The Hormone Content of Ripening Grape Berries and the Effects of Growth Substance Treatments

Abstract

Berries on field-grown Vitis vinifera cv. Doradillo were treated at different times during stage II with benzothiazole-2-oxyace-tic acid or 2-chloroethylphosphonic acid, and measurements were made of their growth and hormone content. The concentration of ethylene was low during stage II and declined as berries ripened. Both 2-chloroethylphosphonic acid and benzo-thiazole-2-oxyacetic acid caused increases in ethylene concentration , yet they had varying effects on ripening: the former applied at the start of stage II and the latter applied 1 week before the end of stage 1I delayed ripening, while 2-chloro-ethylphosphonic acid applied at the end of stage II hastened ripening. The abscisic acid content of berries increased as they ripened, and the effects of 2-chloroethylphosphonic acid and benzo-thiazole-2-oxyacetic acid on abscisic acid levels were correlated with the effect of these compounds on ripening. The roles of abscisic acid and ethylene in the regulation of the ripening of grapes are discussed. The growth curve of the grape berry, like those of many berry and drupaceous fruits, is double sigmoid (Fig. 1). The second phase of rapid growth (stage III), unlike the first (stage I), is nonmeristematic and is entirely due to enlargement of pericarp cells. As well as an increased growth rate, it is characterized by changes in deformability (softening) and chemical composition, changes which are associated with fruit ripening. The inception of this growth phase (the boundary between stages II and III in Fig. 1) is called "veraison" by viticulturists and is marked by a change in color and inflexions in curves for size, sugar concentration, acidity, and deformability. The several stages of growth are probably regulated by hormones. Endogenous ethylene may be involved during stages II and III: this is suggested because of its generally accepted role in the ripening of fruits and also because of the effects of exogenous ethylene and 2-chloroethylphosphonic acid. Explanations of the regulation of these growth stages must take account of the dual nature of the effect of CEPA1 (9), of the delaying effect of exogenous auxin (8, 23), and of the sug-1 Abbreviations: CEPA: 2-chloroethylphosphonic acid; BTOA: benzothiazole-2-oxyacetic acid; TIBA: tri-iodobenzoic acid; GLC: gas-liquid chromatogram; t-ABA: the trans-isomer of ABA; Me-ABA, and Met -ABA: their methyl esters. gestion that auxin-like, biologically active compounds are involved (3, 15). We are studying the changes in the amounts of growth substances in the berry before and after veraison to try to elucidate their role in controlling the onset of stage III. This paper emphasizes the changes in concentration of ethylene and ABA. MATERIALS AND METHODS Mature grapevines, Vitis vitnifera L. cv. Doradillo, growing in the Waite Agricultural Research Institute orchard, were used for two experiments in consecutive seasons. To improve uniformity, inflorescences with synchronous flowering were selected and late-developing berries were removed 5 weeks after anthesis. Plots of...

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