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Chlorophyll a fluorescence reveals adaptation strategies in drought stress in Ricinus communis

Silva Dalberto, Davi, Garbin Martinazzo, Emanuela, Antonio Bacarin, Marcos
Revista brasileira de botânica 2017 v.40 no.4 pp. 861-870
Ricinus communis, acclimation, arid zones, carboxylation, chlorophyll, cultivars, electron transfer, electron transport chain, fluorescence, gas exchange, genetic improvement, greenhouses, irrigation, photochemistry, photosystem II, water stress, water use efficiency, Brazil, China, India
Ricinus communis L. cultivation is an economic alternative in arid regions, particularly in India, China and northeastern Brazil. Research on photosynthetic behavior under conditions of water deficit is valuable for genetic improvement programs and the management of this crop. We aimed to obtain information on the photosynthetic mechanisms and acclimation to stress in young plants of the castor cultivars BRS Gabriela and IAC Guarani grown in the greenhouse, for which irrigation had been suspended for 35 days. Chlorophyll a fluorescence transient and gas exchange were measured every 7 days, and growth was measured at the end of the experiment. Growth and gas exchange were negatively affected by stress, with reductions being detected early during the period of water deficit. There was an increase in water-use efficiency in both cultivars, as well as a reduction in intrinsic carboxylation efficiency. Although gas exchange was reduced initially, the parameters of the JIP test, calculated from the fluorescence transient, indicated an increased activity of the photochemical apparatus, with higher performance indices. A decrease in the activity of the electron transport chain was observed at the end of the stress period, with a concomitant increase in the dissipation and inactivation of photosystem II reaction centers and a consequent reduction in performance indices, with IAC Guarani plants showing greater susceptibility to stress compared to BRS Gabriela plants. Considering the photosynthetic activity in stressed plants, castor bean plants show acclimation of electron transport during the short-term water deficit, however, with decrease in the photosynthesis in long term.