Evaluation of arsenic tolerance in Pistia stratiotes L. (ARACEAE): photosynthetic and respiratory metabolism

• Ano de defesa: 2019
• Autor(a) principal: Ribeiro, Patrícia Cury
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa
• Palavras-chave em Português: Fotossíntese; Respiração; Ativação enzimática; Fisiologia Vegetal
• Link de acesso: https://locus.ufv.br//handle/123456789/27546

Arsenic (As) is a toxic element known to impair the development and growth of plants, as well as triggering various physiological changes when absorbed by plants. The plants, cultivated in nutrient solution, pH 6,5 and 1⁄2 ionic strength, were exposed in two treatments for 24, 48 and 72 hours: control (nutrient solution only) and As (1.5 mg L -1 ). After each day, a part of the experiment was collected for later physiological analyzes. The plants exposed to As presented lower biomass gain over the days, as effect of the damages caused by the contaminant in both leaves and roots. Roots accumulated more As and lower concentrations were found in the leaves. Once As is absorbed by the roots and translocated to the leaves, As changes photosynthesis, respiration, photorespiration and in turn, changes in the synthesis and accumulation of carbohydrates were also observed. Among the effects of As on metabolism, leaves displayed decreased in proteins and increased amino acids contents, while sugars and starch were accumulated. In roots, however, decreases in the concentrations of proteins, amino acids and sugars, mainly after 24 hours were observed. Starch decreased in roots during the 72 hours of exposure to As. Although the pigments did not show differences between control and As, net assimilation rate and the efficiency of photosystem II declined in presence of As. The photorespiration and carboxylation/ oxygenation rates of Rubisco followed the photosynthetic parameters, and decreased leaf stress due to the inhibition of specific enzymes in the presence of As. In contrast, both dark and mitochondrial respiration were higher in stressed leaves, possibly due to the chemical similarity of arsenate to phosphate, which may have led to increased respiration and subsequent collapse throughout the respiratory process. As a consequence of the changes observed in photosynthesis and respiration caused by oxidative stress, the activity of TCA enzymes, TCA intermediates and the NAD, NADH, NADP and NADPH balance also showed differences between the control and As. In leaves, there was an increase in the activity of the enzymes of the TCA cycle, which is in agreement with the respiration results. In roots, the activity of enzymes decreased under stress. Fumarate concentrations were higher for contaminated roots and leaves. However, in leaves with As, an increase in malate was observed, and for roots with As was observed a decrease in the concentration of malate, which suggests that malate can be diverted to other pathways within the cell. Among the pyridine nucleotides, all showed an increase between the contaminated leaves and in roots, the NAD + was not detected. Probably it was not regenerated during the respiratory process in roots with As, and as a consequence, the decrease of NADH was observed. Roots were more severely damaged, which can be explained by the greater accumulation of As in this part of the plant. Complementary analyzes related to leaf and root respiration are necessary to better understand the behavior of organic acids during As stress.