ORIGINAL PAPER Salicylic acid mitigates salinity stress by improving antioxidant defence system and enhances vincristine and vinblastine alkaloids production in periwinkle [Catharanthus roseus (L.) G. Don] Mohd Idrees • M. Naeem • Tariq Aftab • M. Masroor A. Khan • Moinuddin Received: 4 February 2010 / Revised: 1 October 2010 / Accepted: 12 October 2010 Ó Franciszek Go ´rski Institute of Plant Physiology, Polish Academy of Sciences, Krako ´w 2010 Abstract A pot experiment was conducted to find out whether the foliar spray of salicylic acid (SA) could suc- cessfully ameliorate the adverse effects of salinity stress on periwinkle. Thirty-day-old plants were supplied with Control; 0 mM NaCl ? 10 -5 M SA (T 1 ); 50 mM NaCl ? 0 SA (T 2 ); 100 mM NaCl ? 0 SA (T 3 ); 150 mM NaCl ? 0 SA (T 4 ); 50 mM NaCl ? 10 -5 M SA (T 5 ); 100 mM NaCl ? 10 -5 M SA (T 6 ); 150 mM NaCl ? 10 -5 M SA (T 7 ). The plants were sampled 90 days after sowing to assess the effect of SA on stressed and unstressed plants. Salt stress significantly reduced the growth attributes including plant height, leaf-area index, shoot and root fresh weights, shoot and root dry weights. Increasing NaCl concentrations led to a gradual decrease in photosynthetic parameters and activities of nitrate reductase and carbonic anhydrase. Ascorbic acid, total alkaloids and antioxidants enzymes superoxide dismutase, catalase and peroxidase also declined in NaCl-treated plants. The plants, undergo- ing NaCl stress, exhibited a significant increase in elec- trolyte leakage and proline content. Foliar application of SA (10 -5 M) reduced the damaging effect of salinity on plant growth and accelerated the restoration of growth processes. It not only improved the growth parameters but also reversed the effects of salinity. Total alkaloid content was improved by SA application both in unstressed and stressed plants. The highest level of total alkaloid content recorded in leaves of SA-treated stressed plants was 11.1%. Foliar spray of SA overcame the adverse effect of salinity by improving the content of vincristine (14.0%) and vin- blastine (14.6%) in plants treated with 100 M NaCl. Keywords Ascorbic acid  Antioxidant  Catalase  Catharanthus roseus (L.) G. Don  Peroxidase  Salicylic acid  Salt stress  Vincristine  Vinblastine Abbreviations AA Ascorbic acid ACC 1-Aminocyclopropane-1-carboxylic acid LAI Leaf-area index NED-HCL N-(1-Naphthyl) ethylenediamine dihydrochloride OD Optical density PRO Proline ROS Reactive oxygen species SA Salicylic acid TCA Trichloroacetic acid Introduction Salinity is a major cause of decline in agricultural pro- ductivity and the increasing level of salt accumulation in Indian soils has become an exigent issue for the country. India has nearly about 9.38 million ha of salt-affected soil, in which 3.88 million ha are alkaline soil and 5.5 million ha (including coastal lands) are saline soil (Ravindran et al. 2007). Salt stress is known to perturb a multitude of physiological processes including photosynthesis and enzyme activities. It is one of the major environmental factors that limit the efficiency of photosynthesis due to Communicated by M. Rapacz. M. Idrees (&)  M. Naeem  T. Aftab  M. M. A. Khan  Moinuddin Plant Physiology Section, Department of Botany, Aligarh Muslim University, Aligarh 202 002, India e-mail: idrees.amu@gmail.com 123 DOI 10.1007/s11738-010-0631-6 Acta Physiol Plant (2011) 33:987–999 / Published online: 27 October 2010