Effect of Si on the Antioxidative Defense of Young Maize Roots Under NaCl Stress

Salinity stress usually causes a serious yield reduction in crop production. Silicon (Si) has been reported to be able to alleviate stress damage, but the mechanism is still unclear. The aim of this work was to study the effect of exogenous silicon (Si) on the young maize plants welfare. For that the activities of major antioxidant enzymes (superoxide dismutase, SOD; peroxidases, POX; ascorbate peroxidase, APX) and on the lipid peroxidation (content of malondialdehyde, MDA) were investigated in the roots of salt-stressed maize (Zea mays L.). Two maize hybrids (Novania and Almansa) contrasting in their response to NaCl were tested. Four treatments with three replicates were monitored: control (without Si and NaCl), 2.5 mM Si, 150 mM NaCl, 150 mM NaCl and 2.5 mM Si. Maize roots were harvested 10 days after the treatment. MDA, ascorbate content and enzyme activities were assayed spectrophotometrically. The isoenzyme pattern of the antioxidant enzymes was detected by native PAGE. Compared with the plants treated with salt alone, added Si significantly increased MDA content in hybrid Almansa, while in Novania no increase was observed. The addition of Si significantly enhanced the activities of SOD in salt-stressed plants in both hybrids. The activities of POX and APX in salt stressed roots were significantly increased in Almansa hybrid in the presence of Si. The isoenzyme pattern followed changes in the activity of SOD; however in POX and APX such a tendency was not registered. The changes of the intensity and in the case of POX also the number of bands were detected. From these results we conclude, that Si addition fortified enzymatic antioxidative response operates in roots of young maize plants by a still unknown mechanism. The approval effect of Si is evident in the case of the SOD detoxifying system regardless of the hybrid, and for the POX family in the more sensitive maize hybrid Almansa. The presented outputs point out that silicon may protect plant tissues from oxidative damage under salt stress. Since the alleviative effect seems to be hybrid-specific, silicon alleviation of salt stress is probably not a universal feature in general and should be carefully considered between plants and/or hybrids.