Do mature shade leaves of tropical tree seedlings acclimate to high sunlight and UV radiation?

Abstract

Abstract. Seedlings of neotropical forest trees grown in low light were exposed to 0.5-9 h d~' direct sunlight, for up to 3 months, to test the capability of mature shade leaves to acclimate to full solar visible and UV radiation. Photosynthetic pigments and the antioxidant, ascorbate, were analysed in leaves of two pioneer and two latesuccession species. Seedlings of one or two of these species were used to assess further acclimative responses. Sunexposure for 0.5 or 1 h d~ ' resulted in strongly decreased a-carotene and increased ß-carotene and lutein levels. The pool size of xanthophyll-cycle pigments (sum of viola-, anthera-and zeaxanthin) was increased and their turnover was enhanced. These changes were associated with an increase in the capacity of non-photochemical fluorescence quenching and its 'energy-dependent' component, qE, and with reduced susceptibility to photoinhibition of PSII. Prolonged exposure to full direct sunlight (approximately 4 or 9 h d~') resulted in a marked decrease of chlorophyll a + b content and increase in chlorophyll alb ratios and the pool of xanthophyll-cycle pigments (based on chlorophyll), leading to extremely high zeaxanthin levels during high-light periods. Contents of ascorbate and UV-B-absorbing substances were substantially increased. PSI activity exhibited a response to full sunlight that is characteristic of sun leaves. Rates of net photosynthetic CO2 assimilation under saturating light were increased. The data show that mature shade leaves of seedlings of both early-and late-succession tree species can substantially acclimate to full-sunlight conditions by employing similar physiological mechanisms.

Different Roles of α- and β-Branch Xanthophylls in Photosystem Assembly and Photoprotection

“…1B). ␤-Carotene normally binds photosynthetic reaction centers and Lhca, whereas ␣-carotene binds the same sites as ␤-carotene and is found in shade-adapted plants (42,43). In this case, its accumulation is induced by a knock-out mutation in the LUT5 gene, which encodes a cytochrome P450 carotenoid hydroxylase (25,26).…”

“…In fact, this genotype shows higher levels of photoinhibition and lipid peroxidation under stress conditions than any other xanthophyll mutant described to date, including npq1lut2 (7 A clear difference between the two triple mutants is the presence of ␣-carotene in both PSI and PSII core complexes of chy1chy2lut5, partially replacing ␤-carotene (25). 5 This condition mimics acclimation to deep shade (42,43), a condition increasing sensitivity to moderate light stresses (60). However, the lut5 genotype has the same ␣/␤-carotene ratio as chy1chy2lut5, yet no increase in lipid peroxidation under stress was observed (supplemental Fig.…”

Sun-shade patterns of leaf carotenoid composition in 86 species of neotropical forest plants

“…If a-Car and Lx contribute to efficient light harvesting in low-light environments, and if this confers an evolutionary advantage, leaves growing on the forest floor or inside the canopy would contain higher levels of a-Car and Lx than outer-canopy leaves in a wide variety of tropical forest species. Indeed, it has been documented that shade leaves of some neotropical forest plants have large amounts of a-Car and/or Lx (Königer et al 1995;Krause et al 2001Krause et al , 2003Krause et al , 2004Matsubara et al 2008), although the number of species examined in these studies was not large enough to see whether these pigments occur widely in many different species under shaded environments. Therefore, we conducted a pigment survey on leaf carotenoid composition in tropical forest plants, including 86 species from 64 families growing in different types of tropical forests in Panama.…”

“…Accumulation of a-Car has been found in shade leaves of many different plants (e.g. Thayer and Björkman 1990;Demmig-Adams and Adams 1992;Siefermann-Harms 1994;Demmig-Adams 1998), including neotropical forest species (Königer et al 1995;Krause et al 2001Krause et al , 2003Krause et al , 2004Matsubara et al 2008; Table 2). Based on enhanced accumulation in shade environments, a possible function of a-Car in improving light harvesting has been proposed (Krause et al 2001).…”

Leaf Photosynthetic and Growth Responses on Four Tropical Tree Species to Different Light Conditions in Degraded Tropical Secondary Forest, Peninsular Malaysia

“…On the other hand, leaves under shade conditions have higher leaf chlorophyll content and lower LMA, so as to maintain the low light compensation point 36 . Even the old leaves, which had adapted to a previous light condition, usually change their photosynthetic traits such as A max and chlorophyll content to acclimate to a new light environment 31,45,54 . However, it is also known that shade adapted old leaves of several species significantly suffer damage to photosystem II (PSII) by strong sunlight 28 .…”