Chitosan induces plant tolerance to various abiotic stresses, including water deficit. However, its use may be limited, due to its constitution and low solubility in water. Thus, chemical modifications were proposed in this study with the objective of potentializing its biological effects in maize plants. The derivatives were semi-synthesized (N-succinyl and N,O-dicarboxymethyl) and, together with chitosan, they were applied, via the leaf, in a drought-sensitive maize hybrid (BRS1030) under pre-flowering water deficit. The water deficit was maintained for 15 days and the analyses were performed at the beginning and end of stress, and also in rehydration. Leaf water potential, gas exchange, chlorophyll fluorescence, and content of chloroplastidic pigments were evaluated. The use of the derivatives modulated photosynthesis parameters, affecting the involved mechanisms, such as stomatal activity, water use efficiency and photosystem II activity. Chlorophyll fluorescence indicated that the antenna complex was damaged by the water deficit condition, with a decrease in the energy flux in the electron transport chain and in the photochemical phase of photosynthesis. However, the spraying of chitosan derivatives induced tolerance to water deficit, suggesting that chitosan derivatives are more bioavailable to plants. Water stress decreases pigment content, but both the application of chitosan and derivatives increased these contents. It is concluded that chitosan derivatives improved the photosynthetic parameters in maize susceptible to drought, inducing tolerance to this stress, and the possible reasons and consequences are discussed.

The present research seeks to elucidate the feasibility of chitosan (CHT) in the induction of water deficit tolerance in different maize hybrids, contrasting tolerance to water restriction, tolerance and sensitivity. The maize plants were subjected to water deficit and foliar application of different chitosan doses (60, 100, 140, and 180 mg L-1) at the pre-flowering growth stage and evaluated during the stress period of fifteen days. To understand the induction behaviour of the tolerance to water restriction, biophysical parameters, such as water potential, relative water content and chlorophyll content, gas exchange, and biochemical assays, were quantified based on the activity of SOD, CAT, APX, and PAL antioxidant enzymes, lipid peroxidation activity and hydrogen peroxide content. Among the treatments, maize plants subjected to chitosan foliar application at a dose of 140 mg L-1 presented similar behavioural responses to plants under favourable irrigation conditions. Such positive responses are related to the high degree of activity of antioxidant enzymes, gas exchange and low levels of lipid peroxidation and hydrogen peroxide. The results support the potential use of CHT to increase tolerance to water stress.

The spatial variability of the total chlorophyll content and carotenoids content, starch and soluble sugars of coffee canopy were mapped throughout the day. Therefore, evaluations were carried out in a ‘Catuaí Vermelho’ coffee plant with 1.7 meters height. A vertical gradient (from the apex to the base of the plant canopy) and a horizontal gradient (plagiotropic branches) were established to analyze different positions of the canopy. Thus, in the vertical direction, four heights were analyzed in the plant: top, upper, middle and lower regions. In the horizontal gradient, the plagiotropic branches were divided into three parts: basal, median and apical. Collection of leaf samples was performed on the east and west sides of the canopy, at 9 a.m., totaling 24 collection points at each time. Higher content of photosynthetic pigments and concentration of sugars were observed in the western face and in the inner parts of the coffee tree. The content of chloroplast pigments and sugars of an individual coffee leaf diverge considerably from other leaves, which requires caution when scaling estimates at the global canopy level. The analysis of some punctual leaves does not serve to discriminate the overall dynamics of a canopy.

Agricultural species are subjected to a variety of biotic and abiotic stresses, which are the main limitations to crop production. In this context, contamination by trace elements is characterized as an abiotic stress that represents an environmental problem. Due to the physical and chemical similarities between cadmium and zinc, these elements may interact in the environment and may cause antagonistic or synergistic effects. In this way, physiological mechanisms to exclude, detoxify or compartmentalize trace elements that are in excess are crucial for plant survival when exposed to high concentrations of these elements. In this way, the aim of this study was to understand the physiological responses of Phaseolus vulgaris plants subjected to increasing doses of Cd and Zn for 21 days in different soil, Cambisol and Latosol. The activity of antioxidant enzymes, such as SOD, CAT, and APX; hydrogen peroxide content; lipid peroxidation; chlorophyll index; photosynthetic rate; stomatal conductance; and transpiration were analysed. The data obtained showed a specific behaviour of Phaseolus vulgaris plants in each soil analysed. Moreover, it was observed that interactions between both elements resulted in a synergistic effect, negatively affecting all of the parameters analysed.

– This study associated data of performance, gas exchange and morphometric analysis of the root system using the WinRhizo software. The main objective was to verify how the modifications in the root system contribute to maintain the photosynthetic rates and productivity in sorghum hybrids divergent regarding tolerance to water deficit. The 1G 282 tolerant hybrid presented higher tolerance to desiccation of the leaves, higher grain productivity (68.33%) and maintained its photosynthetic rate 2.13 times higher compared to the sensitive BRS 332 during the water deficit. Both hybrids presented responses related to desiccation prevention, characterized by modifications of the root system that are capable to benefit absorption of water and nutrients under stress. Besides, 1G 282 showed more developed and responsive root system, especially due to a higher superficial area of very fine roots (42.67%), volume of fine roots (36.90%) and very fine roots (53.18%) under water deficit when compared to the sensitive BRS 332 at the same conditions.Keywords: Sorghum bicolor, roots, WinRhizo, photosynthesis. MODIFICAÇÕES DO SISTEMA RADICULAR, TROCAS GASOSAS E PRODUTIVIDADE EM HÍBRIDOS DE SORGO CULTIVADOS SOB DÉFICIT HÍDRICO  RESUMO – O estudo em questão associou dados de rendimento, trocas gasosas e morfometria do sistema radicular utilizando o software WinRhizo. O principal objetivo foi verificar como modificações do sistema radicular contribuem para a manutenção da taxa fotossintética e produtividade em híbridos de sorgo divergentes para tolerância ao déficit hídrico (WD), sendo um tolerante (1G 282) e outro sensível (BRS 332). O híbrido tolerante 1G 282 apresentou maior tolerância à desidratação do tecido foliar, além de manter uma taxa fotossintética 2,13 vezes maior e maior rendimento de grãos (68,33%) em relação ao sensível BRS 332 durante o WD. Ambos os híbridos apresentaram respostas de prevenção à seca, caracterizada por modificações do sistema radicular capazes de favorecer a absorção de água na condição de estresse. No entanto,1G 282 demonstrou possuir um sistema radicular mais desenvolvido e responsivo, especialmente por exibir maior área superficial de raízes muito finas (42,67%) e volume de raízes finas (36,90%) e muito finas (53,18%) em condição de WD, quando comparado com o sensível BRS 332 nas mesmas condições de cultivo.Palavras-chave: Sorghum bicolor, raízes, WinRhizo, fotossíntese.

Water stress is among the most severe abiotic stress factors for maize production. The application of chitosan causes various responses in plants, as a function of its structure and concentration. Therefore, chemical modifications were proposed in this study to enhance the biological effects on plants. Hybrid maize plants with drought-contrasting characteristics, were subjected to water deficit and spraying with chitosan (CHI) and semi-synthesized chitosan derivatives, N‑Succinyl (SUC) and N,O‑Dicarboxymethyl (MCA). The obtained data show that the application of CHI and its derivatives (0.5 mg.plant-1) led to an increase in production for the two evaluated hybrids in comparison with the control under stress. Regarding leaf gas exchange, over the stress period, it was observed that the application of the MCA derivative yielded greater Pn than the other treatments in plants subjected to drought, in both hybrids. In the evaluation of chlorophyll content, there was an increase in this content through the application of CHI and its derivatives for both maize hybrids under study. With water recovery in plants, the water potential (Ψmd) of those treated with chitosan derivatives was greater than that of the irrigated control plants. In the quantification of proline concentration, higher values were observed in plants treated with MCA derivatives for the drought-sensitive hybrid. Chitosan derivatives, SUC and MCA, were responsible for higher starch concentrations in both maize hybrids. Evaluating the morphological characteristics of roots, the drought-tolerant hybrid showed higher means for all parameters evaluated when subjected to drought, and MCA was responsible for longer root length and greater mean root diameter. The results support the potential use of chitosan and its derivatives to increase tolerance to water deficit in maize

Low water availability is characterized as an abiotic stressthat limits the agricultural production. Due to the physical and chemicalcharacteristics of the chitosan (CHT), this substance might stimulatephysiological responses on plants to tolerate the water deficit. In this sense,we submitted corn plants to water deficit and application of chitosan on theleaves (140 mg/L) during pre flowering stage. It were analyzed two cornhybrids genotypes contrasting for water deficit tolerance: DKB 390 (tolerant)and BRS1010 (sensitive). Then, we performed evaluations on the rootsystem and production components. Corn plants submitted to the applicationof chitosan presented a specific behavior: when compared the hybrids,the tolerant one presented a root system that was more developed and anexpressive agronomical yield. These results highlight the fact that the chitosanstimulates plant growth, enhancing their root system and contributing toincrease the availability and absorption of water and nutrients. The chitosanpresents a potential to reduce the negative effects of water deficit on the rootsystems, without compromising the agronomical yield.

-Contamination with trace elements is characterized by an abiotic stress that represents a limiting factor in agricultural production. Considering that cadmium (Cd) and Zinc (Zn) are physically and chemically similar, they can interact with the environment, causing antagonistic or synergistic effects. In this sense, physiological mechanisms to exclude, detoxify or compartmentalize the excess of those trace elements is crucial for the survival of the plants under conditions of high concentrations of these elements. In order to understand the responses of the species sensible to the presence of Cd and Zn, this study aimed to access the behavior of maize plants (Zea mays L.) cultivated in Cambisoils and Latosol with growing concentrations of Cd/Zn in a 21 days period. Growth and biochemical analyzes were performed such as antioxidant enzyme SOD, CAT and APX activity, hydrogen peroxide and lipid peroxidation. The data obtained evidenced the specific behavior of maize plants grown in Cambisoils compared to Latosol, showing a superior activity of all the enzymes analyzed, and also a lower content of hydrogen peroxide and lipid peroxidation. The interaction between both the elements resulted in a synergistic effect, negatively influencing all the analyzed parameters. Keywords: trace elements, antioxidant enzymes, ROS, synergistic. CRESCIMENTO E RESPOSTAS BIOQUÍMICAS DE PLANTAS DE MILHO CULTIVADAS EM SOLOS MULTICONTAMINADOS COM CÁDMIO E ZINCORESUMO -A contaminação por elementos traço caracteriza-se como um estresse abiótico que representa um fator limitante para a produção agrícola. Em função das semelhanças físicas e químicas entre cádmio (Cd) e zinco (Zn), esses elementos podem interagir no ambiente, podendo causar efeitos antagônicos ou sinérgicos. Nesse sentido, mecanismos fisiológicos para excluir, desintoxicar ou compartimentalizar o excesso de elementos traço são cruciais para sobrevivência dos vegetais quando expostos a elevadas concentrações desses elementos. A fim de compreender melhor as respostas de espécies sensíveis à presença de Cd e Zn, o presente estudo teve como objetivo avaliar o comportamento de plantas de milho (Zea mays L.) cultivadas em Cambissolo e Latossolo contendo concentrações crescentes de Cd/Zn. As plantas foram expostas a doses crescentes de Cd/Zn, por um período de 21 dias. Foram realizadas análises de crescimento e análises bioquímicas tais como, atividade das enzimas antioxidantes SOD, CAT, APX, assim como a quantificação do peróxido de hidrogênio e peroxidação lipídica. Os dados obtidos evidenciaram comportamento específico das plantas de milho cultivadas em Cambissolo, quando comparado ao Latossolo, apresentando uma atividade superior, em todas as enzimas analisadas, e um menor conteúdo de peróxido de hidrogênio e peroxidação lipídica. Observou-se que a interação entre ambos os elementos resultou em um efeito sinérgico, afetando negativamente todos os parâmetros analisados. Palavras-chave: elementos-traço, enzimas antioxidantes, EROs, sinergismo.