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

Being more sensitive to salt stress among the cereals, growth of rice ( 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) 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. At germination stage, 10 mM and 15 mM CaCl primed rice (cv. - & -) 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 for 15 days. This research revealed that salinity radically slowed down growth of rice seedlings and Ca treatment noticeably improved growth performances. At germination stage, 10 mM CaCl treatment significantly increased the final germination percentage, germination rate index (in -), shoot, root length (89.20, 67.58% in - & 84.72, 31.15% in -) and biomass production under salinity. Similarly, at seedling stage, 10 mM CaCl supplementation in salt-stressed plants enhanced shoot length (42.17, 28.76%) and shoot dry weight (339.52, 396.20%) significantly in - & - respectively, but enhanced root dry weight (36.76%) only in -. In addition, 10 mM CaCl 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 - than - as reflected by the elevated levels of catalase and ascorbate peroxidase activity. The 15 mM CaCl somehow also enhanced some growth parameters but overall was less effective than 10 mM CaCl 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.