No abstract

Summary• High-light leaves of the evergreen herb Galax urceolata exhibit a striking color change from green to red during winter months due to anthocyanin synthesis in outermost mesophyll cells. Here we investigate three possible functions of this color change.• To test the hypothesis that anthocyanins function as light attenuators, maximum photosystem II efficiency ( F v /F m ) of red and green leaves was measured during and after exposure to wavelengths either strongly or poorly absorbed by anthocyanin. To determine whether anthocyanins elevate radical-scavenging capacity, antioxidant activity of red and green leaves was assessed using the α , α -diphenyl-β -picrylhydrazyl assay. Nonstructural carbohydrate levels were analyzed to test the hypothesis that anthocyanins function as a carbon sink.• Declines in F v /F m under white and green light were significantly greater for green than red leaves, but were comparable under red light. Anthocyanin content positively correlated with antioxidant activity. Although levels of anthocyanins did not appear to be related to nonstructural carbohydrate concentration, high levels of sugars may be necessary for their photoinduction.• Results suggest that anthocyanins function as light attenuators and may also contribute to the antioxidant pool in winter leaves.

Summary• Juvenile leaves in high-light environments commonly appear red as a result of anthocyanin pigments, which play a photoprotective role during light-sensitive ontogenetic stages. The loss of anthocyanin during leaf development presumably corresponds to a decreased need for photoprotection, as photosynthetic maturation allows leaves to utilize higher light intensities. However, the relationship between photosynthetic development and anthocyanin decline has yet to be quantitatively described.• In this study, anthocyanin concentration was measured against photopigment content, lamina thickness, anatomical development, and photosynthetic CO 2 exchange in developing leaves of three deciduous tree species.• In all species, anthocyanin disappearance corresponded with development of c. 50% mature photopigment concentrations, c. 80% lamina thickness, and differentiation of the mesophyll into palisade and spongy layers. Photosynthetic gas exchange correlated positively with leaf thickness and chlorophyll content, and negatively with anthocyanin concentration. Species with more rapid photosynthetic maturation lost anthocyanin earliest in development. Chlorophyll a/b ratios increased with leaf age, and were lower than those of acyanic species, consistent with a shading effect of anthocyanin.• These results suggest that anthocyanin reassimilation is linked closely with chloroplast and whole-leaf developmental processes, supporting the idea that anthocyanins protect tissues until light processing and carbon fixation have matured to balance energy capture with utilization.

Summary• Red-pigmented leaf margins are common, but their functional significance is unknown. We hypothesized that red leaf margins reduce leaf herbivory by signalling to herbivorous insects the presence of increased chemical defences.• Leaves were collected from a natural population of Pseudowintera colorata. Margin size, herbivory damage, anthocyanin content and concentrations of polygodial, a sesquiterpene dialdehyde with antifeedant properties, were quantified. Feeding trials involving larvae of Ctenopseustis obliquana, a generalist herbivore, were conducted on red-and green-margined P. colorata leaves in darkness, or under white, green or red light.• Leaves with wider red margins contained higher concentrations of polygodial and anthocyanins, and incurred less natural herbivory. In trials under white light, C. obliquana consumed disproportionately more green-than red-margined leaf laminae. Larvae exhibited no feeding preference when light was manipulated such that leaf colour discrimination was impaired.• Red leaf margins provide a reliable and effective visual signal of chemical defence in P. colorata. Ctenopseustis obliquana larvae perceive and respond to the colour of the leaf margins, rather than to olfactory signals. Our study provides direct experimental evidence for aposematic coloration in red leaves.

SummaryLeaf reddening during autumn in senescing, deciduous tree species has received widespread attention from the public and in the scientific literature, whereas leaf reddening in evergreen species during winter remains largely ignored. Winter reddening can be observed in evergreen herbs, shrubs, vines and trees in Mediterranean, temperate, alpine, and arctic regions, and can persist for several months before dissipating with springtime warming. Yet, little is known about the functional significance of this colour change, or why it occurs in some species but not others. Here, the biochemistry, physiology and ecology associated with winter leaf reddening are reviewed, with special focus on its possible adaptive function. Photoprotection is currently the favoured hypothesis for winter reddening, but alternative explanations have scarcely been explored. Intraspecific reddening generally increases with sunlight incidence, and may also accompany photosynthetic inferiority in photosynthetically 'weak' (e.g. low-nitrogen) individuals. Red leaves tend to show symptoms of shade acclimation relative to green, consistent with a photoprotective function. However, winter-red and winter-green species often cohabitate the same high-light environments, and exhibit similar photosynthetic capacities. The factors dictating interspecific winter leaf colouration therefore remain unclear. Additional outstanding questions and future directions are also highlighted, and possible alternative functions of winter reddening discussed.