Silicon-mediated alleviation of sodium toxicity in wheat under saline conditions

Abstract

Salinity is the major yield constraining problem in many parts of the world, especially in regions having arid to semiarid climate. Pakistan population has increased up to 200 million while the average wheat yield has become stagnant because of the soil salinity and other stresses. So, it is important to sustain wheat production by using the available resources efficiently to secure the food for over-population. Silicon (Si) is a beneficial element for plant growth. Its application plays a multiple role to increase plant growth through influencing physiological and metabolic processes in higher plants under both biotic and abiotic stresses. Four studies were planned to investigate the possible mechanism through which Si improves salt tolerance in wheat crop. In first experiment, 10 wheat genotypes (Lasani-2008, AARI-2011, Sehar-2006, AAS, Faisalabad-2008, Punjab-2011, Millat-2011, L-7076, L-8171 and SARC-5) were grown in ½ strength Hoagland nutrient solution with salinity (control, 100 and 200 mM NaCl) and silicon ( control, 1 mM and 2 mM ) in wire house for 30 days. Two wheat varieties i.e. Faisalabad-2008 as salt tolerant and Millat-2011 as salt sensitive were selected from first experiment on the basis of ionic composition and biomass production. Second experiment was conducted to study the interactive effect of salinity and silicon (Si) on plant physiological and biochemical attributes at two different growth stages by growing both selected wheat varieties in the hydroponic solution using same levels of treatments as in first experiment. It was found that Si significantly increased the salt tolerance of both wheat varieties by improving the plant physiological and biochemical traits. Faisalabad-2008 performed better than Millat-2011at both growth stages (Tillering and stem elongation). Third experiment was conducted in the pots to investigate the role of Si on distribution and compartmentation of ions in the shoot and root tissues of wheat (Faisalabad-2008) through exogenous application of Salinity (control, 200 mM NaCl) and Si (control, 2mM). The Scanning Electron Microscopy and Energy Dispersive X-ray micro analysis of plant tissues showed that Si altered the ion distribution and contributed significantly to enhance salt tolerance in wheat. A fourth pot experiment was carried out to study the role of Si on the yield of both selected wheat varieties (Faisalabad-2008 & Millat-2011) using same level of treatments as in first experiment. Results indicated considerable increase in grain as well as in biological yield of both selected wheat varieties under saline condition. It was concluded from above studies that Si increased salt tolerance and yield of wheat through improving physiological, biochemical and alteration of ions in the plant tissues. The Faisalabad-2008, found efficient Si-accumulator wheat variety. Key words: Wheat (Triticum aestivum L.), Salinity, Silicon, antioxidant enzymes. Ion distribution