ROLE OF SILICON IN PLANT RESISTANCE TO WATER STRESS

Agricultural productivity is strongly affected by different abiotic stresses, among which water stress is the major environmental constraint limiting plants growth. The primary reason for water stress is drought or high salt concentration in soil (salinity). Because both of these stress factors lead to numerous physiological and biochemical changes in plants and result in serious loss in yields, there is a pressing need for finding the effective ways for increasing crops' resistance to stress factors. One of the alternative methods involving alleviation of negative stress effects might be application of silicon as a fertiliser (root or foliar supply). Many plants, particularly monocotyledonous species, contain large amounts of Si (up to 10% of dry mass), In spite of the high Si accumulation in plants (its amount may equal concentration of macronutrients), until now it has not been considered as an essential element for higher plants. Many reports have shown that silicon may play a very important role in increasing plant resistance to noxious environmental factors. Hence, Si is recognised as a beneficial element for plants growing under biotic and abiotic stresses. The main form of Si which is available and easily taken up by plants is monosilicic acid (H(4)SiO(4)). Plants take up Si from soil solution both passively and actively. Some dicotyledonous plants such as legumes tend to exclude Si from tissues - rejective uptake. These plants are unable to accumulate Si and they do not benefit from silicon. Under water stress conditions, silicon might enhance plants' resistance to stress and ameliorate growth of plants. These beneficial effects may result from better and more efficient osomoregulation, improved plant water status, reduction in water loss by transpiration, maintenance of adequate supply of essential nutrients, restriction in toxic ions uptake and efficient functioning of antioxidative mechanisms. Based on the current knowledge and presented data, it can be concluded that the role of Si in plants is not restricted to formation of physical or mechanical barrier (as precipitated amorphous silica) in cell walls, lumens and intercellular voids. Silicon can also modulate plants' metabolism and alter physiological activities, particularly in plants subjected to stress conditions. However, in some plants, increased silicon supply does not improve plant growth. Hence, a better understanding of the interactions between silicon application and plant responses will contribute to more efficient fertiliser practices, especially under stress conditions.