Physiological and Oxidative Response to NaCl of the Salt Tolerant Grevillea ilicifolia and the Salt Sensitive Grevillea arenaria

Abstract

Summary A comparative study of shoot cultures of two Grevillea species exposed to various levels of NaCl (for 6 weeks) indicated that Grevillea ilicifolia was significantly more tolerant to salt than Grevillea arenaria . Growth (explant height and numbers of shoots and leaves) in G. ilicifolia significantly declined at salt concentrations greater than 100 mmol · L -1 , whilst growth of G. arenaria was significantly impaired at 40 mmol. L -1 NaCl. Protochlorophyll, chlorophylls and carotenoids were significantly reduced as the salt concentration was increased, with both of the Grevillea species being equally sensitive to NaCl. The rate of decline of protochlorophyll and chlorophyll b with NaCl exposure was greater than that of chlorophyll a and carotenoids for both species. Anthocyanin pigments on the other hand significantly increased with salt stress in both of the Grevillea species. Levels of Na and Cl were significantly elevated during salt exposure, while K, Ca and Mg levels were markedly reduced. The levels of malondialdehyde significantly declined in both species as a result of salt exposure, and this was accompanied by significant increases in both acid protease and neutral protease activities. Four other key enzymes involved in oxidative stress and tissue degradation (catalase, polyphenol oxidase, superoxide dismutase and lypoxygenase) were also significantly increased in both Grevillea species as a result of NaCl treatment. The main difference between the two Grevillea species appeared to be that the more salt tolerant G. ilicifolia had significantly lower levels of the oxidative/degrading enzymes, compared with the more salt sensitive G. arenaria .