Photoprotective mechanisms during leaf ontogeny: cuticular development and anthocyanin deposition in two morphs of Agave striata that differ in leaf coloration

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 xanthophyl I-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.