Physiological mechanisms of exogenous calcium on alleviating salinity-induced stress in rice (Oryza sativa L.)

Being more sensitive to salt stress among the cereals, growth of rice ( Oryza sativa L.) has been habitually affected by salinity. Although, several practices have evolved to sustain the growth of rice under salinity, the enormous role of calcium (Ca 2+ ) as a signalling molecule in salt stress mitigation is still arcane. Considering this fact, an experiment was performed aiming to explicate the mechanism of salt-induced growth inhibition in rice and its alleviation by exogenous Ca 2+ . At germination stage, 10 mM and 15 mM CaCl 2 primed rice (cv. Binadhan - 10 & Binadhan - 7 ) seeds were grown in petri dishes for 9 days under 100 mM NaCl stress. At seedling stage, 9-day-old rice seedlings grown on sand were exposed to 100 mM NaCl alone and combined with 10 mM and 15 mM CaCl 2 for 15 days. This research revealed that salinity radically slowed down growth of rice seedlings and Ca 2+ treatment noticeably improved growth performances. At germination stage, 10 mM CaCl 2 treatment significantly increased the final germination percentage, germination rate index (in Binadhan - 7 ), shoot, root length (89.20, 67.58% in Bindhan - 10 & 84.72, 31.15% in Bindhan - 7 ) and biomass production under salinity. Similarly, at seedling stage, 10 mM CaCl 2 supplementation in salt-stressed plants enhanced shoot length (42.17, 28.76%) and shoot dry weight (339.52, 396.20%) significantly in Binadhan - 10 & Binadhan - 7, respectively, but enhanced root dry weight (36.76%) only in Binadhan - 10 . In addition, 10 mM CaCl 2 supplementation on salt-stressed seedlings increased the chlorophyll and proline content, and oppressed the accretion of reactive oxygen species thus protecting from oxidative damage more pronouncedly in Binadhan - 10 than Binadhan - 7 as reflected by the elevated levels of catalase and ascorbate peroxidase activity. The 15 mM CaCl 2 somehow also enhanced some growth parameters but overall was less effective than 10 mM CaCl 2 to alleviate salt stress, and sometimes showed negative effect. Therefore, supplementary application of calcium-rich fertilizers in saline prone soils can be an effective approach to acclimatize salt stress and cultivate rice successfully.