γ-Aminobutyric acid (GABA) priming enhances the osmotic stress tolerance in Piper nigrum Linn. plants subjected to PEG-induced stress

The pretreatment of two black pepper varieties, Panniyur 1 (drought-sensitive) and Panniyur 5 (drought-tolerant) with GABA (2 mM) influenced various physiological and biochemical parameters positively and the PEG (poly ethylene glycol 6000; 10 % w/v)-induced stress tolerance was increased in both varieties of black pepper. Although both varieties primed with GABA showed positive responses while encountering PEG-stress, Panniyur 5 showed better performance. When compared to non-primed plants induced with PEG-stress, GABA primed black pepper plants showed enhanced rate of leaf RWC and also a faster reduction of cell osmotic potential. Proline and total sugars were found to accumulate earlier in primed plants and the activity of antioxidant enzymes like guaiacol peroxidase and superoxide dismutase also increased significantly, in response to PEG-stress. When compared to non-primed plants, GABA priming resulted in a reduced rate of lipid peroxidation, and comparatively lesser inhibition of photosynthetic and mitochondrial activity (measured in terms of O-2 evolution/uptake) in primed plants during osmotic stress. Occurrence of GABA in plants of black pepper varieties was detected by HPTLC technique. In PEG-treated plants GABA content was higher than that of control; and a multifold enhancement of GABA was observed in black pepper plants subjected to PEG-stress, after priming with GABA.