No abstract

Guzmania monostachia is an epiphytic tank bromeliad that displays the inducible CAM photosynthesis under stressful conditions and had the highest stomata density in the leaf apex, while the base portion has the highest density of trichomes, which are specialized structures used to acquire water and nutrients from the tank solution. In order to correlate the genetic factors behind these morpho-physiological characteristics along the leaf blade of G. monostachia, a comparative transcriptome analysis was performed to identify the functional enriched pathways and unigenes that could play a role in the apical, middle and basal leaf portions. A total of 653 million reads were used for de novo transcriptome assembly, resulting in 48,051 annotated unigenes. Analysis of differentially expressed genes (DEGs) among distinct leaf regions revealed that 806 DEGs were upregulated in the apex compared to the middle portion, while 9685 DEGs were upregulated in the apex and 9784 DEGs were upregulated in the middle portions compared to the base. Our outcomes correlated some DEGs and identified unigenes with their physiological functions, mainly suggesting that the leaf apex was related to the regulation of stomatal movement, production of chlorophyll, cellular response to stress, and H2O2 catabolic process. In contrast, the middle portion showed DEGs associated with the transport of amino acids. Furthermore, DEGs from the leaf base were mainly correlated with responses to nutrients and nitrogen compounds, regulation of potassium ion import, response to water deprivation, and trichome branching, indicating that, at least in part, this leaf portion can replace some of the root functions of terrestrial plants. Therefore, possibly candidate unigenes and enriched pathways presented here could be prospected in future experimental work, opening new possibilities to bioengineer non-inducible CAM plants and/or improve the fertilization use efficiency by increasing leaf nutrient acquisition of crop plants.

Intermittent water availability characterizes the canopy habitat, but few studies have focused on how C3 epiphytic bromeliads deal with drought. In this context, we investigated how water deficits affect the photosynthetic responses of the epiphytic bromeliad Vriesea gigantea regarding its physiological and anatomical traits that can minimize the effects of stomatal closure. In a controlled experiment in which bromeliads were submitted to 21 days of drought, we demonstrated a reduction in the leaf water content followed by strong reductions in net CO2 exchange and the efficiency of the photochemical system. However, there were increases in the yield of non-photochemical quenching and the activities of hydrophilic antioxidants. We observed substomatal chambers connected with air channels reaching the chlorophyllous parenchyma. Our findings indicate that the low net CO2 exchange and the energy imbalance possibly increased the cyclic transport of electrons and activated the thermal dissipation of energy to avoid damage to the photosynthetic apparatus. Additionally, the aeration channels may passively store CO2 to facilitate its re-assimilation. Because most epiphytic bromeliads are C3 plants and drought is frequent in the canopy, we speculate that some attributes of V. gigantea may occur in other C3 species, favouring their radiation in the epiphytic environment.