ABSTRACT Heavy metal toxicity in plants lead to accumulation of reactive oxygen species (ROS). Antioxidant enzyme system is also not able to revert altered ROS homeostasis. The present study reports the heavy metal induced ROS toxicity by up-regulating the expression of key antioxidant enzyme genes through Brassinosteroids pre-soaking treatment in radish.

The present work was undertaken to study the effects of 24-epibrassinolide (0, 10-10, 10-8 and 10-6 M) on growth (shoot length and number of leaves), protein content and activities of antioxidative enzymes [guaiacol peroxidase (EC 1.11.1.7), catalase (EC 1.11.1.6), glutathione reductase (EC 1.6.4.2), ascorbate peroxidase (EC 1.11.1.11), superoxide dismutase (EC 1.15.1.1), monodehydroascorbate reductase (EC 1.1.5.4) and dehydroascorbate reductase (EC 1.8.5.1)] in leaves of 60 days-old Brassica juncea L. plants treated with different concentrations of Cr metal. It was observed that treatment of different concentrations (0, 0.5, 1.0, 1.5 and 2.0 mM) of Cr metal alone decreased the shoot length and number of leaves and regulated the enzyme activities and protein concentration of plants. However, seed-presoaking treatments of 24-epibrassinolide improved the growth and stimulated the activities of antioxidant enzymes and protein content in leaves of B. juncea plants thus indicating the stress-ameliorative properties of 24-epibrassinolide.

The present study determined the effects of copper and chromium metals on the endogenous titers of polyamines, auxins, abscisic acid and antioxidative enzyme activities in Raphanus sativus L. cv. Pusa chetki seedlings. Among polyamines, putrescine and spermidine contents were enhanced by Cu2+ metal to 62.44 and 402.8 µg g-1 f.w. respectively over control. Spermine which was not observed in control was recorded in highest concentration (1287.9 µg g-1 f.w.) in Cu2+ metal stressed seedlings. On the other hand Cr6+ metal treated seedlings showed reduced contents of putrescine (1.43 µg g-1 f.w.), cadaverine (0.09 µg g-1 f.w.), spermidine (277.99 µg g-1 f.w.) and spermine (2.29 µg g-1 f.w.) when compared to control and Cu2+ metal treated seedlings. Significant decline in free and bound IAA concentration were found under Cu2+ and Cr6+ metal stress when compared to control. Naphthalene acetic acid not recorded in control seedlings was detected in seedlings treated with Cu2+ and Cr6+ metal. Activities of guaiacol peroxidase and catalase were reduced significantly under Cu2+ and Cr6+ metal stress in comparison to control. Superoxide dismutase activity enhanced significantly under Cr6+ rather than Cu2+ metal treatment. In addition the phytotoxicity of Cu2+ and Cr6+ metal on seedling growth was also determined. The data suggest that Cr6+ is more phytotoxic than exposure to Cu2+ metal.

The effects of various conc of (10-11, 10-9 and 10-7 M) 24-epibrassinolide (24-epiBL) on polyamines and auxins contents was analyzed in 7days old seedlings of Raphanus sativus L. cv. Pusa chetki under copper metal stress. Cu metal (0.2mM) treatment significantly increased endogenous levels of putrescine, spermidine and spermine when compared with control values. Cadaverine content got decreased under metal stress. Endogenous polyamines showed varying levels in seedlings when applying 24-epiBL treatment only. Maximum increase was found in putrescine, cadaverine and spermidine in 10-11, 10-9 and 10-7 M conc of 24-epiBL respectively when applied alone to R. sativus seedlings. However, metal treatment supplemented with 24-epiBL revealed small increase in polyamines. Putrescine and cadaverine got enhanced in combination of Cu metal and 10-7 M (24-epiBL) in comparison to metal treatment alone, whereas decrease in spermidine and spermine levels were recorded in combinations of Cu metal and 10-9 and 10-7 M 24-epiBL respectively. Endogenous contents of Indole-3-acetic acid (IAA) and Naphthalene acetic acid (NAA) were significantly affected by 24-epiBL when applied alone or along with Cu metal. Both free and bound forms of NAA were not detected in untreated seedlings, but were recorded in seedlings treated with metal stress. Decreased IAA contents observed in metal treatment got enhanced significantly in seedlings with 24-epiBL supplementation. To the best of our knowledge the present investigation is the first one to explain the effects of 24-epiBL on endogenous contents of polyamines, indole acetic acid and naphthalene acetic acid under copper metal stress.

Efeitos do 28-homobrassinolídeo sobre o crescimento, absorção de zinco e atividades de enzimas antioxidativas em plântulas de Brassica juncea L.: O presente estudo foi conduzido para estudarem-se os efeitos do 28homobrassinolídeo sobre o crescimento, a absorção de zinco e a atividade de enzimas antioxidativas [peroxidases do guaiacol (EC 1.11.1.7), catalase (EC 1.11.1.6), redutase da glutationa, (EC 1.6.4.2), peroxidase do ascorbate (EC 1.11.1.11) e dismutase do superóxido (EC 1.15.1.1)] e concentração de proteínas em plântulas de Brassica juncea L. tratadas com Zn em diferentes concentrações, aos sete dias de idade. O brassinolídeo, à concentração de 10-9 M, reduziu a absorção de Zn e o fator de bioconcentração. O Zn, quando aplicado em diferentes concentrações, isoladamente, acarretou decréscimos nas atividades das enzimas e na concentração de proteínas. Contudo, o efeito do 28-homobrassinolídeo, aplicado antes da semeadura, reduziu a absorção do metal e fez aumentar as atividades das enzimas antioxidativas e a concentração de proteínas nas plântulas.

The present work was undertaken to study the effects of 28-homobrassinolide on growth, zinc metal uptake, antioxidative enzyme [guaiacol peroxidase (EC 1.11.1.7), catalase (EC 1.11.1.6), glutathione reductase (EC 1.6.4.2), ascorbate peroxidase (EC 1.11.1.11), superoxide dismutase (EC 1.15.1.1)] activities and protein content in 7-d-old seedlings of Brassica juncea L. treated with Zn metal at different concentrations. 28-homobrassinolide at 10-9 M concentration lowered Zn uptake and bioconcentration factor. Different concentrations of Zn-metal treatment alone decreased the enzyme activities and protein concentration of seedlings. However, pre-sowing treatments of 28homobrassinolide lowered the uptake of metal and enhanced the activities of enzymes and protein concentration of seedlings.