Combined application of glycinebetaine and potassium on the nutrient uptake performance of wheat under drought stress.

Plants living in different agro-climatic conditions have to face extreme situations like drought which affects their growth and productivity (Ashraf, 2010). For the reason, they evolved with certain mechanisms to abide by the harsh environments and make them competent inhabitants. Drought stress is most prevalent in arid and semi-arid regions of the world (Deng et al., 2004) and water deficit reduces the availability and transport of the mineral nutrients in the rhizosphere which ultimately cause wilting symptoms in plants. Therefore, plants nutritional status can be referred as an indicator of water stress (Raza et al., 2012). To evade the internal damage from water deficit stress, plants regulate their defense mechanism i.e. osmoregulation, hormonal balance, and reactive oxygen species scavenging factors (Yang et al., 2007; Ashraf, 2010; Hossain and Fujita, 2010). Osmotic adjustment has been considered most important phenomenon for mitigating the adverse effects of drought stress in plants (Ashraf, 2010). For that certain organic (proline, soluble sugars, glycine betaine, proline betaine) and inorganic (potassium ions) compatible solutes are accumulated in the plant cells (Taiz and Zeiger, 2002; Zhang et al., 2009; Baysal Furtana et al., 2013). Among these compatible solutes glycine betaine and potassium are very effective in the regulation of plants homeostasis under drought stress. Glycine betaine production is accelerated in plants particularly under drought stress conditions (Hessine et al., 2009). However, its production and accumulation depends on plant type, species, organelles and specific stress condition (Zhu et al., 2003; Moghaieb et al., 2004; Hassine et al., 2008; Zhang et al., 2008). Glycine betaine protects cell membranes, quaternary structure of proteins, stabilizes the membrane structure of photosystem II complex, maintains enzyme activity and boosts the antioxidant defense under drought/ osmotic stress (Ma et al., 2006; Yang et al., 2007; Hossain and Fujita, 2010). Similarly, potassium uptake and accumulation is increased during drought and it plays major role in stomata opening and closing, transpiration, photosynthesis, protective protein synthesis, and osmoregulation of plant cells (Cakmak, 2005; Milford and Johnston, 2007). Deficiency of potassium cause retarded growth under stress (Hermans et al., 2006). Because potassium is vital for enhancing plants resistance or immunity against stress, regulation of physiological processes, translocation of cations, activation of enzymes and regulation of turgor pressure (Mengel and Kirkby, 2001). Therefore, nutrient status of plant is very important and has major role in the adaptation of crop plants to stress (IPIOUAT-IPNI Intern Symposium, 2009). Different plants have varied capacity to synthesis glycine betaine at a considerably lower level than the required to protect them from stress (Subbarao et al., 2001). Similarly, reduced availability of potassium under stress makes crop plants more susceptible to damage from drought. However, exogenous application of glycine betaine or potassium has Pak. J. Agri. Sci., Vol. 52(1), 19-26; 2015 ISSN (Print) 0552-9034, ISSN (Online) 2076-0906 http://www.pakjas. com.pk