Daily balance of leaf sugars and amino acids as indicators of common bean (Phaseolus vulgaris L.) metabolic response and drought intensity.

Leaf soluble sugar, starch and free amino acid amounts were evaluated in two bean genotypes, Carioca and Ouro Negro, grown in 10 L pots in a greenhouse. This was realized during a single day for Carioca and during ten days of water deficit for both genotypes, at 06:00 and 18:00 h. During the day, an increase in all parameters occurred up to midday, while in the afternoon, carbohydrate amounts varied in opposition to amino acids amounts. Under water deficit, the leaf soluble sugars at 18:00 and their daily balance (amount at 18:00 minus amount at 06:00) increased on the 2(nd) day, with starch and amino acid amounts and their respective daily balances decreasing. On the 8(th) and 10(th) days, the soluble sugar daily balance was negative and the starch daily balance approached zero or was negative, while the amino acid daily balance was positive. During rehydration, soluble sugar daily balance was close to zero and starch daily balance increased, whereas amino acid daily balance was negative. The carbohydrate daily balance, strongly related to free amino acid daily balance, were good indicators for evaluating the stage of water deficit and metabolic capacity to respond to the stress in common bean.