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A.A. Gardea, Y.M. Moreno, A.N. Azarenko, P.B. Lombard, L.S. Daley and R.S. Criddle

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. Metabolic heat rates [μJ·s-1·mg-1 dry weight (dw)] decreased during endodormancy and increased during ecodormancy and bud development. Respiration of ecodormant buds was at its minimum (≈1 μJ·s-1·mg-1 dw) in January. Respiration steadily increased, beginning in February and continuing as buds passed through the four developmental stages: ecodormant, initial swelling, fully swollen, and broken bud. Heat of metabolism increased from 5 to 18, 28, and 29 μJ·s-1·mg-1 dw as the buds developed from ecodormant to broken-bud stage. Carbon dioxide evolution from respiring buds increased from 15.9 to 22.2, 57.9, and 68.3 × 10-6 μmol·s-1·mg-1 dw as bud development advanced. Metabolic inefficiency, as quantified by heat (kJ) released per CO2 (mol) produced, was lowest in ecodormant buds, then increased at initial bud swelling and declined again in fully swollen and broken buds. The temperature coefficient of metabolism (μ) [apparent activation energy (Ea)/gas constant (R)] was lower at low temperatures (5 to 15C) in ecodormant buds than at the three more advanced stages. At higher temperatures (20 to 35C), buds at the ecodormant and initial swelling stages had a higher μ than the fully swollen and broken buds. These results suggest there may be a major change in metabolic pathways between the ecodormant bud stage and bud swelling.

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A. A. Gardea, Y. M. Moreno, A. N. Azarenko, P. B. Lombard, L. S. Daley and R. S. Criddle

The increasing respiration of breaking `Pinot Noir' buds was measured by Differential Scanning Calorimetry. Bud development was classified into ecodormant, initial swelling, fully swollen, and breaking buds. Metabolic and CO2 evolution heat rates increased as the buds developed. Activation energy decreased steadily as development proceeded, which implied that less energy was required for metabolism to continue at later bud stages. A decrease in metabolic efficiency noted by a low calorespirometric ratio was observed during the transition from ecodormant to the initial swelling stage. From the second stage on, metabolic efficiency increased. The responsive nature of grape buds to warm temperatures was explained by increasing Q10 (10-20C) values from 2.8 to 3.8, 3.2, and 3.6 for the four developmental stages described above.