Axillary meristem development. Budding relationships between networks controlling flowering, branching, and photoperiod responsiveness

Abstract

Morphology in many animals is preordained during embryonic development and remains unchanged by environment. In contrast, vast differences in phenotype can occur in plants of identical genotype in different environments. Being sessile organisms, plants must rely on morphological and physiological plasticity to cope with a variable environment. The basis for this ability is the maintenance of numerous pluripotent stem cell clusters called meristems. During embryonic development, plants produce a shoot and a root apical meristem. It is unclear whether axillary meristems are produced de novo in leaf axils or whether they are derived from the apical meristem of the primary shoot (Grbiæ and Bleecker, 2000). Variation in the timing of the initiation and development of axillary mersitems can be observed by comparing the rosette crucifer, Arabidopsis, with the caulescent legume, pea (Pisum sativum). Arabidopsis has delayed axillary meristem initiation, causing some nodes to be devoid of axillary meristems (Grbiæ and Bleecker, 2000). Subsequent development of these meristems may also be delayed such that a pronounced axillary bud is often not observed. Pea develops axillary meristems at most nodes along its stem, and development usually proceeds apparently uninhibited up to the stage of a dormant bud that consists of several undeveloped leaves and internodes.