Resumo -Este trabalho teve como objetivo estudar os efeitos da aplicação foliar de H 2 O 2 no crescimento e nos teores de solutos orgânicos e inorgânicos de plantas de milho desenvolvidas sob condições salinas. O experimento foi conduzido em casa de vegetação, sob condições hidropônicas. Oito dias após a semeadura, as plântulas foram pulverizadas com água destilada (controle) ou solução aquosa de H 2 O 2 na concentração de 10 mM e, 48 h após o início da pulverização, foram submetidas ao tratamento com NaCl a 80 mM. Foram realizadas duas coletas, com 96 e 240 h do início da pulverização. O delineamento experimental foi o inteiramente casualizado, em um arranjo fatorial 2 (NaCl a 0 ou 80 mM) x 2 (H 2 O 2 a 0 ou 10 mM), com cinco repetições. Os dados de cada tempo de coleta (96 h ou 240 h) foram submetidos à análise de variância (ANOVA) e as médias comparadas pelo teste de Tukey (P ≤ 0,05). O pré-tratamento de pulverização das plantas de milho com H 2 O 2 induziu aclimatação das plantas de milho ao estresse salino, revertendo parcialmente os efeitos deletérios da salinidade no crescimento. Este efeito pode ser atribuído, pelo menos em parte, a um maior acúmulo de proteínas solúveis, carboidratos solúveis e NO 3 -, bem como a um menor acúmulo de íons tóxicos (Na + e Cl -) nas folhas.Palavras-chave -Aclimatação. Estresse salino. Peróxido de hidrogênio. Pré-tratamento. Zea mays.Abstract -The aim of this study was to evaluate the effects of foliar application of H 2 O 2 on plant growth and on the levels of organic and inorganic solutes in maize plants under salt stress. The experiments were conducted in a greenhouse under hydroponic conditions. Eight days after sowing, the seedlings were sprayed with a 10 mM H 2 O 2 solution or with distilled water (as a control). Forty-eight hours after the beginning of spraying, they were subjected to treatment with NaCl at 80 mM. Two harvests were carried out: 96 and 240 hours after the start of spraying. The experimental design was completely randomized following a factorial arrangment 2 (NaCl at 0 or 80 mM) x 2 (H 2 O 2 at 0 or 10 mM), with five replicates. The data for each harvest time (96 or 240 h) were submitted to analysis of variance (ANOVA) and the means were compared through Tukey's test (P ≤ 0.05).The results showed that foliar application of H 2 O 2 produced acclimation of the plants to salt stress, decreasing the deleterious effects of salinity on the growth of the maize. This effect can be attributed, at least partially, to a larger build up of proteins, and soluble carbohydrates and NO 3 -as well as lower levels of Cl -and Na + in the foliage.

The aim of this study was to evaluate the effects of H 2 O 2 on germination and acclimation of maize plants subject to salt stress. Three experiments using BRS3003 seeds, a triple hybrid of maize, were carried out in a growth room and in greenhouse. In the first experiment, H 2 O 2 accelerated the germination percentage of seeds at 100 mM, but not at 500 mM. In the second experiment, the pretreatment of seeds was observed to induce a pronounced increase in ascorbate peroxidase (APX) and catalase (CAT) enzyme activity after 30 h of soaking in H 2 O 2 . It was also observed that guaiacol peroxidase (GPX) activity was smaller in the seeds soaked in H 2 O 2 for 12, 24, 30, 36 and 42 h, in relation to those soaked in distilled water. The superoxide dismutase (SOD) activity was not affected by the pretreatment of seeds, except for the 24 h treatment. Only one CAT isoform was detected. In the third experiment, seeds were pretreated with 36 h soaking in 100 mM H 2 O 2 solution or in distilled water and later cultivated in Hoagland's nutrient solution or nutrient solution with 80 mM NaCl. The results showed the pretreatment of seeds with H 2 O 2 induced acclimation of the plants to salinity. It decreased the deleterious effects of salt stress on the growth of maize. In addition, the differences in antioxidative enzyme activities may explain the increased tolerance to salt stress of plants originated from H 2 O 2 pretreated seeds.

The effects of supplemental Ca 2? on membrane integrity and lipid composition of cowpea plants submitted to salt stress (75 mM NaCl) were evaluated. The experimental design was factorial (2 9 6 ? 1) corresponding to six saline treatments supplemented with CaCl 2 and six saline treatments supplemented with CaSO 4 , both at 0.5, 1.25, 2.5, 5.0, 7.5 and 10.0 mM, plus control treatment (plants grown in half-strength Hoagland's nutrient solution without supplemental calcium addition). Samples of leaves and root tips were analyzed for total lipid, glycolipid and fatty acid contents and membrane damage symptoms. Salt stress greatly reduced total lipid content in leaves and roots and caused great damage to membrane structures. In leaves, the glycolipid content was differently influenced by calcium treatments. Moreover, salinity increased the saturated/unsaturated fatty acid ratio in leaves and an increase in the concentration of calcium intensified this response. In roots, only saturated fatty acids were detected and their content was strongly influenced by salinity and very little by calcium treatments. Supplemental Ca 2? was unable to ameliorate the negative effects of salinity on the structural integrity and fluidity of plant membranes in cowpea.

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