Abstract
Correlations between developmentally plastic traits may constrain the joint evolution of traits. In plants, both seedling de-etiolation and shade avoidance elongation responses to crowding and foliage shade are mediated by partially overlapping developmental pathways, suggesting the possibility of pleiotropic constraints. To test for such constraints, we exposed inbred lines of Impatiens capensis to factorial combinations of leaf litter (which affects de-etiolation) and simulated foliage shade (which affects phytochrome-mediated shade avoidance). Increased elongation of hypocotyls caused by leaf litter phenotypically enhanced subsequent elongation of the first internode in response to low red∶far red (R∶FR). Trait expression was correlated across litter and shade conditions, suggesting that phenotypic effects of early plasticity on later plasticity may affect variation in elongation traits available to selection in different light environments.
Highlights
Despite extensive research into the adaptive significance of phenotypic plasticity – the ability of genotype to produce multiple phenotypes under different conditions (e.g., [1,2,3,4,5,6,7,8,9,10])– far less work has examined the extent to which responses to multiple environmental cues interact to produce integrated phenotypes (e.g., [11,12,13,14,15])
Foliage shade reduces photosynethetically active radiation available to plants and is characterized by low ratios of red light (,620–700 nm) to far red light (700–800), Many plants have the capacity for phenotypically plastic shade avoidance responses to foliage shade
A key component of shade avoidance is elongation, both as seedlings buried beneath leaf litter and soil, and as vegetative plants growing below an overhead plant canopy
Summary
Despite extensive research into the adaptive significance of phenotypic plasticity – the ability of genotype to produce multiple phenotypes under different conditions (e.g., [1,2,3,4,5,6,7,8,9,10])– far less work has examined the extent to which responses to multiple environmental cues interact to produce integrated phenotypes (e.g., [11,12,13,14,15]). A key component of shade avoidance is elongation, both as seedlings buried beneath leaf litter and soil, and as vegetative plants growing below an overhead plant canopy. In both the pre-photosynthetic seedling stage and photosynthetic vegetative stage, elongation in response to low R:FR is controlled by the phytochrome family of photoreceptors, and involves the developmental responses of cell division and expansion [29,30,31,32,33] that may cause extensive correlations between responses at the two stages. The cessation of elongation (de-etiolation) in response to light is partially mediated by phytochromes interacting with other photoreceptors and other signaling pathways [34,35,36]
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