Silicon is not generally listed in the list of essential elements, it is considered as one of the significant beneficial nutrient for plant growth. The quantity of Si in soil may vary significantly from 1 % to 45 %. However, Silicon is present in soil in different forms, but plants can easily absorb Silicic acid Si (OH)4 from soil. Silicic acid is usually found in the range of 0.1-0.6 mM in soils. While Si is valuable for plant growth it plays significant role as a physiomechanical barrier in the majority plants.
While its facts on cell walls, its active association in a large number of metabolic processes and physiological, is also apparent. Plants deprived of Si often Show poor development and reproduction, but it depends on the type of plant species. For plant growth and production salinity stress is one of the most destructive stressful environments. One possible approach of overcoming the salt-induced deleterious effect on plant growth is the exogenous application of inorganic nutrients and osmo protectants.
By adopting this approach, the supplements of Si to plants subjected to the salt affected soils, because Si has been considered valuable for improving crop tolerance to both abiotic and biotic stresses. According to different investigation the ameliorative role of Si to adverse effects of salinity has been examined in different crops e.g., cucumber, tomato, wheat, rice and barley.
Silicon uptake in the form of uncharged molecule-silicic acid and in plants three different modes of silicon taken up (active, passive, and rejective) may function. In aerial parts of plants silicon distribution is dependent on intensity of transpiration. During the transpiration stream in xylem, silicic acid is transported to leaves and it is accumulated in older tissues. In the shoot, due to the loss of water, silicic acid is concentrated and polymerized
Demonstrating the advantageous effects of silicon appliance in improve salt-induced harmful effects on growth of plant. Decrease in plant photosynthesis under salt stress take place due to closing of stomata that reduced photosynthetic rate leads to reduced plant growth in the majority of plants. Under salinity the closing of stomata that result in decrease in leaf internal CO2 concentration and reduced leaf transpiration rate.
Silicon-induced improvement in plant growth under salt stress may have been due to the important role of Silicon in the improvement of plant water status. Silicon affects plant growth under stressed conditions by affecting a variety of processes including the improvement in plan water status, changes in ultra-structure of leaf organelles, up regulation of plant defense system and mitigation of specific ion effect of salt.
Silicon application to saline medium enhances the photosynthetic activity, chlorophyll content and ribulose bis-phosphate carboxylase (RUBP) activity in leaf cell organelles and also minimizes the salt-induced H2O2 production. Exogenously applied Si improved all those parameters both under non-saline and saline regimes. The other mechanisms for salinity tolerance induced by Si application are; enhanced bioactive gibberellins (GA1 and GA4) contents and reduced jasmonic acid (JA) contents under salinity stress. Si application under saline conditions, detoxifying ROS enhanced under salt stress; as a result chlorophyll increases which lead to the improve (Fv/Fm).
According to different investigations the decrease in value of (Fv/Fm) with salt application and increase in (Fv/Fm) with Si application under abiotic stress might be due to less photoinhibition; where Fv/Fm has a significant positive correlation with A and SPAD values. Salinity stress imposes injurious effects on plant growth, its photosynthetic activity and photochemical efficiency of photosystem II, Silicon application improved all parameters under salt stress by enhancing the A, gs and WUE under salt stress.
Silicon treated plants have higher photochemical efficiency of photosystem II which leads to healthy growth under salt stress conditions. Thus, Si application would be beneficial under salt stress conditions and its beneficial effects should be tested on a larger scale i-e field conditions.