Research has shown that chitosan induces plant stress tolerance and protection, but few studies have explored chemical modifications of chitosan and their effects on plants under water stress. Chitosan and its derivatives were applied (isolated or in mixture) to maize hybrids sensitive to water deficit under greenhouse conditions through foliar spraying at the pre-flowering stage. After the application, water deficit was induced for 15 days. Analyses of leaves and biochemical gas exchange in the ear leaf were performed on the first and fifteenth days of the stress period. Production attributes were also analysed at the end of the experiment. In general, the application of the two chitosan derivatives or their mixture potentiated the activities of the antioxidant enzymes superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase and guaiacol peroxidase at the beginning of the stress period, in addition to reducing lipid peroxidation (malonaldehyde content) and increasing gas exchange and proline contents at the end of the stress period. The derivatives also increased the content of phenolic compounds and the activity of enzymes involved in their production (phenylalanine ammonia lyase and tyrosine ammonia lyase). Dehydroascorbate reductase and compounds such as total soluble sugars, total amino acids, starch, grain yield and harvest index increased for both the derivatives and chitosan. However, the mixture of derivatives was the treatment that led to the higher increase in grain yield and harvest index compared to the other treatments. The application of semisynthetic molecules derived from chitosan yielded greater leaf gas exchange and a higher incidence of the biochemical conditions that relieve plant stress.

The aim of the present research was to verify the in vitro growth of orchids in different systems of micropropagation, being cultivated in a bioreactor

ABSTRACT:Micropropagation is an alternative to produce orchid plants in large scale. However, this process presents losses during acclimatization. Exogenous proline use in vitro plant tissue culture can reduce the stress of the plant acclimatization phase. We aimed to verify the growth of orchids in different micropropagation systems with the addition of proline in the culture medium. Cattleya walkeriana plants were obtained from the germination of seeds in culture medium. Seeds were germinated in MS medium, added 20 g. L -1 of sucrose, solidified with 6 g. L -1 of agar and pH adjusted for 5,8. The cultures were incubated in a growth room with temperature of 24 ± 2 0 C, under photoperiod of 16 h. After 5 months, 1-cm long seedlings were placed in a culture vessel according to the treatments, which were composed of two micropropagation systems (conventional and natural ventilation) and three proline concentrations (0, 1, and 2 g·L -1 ). The experiment was carried out in an entirely randomized design consisting of a 2 × 3 factorial, for a total of 6 treatments, each with 5 replicates. The natural ventilation system with the use of proline (1 g·L -1 ) promoted higher dry mass accumulation and better control of water loss by plants.

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 objective of this study was to evaluate the the ability of foliar application of potassium nitrate (KNO3) to induce water deficit tolerance in sorghum plants (Sorghum bicolor cv. P898012) subjected to water deficit at pre-flowering. The experiment was conducted under greenhouse conditions with 4 treatments: field capacity (FC), water deficit (WD), field capacity + KNO3 (FC + KNO3), and water deficit + KNO3 (WD + KNO3). Two foliar applications of 3% (m/v) KNO3 were made, the first on day zero of stress and the second on the fifth day. All analyses were performed after 12 days of stress (end of stress). Foliar application of KNO3 to irrigated plants led to increases in relative chlorophyll content, photosynthetic rate, stomatal conductance, transpiration, and carboxylation efficiency. It also induced increases in leaf concentrations of P, Mg, S, Cu, and Fe, in addition to height growth. Under water deficit conditions, plants treated with KNO3 presented higher relative chlorophyll content, leaf area, photosynthetic rate, stomatal conductance, transpiration, carboxylation efficiency, and higher levels of P, K, Mg, S, Cu, and Fe than those not treated with KNO3. The morphometry of the root system was not altered by the treatments. In addition, plants treated with KNO3 under water deficit conditions showed higher growth and a grain yield 32.2% higher than those that did not receive KNO3. These results demonstrated that KNO3 applied to the leaves induced water deficit tolerance in sorghum plants subjected to severe water stress at pre-flowering.

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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

Ornamental pineapple is a hard plant with significant landscaping value. Typically, conventional propagation is performed by clump division with low yields, and may even spread diseases. Plant tissue culture is viable, yielding plants with a high phytosanitary and genetic quality over a short time period. This study aimed to verify the in vitro multiplication of ornamental pineapple plants (Ananas comosus var. bracteatus L.) in different micropropagation systems, in association with BAP concentrations. Plants with about 2 cm were used, transplanted to the different treatments: bioreactor, natural ventilation and conventional micropropagation, combined with 3 BAP concentrations (0, 1 and 2 mg L-1). The basic medium used consisted of MS salts. The highest number of shoots and in vitro culture growth were obtained with the use of bioreactor and culture medium containing 2 mg L-1 BAP. The temporary immersion bioreactor allows air renewal inside the bottles, leading to a better performance of in vitro cultivation of ornamental pineapple, when compared to conventional micropropagation.