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Biology and Biotechnology of Environmental Stress Tolerance in Plants, Volume 3

osmotic balance, enzymatic activities, and increase in ROS levels (Parida

& Das, 2005; Parihar et al., 2015), altered stomatal functions, and nutrient

imbalance in plants (Munns et al., 2006). Other physiological processes like

seed germination, growth, flowering, and fruiting are also affected due to

high levels of sodium (Parihar et al., 2015; Singh et al., 2013). However,

plants may induce different morphological and physiological adaptations to

acquire salt stress tolerance without affecting the normal functioning of the

plant (Farooq et al., 2015; Shannon & Grieve, 1998). Under stress, the quality

and composition of grain may change due to excess of a certain metabolite

that helps the plant to tolerate the adverse effects of environmental factors.

Once exposed to one stress, plants may exhibit tolerance to other or conse­

quent stress in coming generations (Ćuk et al., 2010). Such transgenerational

memory involves modifications in proteome and metabolome with upregu­

lated expression of solutions and proteins required to overcome stress (Joyce

et al., 2003; Walter et al., 2013). Seed priming induces metabolic alterations

during seed germination and enhances osmolyte accumulation (Delavari et

al., 2010), and lipid peroxidation, antioxidant activities, and proteins (Afzal

et al., 2008; Jafar et al., 2012). The production of metabolites aids in setting

up a defense mechanism. Seed priming has been efficient for salt tolerance

in wheat (Jafar et al., 2012), mustard (Srivastava et al., 2010), maize (Aliu

et al., 2015), and barley (Rashid et al., 2006). In Solanum villosum, the

hydroprimed seeds showed synchronized germination, low oxidative stress,

higher content of chlorogenic acid iso-orientin, and rutin. Hydropriming of

maize seeds for 48 hrs. was beneficial in tolerating salinity stress. Similarly,

hydroprimed sunflower seeds displayed better vigor and high germination

rate under salinity stress (Matias et al., 2018).

4.3.2 DROUGHT STRESS

Water scarcity is considered to be one of the most destructive factors and

a serious threat to agriculture, mostly in arid and semi-arid areas of the

world. Inadequate rainfall, modern agriculture systems, and climate change

are major causes of drought (Lobell et al., 2011). It adversely affects the

germination, growth, and development of the plant. The severity of drought

is unpredictable owing to the moisture content of soil, evaporation, and rain­

fall, etc. (Farooq et al., 2009). Drought can happen in all stages, and severely

affects seed germination (Harris et al., 2002) and early seedling growth

(Okçu et al., 2005), and crop stand (Kaya et al., 2006). In alfalfa, it was

found that drought alters the fresh and dry weight of shoot and root, rate of