Respostas fisiológicas de indivíduos jovens de Myracrodruon urundeuva Allemão (Anacardiaceae) cultivados em condições de deficiência hídrica

Abstract

Myracrodruon urundeuva (aroeira do sertão) is a species exploited economically for its high commercial value. It has a wide geographical distribution and occurs in some plant formations, including the Caatinga, a semi-arid environment. The semi-arid region is characterized by high temperatures, high radiation and low relative humidity during most of the year. Plants that live in the Caatinga are constantly subjected to water deficit, which, in addition to other implications, leads to the loss of cell turgor, alters some morphophysiological aspects and leads to the paralysis of several processes that are essential to the plant. In this scenario, M. urundeuva has great potential to be used in the recovery of altered areas because it is found in the semiarid region and it can be used for this purpose. It can also contribute to the rehabilitation of the environment, since it is able to survive the weather in these areas. Thus, this work aimed to verify the tolerance of young M. urundeuva individuals submitted to water deficiency. The experiment was carried out with twenty-two aroeira seedlings, which were distributed in two treatments: control and rainfed. After a period of acclimatization, the rainfed plants were no longer hydrated until photosynthesis rates approached zero, which lasted for seven days. Daily gas exchange data (gs, E and A) was collected, in addition to the determination of instantaneous water-use efficiency (WUE), intrinsic water-use efficiency (IWUE) and carboxylation efficiency (CE), using an infrared gas analyzer (IRGA). At the end of the seven days, the leaf water potential ( wp) was determined in the morning and at midday. Material was collected to quantify the levels of leaf proline, leaf nitrate (LN) and activity of the enzyme nitrate reductase (NR). In addition, analyses of the quantum efficiency of PSII (YIELD), efficiency of photochemical PSII (Fv/Fm), total chlorophyll (SPAD Index) and dry matter determination were performed. Photosynthesis reached values close to zero on the seventh day of water suspension, when the efficiency of photochemical and chlorophyll content were analyzed and neither photoinhibition damage nor a decrease in the leaf chlorophyll index were observed wp was lower in rainfed treatment, in the morning and at midday, and higher concentrations of leaf proline were registered. These findings suggest that M. urundeuva responded to water deficit and VPD by accumulating compatible solutes (proline). There were no differences in the levels of leaf nitrate, dry matter, IWUE and WUE. CE mean values decreased during the irrigation suspension. Thus, we have come to the conclusion that the accumulation of proline was a strategy used by the plant to adjust the osmotic potential in order to guarantee the water status of the plants. On the other hand, after the imposition of water suspension, the photosynthetic rates of M. urundeuva presented a very prominent reduction, even though the integrity of the photosynthetic apparatus was maintained. It indicates that this species has strategies to survive under conditions of water restriction.