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Catalase activity in grapevine (Vitis vinifera L.) buds cv. ;Perlette.' increased to a maximum in October and thereafter decreased within 3 months to less than half its maximal rate. The decrease in catalase activity coincided with the decline in temperature during winter. The rate of sprouting of buds forced at 23 degrees C was negatively related to the activity of catalase. Artificial chilling of grapevine canes at 5 degrees C resulted in a 25% decrease of catalase activity in the buds after 3 days and 31% after 17 days. The activity of catalase increased to the control level only 96 hours after removing canes from 5 degrees C to room temperature. Efficient buddormancy breaking agents, such as thiourea and cyanamide decreased catalase activity to 64 and 50% of the controls respectively, while the activity of peroxidase remained the same under those conditions. A less efficient dormancy breaking agent dinitro-ortho-cresol, did not decrease catalase activity.

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The seasonal development of vine canopy size and vine morphology of minimal- and cane-pruned Sultana was examined by destructive harvests during the 1982-83 growth period. Leaf canopies of minimal-pruned vines developed more quickly, grew larger, and filled sooner than those of cane-pruned vines. Minimal-pruned vines had 4 times the number of shoots and 3 times the number of nodes on current seasons's shoots at 34 days after budburst. This largely explains the more rapid canopy development and fill of minimal-pruned vines. Minimal pruning had a stunting effect on growth, resulting in shorter shoots, shorter internodes, and smaller leaves compared with cane pruning. Indirect optical measurements of the seasonal leaf canopy development of Sultana vines in the same experimental vineyard during the 1991-92 growth period confirmed the results obtained in 1982-83.