Seeds of Cassia angustifolia Vahl. were subjected to 0, 20, 50, 100 mM NaCl for 7 d in order to study the effect of salt stress on growth parameters, endogenous Na + and Clconcentrations, antioxidant system, lipid peroxidation, hydrogen peroxide, and proline contents. Salinity affected all of the considered parameters and caused a great reduction in plant biomass. The root and shoot length, fresh and dry mass and germination percentage were inhibited by NaCl treatments. These changes were associated with an increase in the Na + and Clcontents in the seedlings and increased activities of superoxide dismutase, catalase, peroxidase, and polyphenol oxidase. The increased enzyme activity coincided with decreased ascorbate content and enhanced H 2 O 2 and proline content.
Cassia auriculata L. seedlings were irradiated with ultraviolet B (UV-B) in an environment-control chamber. The two doses assayed (7.5 and 15.0 kJ m -2 ) induced oxidative damage with an increase in lipid peroxidation and hydrogen peroxide and a decrease in chlorophyll and total phenol contents. The ascorbate and dehydroascorbate content as well as the reduced glutathione/oxidized glutathione content and ratio were significantly increased. The UV-B stress led to significant increases of the activity of superoxide dismutase, catalase, peroxidase and polyphenol oxidase. It is suggested that Cassia seedlings try to counteract high concentrations of oxygen species produced under UV-B stress through a co-ordinated increase in the contents and activities of antioxidants involved in their detoxification.
The purpose of the present work was to evaluate both the antioxidant response system and oxidative stress in leaves from bitter gourd (Momordica charantia L) subjected to NaCl, UV-B and water stresses at three different stages of plant growth: pre-flowering, flowering and post-flowering. Except for peroxidase (POX), all enzyme activities including superoxide dismutase (SOD), catalase (CAT), polyphenol oxidase (PPO), glutathione reductase (GR), as well as concentrations of ascorbate (ASA), hydrogen peroxide (H 2 O 2 ) and thiobarbituric acid reactive substances (TBARS) exhibited maximum values at the flowering stage under all three stresses. All the enzyme activities, SOD, CAT, POX, PPO, GR and the concentrations of ASA, H 2 O 2 and TBARS were elevated under NaCl and UV-B stresses at all growth stages with the exception of H 2 O 2 concentration at the post-flowering stage under UV-B radiation. Greater quantities of the inorganic ions Na + and Cl -were accumulated at all growth stages under salt stress. Drought led to decreases in the concentrations of H 2 O 2 , ASA and activities of PPO and GR; conversely, it led to elevated concentrations of TBARS and activities of SOD, CAT, POX at all three stages in comparison with control values. The POX activity at the third stage was, however, reduced. The photosynthetic pigments decreased at all stages under all stresses. The chlorophyll stability index decreased under NaCl stress, accelerated only at the post-flowering stage under UV-B radiation and significantly increased at pre-and post-flowering stages under water stress. The protein concentration under NaCl stress decreased except at the pre-flowering stage and under UV-B and water stresses the protein concentration was higher than that of the control and NaCl treatment. It is suggested that M. charantia exhibits a protection mechanism against oxidative damage by maintaining a highly induced antioxidant system under all three stresses. Key words: antioxidative enzymes, environmental stresses, H 2 O 2 , ion concentration, thiobarbituric acid-reactive substances Estímulo do sistema antioxidativo e peroxidação de lipídios causados por estresses abióticos em folhas de Momordica charantia: O objetivo deste trabalho foi avaliar as respostas do sistema antioxidativo e o estresse oxidativo em folhas de plantas de Momordica charantia L. submetidas a NaCl, radiação UV-B e déficit hídrico, em três estádios de crescimento: pré-floração, floração e pós-floração. Com exceção da peroxidase (POX), as atividades das enzimas dismutase do superóxido (SOD), catalase (CAT), oxidase de polifenóis (PPO) e redutase da glutationa (GR), assim como as concentrações de ascorbato (ASA), H 2 O 2 e de substâncias reativas ao ácido tiobarbitúrico (TBARS) foram máximas no estádio de floração, independentemente do tipo de estresse aplicado. As atividades das enzimas e dos metabólitos supramencionados forma maiores sob estresses associados ao NaCl e à radiação UV-B em todos os estádios de crescimento, exceto a concentração de H 2 O 2 , que foi maior ...
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