The effect of leaf area and crop level on the concentration of amino acids and total nitrogen in 'Thompson Seedless' grapes

20 to 50% of the leaves and 25 to 75% of the clusters on 'Thompson Seedless' vines were removed 12 to 16 days after anthesis. In addition, 25 and 50% of the   leaves on other vines were removed 35 and 58 days after anthesis, with no cluster thinning. Total soluble solids in fruits from vines with less than 5 cm 2 of leaf surface per gram of fruits was markedly reduced, while concentration in fruits from vines with a ratio above 10 was considerably higher, compared to the concentration in fruits from vines with ratios intermediate between these two values. The concentrations of arginine, proline, total free amino acids, and total N in berry juice were greatly increased by reducing the crop load. Also, the concentration of each of these substances increased during fruit ripening. A significant correlation between leaf area per vine and level of arginine in the juice was obtained. The concentration of proline in the juice was highly correlated with fruit maturity (°B) and with leaf area per unit weight of fruits. Total nitrogen was also correlated with leaf area per unit weight of fruits. Between 4 and 12 cm 2 leaf area per gram of fruits there was a linear increase in the concentration of proline and total nitrogen in berry juice, while above 12 cm 2 there was generally little further increase in the level of these substances. The ratio of arginine to proline decreased with fruit maturity and with smaller crop weights per vine. Total free amino acids accounted for 64 to 75% of the total nitrogen in the juice of grapes during the fruit-ripening period. Defoliation within 16 days after anthesis reduced crop yields, while later defoliations did not significantly reduce yields.