Changes in leaf anatomy and ultrastructure are associated with physiological performance in the context of plant adaptations to climate change. In this study, we investigated the isolated and combined effects of elevated atmospheric CO 2 concentration ([CO 2 ]) up to 600 μmol mol -1 ( eC ) and elevated temperature ( eT ) to 2°C more than the ambient canopy temperature on the ultrastructure, leaf anatomy, and physiology of Panicum maximum Jacq. grown under field conditions using combined free-air carbon dioxide enrichment (FACE) and temperature free-air controlled enhancement (T-FACE) systems. Plants grown under eC showed reduced stomatal density, stomatal index, stomatal conductance ( g s ), and leaf transpiration rate ( E ), increased soil-water content ( SWC ) conservation and adaxial epidermis thickness were also observed. The net photosynthesis rate ( A ) and intrinsic water-use efficiency ( iWUE ) were enhanced by 25% and 71%, respectively, with a concomitant increase in the size of starch grains in bundle sheath cells. Under air warming, we observed an increase in the thickness of the adaxial cuticle and a decrease in the leaf thickness, size of vascular bundles and bulliform cells, and starch content. Under eCeT , air warming offset the eC effects on SWC and E , and no interactions between [CO 2 ] and temperature for leaf anatomy were observed. Elevated [CO 2 ] exerted more effects on external characteristics, such as the epidermis anatomy and leaf gas exchange, while air warming affected mainly the leaf structure. We conclude that differential anatomical and physiological adjustments contributed to the acclimation of P . maximum growing under elevated [CO 2 ] and air warming, improving the leaf biomass production under these conditions.

The opening and closing of stomata are controlled by the integration of environmental and endogenous signals. Here, we show the effects of combining elevated atmospheric carbon dioxide concentration ( eCO 2 ; 600 μmol mol -1 ) and warming (+2°C) on stomatal properties and their consequence to plant function in a Stylosanthes capitata Vogel (C 3 ) tropical pasture. The eCO 2 treatment alone reduced stomatal density, stomatal index, and stomatal conductance ( g s ), resulting in reduced transpiration, increased leaf temperature, and leading to maintenance of soil moisture during the growing season. Increased CO 2 concentration inside leaves stimulated photosynthesis, starch content levels, water use efficiency, and PSII photochemistry. Under warming, plants developed leaves with smaller stomata on both leaf surfaces; however, we did not see effects of warming on stomatal conductance, transpiration, or leaf water status. Warming alone enhanced PSII photochemistry and photosynthesis, and likely starch exports from chloroplasts. Under the combination of warming and eCO 2 , leaf temperature was higher than that of leaves from the warming or eCO 2 treatments. Thus, warming counterbalanced the effects of CO 2 on transpiration and soil water content but not on stomatal functioning, which was independent of temperature treatment. Under warming, and in combination with eCO 2 , leaves also produced more carotenoids and a more efficient heat and fluorescence dissipation. Our combined results suggest that control on stomatal opening under eCO 2 was not changed by a warmer environment; however, their combination significantly improved whole-plant functioning.

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Citrus canker is a very destructive disease of citrus species. The challenge is to find new compounds that show strong antibiotic activity and low toxicity to plants and the environment. The objectives of the present study were (1) to extract, purify and evaluate the secondary metabolites with antibiotic activity produced by Pseudomonas aeruginosa LV strain in vitro against Xanthomonas citri subsp. citri (strain 306), (2) to determine the potential of semi-purified secondary metabolites in foliar application to control citrus canker under greenhouse conditions, and (3) to identify antibiotic activity in orange leaf mesophyll infected with strain 306, by electron microscopy. Two pure bioactive compounds were isolated, an organocopper antibiotic compound (OAC) and phenazine-1-carboxamide. Phenazine-1-carboxamide did not show any antibiotic activity under the experimental conditions used in this study. The OAC showed a high level of antibiotic activity with a minimum inhibitory concentration of 0.12 μg mL-1. In greenhouse tests for control of citrus canker in orange trees, the semi-purified fraction F3d reduced lesion formation by about 97%. The concentration used was 500 times lower than that for the recommended commercial copper-based product. Electron microscopy showed that F3d altered the exopolysaccharide matrix and caused cell lysis of the pathogen inside the citrus canker lesions. These results suggest that secondary metabolites produced by inducing P. aeruginosa LV strain have a high potential to be used as a bioproduct to control citrus canker.