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Effect of drought on the mechanisms of energy dissipation was evaluated in two-month-old Arachis hypogaea cvs. . Plants were submitted to three treatments: control (C), mild water stress (S1), and severe water stress (S2). Photosynthetic performance was evaluated as the Hill and Mehler reactions. These activities were correlated with the contents of the low and high potential forms of cytochrome (cyt) b 559, plastoquinone, cyt b 563 , and cyt f. Additionally, the patterns of carotenoids and chlorophylls (Chls), as well as the alterations of Chl a fluorescence parameters were studied. Under mild water stress the regulatory mechanism at the antennae level was effective for 57-422 and GC 8-35, while in the cv. 73-30 an overcharge of photosynthetic apparatus occurred. Relative to this cv., under S1 the stability of carotene and the dissipative cycle around photosystem (PS) 2 became an important factor for the effective protection of the PS2 reaction centres. The cyclic electron flow around PS1 was important for energy dissipation under S1 only for the cvs. 57-422 and 73-30.

The photosynthetic response of three Arachis hypogaea L. cultivars grown for two months was measured under water available conditions, severe water stress, and 24, 72, and 93 h following re-watering. At the end of the drying cycle, all the cultivars reached dehydration, relative water content (RWC) ranging between 40 and 50 %. During dehydration, leaf stomatal conductance (g s ), transpiration rate (E), and net photosynthetic rate (P N ) decreased more in cvs. 57-422 and GC 8-35 than in 73-30. Instantaneous water use efficiency (WUE i ) and photosynthetic capacity (P max ) decreased mostly in cv. GC 8-35. Except in cv. GC 8-35, the activity of photosystem 1 (PS1) was only slightly affected. PS2 and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) were the main targets of water stress. After re-watering, cvs. 73-30 and GC 8-35 rapidly regained g s , E, and P N activities. Twenty-four hours after rewatering, the electron transport rates and RuBPCO activity strongly increased. P N and P max fully recovered later. Considering the different photosynthetic responses of the studied genotype, a general characterisation of the interaction between water stress and this metabolism is presented.