ABSTRACT
The light screen hypothesis states that foliar anthocyanins shade the photosynthetic apparatus from excess light. In this paper we extend the light screen hypothesis, postulating that plant species at risk of photoinhibitory conditions during autumnal leaf senescence often utilize anthocyanins to protect the photosynthetic apparatus during the period of nutrient resorption. When senescence-related photosynthetic instabilities are compounded by other environmental stresses, particularly low temperature, severe photoinhibition may result in reduced resorption of critical foliar nutrients, which can significantly affect plant fitness. There is evidence that environments where low and often freezing temperatures are common in autumn selectively favor the production of anthocyanins in senescing foliage. The stimuli for, and the timing and location of, autumnal anthocyanin production are all consistent with a photoprotective role for these pigments in senescing leaves. Furthermore, differences in nitrogen allocation strategies between early and late successional species appear to affect photosynthetic stability during leaf senescence, resulting in a reduced need for foliar autumnal anthocyanins in many early successional plants. The ecological and physiological evidence presented in this paper suggest that, for many deciduous species, the production of anthocyanins provides effective photoprotection during the critical period of foliar nutrient resorption.
Subject(s)
Anthocyanins/metabolism , Plant Leaves/physiology , Trees/physiology , Light , Plant Leaves/metabolism , Seasons , Trees/metabolismABSTRACT
Thirteen Betula species were tested for resistance to the birch leafminer, Femusa pusilla (Lepeletier), using no-choice assays. Birch leafminers were able to oviposit into expanding leaves of all Betula individuals tested. Larvae did not survive within any of the tested individuals of three species, B. alleghaniensis (Britt.), B. grossa (S. & Z.), and B. lenta (L.). Leafminer eggs deposited into the leaves of these species hatched, and larvae fed for a short period before dying. These three species were classified as highly resistant to birch leafminer, based on very low percent of mines (0.6-3.1%) with a diameter >3 mm. Eight species, B. papyrifera (Marsh), B. pendula (Roth), B. turkestanica (Litvin), B. glandulifira (Regal), B. ermanii (Cham.), B. platyphylla variety japonica [(Miq.) Hara], B. populifolia (Marsh) and B. maximowicziana (Regal) were classified as susceptible, with percent of mines >3 mm diameter of 87-94%. Two species, B. costata (Trautv.) and B. davurica (Pall.), displayed intermediate and variable resistance. B. davurica exhibited a mechanism of resistance not observed in the other species, Eggs oviposited into the leaves of resistant B. davurica individuals became surrounded by an area of discolored and necrotic tissue, and died. This response resembles the programmed cell death associated with a hypersensitive response.
