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Abstract
Plants growing in high-light environments during winter often exhibit leaf reddening due to synthesis of anthocyanin pigments, which are thought to alleviate photooxidative stress associated with low-temperature photoinhibition through light attenuation and/or antioxidant activity. Seasonal high-light stress can be further exacerbated by a limited photosynthetic capacity, such as nitrogen-deficiency. In the present study, we test the following hypotheses using three populations of the semi-evergreen vine Lonicera japonica: (1) nitrogen deficiency corresponds with reduced photosynthetic capacity; (2) individuals with reduced photosynthetic capacity synthesize anthocyanin pigments in leaves during winter; and (3) anthocyanin pigments help alleviate high-light stress by attenuating green light. All populations featured co-occurring winter-green and winter-red leafed individuals on fully-exposed (high-light), south-facing slopes in the Piedmont of North Carolina, USA. Consistent with our hypotheses, red leaves consistently exhibited significantly lower foliar nitrogen than green leaves, as well as lower total chlorophyll, quantum yield efficiency, carboxylation efficiency, and photosynthesis at saturating irradiance (Asat). Light-response curves measured using ambient sunlight versus red-blue LED (i.e., lacking green wavelengths) demonstrated significantly reduced quantum yield efficiency and a higher light compensation point under sunlight relative to red-blue LED in red leaves, but not in green leaves, consistent with a (green) light-attenuating function of anthocyanin pigments. These results are consistent with the hypothesis that intraspecific anthocyanin synthesis corresponds with nitrogen deficiency and reduced photosynthetic capacity within populations, and support a light-attenuating function of anthocyanin pigments.
Highlights
Anthocyanins are vacuolar, flavonoid pigments synthesized via the shikimic acid pathway that impart red to purplish colors in plant tissues [1]
When individual sites were compared, winter leaf N content was highest at the RR site, with mean N content of 2.8% and 2.1% for green and red leaves respectively
When summer leaves were compared from Interstate 40 Westbound (I40), leaves on the winter-green side of the embankment continued to exhibit higher average N content relative to leaves on the winter-red side, though this difference was only marginally significant (p = 0.12)
Summary
Anthocyanins are vacuolar, flavonoid pigments synthesized via the shikimic acid pathway that impart red to purplish colors in plant tissues [1]. Of special interest to plant physiologists is the synthesis of anthocyanin pigments in photosynthetic tissues during periods of high-light stress, which may be defined generally as seasons, ontogenetic stages, and/or environmental conditions corresponding with an imbalance of light capture relative to energy processing (for reviews see [1,2,3]). According to the photoprotection hypothesis, anthocyanins protect photosynthetic tissues vulnerable to high-light stress through antioxidant activity, and/or by intercepting green quanta, thereby alleviating excess chlorophyll excitation pressure in underlying cells [1,2,3]. According to the ecological defense hypothesis, anthocyanins function to reduce damage by potential herbivores or pathogens by either: (a) reducing visibility to herbivores lacking a red photoreceptor (i.e., camouflage);
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