Seed Priming and Organic Nutrient (DFYM) as a New Agricultural Technology in Improving Seed Quality

Abiotic stresses are the primary cause of crop loss worldwide, resulting in average yield losses of more than 50% for major crops. Among environmental stresses, drought, high salinity, and temperature extremes have deleterious effects on the plant growth. A low temperature and freeze are among the most important environmental stresses (Rana et al., 2017). The reason is that more than 93% of land in the world is prone to cold, of which 81% is exposed to freeze. Hence, plant growth and development are affected by a temperature change in the majority of temperate regions on Earth. Placement in autumn and survival in winter are the comparative advantages of autumn cereals over spring cereals (Rana et al., 2017). This difference is the main factor, which determines the geographic distribution and economic potential of these cereals. The yield of autumn barley cultivars is considerably more than that of spring cultivars. On the other hand, in order to avoid heat and drought stress at the end of the season, it is necessary to plant spring cultivars earlier (Rana et al., 2017). Therefore, it is probable that cold stress will damage both autumn and spring cereals. In order to survive in cold stress, plants utilize strategies, which help them tolerate severe conditions in winter. These mechanisms are genetically controlled and are induced during exposure to low temperatures.

It is believed that the cell membrane is the first possible target of cold. Cold deforms the membrane, thereby disturbing its activity. The damage to cell membranes in cold stress is caused by two conditions: (1) when the intracellular ice is formed and (2) when the climate is getting warmer. Obviously, the intracellular ice formation is detrimental (Rana et al., 2017). Since ice crystals cannot exert the hydrophobic force, which is required to maintain the lipid bilayer, the interaction of ice crystals with a bio membrane leads to the disintegration of the membrane. On the other hand, the so-called antifreeze proteins attach to ice crystals and form a hydrophobic coat, which can mitigate the disintegration caused by ice crystals. In the second condition, membrane damage is caused when the climate is getting warmer (Rana et al., 2017). Considering the fact that cells should absorb water to balance the pressure and this absorption increases the turgor pressure, it could be said that the reason is that upon the melting of ice in cells, the extra pressure damages cytoplasmic membranes and ruptures it at some points (Rana et al., 2017). Therefore; the cell dies of this rupture. Cold brings about the membrane electrolyte leakage for tissues in the sensitive plants, which cannot increase the fluidity of the living membrane by increasing unsaturated fatty acids.

Freeze and cold stress, like other environmental stresses, can create disorder in plant metabolism and increase the production of various active oxygen molecules under the title of free radicals. These radicals, through the oxidation of biotic molecules, cause damage to all kinds of cell macromolecules and impose on the plant a type of secondary stress called plant oxidative stress (Rana et al., 2017). One of the free radicals is hydrogen peroxide (H2O2), which, through the peroxidation of unsaturated fatty acids in membrane lipids, affects their selective permeability, thereby damaging membranes. The destruction of membrane unsaturated fatty acids brings about the production of malondialdehyde, which is regarded as a suitable marker for identifying the rate and intensity of oxidative damage to measured biotic membranes (Rana et al., 2017). In order to resist active oxygen radicals and diminish their detrimental effects, the cell employs the mechanism of producing antioxidants and synthesis or activating antioxidant enzymes. Among important antioxidant enzymes are superoxide dismutase, catalase, ascorbate peroxidase, monodehydro ascorbate reductase, dehydro ascorbate reductase, glutathione reductase, glutathione peroxidase, and melatonin. Several studies have demonstrated that tolerance to cold increases by collecting oxygen free radicals via antioxidants and antioxidant enzymes. This means that tolerant genotypes show more antioxidant activity during exposure to cold stress (Rana et al., 2017).