The foliar application of a mixture of semisynthetic chitosan derivatives induces tolerance to water deficit in maize, improving the antioxidant system and increasing photosynthesis and grain yield.

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.

Effects of exogenous proline and a natural ventilation system on the in vitro growth of orchids / Efeitos da prolina exógena e sistema de ventilação natural no crescimento in vitro de orquídeas

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 0C, 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.

A micropropagação é uma alternativa para a produção de plantas de orquídeas em larga escala. Entretanto, este processo apresenta perdas durante a fase de aclimatização. O emprego de prolina exógena na cultura de tecidos vegetais é uma alternativa para reduzir o estresse das plantas na fase de aclimatização. O objetivo da presente pesquisa foi verificar o crescimento de orquídeas em diferentes sistemas de micropropagação com prolina adicionada no meio de cultura. Plantas de Cattleya walkeriana foram obtidas a partir da germinação de sementes em meio de cultura. Sementes foram germinadas em meio MS, adicionado de 20 g. L-1 de sacarose, solidificado com 6 g. L-1 de ágar e pH ajustado para 5,8. Após 5 meses, plântulas com 1 cm de comprimento foram inoculadas nos frascos de cultivo de acordo com os tratamentos, os quais foram compostos por dois sistemas de micropropagação (convencional e ventilação natural) em combinação com prolina (0, 1 e 2 g L-1). O experimento foi conduzido em esquema inteiramente casualizado, constando de um fatorial 2x3, totalizando 6 tratamentos com 5 repetições. O sistema de ventilação natural com o uso de prolina (1 g L-1) promoveu o maior acúmulo de massa seca e melhor controle da perda de água das plantas.

Cattleya walkeriana growth in different micropropagation systems / Crescimento de Cattleya walkeriana em diferentes sistemas de micropropagação

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, with natural ventilation and conventional systems. Cattleya walkeriana plants were obtained from the germination of seeds in culture medium. After 8 months, seedlings with 1 cm of length were placed in a culture vessel according to the treatments, which counted with two micropropagation systems (conventional and natural ventilation) in three media of culture (liquid, solid with 5 or 6g L-1 of agar). Two additional treatments in bioreactor of temporary and continuous immersion were performed. The design was entirely randomized (ERD), consisting of a 2x3 factorial with two additional treatments, totaling 8 treatments with three repetitions. The temporary immersion bioreactor promoted a bigger growth of the aerial part and of the root system, bigger accumulation of dry mass and better control of water loss by the plants. The temporary immersion bioreactor is the best micropropagation system for the C. walkeriana growth in vitro.

O objetivo do presente trabalho foi verificar o crescimento in vitro de orquídeas em diferentes sistemas de micropropagação, sendo cultivado em biorreator, sistema de ventilação natural e convencional. Plantas de Cattleya walkeriana foram obtidas a partir da germinação de sementes em meio de cultura. Após o a germinação, as plantas foram uniformizadas com aproximadamente 1,0cm de comprimento e inoculadas nos diferentes tratamentos. Os tratamentos contaram dois sistema de micropropagação (convencional e ventilação natural) e três meios de cultura (líquido, sólido com 5 e 6g L-1 de ágar). Foram realizados dois tratamentos adicionais em biorreator de imersão temporária e contínua. O delineamento foi o inteiramente casualizado, consistindo de um fatorial 2x3 com dois tratamentos adicionais, totalizando oito tratamentos com três repetições. O biorreator de imersão temporária promoveu o maior crescimento da parte aérea e do sistema radicular, maior acúmulo de massa seca e melhor controle da perda de água das plantas. O biorreator de imersão temporária é o melhor sistema de micropropagação para o crescimento in vitro de C. walkeriana.