Eficiência e plasticidade fotossintética em plantas de ora-pro-nóbis submetidas ao déficit hídrico

Abstract

Pereskia aculeata Mill (Ora-Pro-Nobis) Cactaceae, is a C3 species whose characteristic or metabolism is CAM as an optional form of CO2 assimilation. Thus, this species has both photosynthetic pathways (C3/CAM), which can be modulated in response to some environmental factors, such as water stress, which exerts control over CO2 fixation. Water deficit has been shown to induce a change in C3 to CAM metabolism in these species. However, the biochemical and physiological mechanisms involved with this acclimatization shift to CO2 assimilation are still poorly understood. Thus, the present study aims to characterize the C3-CAM photosynthetic transition physiologically and associate this modulation with the photosynthetic efficiency in Pereskia aculeata plants subjected to water stress. For that, two DIC experiments were carried out, aiming to evaluate the effect of water stress in the long term (experiment I) and short term (experiment II). Experiment I was mounted in a growth chamber, while Experiment II in a greenhouse. Where, one group of plants was well irrigated and another group submitted to water deficit, with subsequent rewatering. As physiological and biochemical markers of C3-CAM modulation were evaluated photosynthesis, by means of gas exchange and photochemical parameters, water status, stomatal variables, as well as chemical indicators associated with titratable acidity, soluble carbohydrates, reduced ascorbate and glutathione contents, while damages were evaluated by substances reactive to thiobarbituric acid (TBARS) accumulation. The results showed a small induction of CAM in Ora-Pro-Nóbis plants submitted to water deficit, characterized as CAM-Cycling, with daytime gas exchange and nocturnal internal carbon fixation. Additionally, we found changes in acidity, osmolyte metabolism, membrane peroxidation and antioxidant capacity. Starting rewatering, plants return to physiological C3 standards. This photosynthetic plasticity reduces impairment in photosynthetic efficiency, ensuring plant establishment in environments with abiotic pressures. Thus, the understanding of these physiological mechanisms becomes important in understanding the ecophysiological strategies of plants in the face of environmental adversities. In addition, these CAM species, being productive, can be selected to replace C3 crops, with the aim of conserving agricultural production in a scenario of worsening climatic conditions.