Resistência de folhas de plântulas de cajueiro (Anacardium occidentale L.) anão-precoce aos danos oxidativos induzidos pelos estresses salino e osmótico

Abstract

SaIt stress promotes a set of biochemical and physiological disturbs on plants. Among that, there is the generation of active oxigen species (AOS). The AOS are parcially reduced forms of atmosferic 02 that may act instantaneously on proteins, lipids and nucleic acids causing cellular damage. This work, evaluated the effect of salt stress on oxidative metabolism of cashew's tissues leaves ( Anacardium occidentale), through antioxidative enzymes activities study, like superoxide dismutase (SOD), ascorbate peroxidase (APX) and phenol peroxidase (POX). Others physiological stress indicators like ascorbate content and membrane integrity were studied. The progenies CCP 06 and CAPI 9 were grown on sand under natural conditions and irrigated with NaCI 100 mmol.L-1 . They were harvest after 15 and 30 days after treatment. The resuIts demonstred that this progenies showed growth velocity diferenciated and salinity had effect on growing stage acceIerated, however CAPI 9 showed to be much more tolerant because got to grow under salt stress. This best performance was associated with a better membrane integrity and increased antioxidant enzymes activities exhibited by this progeny. Others experiments utilizing CCP 06 progeny on hidroponic and controlled conditions were did. The results showed, specially through membrane integrity analysis, that damage on cashew seedling under increased NaCI Ievel, were not because oxidative stress. The APX enzyme was particularly induced on high salinity conditions and SOD activity not had a substancial increase. It was observed, however, that to enzymes activities be induced was necessary a proIongated saIt stress exposition. To clarify this, as well as to evaluate the osmotic and toxic effects of NaCI, another experiment with PEG 6000 on isosmotic concentration to NaCI 200 mmol.L-1 were did. The plants were harvest on different times. Osmotic stress induced by PEG was much more efficient to induce oxidative damage than NaCI. PEG affected membrane integrity and raised SOD and POX activities, but APX activities maintained unchanged. NaCI not affect membrane integrity and not induced increase on enzymes activities. To evaluated if this adaptative responses of cashew leaves were due to inherent properties of this tissue or if were influenced by a organization leveI higher, a experiment utilizing discs leaves was did. The results showed that the resistance exhibited by tissue leaves of cashew seedling were, in part, due to a response a leveI wholeplant, that involved osmotic ajustment, íons transport between different organs and probably honnonaI processes. However, the membrane resistance to AOS might be a celluIar caractheristic that was independent of adaptative responses a leveI whole-plant. In conclusion, cashew's tissues leaves were resintante to oxidative stresss induced by salt and osmotic stress.