The existing inconsistent data on the irradiance needs of Brazilwood plants Paubrasilia echinata (Lam.) Gagnon,H.C.Lima and G.P.Lewis. can be explained by their phenotypical variations. While small-leaf morphotypes grows better in the shade, not tolerating environments with high irradiance, a recently discovered population of medium morphotype presents different behavior: better performance under direct sunlight and limited growth in the shade. In order to understand the physiological mechanisms of the medium morphotype in response to the available irradiance, this study was performed to characterize the oxidative stress metabolism, photochemical and biochemical photosynthesis efficiency, as well as anatomical adjustments of leaves of the medium morphotype of P. echinata under different intensities of irradiance. The analyses were performed at direct sunlight condition (2000 µmol m-2.s-1) and within a dense ombrophilous forest with 80% shading (192 µmol m-2.s-1). Growth, leaf anatomy, chloroplast pigments, photochemical (chlorophyll a fluorescence), and biochemical (gaseous exchanges) efficiency, soluble carbohydrates, and antioxidants were measured. The results showed that the higher efficiency in light energy uptake, paired with better photochemical performance and better CO2 fixation in plants under direct sunlight resulted in higher concentration of soluble sugars and growth. The energy that should have been used in photochemical and/or biochemical reactions of shaded plants was dissipated in the form of heat, re-emitted as fluorescence or translocated to the production of antioxidant defense compounds of the secondary metabolism. Therefore, the medium morphotype of P. echinata presents an ecological profile of sun-tolerant or pioneer species, and as such, it is recommended its planting in full sunlight. These results differ from previous studies on small morphotype of P. echinata and suggest the need for a taxonomic reconstruction of this species, which is essential to adequate management practices in Atlantic rainforest recovery programs.
This study aimed to verify the efficiency of silicon leaf application in the physiological and biochemical characteristics in a Theobroma cacao genotype inoculated with Moniliophthora perniciosa fungus, which causes the witches' broom disease, important cocoa disease in Brazil and worldwide. Seedlings of Catongo genotype were used. The experimental design used was a randomized block design with four replicates, including two inoculation factors (inoculated and non-inoculated plants), each one with two levels of silicon application (0.0 mg and 1.0 mg mL-1 with AgriSil containing 98% of SiO 2). We observed that plants that were inoculated with M. perniciosa and subjected to leaf application with silicon presented enhanced photosynthesis, peroxidases, chitinase, polyphenoloxidases activities and stomatal density. Results have shown that silicon application is beneficial and increases the defenses against Moniliophthora perniciosa in cocoa seedlings.
ABCTRACTIncreased UV-B radiation, a topic of concern due to climate change, can affect plant development through structural and physiological changes. Common bean (Phaseolus vulgaris L.) is a legume of great economic relevance, being one of the basic components of the human population's diet. Seeds of P. vulgaris var. Carioca were sown and grown in a growth chamber, and at 12 days of age were exposed for 15 min daily to UV-B radiation for a period of 14 days. Growth, leaf anatomy, gas exchange and pigments were evaluated. It was observed that UV-B radiation negatively affected the initial growth of bean plants, which had a reduction in height, number of leaves, fresh and dry leaf masses, leaf area, as well as reduction of stem and root dry masses. There was a reduction in the epidermis thickness, increase in the thickness of the palisade parenchyma and the leaf blade. It was verified yet reduction of the photosynthetic and photoprotectors pigments, reduction of the photosynthetic rate and alterations on the absorbent compounds of the UV-B radiation. The results obtained showed that the increase in UV-B radiation was harmful to the initial development of this crop.Palavras-chave: Agriculture, Anatomy, Beans, Pigments. RESUMOO aumento da radiação UV-B, tema preocupante em virtude das mudanças climáticas, pode afetar o desenvolvimento das plantas, por meio de mudanças estruturais e fisiológicas. O feijoeiro-comum (Phaseolus vulgaris L.) é uma leguminosa de grande relevância econômica, sendo um dos componentes básicos da alimentação humana. Sementes de P. vulgaris var. Carioca foram germinadas e cultivadas em uma câmara de crescimento, sendo aos 12 dias de idade expostas a 15 min diários de radiação UV-B, por um período de 14 dias. Foram avaliados crescimento, anatomia foliar, trocas gasosas e pigmentos. Observou-se que a radiação UV-B afetou negativamente o crescimento inicial do feijoeiro, o qual teve redução em altura, número de folhas, massa fresca, massa seca e área foliares, bem como, redução da massa seca de caule e raiz. Houve redução na espessura da epiderme e aumento nas espessuras do parênquima paliçádico e do limbo. Verificou-se, ainda, redução dos teores de pigmentos fotossintéticos e fotoprotetores, redução da taxa fotossintética e alterações nos compostos absorventes da radiação UV-B. Os resultados obtidos mostraram que o aumento da radiação UV-B foi prejudicial para o desenvolvimento inicial desta cultura.
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