Physiological characterization of different genotypes of upland riceThe experiment was carried out at University of São Paulo, during the years 2011 and 2012, in Piracicaba, State of São Paulo. Ten contrasting genotypes were used, nine to be cultivated on uplands (two modern and seven traditional) and one (modern) for lowlands (irrigated area). The genotypes were grown in pots and kept without water restriction in the greenhouse until the issue of the flag leaf. After the flag leaf issuance, eight pots of each genotype containing one plant were kept inside of a growth chamber (phytotron) under strictly controlled climatic conditions during eight days. During this period, four pots were kept with water stress and four without. After five and six days, assimilation rate (A), stomatal conductance (g s ), internal CO 2 concentration (C i ), transpiration (E), water use efficiency (WUE) and relative leaf water content (RWC) were evaluated. After seven days, responsiveness curves according to light intensity changes were done, which A, g s , C i , E and RWC were determined. After eight days, responsiveness curves according to CO 2 changes were done, which stomatal (L s ) and metabolic limitation (L m ), mesophyll conductance (g m ) and Rubisco activity (V cmax and J max ) were determined. After five and six days, it was found that, on condition of low water availability, the modern genotype 'BRS-Primavera' showed the lowest values of A, g s , C i , E and CHF, and 'Douradão' (traditional genotype) the highest values. 'BRSCirrad' (modern genotype) cultivar also showed low values for these variables. Other genotypes showed similar behavior. At condition of the greater water availability, 'BRS-Cirrad', 'BRS-Curinga' and 'BRS-Primavera' (modern genotypes) showed the highest values for A, g s , C i , E and CHF. The traditional genotypes behaved similarly to each other. Evaluating the same genotype under two water availability conditions, it was observed that modern genotypes showed large reductions of the A, g s , and E as compared to traditional. It was found that the adjustment of g s influenced strongly all observed variables, and the WUE did not show good correlation with photosynthetic rate. On the light curves, the modern genotypes presented superior performance than traditional under largest water availability and similar in lower water availability condition, showing strong effect of g s on rates of A and E in all genotypes. On the CO 2 curves, under lower water availability condition, it was observed that the modern genotypes presented superior values of L m and L s , and similar values of V cmax , J max and g m when compared to traditional genotypes. Under higher water availability, the modern genotypes ('BRS-Cirrad' and 'BRS-Curinga') presented higher values of V cmax and J max and lower values of L s . The modern genotypes presented higher photosynthetic capacity under high water availability, however, when subjected to the condition of low water availability showed high reductions compared to tradition...