Photosynthetic performance in jack bean [Canavalia ensiformis (L.) D.C.] under drought and after rehydration

the effects of drought and rehydration on canavalia ensiformis (l.) d.c. (jack bean) plants were evaluated using the following gas exchange parameters: net carbon assimilation rate (a), stomatal conductance (gs), ci/ca ratio and transpiration rate (e); chlorophyll a fluorescence: fv/fm and fv/f0 ratio. the plants were cultivated under greenhouse conditions and after 30 days from the emergence, irrigation was suspended in the plants submitted to drought, to obtain the following predawn leaf water potential (ypd): -0.40 mpa (control), -1.00 mpa (moderate drought) and -2.30 mpa (severe drought). afterwards, the gas exchange and fluorescence analysis were initiated , and 24 h after rehydration the same analyses were repeated. the a, e, gs and ci/ca values decreased significantly under both drought treatments, without however changing the fv/fm and fv/f0 values. the gas exchange parameters recovered after rehydration. it seems that drought affected photosynthesis by stomatal inhibition, as shown by the decreased gs and ci/ca values, besides the maintenance of psii phtotochemical efficiency. the recovery of gas exchange after rehydration could be due to plant protection mechanisms.