DISSERTATION RESEARCH: Evolution of Mangrove Seed Physiology

建议：9623313 PI：凯洛格和法恩斯沃斯全面了解种子干燥和休眠机制，对于为农场、植物园、植物园和种子保护库制定适当的储存、种植和萌发方案至关重要。脱水不耐受的进化及其发育表现、胎生和顽固，将在四个系统发育独立的红树林谱系的种子中进行研究。休眠(正统)种子的胚胎在进入代谢休眠之前通常会失去水分；相比之下，不能忍受干燥的“顽固”种子没有表现出休眠，一些种子在亲本植物上生动地萌发。虽然这种现象在旱地被子植物中很少见，但在沿海红树林、水稻和潮湿的森林树木中经常出现，对农业和种子保护具有重要意义。我们假设，脱水不耐受是由三种不相互排斥的进化修饰之一引起的：(1)胚胎发生期间植物激素脱落酸(ABA)水平的降低(它控制着整个植物对淹水的渗透调节，以及正统种子的休眠)；(2)顽固种子中脱水蛋白、碳水化合物储备或其他激素的差异水平；(3)种皮、母体转移组织或胚胎/胚乳关系的解剖改变，可能使胚胎免受物理或生化萌发抑制物的影响。为了验证这些假设，我们将在一项关于种子发育和萌发的研究中，检查四个胎生红树林家族共有的干燥不耐受的激素、生理和解剖学基础。胎生物种的种子将与亲缘关系密切的非胎生类群的种子进行比较，以确定在这种平行进化模式中是否在种子结构和生理上一致地出现了类似的、功能上的显著变化。这一综合方法将在几个生物学水平上阐明这种进化趋同的性质；澄清胎生和正统种子发育过程中解剖学、激素生理学、蛋白质和糖代谢之间的关系；并提供一些关于激素在植物生活史进化中作用的第一批文献。这些关于控制种子休眠和顽固的多种相互作用因素的比较数据可以为植物保护、繁殖和农业战略提供有用的信息。

Proposal: 9623313 PI: Kellogg and Farnsworth A comprehensive understanding of mechanisms of seed drying and dormancy is critical to developing appropriate storage, planting, and germination protocols for farms, arboreta, botanical gardens, and seed conservation banks. The evolution of desiccation-intolerance, and its developmental manifestations, vivipary and recalcitrance, will be studied in seeds of four phylogenetically independent mangrove lineages. Embryos of dormant (orthodox) seeds normally lose water prior to entering metabolic quiescence; by contrast, "recalcitrant" seeds that are intolerant of desiccation show no dormancy, and some sprout viviparously on the parent plant. While rare among upland angiosperms, this phenomenon appears frequently among coastal mangroves, rice, and wet- forest trees, with important implications for agriculture and seed conservation. We hypothesize that desiccation- intolerance results from one of three alternative evolutionary modifications that are not mutually exclusive: (1) decreased levels of the plant hormone abscisic acid, ABA, during embryogenesis (which controls both osmotic adjustment of the whole plant to flooding, and dormancy in orthodox seeds); (2) differential levels of dehydrin proteins, carbohydrate reserves, or other hormones in recalcitrant seeds; (3) altered anatomy of the seed coat, maternal transfer tissues, or embryo/endosperm relationship that may free the embryo from influences of physical or biochemical germination inhibitors. To test among these hypotheses, we will examine the hormonal, physiological, and anatomical bases of desiccation-intolerance that are shared among four viviparous mangrove families, in a study of seeds through development and germination. Seeds of viviparous species will be compared with seeds of closely related, non- viviparous taxa to determine whether similar, functionall y significant changes in seed structure and physiology have arisen consistently in this pattern of parallel evolution. This integrated approach will elucidate the nature of this evolutionary convergence at several biological levels; clarify relationships between anatomy, hormonal physiology, proteins and sugar metabolism during development of viviparous and orthodox seeds; and provide some of the first documentation of the role of hormones in the evolution of plant life histories. These comparative data on multiple, interacting factors controlling seed dormancy and recalcitrance can usefully inform strategies for plant conservation, propagation, and agriculture.