Inhibitory Effect of a Rhizobitoxine Analog on Bud Growth after Release from Dormancy

Abstract

Application of the ethoxy analog of rhizobitoxine (L-2-amino-4-[2'-aminoethoxyl-trans-3-butenoic acid), an inhibitor of ethylene biosynthesis, inhibited growth of apple, crabapple, and apricot buds released from dormancy by chilling or by treatment with benzyladenine. When tea crabapple (Malus hupehensis [Pamp.] Rehd.) buds were sprayed once with 8.8 x 10-3 M benzyladenine, ethylene production by the buds increased significantly 24 to 48 hours after benzyladenine treatment.Application of the rhizobitoxine analog to the buds at the time of benzyladenine treatment reduced ethylene evolution to the level of the controls for up to 2 weeks after treatment. Increase in bud weight was inhibited also but to a lesser extent. These data suggest that growth of buds is accompanied by ethylene production and that the inhibition of ethylene biosynthesis also inhibits bud growth. Since additional metabolic effects result from the action of the rhizobitoxine analog, no firm conclusions on its role can be drawn at this time.Hormonal control of bud growth appears to involve the integrated interactions of various plant hormones. Benzyladenine has been shown to stimulate or accelerate release of buds from dormancy (2). The mode of action is assumed to relate to the function of cytokinins in stimulating cell division. Cytokinins are also known to stimulate C2H4 production in some plants (3,4).With this in mind, we attempted to determine the involvement of C2H4 in bud development by the use of the ethoxy analog of rhizobitoxine (L-2-amino-4-12'-aminoethoxy]-trans-3-butenoic acid), an inhibitor of C2H4 biosynthesis which is known to inhibit conversion of methionine to C2H4 (6,8).Preliminary trials with buds of apricots and 'Jonathan' apples showed that the rhizobitoxine analog inhibited growth of buds released from dormancy by chilling or by BA treatment. Experiments described herein were then conducted using buds of tea crabapple which had been activated by BA (1) to determine: (a) the amount of the rhizobitoxine analog needed to inhibit bud growth; (b) the effectiveness of this inhibitor at various times after bud activation; and (c) the effect of the rhizobitoxine analog on C2H4 production by activated buds. MATERIALS AND METHODSTwelve to 18-month-old seedling trees of tea crabapple (Malus hupehensis [Pamp.] Rehd.) grown in the greenhouse as described previously (1) were used in the experiments. In one experiment, trees were defoliated, moved into a root cellar in January, and chilled for 3 months. In all other experiments, seedlings were not moved from the greenhouse but were defoliated prior to treatment.Spray application of BA and methionine was done as described previously (1) and the rhizobitoxine analog was dissolved in water and 1 to 2 ,ul applied directly to the buds with a microsyringe.For measurement of C2H4 production, three buds were excised and placed directly into a 5-ml plastic syringe, the plunger was reinserted, and adjusted to the 3-ml mark. A serum tube stopper was then placed over the tip of the syri...

Interaction of Ethylene and a Cytokinin in Promoting Hypocotyl Elongation in a Dwarf Strain of Watermelon

“…Synergistic cytokinin-ethylene interactions have been reported for promotion of growth of dormant buds of tea crabapple (12), for stimulation of germination of Vanguard lettuce seeds at 35 C (1 1), and for reversal of ABA inhibition of germination in Grand Rapids lettuce seed (10). A synergistic cytokinin-ethylene interaction in nondwarf watermelon seedlings is suggested from observations that AVG suppresses both BA-promoted and normal hypocotyl elongation (Loy and Pollard, unpublished data).…”

Allelopathy

“…The retarded germination/growth, besides being a consequence of the reduced amylase/protease level, could also result, at least partly, through an effect on the hormonal balance in the plant, for many allelochemicals have been found adversely to affect the level of growth hormones in plants (Green and Corcoran, 1975;Zimmerman et at., 1977;.…”

Metabolic changes in cherry flower buds associated with breaking of dormancy in early and late blooming cultivars

“…However, Paiva and Robitaille break the dormancy. The length of chilling required (1978) and Zimmerman et al (1977) found no evidence varies with cultivars. Inadequate chilling may limit cell that ethylene was involved in emergence from dordivision, spring bud development, and result in an ex-mancy of buds of 'Golden Delicious' apple and tea crabtended period of sporadic flowering (Westwood 1978).…”