Effects of iso-osmotic NaCl and mannitol on growth, proline content, and antioxidant defense in Mammillaria gracilis Pfe
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YSIOLOGY
Effects of iso-osmotic NaCl and mannitol on growth, proline content, and antioxidant defense in Mammillaria gracilis Pfeiff. in vitro-grown cultures Biljana Balen & Mirta Tkalec & Tea Rogić & Matija Šimac & Petra Peharec Štefanić & Sanda Rončević & Lovorka Pitarević Svedružić & Marijana Krsnik-Rasol
Received: 23 November 2012 / Accepted: 11 April 2013 / Published online: 26 April 2013 / Editor: John Chen # The Society for In Vitro Biology 2013
Abstract Effects of iso-osmotic concentrations of NaCl and mannitol were studied in Mammilaria gracilis (Cactaceae) in both calli and tumors grown in vitro. In both tissues, relative growth rates were reduced under osmotic stress, which were accompanied by a decrease in both tissue water and K+ content. However, growth was inhibited to a lesser extent after exposure to NaCl, when accumulation of Na+ ions was observed. In calli, only salinity increased proline content, whereas with tumors proline accumulated after both osmotic stresses. Osmotic stresses also induced oxidative damage in both cactus tissues, although higher oxidative injury was caused by mannitol in calli and by salt in tumors. Low isoosmotic concentrations of NaCl (75 mM) and mannitol (150 mM) increased peroxidase, ascorbate peroxidase, and esterase activities, whereas elevated catalase activity was recorded only after mannitol treatment in both tissues. High osmotic stress generally decreased enzymatic activities. However, in calli, esterase activity increased in response to high salinity, whereas ascorbate peroxidase activity was B. Balen (*) : T. Rogić : M. Šimac : P. P. Štefanić : M. Krsnik-Rasol Department of Molecular Biology, Division of Biology, Faculty of Science, University of Zagreb, Horvatovac 102a, 10 000 Zagreb, Croatia e-mail: [email protected] M. Tkalec Department of Botany, Division of Biology, Faculty of Science, University of Zagreb, Rooseveltov trg 6, 10 000 Zagreb, Croatia S. Rončević : L. P. Svedružić Laboratory of Analytical Chemistry, Department of Chemistry, Faculty of Science, University of Zagreb, Horvatovac 102a, 10000 Zagreb, Croatia
enhanced after high mannitol stress. In conclusion, both in vitro-grown cactus tissues were found to be sensitive to osmotic stress caused by either mannitol or NaCl, but accumulation of Na+ ions in response to salt somewhat contributed to osmotic adjustment. However, more prominent oxidative damage induced by NaCl compared to mannitol in tumor could be related to ion toxicity. The mechanisms that mediate responses to salt- and mannitol-induced osmotic stresses differed and were dependent on tissue type. Keywords Cactus . Salt . Mannitol . Callus . Tumor
Introduction Abiotic stresses can severely limit crop plant production. Such stresses include extreme variations in temperature, irradiation, nonoptimal levels of minerals, and water shortages. The two most important environmental factors that reduce plant productivity are drought and salinity, especially in arid and semiarid regions where fresh water is scarce and the use of saline wate
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