Effect of High Temperature on Grapevines (Vitis vinifera L.). I. Translocation of 14C-Photosynthates

Non-bearing Chenin blanc and bearing Chardonnay vines grown in pots in a greenhouse at 25° to 29°C/15° to 16°C day/night temperatures were transferred to heat stress conditions in a phytotron (40°/20°C day/night) for periods of four, eight, and 12 days before returning to the original greenhouse for an eight-day "recovery period". Comparable control plants were kept inside the greenhouse for an equivalent period. 14 CO 2 was administered to a fully-expanded leaf of each plant at the end of the stress period. Twenty-four hours thereafter, entire vines were harvested and individually divided into 12 or 13 fractions for 14 C counting. The distribution pattern of 14 C-photosynthates was similar for both cultivars. The amount of 14 C in fruit clusters of Chardonnay vines subjected to heat stress was about 2.5% that of control fruit. Accumulation of 14 C in heat-stressed vines was significantly greater in the shoot tip and less in the trunk and roots than in control plants. Shoot growth rate of control Chenin blanc plants was greater than plants subjected to heat stress, whereas bearing Chardonnay vines showed the opposite relationship. Dry weight of various plant parts at harvest, root to shoot dry weight ratio, total amount of 14 C recovered per plant, and relative amounts of 14 C recovered from the treated leaf were not affected by heat stress in both cultivars.