ORIGINAL PAPER c-Aminobutyric acid (GABA) priming enhances the osmotic stress tolerance in Piper nigrum Linn. plants subjected to PEG-induced stress K. Vijayakumari 1 • Jos T. Puthur 1 Received: 17 November 2014 / Accepted: 28 April 2015 Ó Springer Science+Business Media Dordrecht 2015 Abstract The pretreatment of two black pepper varieties, Panniyur 1 (drought-sensitive) and Panniyur 5 (drought- tolerant) with GABA (2 mM) influenced various physio- logical and biochemical parameters positively and the PEG (poly ethylene glycol 6000; 10 % w/v)-induced stress tol- erance was increased in both varieties of black pepper. Although both varieties primed with GABA showed posi- tive 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 sig- nificantly, in response to PEG-stress. When compared to non-primed plants, GABA priming resulted in a reduced rate of lipid peroxidation, and comparatively lesser inhi- bition of photosynthetic and mitochondrial activity (mea- sured 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. Keywords Antioxidation Á GABA Á PEG Á Osmolytes Á Photosystem Á RWC Abbreviations GABA c-aminobutyric acid PEG Poly ethylene glycol RWC Relative water content MDA Malondialdehyde GPX Guaiacol peroxidase SOD Superoxide dismutase ROS Reactive oxygen species PS I Photosystem I PS II Photosystem II HPTLC High performance thin layer chromatography OP Osmotic potential Introduction Among various abiotic stresses, drought is the most severe stress that limits growth and yield of the crops under field conditions. On inadequate water conditions, crop plants undergo various physiological, biochemical and molecular changes viz. enhanced ABA synthesis, stomatal closure, reduced rate of cell growth and photosynthesis, increased respiration, loss of relative water content (RWC), increased root:shoot ratio, degradation of photosynthetic pigments and apparatus, higher rates of lipid peroxidation due to ROS production, increased accumulation of osmolytes and stress related proteins etc. (Shinozaki and Yamaguchi- Shinozaki 2007; Pyngrope et al. 2013). In order to combat Electronic supplementary material The online version of this article (doi:10.1007/s10725-015-0074-6) contains supplementary material, which is available to authorized users. & Jos T. Puthur jtputhur@yahoo.com 1 Plant Physiology and Biochemistry Division, Department of Botany, University of Calicut, C. U. Campus P.O., Malappuram 673635, Kerala, India 123 Plant Growth Regul DOI 10.1007/s10725-015-0074-6