Modulation of manganese toxicity in Pisum sativum L. seedlings by kinetin

In the present study, the effects of kinetin (KN; 10 and 100 mu M) application under manganese toxicity (Mn; 50, 100 and 250 mu M) were investigated, on growth, photosynthetic pigments, total protein, total nitrogen, ammonium (NH4+) content. NH4+ assimilating enzymes and antioxidant system in pea seedlings. The exposure of pea seedlings to Mn and 100 mu M of KN alone and in combination, caused decrease in growth, photosynthetic pigments, total protein and total nitrogen contents. and an increase in NH4+ content. However, application of 10 mu M of KN together with Mn reduced the Mn toxicity symptoms. promoted the growth of seedlings and led to the decrease in NH4+ content compared to Mn treatments alone. The root and shoot activities of glutamine synthetase (GS), glutamate oxoglutarate aminotransferase (GOGAT) and catalase (CAT) were decreased while glutathione reductase (GR) and dehydroascorbate reductase (DHAR) activities exhibited differential responses when pea seedlings were exposed to Mn and 100 mu M of KN. However, under similar treatments, activities of glutamate dehydrogenase (GM), superoxide dismutase (SOD) and ascorbate peroxidase (APX) in root and shoot were increased. It was noticed that addition of 10 mu M of KN together with Mn. caused significant stimulation in activities of enzymes of NH4+ assimilation and antioxidant defense system even over then respective control values Non-enzymatic antioxidants (ascorbate and glutathione) in root and shoot of pea seedlings exposed to Mn stress were significantly increased by the addition of 10 mu M of KN. Therefore, ameliorative effect of 10 mu M of KN against Mn toxicity was observed. This study thus suggests that 10 mu M of KN appreciably improves Mn tolerance of pea seedlings under Mn toxicity while reverse effects were exhibited by 100 mu M of KN. (C) 2010 Elsevier B.V. All rights reserved.