The effect of salt shock on photosystem II and antioxidant activity in two maize genotypes

Abstract

In this study, variations in antioxidant systems and photosystem II activity under salt shock (500 mM NaCl) among two maize (Zea mays L.) genotypes (C955 and DKC7221) were investigated. Salt shock induced a marked reduction in plant height, fresh and dry matter gain in roots and shoots in C955 and DKC7221. For both genotypes, salt shock led to oxidative stress as indicated by the considerable increase in hydrogen peroxide and malondialdehyde content. Photosynthetic pigment content was found to be lowered in both genotypes probably as a result of salt shock-induced oxidative stress. Free proline content and guaiacol peroxidase activity were more remarkably increased by salt shock in the genotype C955 in comparison with DKC7221, which may be related to higher salt tolerance. Superoxide dismutase activity was not affected by salt shock in DKC7221 while it was considerably higher in C955. Ascorbate peroxidase and glutathione reductase activity were not induced by salt shock in maize genotypes, which could demonstrate that ascorbate-glutathione cycle was inactivated by salt shock. Changes in maximum fluorescence indicated restrictive effect of salt shock on electron transport reactions in photosystem II acceptor side in both genotypes while water-splitting reaction was more tolerant to salinity in C955 as shown by higher Fv/Fo ratio. Changes in JIP-test parameters demonstrated that electron movements were partly inhibited by salt shock in some specific points on the photosystem II units. As a consequence, the results of the present study showed that the metabolic responses of C955 and DKC7221 to salinity were similar. However, especially on the basis of the JIP-test parameters and antioxidant responses, it may be concluded that metabolic changes in C955 are associated with the regulatory mechanism(s), while it was related to salinity damage in DKC7221.