Franklin Aragão Gondim

Catalase plays a key role in salt stress acclimation induced by hydrogen peroxide pretreatment in maize.

Pretreatment in plants is recognized as a valuable strategy to stimulate plant defenses, leading to better plant development. This study evaluated the effects of H₂O₂ leaf spraying pretreatment on plant growth and investigated the antioxidative mechanisms involved in the response of maize plants to salt stress. It was found that salinity reduced maize seedling growth when compared to control conditions, and H₂O₂ foliar spraying was effective in minimizing this effect. Analysis of the antioxidative enzymes catalase (EC 1.11.1.6), guaiacol peroxidase (EC 1.11.1.7), ascorbate peroxidase (EC 1.11.1.1) and superoxide dismutase (EC 1.15.1.1) revealed that H₂O₂ spraying increased antioxidant enzyme activities. Catalase (CAT) was the most responsive of these enzymes to H₂O₂, with higher activity early (48 h) in the treatment, while guaiacol peroxidase (GPX) and ascorbate peroxidase (APX) were responsive only at later stages (240 h) of treatment. Increased CAT activity appears linked to gene expression regulation. Lower malondialdehyde levels were detected in plants with higher CAT activity, which may result from the protective function of this enzyme. Overall, we can conclude that pretreatment with H₂O₂ leaf spraying was able to reduce the deleterious effects of salinity on seedling growth and lipid peroxidation. These responses could be attributed to the ability of H₂O₂ to induce antioxidant defenses, especially CAT activity.

Pretreatment with H2O2 in maize seeds: effects on germination and seedling acclimation to salt stress

The aim of this study was to evaluate the effects of H2O2 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, H2O2 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 H2O2. It was also observed that guaiacol peroxidase (GPX) activity was smaller in the seeds soaked in H2O2 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 H2O2 solution or in distilled water and later cultivated in Hoaglands nutrient solution or nutrient solution with 80 mM NaCl. The results showed the pretreatment of seeds with H2O2 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 H2O2 pretreated seeds.

Enhanced salt tolerance in maize plants induced by H2O2 leaf spraying is associated with improved gas exchange rather than with non-enzymatic antioxidant system

Hydrogen peroxide (H2O2) is an essential signaling molecule that mediates plant responses against several biotic and abiotic stresses. H2O2 pretreatment has emerged as a signaling way, inducing salt stress acclimation in plants. Here, we analyzed the effects of H2O2 leaf pretreatment on the non-enzymatic defense system (ascorbate and glutathione), plant growth, relative water content (RWC), relative chlorophyll content, H2O2 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 H2O2 significantly improved the growth of salt stressed plants. Photosynthesis and transpiration, stomatal conductance and intercellular CO2 concentration were strongly decreased by salinity after 7 and 14 days of salt exposure; however, the decrease was lower in plants sprayed with H2O2. The improved gas exchange in H2O2-sprayed stressed plants correlated positively with higher RWC and relative chlorophyll content and lower leaf H2O2 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 H2O2 leaf pretreatment is attributed to a reduction in the H2O2 content and maintenance of RWC and chlorophyll in maize leaves. These characteristics allow maize plants to maintain high rates of photosynthesis under salt stress and improve the growth.

Increased drought tolerance in maize plants induced by H2O2 is closely related to an enhanced enzymatic antioxidant system and higher soluble protein and organic solutes contents

Drought stress is one of the most important agricultural problems limiting development and growth in plants. Therefore, mechanisms to alleviate drought stress have been one of the major limiting factors in production. H2O2 pretreatment has emerged as a method to induce stress acclimation in plants. In this study, the effects of H2O2 leaf pretreatment on plant growth, antioxidative enzymes, soluble protein, and organic solute content in maize plants under conditions of drought stress were analyzed. Results demonstrated that drought stress reduced shoot and root mass compared with the control, and H2O2 leaf spraying significantly improved the growth of drought-stressed plants. In general, in drought-stressed plants, CAT, APX, GPX, and SOD activities in roots and leaves were increased by H2O2 leaf spraying relative to water spraying. GPX was the main H2O2-scavenging enzyme in leaves and roots, and CAT activity was not detected in the leaves of maize plants. Increased organic solute contents (proteins, carbohydrates, soluble proline, and amino acids) were found in the leaves and mainly in the roots of H2O2-stressed plants relative to water-stressed plants. In conclusion, it was found that H2O2 leaf spraying pretreatment reduced the deleterious effects of drought stress on maize plant growth. This treatment proved to be a beneficial health strategy in plants. This effect could be attributed to the ability of H2O2 to induce antioxidant defense system activity, particularly GPX, and to increase organic solute (protein, carbohydrate, proline, and free amino acid) content in roots and leaves.

Efeitos do H2O2 no crescimento e acúmulo de solutos em plantas de milho sob estresse salino

Este trabalho teve como objetivo estudar os efeitos da aplicacao foliar de H2O2 no crescimento e nos teores de solutos orgânicos e inorgânicos de plantas de milho desenvolvidas sob condicoes salinas. O experimento foi conduzido em casa de vegetacao, sob condicoes hidroponicas. Oito dias apos a semeadura, as plântulas foram pulverizadas com agua destilada (controle) ou solucao aquosa de H2O2 na concentracao de 10 mM e, 48 h apos o inicio da pulverizacao, foram submetidas ao tratamento com NaCl a 80 mM. Foram realizadas duas coletas, com 96 e 240 h do inicio da pulverizacao. O delineamento experimental foi o inteiramente casualizado, em um arranjo fatorial 2 (NaCl a 0 ou 80 mM) x 2 (H2O2 a 0 ou 10 mM), com cinco repeticoes. Os dados de cada tempo de coleta (96 h ou 240 h) foram submetidos a analise de variância (ANOVA) e as medias comparadas pelo teste de Tukey (P < 0,05). O pre-tratamento de pulverizacao das plantas de milho com H2O2 induziu aclimatacao das plantas de milho ao estresse salino, revertendo parcialmente os efeitos deleterios da salinidade no crescimento. Este efeito pode ser atribuido, pelo menos em parte, a um maior acumulo de proteinas soluveis, carboidratos soluveis e NO3-, bem como a um menor acumulo de ions toxicos (Na+ e Cl-) nas folhas.

SEEDLING GROWTH OF TREE SPECIES UNDER DOSES OF HYDROGEL AND TWO LEVELS OF LUMINOSITY

http://dx.doi.org/10.1590/1806-90882018000100012 ABSTRACT – 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. 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 respectively. For shaded seedlings the lowest ratio (8.14) occurred at the dose of 3.0 g L, but with a lower coefficient of determination (R = 0.68). Shoot dry weight increased with the dose of 2 g L in full sun, and 3.5 g L under shaded conditions. The doses of hydrogel giving the best initial development in seedlings under evaluation were 2 g L in full sun and 3.5 g L 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.

Effects of Different Concentrations of Organic Waste on Selected Traits of Individuals Capsicum Chinense Jacq.

At present, excessive waste production makes it necessary to carry out research aimed to minimize the problems arising from waste generation and inadequate disposal. In this sense, this study aimed to analyze plant growth, fruit production, antioxidative enzyme activities and organic solute contents in fruits of Capsicum chinense Jacq. plants (BRS Moema cultivar) growing in substrates with different concentrations of municipal organic solid waste (MW) or shrimp waste (SW) under greenhouse conditions. A completely randomized design was used with seven treatments (control; MW at 50, 100 and 200% of recommendation; and SW also at 50, 100 and 200%) and five replications. The MW and SW were mixed with the soil. When plants already had fruits, 122 days after sowing (DAS), shoot height, stem diameter and number of leaves were determined, and 134 DAS, the visibly ripe fruits were collected and stored at -20 °C for subsequent biochemical analysis. The MW and SW provided a linear increase in the parameters of shoot height, stem diameter and number of leaves. The numbers of fruits in the treatments were quite variable, but it can be concluded that the MW 200 and SW 100 treatments provided higher fruit production. The best results for the activities of catalase (CAT), ascorbate peroxidase (APX) and guaiacol peroxidase (GPX) in the fruits occurred in the MW 100 and SW 200 treatments. Both provided an increase in CAT and reductions in APX and GPX, which can contribute to greater postharvest life of C. chinense Jacq. fruits. In relation to soluble protein and carbohydrate contents, the MW 100 and SW 100 treatments did not contribute to their increase; in the other residue concentrations, the results were variable. However, considering all parameters analysed in this study, the most suitable treatments would be MW 100 and SW 100. Therefore, the results demonstrate the susceptibility of using substrates with MW and SW in the cultivation of C. chinense Jacq. plants.

CRESCIMENTO INICIAL DE DOIS CULTIVARES DE GIRASSOL EM CASA DE VEGETAÇÃO SOB CONDIÇÕES DE CLIMA TROPICAL QUENTE SUBÚMIDO

Este trabalho objetivou analisar o crescimento inicial de dois cultivares de girassol, ’BRS 323’ e ’BRS 324’, determinando-se: percentual de emergencia de plântulas do solo, numero de folhas, diâmetro dos caules e, as materias fresca e seca da parte aerea, das raizes e total. O trabalho foi conduzido em casa de vegetacao, localizada no Instituto Federal do Ceara, na cidade de Maracanau, Ceara, Brasil. As sementes dos cultivares ’BRS 323’ e ’BRS 324’ foram semeadas em vasos de plastico de 6 L preenchidos com humus de minhoca e vermiculita na proporcao de 1:1, com cinco repeticoes. Os resultados de diferentes periodos de coleta (14 e 21 dias) foram submetidos a analise de variância (ANOVA) e as medias comparadas pelo teste de Tukey (P ≤ 0,05). Nas condicoes experimentais empregadas, constatouse que o cultivar ’BRS 323’ apresentou uma melhor aclimatacao do que o ’BRS 324’. O ’BRS 323’ apresentou parâmetros de crescimento (percentual de emergencia de plântulas do solo, numero de folhas, diâmetro dos caules, materias fresca e seca da parte aerea, das raizes e total) mais elevados do que o ’BRS 324’. No entanto, estudos em campo fazem-se necessarios para confirmar uma possivel indicacao do cultivar ’BRS 323’ para regioes que apresentem condicoes climaticas semelhantes as empregadas.