Arginine Synthesis in Grapevine Leaves and Berries: Diurnal and Seasonal Patterns, Environmental and Physiological Influences

Abstract

The diurnal and seasonal pattern of de novo arginine synthesis from ¹⁴C-labeled bicarbonate in basal and apical leaf blades and berries of grapevines (Vitis vinifera L.) was investigated using an enzymatic assay procedure. The amount of NaH¹⁴CO₃ incorporated into arginine in leaves was low during the pre-bloom and post-harvest periods, rose to its highest level during the beginning and middle of the ripening period, and decreased to low levels at the end of the ripening period. Arginine synthesis in basal fully expanded leaves was greater than in young apical leaves. On a fresh weight basis, berries were not as active as leaves in arginine formation. In both leaves and berries, NaH¹⁴CO₃ incorporation into arginine was low at night and early morning, and maximal mid-day. Leaves well exposed to sunlight synthesized more arginine than shaded leaves during the mid-day period. Arginine formation in shaded leaves, leaves collected predawn, and berries collected predawn was increased by supplying glucose or NADPH. Arginine formation in leaf and berry tissue collected pre-dawn were significantly increased by exogenously supplied ornithine. These results suggest that both carbohydrate status and reductant supply influence the rate of arginine synthesis in grape berries by affecting the arginine pathway prior to the formation of ornithine.