Physiology and Grain Germination

Gibberellins are mainly responsible for triggering the synthesis of key enzymes that will degrade nntrients stored in the first and second reserve tissues of the germ and endosperm, respectively. Two gibberellic acids (GA, and GA3) are the major hormones produced by the anbryo. These hormones are later transported along with the absorbed water to the endosperm through the tube cells, and induce aleurone cells 

Most phosphorus associated with cereal grains exists in the form of phytic acid (myoinositol hexaphosphate) that is stored in phytic bodies mainly loeated in the aleurone layer. These molecules bind potassium, magnesium, and other minerals. The phytases degrade these compounds to release phosphate, other minerals, and myoinositol. The myoinositol is a known precursor of sugars associated with cell wall polysaccharides and a promoter of seedling growth. The free phosphorus is critically important for synthesis of nucleic acids and phospholipids for cellular membrane proliferation, and ATP and energy production. 

Fibrolitic or cell wall degrading enzymes are constituted by ceUulases, hemicellu-lases, pectinases, xylanases, p-glucanases, and others that synergistically attack cell walls and enhance the entrance of the other enzymes into the cells. The enzymes are mainly secreted from the aleurone or scutellum, and therefore approach their substrates from outside the cells of the starchy endosperm. The simple sugars released from wall polysaccharides make a contribution to the total energy needed for seedling development. 

Main Enzymes Synthesized during Germination of Cereal Grains 

Attacks triglycerides releasing fatty acids. Lipase A, hydrolyzes fatty acids located on the ends of triglycerides, whereas Upase A2has specificity for the middle fatty acid. Lipases are mainly produced in the aleurone layer. 

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