Models of shoot apical meristem function

Abstract

Contents Summary 37 Introduction 37 How things began 38 Cytology 39 Morphology 41 Developmental genetics 44 Conclusions 49 Acknowledgements 50 References 50 Summary In this review we describe how concepts of shoot apical meristem function have developed over time. The role of the scientist is emphasized, as proposer, receiver and evaluator of ideas about the shoot apical meristem. Models have become increasingly popular over the last 250 years, and we consider their role. They provide valuable grounding for the development of hypotheses, but in addition they have a strong human element and their uptake relies on various degrees of persuasion. The most influential models are probably those that most data support, consolidating them as an insight into reality; but they also work by altering how we see meristems, re‐directing us to influence the data we collect and the questions we consider meaningful.

INCOMPOSITA: a MADS-box gene controlling prophyll development and floral meristem identity inAntirrhinum

“…According to the theory of the 'first available space', based on microsurgical manipulations, the timing and positioning of organ initiation is regulated by the availability of the minimal free area on the meristem surface, at a minimal distance from the summit and from pre-existing primordia (Snow and Snow, 1931;Snow and Snow, 1933). In other interpretations, space itself is not decisive; a new primordium emerges at the position of weakest inhibition where the most recently formed primordium is the strongest source of inhibition (Tooke and Battey, 2003;Wardlaw, 1949). Indeed, in inco mutants, development of lateral sepal primordia is significantly delayed, owing to the aberrant initiation of prophyll primordia, but the temporal order and the principal site of their initiation are not affected.…”

ARABIDOPSIS THALIANA HOMEOBOX GENE1Establishes the Basal Boundaries of Shoot Organs and Controls Stem Growth

“…The pattern of organ initiation in the peripheral region is controlled by auxin transport (Fleming, 2005), and subsequent internode growth completes the process of establishing the arrangement of organs around the stem (Peaucelle et al, 2007). During the last several decades, cellular and genetic analysis of meristem function has focused on the central and peripheral regions, on organ initiation, and on the establishment of the lateral boundaries of primordia (Tooke and Battey, 2003). By contrast, events at the interface between the stem and the meristem or primordia have remained largely uncharacterized.…”

Charles Darwin and the Origins of Plant Evolutionary Developmental Biology

“…As Goethe would discover years after publishing his Metamorphosis of Plants, he was preceded (indeed anticipated) in the articulation of the hypothesis that the leaf is the basic constructional unit of the plant by the German natural historian Caspar Friedrich Wolff (Goethe, 1817). In 1759, Wolff published his doctoral thesis, Theoria Generationis, on epigenesis in plants and animals (Coen, 2001; see Tooke and Battey, 2003 for a synopsis of Wolff's contributions). Importantly, as Goethe later recognized, Wolff advanced the hypothesis that the leaf is the fundamental building block of the plant and that the organs of the flower (for example, petals) are transformed leaves.…”

“…Wolff was able to determine that the various determinate lateral organs of the shoot system are the same type by observing that vegetative leaves and floral organs all share a similar developmental inception from undifferentiated structures on the flanks of the shoot apex (Huxley, 1853;Tooke and Battey, 2003;Steeves, 2006). Wolff, who proved that leaves are not preformed (that is, the mature structure does not exist in miniature form) but are initiated de novo (epigenesis), was the first to illustrate the shoot apex of a plant ( Figure 2) with its leaf primordia and to demonstrate the common developmental origin of all mature leaf types.…”