) contained in 33 X 10 x 10 cm plastic trays.…”

Section: Methodsmentioning

confidence: 99%

Water Stress Enhances Ethylene-mediated Leaf Abscission in Cotton

Jordan¹,

Morgan²,

Davenport³

1972

Plant Physiol.

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(14) were unable to demonstrate a clear relation between the magnitude of the stress-induced ethylene production and level of water deficit or abscission. They concluded that the level of ethylene production per se may not be the controlling factor in leaf abscission, but that the physiological state of each leaf governs the response to increased endogenous ethylene production. In a second paper, McMichael et al. (15) demonstrated that the extent of leaf abscission from cotton plants following water stress was related to the severity of the stress in a linear manner.In view of these findings, it would seem attractive to propose a role for ethylene in stress-induced abscission. This report provides evidence for the involvement of ethylene in leaf abscission induced by plant water deficit. MATERIALS AND METHODSThe involvement of ethylene as an endogenous regulator in natural leaf abscission has been strongly implicated in recent studies (5, 11). Ethylene appears to play multiple roles in leaf abscission resulting in a reduction in auxin transport to the abscission zone (4,5,7), and by the induction of hydrolytic enzyme synthesis (1,2,10,13,16,17,19,21) Plant Materials. Cotton seedlings (Gossypium hirsutum L. cv Stoneville 213) were grown in a controlled environment chamber in a mixture of sand, peat, and vermiculite (3:2:1) contained in 33 X 10 x 10 cm plastic trays. Growth conditions were as follows: 1800 ft-c; 15 hr photoperiod; temperature 27 + 1 C day, 22 + 1C night; ambient relative humidity. The plants were watered daily with a modified Hoagland's solution (14). Water stress was induced by withholding nutrient solution until the desired stress was reached, usually over a period of 4 to 6 days. A range of plant water stress was attained by thinning the number of plants to between 10 and 20 plants per tray. The level of stress was quantified by plant water potential determinations made with a pressure bomb (18) near the end of the dark period on the day treatments were initiated.Ethylene and CO. Fumigations. The water-stressed plants were fumigated with ethylene or ethylene plus CO2 in 268-liter Plexiglas chambers for 24 hr. The chambers were kept in the dark at 23 + 1 C during the fumigation period. CO2 was removed with 10% KOH on filter paper wicks in those treatments not involving fumigations with CO2. Ethylene concentrations were determined by gas chromatography (5) at 6 and 24 hr after injection. The concentration measured within the first 6 hr was maintained within +5% during the 24-hr treatment period. Following the treatment period the chambers were opened, the leaves tested for abscission, and the pots fully watered.Abscission Measurements. All leaves were tested for abscission by applying slight pressure (about 5 to 10 g) by hand to each petiole near the blade. After this initial testing, all trays were fully watered and placed in a growth room under the fol-756 www.plantphysiol.org on May 11, 2018 -Published by Downloaded from

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“…If this hormone balance is forced out of normal maintenance limits, the sequence of steps leading to eventual separation may be irreversibly triggered. Although the identity of all the hormones comprising this balance are probably not known, ample evidence is available that IAA may play a key role in leaf abscission (8 , 1 1). Using cotton explants, Addicott and Lynch (1) concluded that distally applied IAA retards formation of the abscission zone.…”

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confidence: 99%

An Effect of Water Stress on Ethylene Production by Intact Cotton Petioles

1972

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The concept that ethylene is an endogenous growth regulator has evolved in the past few years (16). This concept has been strengthened by recent findings that internal concentrations of endogenous ethylene in vegetative tissues reach physiologically active levels (3,12,13). These internal concentrations have been directly related to the corresponding production rates of excised tissues (13), although parallel data on production rates of intact plant tissues are not available. Using excised abscission zones from primary bean leaves, Jackson and Osborne (9) presented evidence that the timing of abscission of explant petioles can be related to the extent of ethylene production adjacent to the separation zone. They suggest that the ethylene production is coupled to a particular stage of senescence. Further, they proposed that in natural leaf abscission ethylene initiates the biochemical sequences leading to separation, but the mechanism is not clear. Beyer and Morgan (4) have recently shown that ethylene production by and internal levels in detached cotton cotyledons increases as auxin transport declines. Amounts of exogenous ethylene necessary to induce abscission and inhibit auxin transport were similar. They propose that the rise in ethylene production and decline in auxin transport capacity are causally related and that reduced auxin transport is one of the ethylene mediated actions which precede induction of hydrolytic enzymes in the separation layer. Their measurement of ethylene involved whole cotyledons and was not restricted to the petiole. McAfee and Morgan (13) found internal ethylene levels and production rates were several times higher in petioles than leaf blades. Since auxin must be translocated through the petiole to the abscission zone, this observation strengthens the proposed role of ethylene in auxin transport inhibition preceding cotton leaf abscission (4). Alternatively, high rates of ethylene production by petiole tissue near the abscission zone may directly trigger the biochemical changes preceding separation independent from the proposed effect on auxin supply to the abscission zone.Aside from abscission related to senescence, little attention has been directed to other problems of natural abscission, particularly those involving environmental stresses. Plant water deficits may induce both leaf and boll abscission from cotton under field conditions (5, 6, 18). In most instances, actual separation follows relief from the deficit and rehydration of the abscission zone. This communication describes the effect of a brief period of water deficit on ethylene production by intact cotton petioles. MATERIALS AND METHODSCotton plants (Gossypium hirsutum L. var TM-1) used in this study were grown in pots containing sand in a greenhouse and were between 75 and 90 days of age. Each pot contained two plants of equal size, each with 15 to 17 leaves on the main stem. The use of paired plants made possible the determination of leaf water potential on one plant, while ethylene production was measured on the ...

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Abscission and its Control

Cited by 40 publications

References 33 publications

Activity of Pectin Esterase and Cellulase in the Abscission Zone of Citrus Leaf Explants

Activity of Pectin Esterase and Cellulase in the Abscission Zone of Citrus Leaf Explants

Water Stress Enhances Ethylene-mediated Leaf Abscission in Cotton

An Effect of Water Stress on Ethylene Production by Intact Cotton Petioles

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