Response to Crowding and Vegetation Shade in Impatiens capensis: Genetic Variation and Fitness Consequences

施密特9806858许多植物对拥挤和植被遮荫表现出独特的形态和生理反应。这种“遮荫”反应是由透过或反射绿色植物的光中红光与远红光波长(R：FR)的比率降低而产生的。这种R：FR信号被称为光敏色素的光敏分子所感知。据推测，光敏色素介导的遮荫回避反应对植物是有益的，因为它使植物能够预见和避免密集林分中对光的竞争。一个相关项目的最新结果有力地支持了这一假设。在田间试验中，光敏色素介导的茎伸长增加了本地一年生凤仙花(珠宝草或Touch-Me-Not)在密林中的繁殖，但在低密度下诱导表现出遮荫回避反应的植株比未伸长的植株适合度降低，显然是由于未测量的生理成本。这项研究的目的是调查这一成本背后可能的生态、生理和遗传机制，并量化自然种群中遮荫回避特征的自然选择的频率和模式。一个具体的目标是确定遮荫回避反应是否导致由于缺乏保护性色素而增加紫外线-B辐射的损害，并测试形态反应的遗传变异或对紫外线-B的敏感性。为了解决这些问题，将通过操纵R：FR球杆从复制的自交系中产生伸长和非伸长的幼苗，并将其种植到自然种群和实验园的一系列处理中。该项目的结果将提供有关光敏色素介导的遮荫反应在自然植物种群中的作用的重要信息，并将为当前植物对光反应的分子、遗传、发育和生理机制的研究提供生态和进化背景。它还将有助于为作物改良的选择战略提供信息，并为最近提出的通过对遮荫反应受阻的作物进行基因工程来提高产量的提议提供生态背景。这一结果也将有助于理解野生植物在当前全球快速变化时期将如何应对日益增加的紫外线辐射水平。

Schmitt 9806858 Many plant species exhibit characteristic morphological and physiological responses to crowding and vegetation shade. This "shade avoidance" response is cued by a reduction in the ratio of red to far-red wavelengths (R:FR) in light transmitted through or reflected from green vegetation. This R:FR signal is perceived by light-sensing molecules known as phytochromes. It has been hypothesized that phytochrome-mediated shade avoidance responses are beneficial to plants because it enables them to anticipate and avoid competition for light in dense stands. Recent results from a related project strongly support this hypothesis. In a field experiment, phytochrome-mediated stem elongation increased the reproduction of the native annual Impatiens capensis (jewelweed or touch-me-not) in dense stands, but plants induced to display the shade avoidance response at low density suffered reduced fitness relative to non-elongated plants, apparently due to an unmeasured physiological cost. The objectives of the proposed research are to investigate the possible ecological, physiological, and genetic mechanisms underlying this cost, and to quantify the frequency and pattern of natural selection on shade avoidance traits within a natural population. A specific goal is to determine whether the shade avoidance response results in increased damage from ultraviolet-B radiation due to a lack of protective pigments, and to test for genetic variation in morphological responses or sensitivity to UV-B. To address these questions, elongated and non-elongated seedlings from replicated inbred lines will be produced by manipulation of the R:FR cue, and planted into a series of treatments in a natural population and an experimental garden. The results of this project will provide important information about the role of phytochrome-mediated shade avoidance responses in natural plant populations, and will provide an ecological and evolutionary context for current research on the molecular, genetic, developmental, and physiological mechanisms underlying plant responses to light. It will also help to inform selection strategies for crop improvement and provide an ecological context for recent proposals to increase yield by genetically engineering crops in which shade avoidance responses are blocked. The results will also be valuable for understanding how wild plants will respond to increasing UV radiation levels during the current period of rapid global change.