Insect attack-wound in plant cells stimulate huge number of signal molecules to induce and activate defense system. Among these one of the intracellular signal molecules are small peptide systemin (18AAs long) produced by proteolytic cleavage in wounded cells from prosystemin (200As) precursor protein. Systemin then bind to its SR-160 (Systemin Cell Surface Receptor) protein (160 kD) and activate phospholipase A2 (PLA-2) that releases linolenic acid, which is initial precursor for JA biosynthesis. Consequently JA induces expressions of many genes encoding defense related proteins and biologically functional molecules such as protease inhibitors, secondary metabolite etc. However, very less is known about how some peptides like systemin actually induces JA biosynthesis in wounded and healthy leaves. Like biotic stress, systemin may also be involved in abiotic stress tolerance.

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