DISSERTATION RESEARCH: The Role of Programmed Cell Death in Heartwood Formation

论文研究：程序性细胞死亡在心材形成中的作用rachel Spicer和N. Michele HolbrookHarvard university几乎在所有已知的树种中都发生心材形成，它标志着次生木质部的衰老，因此它不再在活树中起水运输或碳水化合物储存的作用。心材的形成过程是由茎内轴向和径向的薄壁细胞死亡所驱动的。这些细胞表现出惊人的寿命范围（根据物种和地点，从2年到200年不等），但实际死亡原因尚不清楚。本研究旨在验证心材形成过程中薄壁细胞死亡是一种程序性细胞死亡（programmed cell death， PCD）的假设，并推动木本植物发育的一个重要阶段。这一假设将通过将分子生物学技术应用于木材发育，包括通过荧光标记试验（TUNEL试验）原位检测核DNA片段（PCD的一个标志），以及使用凝胶电泳检测DNA片段的形成来验证。薄壁细胞死亡期间细胞超微结构的变化（即细胞膜、线粒体和细胞核形态的变化）也将与植物中与PCD相关的其他例子进行比较。所研究的物种代表了一系列木质部结构和生理，包括针叶树（东部铁杉，Tsuga canadensis），环状多孔被子植物（白蜡树，美洲白蜡树）和弥散多孔被子植物（大齿白杨，大叶杨）。这项工作的结果将为树木心材形成的新的生物学模型奠定基础。

Dissertation research: The role of programmed cell death in heartwood formationRachel Spicer and N. Michele HolbrookHarvard UniversityHeartwood formation occurs in nearly all known tree species and marks the senescence of secondary xylem, such that it no longer functions in water transport or carbohydrate storage in the living tree. The process of heartwood formation is driven by the death of parenchyma cells oriented both axially and radially within the stem. These cells exhibit a remarkable range of longevities (from 2 to 200 years, depending on species and site), but the actual cause of death is not known. This research is designed to test the hypothesis that parenchyma cell death during heartwood formation is a form of programmed cell death (PCD), and drives an important stage in woody plant development. This hypothesis will be tested through the application of molecular biological techniques to wood development, including the in situ detection of fragmentation of nuclear DNA (a hallmark of PCD) via a fluorescent-labeling assay (TUNEL assay), as well as tests for the formation of DNA fragments using gel electrophoresis. Changes in cell ultrastructure (i.e., changes in the morphology of cell membranes, mitochondria, and the nucleus) during parenchyma cell death will also be compared against those associated with other examples of PCD in plants. Species to be studied represent a range of xylem structures and physiologies, including a conifer (Eastern hemlock, Tsuga canadensis), a ring-porous angiosperm (white ash, Fraxinus americana), and a diffuse-porous angiosperm (bigtooth aspen, Populus grandidentata). Results from this work will create the foundation for a new, biological model of heartwood formation in trees.