Characterization of the capacity to induce CAM in plants of Vriesea gigantea (Bromeliaceae) under water deficit

Abstract

Crassulacean acid metabolism (CAM) is an adaptation characterized mainly by fixation of atmospheric carbon dioxide at night by the enzyme phosphoenolpyruvate carboxylase (PEPC). Due to the closure of stomata during the day, the water use efficiency of CAM plants is higher than that of plants that carry out C3 or C4 photosynthesis, allowing the colonization of more xeric environments. CAM can be expressed in different intensities, and this led to the characterization of various types of CAM, such as C3 -CAM facultative. This is of fundamental importance to some epiphytes, such as the bromeliad Guzmania monostachia, which has the evolutionary advantage of transiting from C3 to CAM photosynthesis when exposed to highly variable conditions in available light, water or nutrients. The expression of CAM may also have a large plasticity regarding the leaf development, probably due to the capacity of malate storage in the vacuoles. Studies in the bromeliad Vriesea gigantea regarding its photosynthetic activity began recently in the Laboratory of Plant Developmental Physiology - USP. Through preliminary experiments, we observed that this bromeliad may have some degree of CAM expression when detached leaves are subjected to drought simulation (achieved by 30 % PEG 6000). However, this finding was surprising because this bromeliad is always cited as a C3 species in the literature. Therefore, it is necessary to conduct further studies on its photosynthetic behavior, since V. gigantea could actually be a C3 - CAM facultative, expressing CAM when subjected to drought stress. Therefore, this project aims to investigate the capacity of induction and modulation of CAM expression in plants of Vriesea gigantea under watering suspension. Furthermore, it will investigate whether leaves at different stages of development would have a different capacity to express CAM. To induce CAM, plants V. gigantea will have watering suspended for 7, 14 or 21 days. For biochemical analysis, the leaves of the entire plant will be grouped into three sets: young leaves, fully expanded young leaves and mature leaves. These leaves will be divided in three regions (apical, middle and basal), since the CAM can be expressed with different intensities along the leaf. The induction of CAM will be verified by 1) the relative levels of expression of PEPC and MDH genes, 2) the activity of PEPC and MDH, and 3) the quantification of the night time accumulation of organic acids (through analysis by gas chromatography/mass spectrometry). The addition of molecular biology techniques that will be used in this work coupled with biochemical/physiological approaches constitute an important step to further investigate the photosynthetic behavior of this species. Such an approach is still uncommon in CAM photosynthesis research, both nationally and internationally. (AU)