_________________________________________________________ Journal of Experimental Biology and Agricultural Sciences http://www.jebas.org KEYWORDS Groundnut (Arachis hypogaea L.) Proline metabolism Quaternary ammonium compounds Drought tolerance Chlorophyll stability Relative water content Water stress ABSTRACT A comparative study was carried out for two groundnut cultivars (cv K-134 and cv JL-24, drought tolerant and drought sensitive, respectively) during water stress at different soil moisture levels [100 (control), 75, 50 and 25%]. The free proline content, activities of pyrroline-5-carboxylate reductase (P- 5-CR), proline oxidase, proline dehydrogenase (PDH) along with levels of quaternary ammonium compounds, leaf relative water content and chlorophyll stability were investigated. Water stress resulted in a significant accumulation of free proline content in leaves of both groundnut cultivars. However cv K-134 accumulated relatively higher amounts of proline than cv JL-24. Water stress resulted 2.5 fold higher accumulation of proline in cv K-134 and 2.0 fold in cv JL-24 on day-5 at 25% SMLs. Furthermore, the tolerant cv K-134 shows a greater activity of pyrroline-5-carboxylate reductase and lesser inhibition of proline oxidase and proline dehydrogenase than susceptible cv JL-24. The greater proline levels were due to both the higher rates of proline synthesis and lower rate of proline oxidation in cv K-134 compared to cv JL-24. Results of this study indicated that water stress altered the proline metabolism and this alternation was significantly varied between the cultivars. Further, drought tolerance of cv K-134 can be justified by the higher accumulation of quaternary ammonium compounds (glycine betaine) which helps in the maintenance of leaf relative water content and higher chlorophyll stability during water stress as compared to cv JL-24. Abbreviations: SMLs: soil moisture levels; P-5-CR: pyrroline-5-carboxylate reductase; PDH: proline dehydrogenase; QACs: quaternary ammonium compounds; CSI: chlorophyll stability index; RWC: relative water content; DCPIP: dichloro phenol indophenol; EDTA: ethylene diamine tetra acetic acid. Ranganayakulu G S 1,* , Chinta Sudhakar 2 and Sivakumar Reddy P 3 1 Department of Botany, Rayalaseema University, Kurnool-518002, India 2 Department of Botany, Sri Krishnadeveraya University, Anantapur- 515 003, India 3 Department of Botany Yogi Vemana University, Kadapa-516003, India Received – December 14, 2014; Revision – January 07, 2015; Accepted – February 24, 2015 Available Online – February 24, 2015 EFFECT OF WATER STRESS ON PROLINE METABOLISM AND LEAF RELATIVE WATER CONTENT IN TWO HIGH YIELDING GENOTYPES OF GROUNDNUT (Arachis hypogaea L.) WITH CONTRASTING DROUGHT TOLERANCE E-mail: gsranganaayakulu@gmail.com (Ranganayakulu GS) Peer review under responsibility of Journal of Experimental Biology and Agricultural Sciences. * Corresponding author Journal of Experimental Biology and Agricultural Sciences, February - 2015; Volume – 3(1) Journal of Experimental Biology and Agricultural Sciences http://www.jebas.org ISSN No. 2320 – 8694 Production and Hosting by Horizon Publisher (www.my-vision.webs.com/horizon.html). All rights reserved.