Protein Synthesis in Abscission: The Distinctiveness of the Abscission Zone and its Response to Gibberellic Acid and Indoleacetic Acid

Abstract

A bstract. Abscission zone tissue of citrus was shown to have a higher rate of protein synthesis than tissue distal or proximal to it. based on the incorporation of leucine-1-14C. The proximal tissue had the slowest rate of protein synthesis. As the tissue approached abscission, the rate of synthesis in the abscission zone decreased and the differences in rate of protein synthesis between the 3 zones almost disappeared. IAA, which delayed abscission, maintained the protein synthesis gradient between the abscission and proximal zones, but the distal zone tissue was as active in protein synthesis as the abscission zone. Differences in uptake of the leucine were also observed between different zones and treatments.Regardless of the tissue or the treatment, there was a sharp increase in uptake at. the 24 hour point.Direct incubation of abscission zones in IAA and gibberellic acid (GA) indicated that the action of gibberellic acid on abscission is probably through a stimulation of protein synthesis, while IAA seems to act by maintaining the existing rate of protein synthesis in the cells of the abscission zone.The potential of hormones such as auxin and gibberell,in to act as effector sulbstances (5, 16) th,at conitrol repression and derepression o.f different pants of the genome and their involvement in abscission control (2,12) led us to look at the effect of these hormones on the rate of protein synthesis in the tissue associated with abscission. This paper demonstrates the biochemical distinctiveness with respect to protein synthesis of the abscission zone from the adjacenit tissue. Materials and MethodsSeedlings of sweet orange (Citrus sinensis, Osbeck) were the source of ithe plant miaiterial used in these experiments. Planits about 9 months old were selected for uniformity of height, leaf color, and leaf qutaliilty. The growing terminal was removed so that only mature le-aves were tused. 'T'he leaf blade and petiolar winigs were removed, leaving a 4 mm 'porition of the leaf midrib (the debladed midrib) aittached to the petiole (12). Preliminary experiments showed no correlation between the position of the deblialded midrib on the seedling and the order in which they aibscised. Hormones to be tested were dissolved in 0.1 At citrate buffer, pH 6.0, and incorporated into an equlal vollume of 2 % (w/v) agar. A 5 juliter dropleft of the agar gel, containing the test compound was applied to the 1 Present address: Punjal) Agrictlltural University.Hissar, India. distal eni,d of each explaant with a tuberculin syringe. Con'troll plianits were treated with a simil,ar drop of buffered 1 % (w/v) agar. Treated seed,l1ings were reotained in the growth ch,amber in the dark at 250 and a relative hutmidcity of 60 % or higher.Incorporation of L-leucine-1-'AC (specific activiity 180 uc/mg) into the alcohol and oxalate insolluble fraction w'as used ais a meialsure of the ra'te of protein synthesiis associated wilth various stages of abscission. In 1 series of experimnents, abscission zone sections abouirt 1 mm thick were incubate...

Interrelationship of Abscisic Acid and Gibberellic Acid in the Promotion of Callus Formation in the Abscission Zone of Citrus Bud Cultures

“…This was evident from the fact that the petiole section distal to the separation layer remained on top of the callus (Altman and Goren 1971). The present system differs from previously reported systems by the general decrease in protein synthesis which occurs during the inductive stage of callus formation (first 5 days from excision), instead of the usual increase in protein synthesis which is characteristic of the inductive period of abscission (Abeles and Holm 1967, Abeles 1968, Lewis and Bakhshi 1968, Osborne 1968). These results are in accordance with the decrease in protein synthesis in the abscission zone of young citrus fruits during the first stages of abscission (Goren et al 1974).…”

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

“…The fact that CHI was found to inhibit cellulase activity in the presence of ethylene or in the absence of the hormone is not surprising, since abscission is known to be related to RNA and to protein synthesis (4,14,17,22,30). Results presented in talble II show that the RNA analogue 2-thio-uracil (2-TU), significantly inhibited abscission and cellulase activity.…”

“…Recently, Lewis (16,17) studied the effects of GA8 and IAA on the albscission of citrus leaf explants, and showed that the acceleration of abscission by GA3 is probably due to stimulation of protein synthesis, while IAA maintains the rate of protein synthesis in the cells of the abscission zone. These findings are compatible with the results reported by Abeles (4), who showed that the abscission process is characterized by "de novo" synthesis of RNA and protein.…”

Auxin‐induced delay of abscission: The involvement of calcium ions and protein phosphorylation in bean explants

“…al, 1988). Likewise, auxin seems to maintain existing rates of protein synthesis in abscission zones of citrus (Lewis and Bakhshi 1968).…”