Aspectos fisiológicos e bioquímicos do híbrido Eucalyptus urophilla x Eucalyptus camaldulensis submetidos ao déficit hídrico

Abstract

Drought is one of the major concerns for the agricultural sector, as it is an environmental factor that greatly limits crop growth and productivity. Focused on better understand the physiological and biochemical responses of eucalyptus to drought conditions, two Eucalyptus urophylla x Eucalyptus camaldulensis hybrid genotypes (VM1 and VM5) were compared in a sought to identify the major contrasts under drought stress, as well as verify if recurrent water deficits promote epigenetic changes capable of becoming the plants more tolerant upon next exposures to dry condition. The first experiment performed was based on the imposition of water deficit with daily suspension of irrigation in each group of plants. Upon sixth day plants previously undergone to different amount of days (one to six) of drought stress were obtained altogether with a control treatment (plants always irrigated) and another for resilience. During the stress period, leaf water potential decreased gradually in all treatments reaching a minimum of -2.7 MPa at sixth day of water deficit. The VM5 genotype presented the higher values for all gas exchange variables. Regarding the biochemical aspects, as higher was the water deficit greater the H2O2 and MDA concentrations in both genotypes. No differences were verified for antioxidant enzymes which displayed peak activity on the third and fourth day of water deficit. The resilience treatment recovered itself after stress imposition with values close to the control, whereas VM1 was able to recover faster than the VM5. According to the data, clone VM1 seems to be more tolerant because its variables responsible to confer accumulation of biomass are reduced in water deficit but also in reason of an earlier acivation of defense mechanisms. In the second experiment three groups of plants were submitted to three different cycles of water deficit (one, two and three weekly stresses, respectively) during three weeks, and two other groups were always kept well irrigated. Afterwards, plants were transferred to 3 dm3 vessels and the irrigation was completely suspended. Nine days upon complete suspension of water supply, plants had already marked signs of wilting especially those that did not go through stress cycles and those who suffered stress once a week. The plants undergone to two and three cycles of weekly stresses kept their water potential close to the control. In general, gas exchange values indicating a better hydration condition were observed in plants undergone to early cycles of water deficit. The H2O2 and MDA contents were significantly reduced probably as a function of previous exposure to water stress. Results show that plants exposed to multiple cycles of water deficit adjust themselves biochemical and phisyologically, what boosts cellular defense mechanisms to respond faster and more vigorously in future drought situations.