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ABSTRACT:Hydrogen peroxide (H 2 O 2 ) is an essential signaling molecule that mediates plant responses against several biotic and abiotic stresses. H 2 O 2 pretreatment has emerged as a signaling way, inducing salt stress acclimation in plants. Here, we analyzed the effects of H 2 O 2 leaf pretreatment on the non-enzymatic defense system (ascorbate and glutathione), plant growth, relative water content (RWC), relative chlorophyll content, H 2 O 2 content, and gas exchange in maize plants under NaCl stress. The results showed that salinity reduced the leaf area and shoot and root dry mass as compared to control, and the leaf spraying with H 2 O 2 significantly improved the growth of salt stressed plants. Photosynthesis and transpiration, stomatal conductance and intercellular CO 2 concentration were strongly decreased by salinity after 7 and 14 days of salt exposure; however, the decrease was lower in plants sprayed with H 2 O 2 . The improved gas exchange in H 2 O 2 -sprayed stressed plants correlated positively with higher RWC and relative chlorophyll content and lower leaf H 2 O 2 accumulation under NaCl stress conditions. Ascorbate and glutathione did not play any obvious effects as non-enzymatic antioxidants in the ROS scavenging. In conclusion, the salt tolerance induced by H 2 O 2 leaf pretreatment is attributed to a reduction in the H 2 O 2 content and maintenance of RWC and chlorophyll in maize leaves. These characteristics allow maize plants to maintain high rates of

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.

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Hydrogels (polyacrylamide compounds) are recommended in agriculture and forestry as soil conditioners because they are able to absorb water and increase its stocks in the soil. The aim of this study was to determine the most suitable dose of hydrogel to establish seedlings of Enterolobium contortisilliquum (Vell.) Morong under two levels of luminosity. Seedlings of Enterolobium contortisilliquum (Vell.) Morong were planted in pots, following a design of subdivided plots, consisting of two levels of luminosity in the plots: full sun and 50% luminosity, and 10 doses of hydrogel in the sub-plots: 0.0, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5 and 6.0 g L-1. Seventy-two days after the seedlings were transplanted to the pots, plant height and diameter were determined, together with the height to diameter ratio, root length and diameter, shoot and root dry weight, and the shoot to root ratio. The lowest ratios between height and stem diameter (8.50 and 8.68) occurred in the seedlings in full sun at the doses of 0 and 2 g hydrogel L-1 respectively. For shaded seedlings the lowest ratio (8.14) occurred at the dose of 3.0 g L-1, but with a lower coefficient of determination (R2 = 0.68). Shoot dry weight increased with the dose of 2 g L-1 in full sun, and 3.5 g L-1 under shaded conditions. The doses of hydrogel giving the best initial development in seedlings under evaluation were 2 g L-1 in full sun and 3.5 g L-1 in the shaded environment. Although a response by the species to the doses of hydrogel was found, the benefits of the polymer were not evident under the conditions of the present study.

Crescimento foliar e atividades das enzimas antioxidativas em plântulas de girassol suplementadas com percolado de aterro sanitário e submetidas a estresse hídrico RESUMOEm regiões áridas ou semiáridas, a escassez hídrica tem sido um dos principais fatores limitantes da produção agrícola. Diante disso, o presente trabalho objetivou analisar os efeitos da aplicação de percolado de aterro sanitário no crescimento foliar (número de folhas e área foliar) e as atividades das enzimas antioxidativas: superóxido dismutase (SOD), catalase (CAT), peroxidase do ascorbato (APX) e peroxidase do guaiacol (GPX) em folhas e raízes de plântulas de girassol submetidas às condições de estresse hídrico. O delineamento experimental foi o inteiramente casualizado, disposto em arranjo fatorial dois (irrigadas ou não irrigadas) x quatro (areia; areia + adubo orgânico 100 kg N ha -1 ; areia + percolado de aterro sanitário 100 kg N ha -1 ; areia + percolado de aterro sanitário 150 kg N ha -1 ), com cinco repetições. Em relação aos parâmetros foliares, o tratamento 100 kg N ha -1 suplementado com percolado de aterro sanitário obteve os melhores incrementos no número de folhas e área foliar. Além disso, verificaram-se aumentos nas atividades das enzimas antioxidativas em folhas e raízes de plântulas de girassol suplementadas com percolado de aterro sanitário, sendo provável que as reduções dos efeitos deletérios do estresse hídrico nas variáveis foliares dos tratamentos suplementados com percolado de aterro sanitário tenham ocorrido em virtude das maiores atividades das enzimas antioxidativas, especialmente as da CAT nas folhas e GPX nas raízes. Rev. Ambient. Água vol. 12 n.

One effect of the tidal dynamics is the accumulation during the low tide of large volumes of macroalgae, named “arribadas algae”. The objective of this work was to analyze the effects of using arribada alga e organic residues (AAOR) on the initial growth of sunflower plants, where the following were evaluated: plant growth, relative chlorophyll content and inorganic solids content (Na, K, Cl and NO3). The algae were collected on Praia do Pacheco in Caucaia, state of Ceará, Brazil, washed in running water and placed to dry in the sun for seven days, then dried in a forced circulation oven at 80 ºC and crushed. The sunflower seeds were sown in 5L plastic buckets, containing: 1) 100% (in volume) of sand; 2) sand + 100% of nitrogen recommendation - NR in commercial fertilizer (80kg of N.ha-1); 3) sand + 50% of the NR in macroalgae; 4) sand + 100% of NR in macroalgae; and 5) sand + 150% of the NR in macroalgae. The use of AAORimproved the growth of the analyzed variables in relation to the plants grown in substrate with sand or sand + fertilizer. The best results were observed at 50% of the NR in AAOR. The addition of increasing concentrations of AAOR allowed a greater accumulation of beneficial ions such as K and NO3 while no significant differences were observed for toxic ions such as Na and Cl in relation to plants supplemented with fertilizer or sand. The use of AAOR in substrates can be an alternative to fertilizers in plant cultivation since it reduces production costs besides being a sustainable destination.