Variações diurnas das trocas gasosas, eficiência do fotossistema ii e acumulação de osmoprotetores em tabebuia aurea bignoniaceae submetida ao estresse por alagamento

Abstract

Global climate changes are responsible for large variations in the precipitation regime, increasing the possibility of non-uniform and excessive rainfall, causing floods. In this way, the study of plants‟ physiological and biochemical behavior, in the face of these conditions, can be considered a relevant ecological indicator of plant species adaptation as well as supporting projects for degraded area recovery. In this regard, the objective was to qualify and quantify tolerance in young Tabebuia aurea plants subjected to flooding stress, through diurnal variations in gas exchange, photosystem II efficiency and osmoprotectant accumulation. The experimental design used was completely randomized (DIC), with treatments arranged in a factorial scheme (2 x 12), with five replications. In the first factor, the water regimes were assessed: (1) control, in which plants were cultivated under field capacity, being daily hydrated throughout the experiment; (2) flooded, in which plants were subjected to soil flooding. Plant flooding was induced in vases flooded by a water depth of 2 to 3 cm above the ground for six days, when they were drained and maintained at field capacity, and plant recovery was monitored until the fourth day after draining the water from the soil. For the second factor, physiological measurements throughout the day were considered, in a total of 12 assessments of gas exchange, maximum and effective photosystem II efficiency. Leaf water potential and chlorophyll content index were determined at noon every day. Leaves were collected for the determination of photosynthetic pigments and for further analysis of amino acids, proteins, proline and total soluble sugars. Soil flooding reduced photosynthetic rates, stomatal conductance, intracellular CO2 concentration, transpiration, water use efficiency, maximum (FV/FM) and effective (Yield) photosystem II efficiency on the sixth day of stress, but the plants recovered after four days of stress suppression. Furthermore, on the sixth day of the experiment, it was found that flooding stress in Tabebuia aurea plants significantly reduced amino acids and increased levels of proline and soluble sugars. The high cellular osmoprotectant accumulation in plants is an important evolutionary strategy for survival in environments under stress, since these compounds have the ability to regulate osmotic balance in plants, maintaining cell turgor pressure through osmoregulation. Moreover, they stabilize cellular structures and enzymes, act as metabolic signals, and scavenge reactive oxygen species produced under stressful cellular conditions. On the other hand, flooding did not affect leaf water potential, Spad index, proteins and photosynthetic pigments in Tabebuia aurea plants. Therefore, the responses presented by Tabebuia aurea plants, through gas exchange, amino acids, proline and sugars, indicate that it can survive during short periods of soil flooding and that it presents good recovery of post-flooding gas exchanges. Osmoprotectant accumulation, such as proline and soluble sugars in Tabebuia aurea during the period of soil flooding, is potential mechanism of acclimatization and tolerance to flooding in these plants. These characteristics indicate that young Tabebuia aurea plants are capable of surviving for short periods of time in flooded soil. Keywords: Hypoxia Tolerance; Craibeira; Photosynthesis; Chlorophyll A Fluorescence; Osmoprotectants.