Regulation of Period and Pattern of Vegetative Development in Maize

从营养生长(不确定生长)到生殖生长(确定生长)的转变是高等植物枝条发育的一个重要转变。这种转变发生在茎顶端分生组织，该区域启动原基，在营养发育过程中分化为茎组织分隔的叶，或在生殖发育过程中分化为花器官。这一转变的时机对枝条的构型有深远的影响，也影响作物的产量。在植物中，调控向开花过渡的机制开始被理解，在植物中，这种过渡发生在对环境提示的反应中。然而，许多其他植物在不同的环境中开花。在这些植物中，人们认为从营养生长到开花的时间转换的主要决定因素是发育程序，而人们对此知之甚少。这里提出的实验的目的是检查在后一类植物玉米中转换成花的发育程序的各个方面。分生组织从植物的其他地方接收信息，并通过持续的叶起始(不确定的)或决定确定的生长并形成花序--雄穗--来作出反应。这位研究人员将通过器官培养技术检查该信息的潜在来源。这些实验将为最终识别信号奠定基础，这些信号通过个体发育向分生组织告知它们的进展，从而导致对玉米新梢形态的精确调控。玉米营养枝顶端分生组织是层次分生的，通常分生组织的最下层细胞(在外围)将形成植株的第一个节，中分生组织细胞形成后的节，上层细胞形成植株的顶端。最有可能参与再生组织结构形成的细胞位于分生组织的顶端。通过切除和培养来重置分生组织，会导致分生组织形成比正常情况下更多的节点。一个不可避免的结果是，分生组织中至少一些细胞对新梢的贡献发生了变化。这位调查者将使用克隆分析来确定重置植物额外节内分生组织的起源。这些信息将有助于理解分生组织内细胞相对于它们将贡献的植物部分的灵活性，以及由于切除和培养而重置分生组织所发生的重组的性质。这也可能对通过茎分生组织转化玉米具有实际意义。还计划进行实验，通过培养携带光合作用突变的植物来检验重置枝条发育程序的分子本质，这种突变可以在枝条的正常发育过程中受到抑制。作为植物发育程序的一部分，这些实验有望提供对连续节分化过程中基因表达水平的正常变化的洞察。

Switching from vegetative (indeterminate) to reproductive (determinate) growth is a major transition in the development of the shoot in higher plants. This transition occurs at the shoot apical meristem, the region that initiates primordia that differentiate as leaves separated by stem tissue during vegetative development or as floral organs during reproductive development. The timing of this transition has profound effects on the architecture of the shoot, as well as influencing yield in crop plants. The mechanism regulating the transition to flowering is beginning to be understood in plants in which the transition occurs in response to environmental cues. However, many other plants flower in a variety of environments. In these plants it is believed that the primary determinant of the timing of the transition from vegetative growth to flowering is a developmental program, of which little is known. The objective of the experiments proposed here is to examine various aspects of the developmental program underlying the switch to flowering in a plant of the latter group, maize. The meristem receives information from elsewhere in the plant and responds by either continuing leaf initiation (indeterminate) or becoming determined for determinate growth and forming an inflorescence, the tassel. This investigator will examine potential sources for that information by organ culture techniques. These experiments will lay the groundwork for the eventual identification of the signals that inform meristems of their progress through ontogeny, which results in the precise regulation of the morphology of maize shoots. The maize vegetative shoot apical meristem has been deduced to be organized in tiers, in which typically the lowermost cells (at the periphery) of the meristem will give rise to the first-formed nodes of the plant, midmeristem cells to the later nodes, and upper cells to the top of the plant. Cells most likely to participate in the formation of reproduct ive structures are located in the apex of the meristem. Resetting of the meristem by excision and culture results in more nodes being formed by the meristem than would normally occur. An inevitable result of this is a change in the contribution of at least some cells in the meristem to the shoot. This investigator will use clonal analysis to determine the origin within the meristem of the extra nodes of reset plants. This information will be useful for understanding the flexibility of cells within a meristem with respect to the portions of the plant to which they will contribute and the nature of the reorganization that takes place as a meristem is reset by excision and culture. This may also have practical implications for transformation of maize via the shoot meristem. Experiments are also planned to examine the molecular nature of the resetting of the shoot's developmental program by culturing plants carrying a photosynthetic mutation that can become suppressed through the course of normal development of a shoot. These experiments are expected to provide insight into normal changes at the level of gene expression in differentiation of successive nodes as part of the developmental program of the plant.