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Our objectives were to test whether in Agave striata Zucc., a plant with crassulacean acid metabolism (CAM plant), leaf wax development is a delayed response to sunlight exposure following cutin development, and whether energy dissipation shifts from non-photochemical quenching to photochemical quenching during leaf ontogeny. Under field conditions, photosynthesis, cuticular development, and anthocyanin deposition were studied in two morphs of A. striata that differ in leaf coloration (green vs. red). We quantified leaf anthocyanin, wax, and cutin content, and also measured chlorophyll a fluorescence and leaf surface temperature. In addition, using three leaf reflectance indices, we measured relative chlorophyll and anthocyanin content, and also xanthophyll-cycle de-epoxidation state (xanthophyll conversion). Our results revealed that the main components of cuticle (wax and cutin) in leaves of A. striata are deposited during different developmental windows, which are similar to leaves of monocots such as grasses. Exposure to sunlight was found to be the most likely candidate to affect wax and anthocyanin deposition. Chlorophyll a fluorescence data revealed that the sunlight conditions experienced by both morphs predisposed the young leaves of the green morph and old leaves of both morphs to photoinhibition. Our results also revealed that old leaves of the red morph, which contain a reduced level of chlorophyll and anthocyanin, had additional photoprotection via xanthophyll conversion. The results presented here support the photoprotective function of leaf anthocyanins and wax accumulation during leaf ontogeny, indicating that their presence may compensate for the reduced dependence of non-photochemical quenching and the xanthophyll-cycle pigment conversion.

Oil pollution is a worldwide threat to the environment that affects the development of plants. The effect of soil contaminated by diesel on the physiological responses of seedlings of Quercus oleoides was investigated in two independent experiments. We proposed that physiological performance will decrease when seedlings are exposed to higher concentration of contamination. At the first experiment, levels of pollution with diesel were of 0%, 5%, 10% and 15%, and 0%, 2% and 3.5% in the second one. In the first experiment, photosynthetic rate, stomatal conductance, transpiration and total chlorophyll of Q. oleoides were higher in the control seedling, and lower in treatments of pollution with 5%, 10% and 15% of diesel during 3 days of treatment. Only, seedlings in soil polluted with 5% of diesel survived up to 16 days; they showed a photosynthetic rate of 5 μmol m −2 s −1 , which was lower than control seedlings (9 μmol m −2 s −1). This pattern was observed in stomatal conductance, transpiration and relative water content. Surprisingly, in the second experiment, seedlings showed a higher photosynthetic rate and growth at 2% of diesel-contaminated soil than control seedlings, a phenomenon known as hormesis. In both experiments, soil respiration was proportional to soils contaminated. We concluded that Q. oleoides is highly vulnerable in soils contaminated with above 5% of diesel, but it maintains its physiological activities in soils contaminated below 2%, suggesting that seedlings can grow under low concentration of diesel contaminant, and may be used in phytoremediation of soils with low concentrations of diesel contamination.

The aim of this study was to compare sugarcane (Saccharumspp.) canopy developmental components of three commercial varieties (CP 72-2086, Mex 79-431, and Mex 68-P-23) in a subtropical environment under rainfed and high temperature conditions, a poorly described topic in the literature. A field experiment was carried out in southern Tamaulipas, Mexico, throughout November 2011–January 2013 crop cycle, during which 111 of the days had daily maximum temperatures at or above 35°C. Number of leaves, leaf area, leaf appearance rate, and leaf area index (LAI) were determined. Thermal time exposure, °Cd (°C day−1), was determined based on total number of green ligulate leaves using 10°C as the base temperature. At 5000°Cd the number of leaves per plant ranged from 32 to 40 and the dependence of leaf emergence rate as a function of temperature was confirmed. The leaf emergence rate of CP 72-2086 was significantly greater than that of the other two varieties. Cultivars did not differ with respect to leaf length but differed for all other parameters measured. These results show the potential importance of considering sugarcane varietal differences in leaf phenology and canopy development for breeding programs focusing on rainfed and high temperature conditions.