STUDIES OF BUD REST IN APPLE AND SOUR CHERRY
Abstract
The effect of light on both chilling and break of apple (Malus domestica Borkh.) buds was examined using detached shoots in controlled environments and intact shoots in the field. Both chilling and budbreak occurred in total darkness. Light levels of 85 (mu)Em('-2)s('-1) (1979-1980) or 100 or 300 (mu)Em('-2)s('-1) (1980-1981) for 8 hours per day during controlled chilling at 5(DEGREES)C enhanced the rate of bud development upon subsequent forcing. Light levels above 150 (mu)Em('-2)s('-1) during forcing accelerated budbreak, but there was no difference between 8 and 16 hour photoperiods during forcing. Field shoots covered at various times during winter and early spring responded similarly. Dormant apple shoots fixed 7 times as much ('14)CO(,2) at 5(DEGREES)C in the light as in darkness. A controlled chilling technique for flower buds on detached sour cherry (Prunus cerasus L.) shoots was developed. Chilling accumulated at 5(DEGREES)C, and was nullified at 15(DEGREES)C. A 5/15(DEGREES)C, 16/8 hour daily cycle increased chilling efficiency over constant 5(DEGREES)C. Shoots in which chilling was nullified by 2000 hours at 15(DEGREES)C responded to subsequent chilling at 5(DEGREES)C. Intact trees responded the same as did detached shoots. Shoots collected at different times in the fall responded differently to controlled chilling. Gibberellic acid accelerated budbreak of partially chilled field shoots, or of shoots held for 2000 hours at 15(DEGREES)C (chilling nullified). Chilling accumulation and growing degree hour accumulation overlap, and the end of rest is gradual rather than discrete. Flower buds chilled in the field and in the laboratory were studied using light and electron microscopy. Starch accumulation was examined histochemically using the periodic acid - Schiff (PAS) reaction. While no morphological development occurred until visible budbreak began, starch accumulated significantly in most tissues directly in response to chilling. No major ultrastructural changes accompanied chilling, but starch grains were prevalent in chilled tissue. Cells of buds held at 15(DEGREES)C had irregularly shaped nuclei and more mitochondria than cells of chilled buds. Results of these studies suggested that the chilling mechanism may involve carbohydrate metabolism and transport of food reserves into the buds.
Degree
Ph.D.
Subject Area
Plant sciences
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