Effect of Salt Stress on Proline Accumulation, Photosynthetic Ability and Growth Characters in Two Maize Cultivars

Salt stress strongly affects on plant growth and development, especially maize plant, which is reported as a salt sensitive species. The salt tolerant identification in the large genetic resources and breeding population is a profitable research topic for solving the salinity problem. Two maize cultivars, viz., sweet (Zea mays L. cv. Saccharata) and waxy (Z. mays L. cv. Ceratina) seedlings were treated with 0 (control), 100, 200, 300 or 400 mM NaCl. Osmotic potential (ψs) or water availability in the culture media was limited, relating to increase in the NaCl concentrations of the growth medium. The chlorophyll degradation in the salt stressed seedlings was positively related to ψs in the culture media. Chlorophyll a (Chla), chlorophyll b (Chlb) and total chlorophyll (TC) concentrations in the salt stressed leaves significantly dropped, depending on salt treatments except total carotenoids (Cx+c) content which was decreased by the factors of salt concentrations, cultivars and their interaction. Proline in the salt stressed leaves accumulated to 600.9 μmol gFW, especially in sweet maize treated with 400 mM NaCl. The chlorophyll degradation in both cultivars was progressively correlated with maximum quantum yield of PSII (Fv/Fm) as well as the photon yield of PSII (ΦPSII) was related to net photosynthetic rate (Pn), leading to growth reduction. Chlorophyll a fluorescence parameters, Fv/Fm, ΦPSII and photochemical quenching (qP), in the leaf tissues were reduced, while non-photochemical quenching (NPQ) was exhibited. The biochemical, physiological and morphological changes in salt stressed maize cultivars were subjected to K-Means Cluster in SPSS software and classified the two cultivars as waxy salt tolerant and sweet salt sensitive.