CHANGES IN METABOLIC PROPERTIES OF GRAPE BUDS DURING DEVELOPMENT

The pattern of respiratory changes during dormancy and development of 'Pinot noir' primary grape (Vitis vinifera L.) buds through the broken -bud stage was determined using differential scanning calorimetry. Met abolic heat rates [muJ.s-1.mg-1 dry weight (dw)] decreased during endo dormancy and increased during ecodormancy and bud development. Respira tion of ecodormant buds was at its minimum (almost-equal-to 1 muJ.s-1. mg-1 dw) in January. Respiration steadily increased, beginning in Febr uary and continuing as buds passed through the four developmental stag es: ecodormant, initial swelling, fully swollen, and broken bud. Heat of metabolism increased from 5 to 18,28, and 29 muJ.s-1-mg-1 dw as the buds developed from ecodormant to broken-bud stage. Carbon dioxide ev olution from respiring buds increased from 15.9 to 22.2; 57.9, and 68. 3 x 10(-6) mumol.s-1.mg-1 dw as bud development advanced. Metabolic in efficiency, as quantified by heat (kJ) released per CO2 (mol) produced , was lowest in ecodormant buds, then increased at initial bud swellin g and declined again in fully swollen and broken buds. The temperature coefficient of metabolism (mu) [apparent activation energy (E(a))/gas constant (R)] was lower at low temperatures (5 to 15C) in ecodormant buds than at the three more advanced stages. At higher temperatures (2 0 to 35C), buds at the ecodormant and initial swelling stages had a hi gher mu than the fully swollen and broken buds. These results suggest there may be a major change in metabolic pathways between the ecodorma nt bud stage and bud swelling.