Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, 80309, USA.
Am J Bot. 2011 Dec;98(12):1924-34. doi: 10.3732/ajb.1100098. Epub 2011 Nov 28.
Shoot architecture is a fundamentally developmental aspect of plant biology with implications for plant form, function, reproduction, and life history evolution. Mimulus guttatus is morphologically diverse and becoming a model for evolutionary biology. Shoot architecture, however, has never been studied from a developmental perspective in M. guttatus.
We examined the development of branches and flowers in plants from two locally adapted populations of M. guttatus with contrasting flowering times, life histories, and branch numbers. We planted second-generation seed in growth chambers to control for maternal and environmental effects.
Most branches occurred at nodes one and two of the main axis. Onset of branching occurred earlier and at a greater frequency in perennials than in annuals. In perennials, almost all flowers occurred at the fifth or more distal nodes. In annuals, most flowers occurred at the third and more distal nodes. Accessory axillary meristems and higher-order branching did not influence shoot architecture.
We found no evidence for trade-offs between flowers and branches because axillary meristem number was not limiting: a large number of meristems remained quiescent. If, however, quiescence is a component of meristem allocation strategy, then meristems may be limited despite presence of quiescent meristems. At the two basalmost nodes, branch number was determined by mechanisms governing either meristem initiation or outgrowth, rather than flowering vs. branching. At the third and more distal nodes, heterochronic processes contributed to flowering time and branch number differences between populations.
芽结构是植物生物学中一个基本的发育方面，对植物形态、功能、繁殖和生活史进化都有影响。金光菊（Mimulus guttatus）形态多样，正在成为进化生物学的模式生物。然而，从发育的角度来看，金光菊的芽结构从未被研究过。
我们研究了来自两个具有不同开花时间、生活史和分枝数的当地适应种群的金光菊植物的分枝和花的发育。我们在生长室中种植第二代种子，以控制母体和环境的影响。
大多数分枝发生在主轴的第一和第二个节点上。分枝的起始时间在多年生植物中比在一年生植物中更早，频率更高。在多年生植物中，几乎所有的花都发生在第五个或更远的节点上。在一年生植物中，大多数花发生在第三和更远的节点上。副腋生分生组织和更高阶的分枝不会影响芽结构。
我们没有发现花和分枝之间存在权衡的证据，因为腋生分生组织的数量不受限制：大量的分生组织处于静止状态。然而，如果静止是分生组织分配策略的一个组成部分，那么尽管存在静止的分生组织，分生组织可能仍然受到限制。在最下面的两个节点上，分枝的数量由控制分生组织起始或生长的机制决定，而不是开花与分枝。在第三和更远的节点上，异时性过程对种群之间的开花时间和分枝数量差异有贡献。
