Silicon Mediated Alleviation of Salinity Stress Regulated by Silicon Transporter Genes (Lsi1 and Lsi2) in Indica Rice

Abstract Silicon accumulation is known to improve tolerance of plants under both biotic and abiotic stress. Salinity stress is an inevitable crisis causing wide spread damage to rice leading to food insecurity. The influence of Si (1mM) on two rice cultivars cv. Ghanteswari (high accumulator) and cv.Badami (low accumulator) which differs in Si uptake potential under saline (10ds/m EC) and non- saline conditions were studied in nutrient culture. The Si transporter genes were isolated and characterized to determine their function in salinity tolerance. Under stress, there was an increase in Si accumulation, Na+/K+ ratio, electrolyte leakage, lipid peroxidation and antioxidant activities. On addition of silicon, the K+ uptake increased, membrane damage reduced and osmolytes balance improve under salinity. But, the level of resurgence was varied in both cultivars, due to their differential Si-accumulation. Molecular characterizations of Lsi1 protein revealed its involvement in the movement of ion and water and therefore prevent osmotic stress. The Lsi2 is responsible for removal of Na+, reducing salt toxicity. Silicon accumulation is responsible for maintenance of cell water status, osmotic balance and Na+ ion exclusion during high salinity. The variable relative expression of Lsi2 provides a possible explanation for differential genotypic uptake of silicon.

Metabolism of silicon as a probable pathogenicity factor for Mycobacterium & Nocardia spp.

The role of silicon (Si) in metabolism and growth of 22 strains of mycobacteria and 3 strains of nocardiae, which were mostly pathogenic, was studied on Kirchner's medium solidified with sodium metasilicate (KSM) and the C-free solidified metasilicate minimal medium (SMM) consisting of mineral salts only. On KSM, initial growth of mycobacteria appeared to be better, compared with that on Lowenstein-Jensen medium (LJM), although subsequent growth on the former was slower. On SMM lacking C, growth of mycobacteria and nocardiae could be achieved, only after repeated passages. These findings indicate that the mycobacteria and nocardiae are able to utilise Si at least to a limited extent, possibly as an alternative to C, with greater chances of survival.