Going with the wind--adaptive dynamics of plant secondary meristems

Abstract

The developmental plasticity of organisms is a natural consequence of adaptation. Classical approaches targeting developmental processes usually focus on genetics as the essential factor underlying phenotypic differences. However, such differences are often based on the inherent plasticity of developmental programs. Due to their dependence on environmental stimuli, plants represent ideal experimental systems in which to dissect the contribution of genetic and environmental variation to phenotypic plasticity. An evident example is the vast repertoire of growth forms observed in plant shoot systems. A fundamental factor underlying the broadness of this repertoire is the activity of secondary meristems, namely the axillary meristems that give rise to side shoots, and the cambium essential for stem thickening. Differential activities of both meristem types are crucial to the tremendous variation seen in higher plant architecture. In this review, we discuss the role of secondary meristems in the adaptation of plant growth forms, and the ways in which they integrate environmental input. In particular, we explore potential approaches for dissecting the degree to which this flexibility and its consequences for plant architecture is genetically predetermined and how much it represents an adaptive value.

Fig. 1

The influence of environmental cues on SL biosynthesis and shoot architecture and the role of SLs.

Fig. 2

Secondary growth and natural variation of secondary growth in Arabidopsis thaliana. (A) Schematic illustration of the anatomy of the primary and secondary stem. Note that the primary stem shows several discrete vascular bundles composed of phloem (yellow), xylem (blue) and cambium (red), while the secondary stem carries closed cylinders of phloem (yellow), xylem (blue) and cambium (red). (B and C) Examples of natural variation in secondary growth in Arabidopsis thaliana. B shows a cross-section collected immediately above the uppermost rosette leaf of the main stem of the Pla-1 accession. (C) shows a cross-section of the main stem of the Rou-0 accession collected at the same position. Note that Pla-1 displays more IC-derived cells (ICD) than Rou-0 (indicated by red brackets). Both accessions were harvested when the height of the main stem was 20 cm. Asterisks indicate the position of primary vascular bundles.