Internal and external photoprotection in developing leaves of the CAM plant Cotyledon orbiculata

Abstract

Leaves of the CAM plant Cotyledon orbiculata produced a dense epidermal wax which decreased the ahsorption of light, possibly functioning as an external photoprotective mechanism (Robinson et al. 1993). However, developing leaves did not accumulate wax until after 21 d with full wax coating not achieved until at least 35 d. In addition, young leaves had lower rates of electron transport than mature leaves. Leaf development therefore occurs at higher incident PFD than that experienced by the mature leaves, and, for young leaves, can lead to an increase in the proportion of light energy which is excess to requirements and must be dissipated non-photochemically. Changes in the photosynthetic capacity, PSII efficiency, rate of energy dissipation, and the content of chlorophyll (Chi), carotenoids, wax and anthocyanins were followed in developing leaves of C. orbiculata in an attempt to elucidate the relative importance of the various photoprotective mechanisms during leaf ontogeny. The largest pools of xanthophyll cycle pigments (on a Chi basis) were found in the waxless, young leaves and were correlated with greater levels of energy dissipation activity. The importance of xanthophyll cycledependent energy dissipation in young C. orbiculata leaves prior to development of a reflective wax covering, and full photosynthetic capacity which for CAM plants includes appreciable nocturnal acid accumulation, is discussed. Also, we consider the possibility that anthocyanin pigments in the upper and lower epidermis may increase reflectivity and act as external photoprotectants.

Physiological Roles of Betacyanin in a Halophyte,Suaeda japonicaMakino

“…These observations prompted researchers to postulate hypotheses in physiological function to account for the presence of anthocyanins in leaves, including (i) protection of tissues against harmful effects of UV-B irradiation (Burger and Edwards, 1996;Klaper et al, 1996), (ii) modifi cation of the quantity and quality of absorbed light (Lee, 1986;Barker et al, 1997), (iii) ROS scavenging (Yamasaki, 1997; Sherwin and Farrant, 1998), and (iv) protection of photosynthetic apparatus against photoinhibition (Gould et al, 1995;Dodd et al, 1998). Similarly, betacyanin production was induced by abiotic and biotic stresses, which potentially cause ROS production.…”

Spatial and temporal variation in spectral reflectance: Are seagrass species spectrally distinct?

“…Declines in photosynthetic rate because of environmental stress are often accompanied by reductions in chlorophyll pigments, increases in various carotenoids, changes to the Chl a/b ratio (Demmig-Adams and Adams 1992), and in-creases in nonphotosynthetic accessory pigments (Barker et al 1997). For example, seagrass plants exposed to low light intensities have higher total chlorophyll content (Alcoverro et al 2001) and lower Chl a/b ratios (Longstaff and Dennison 1999).…”

Molybdenum Sequestration in BrassicaSpecies. A Role for Anthocyanins?

“…The relation of Mo influx versus concentration is approximately linear in soil systems (Barber, 1995). Bioavailability of Mo is positively correlated with soil pH (Karmian and Cox, 1978).…”