Effect of salinity stress on finger millet (Eleusine coracana (L.) Gaertn): Histochemical and morphological analysis of coleoptile and coleorhizae

The current study deals with the impact of salinity stress on growth and development of finger millet genotype ‘CO(Ra)-14’. The seeds were germinated on Murashige and Skoog solid medium supplemented with various concentrations of sodium chloride (NaCl) (0, 50, 100, 150 or 200 mM) for 15 days. Several physiological indices, including relative growth rate, electrolyte leakage, proline and chlorophyll (a, b and a + b) content, cell viability, hydrogen peroxide and caspase-like activity were measured to analyze the physiological and biochemical characteristics of saline stress. In addition, we also analyzed saline stress induced histochemical changes and level of lignin in the coleoptile and coleorhizae tissues. Relative growth of leaves and shoots of finger millet genotype ‘CO(Ra)-14’ exposed to 150 mM NaCl concentration was decreased while root length was increased. In addition, there was a significant increase in the levels of electrolyte leakage, contents of proline and hydrogen peroxide, and caspase-like activity from 0 to 200 mM NaCl. Chlorophyll and relative water contents were significantly reduced with decreased leaf succulence under increasing salinity. The microscopic observations of coleoptile and coleorhizae cross sections revealed considerable variations viz., length of epidermal cells, surface area and width of the cells with increasing salinity. Saline treated tissues were severely damaged and were intensely stained with phloroglucinol (suggesting the accumulation of cell bound phenolic compounds). Overall finger millet genotype ‘CO(Ra)-14’ showed a diverse response to salinity stress starting from seed germination to growth, and above 100 mM NaCl salinity is toxic to finger millet genotype ‘CO(Ra)-14’.