Morpho-physiological and micrographic characterization of maize hybrids under NaCl and Cd stress

A hydroponic experiment was conducted to investigate single and combined effects of 5 µmol/L Cd and 100 mM NaCl on growth, root morphology, photosynthetic parameters, leaf and root ultra-structure of two maize hybrids (26204 and 8441) differing in salt tolerance. A more pronounced reduction on growth, root morphology, SPAD value, chlorophyll fluorescence and leaf gas exchange indicated that 8441 was more sensitive than 26204 to both Cd and NaCl stresses. Transmission electron microscopy of 8441 revealed a more severe destruction in root and leaf cells as compared to 26204. The reduction in growth and photosynthetic parameters were associated with severe disorganization of nucleus, chloroplast, mitochondrial damage, vacuolation, and increased number and size of pastoglobuli. Interestingly, the combined stress of both NaCl and Cd had obvious beneficial effect on the plant growth, photosynthetic parameters and cell ultra-structure relative to Cd or Na stress alone in the two maize hybrids. The study suggested that there is involvement of same genetic and physiological mechanisms in response to both Cd and NaCl stresses.