Biology · Ch 13 — Plant Growth and Development
Development: The Developmental Sequence in a Plant Cell
Development: The Developmental Sequence in a Plant Cell
Development is the term used to describe everything a plant does, over its life, to build its final form and function -- formally, it is the sum of growth (an irreversible increase in size) and differentiation (the acquisition of specialised structure and function), taken together. Because a plant's overall genetic programme allows it to build very different kinds of structures at different times, plant development is generally described as branching into two broad pathways: a vegetative pathway, producing roots, stems and leaves, and, once the plant receives the appropriate internal and external cues, a reproductive (floral) pathway, producing flowers, fruits and seeds instead.
Traced at the level of a single cell, the developmental sequence a plant cell derived from a root or shoot apical meristem is capable of following runs: the cell begins as an actively dividing meristematic cell; it then undergoes growth, chiefly by vacuolar water uptake during the elongation phase described earlier in this chapter; it then differentiates into a specific, mature cell type suited to a particular function (such as a xylem vessel element or an epidermal cell); depending on the tissue and the conditions the plant later encounters, some already-differentiated cells may subsequently dedifferentiate, regaining the capacity to divide, and the cells this dedifferentiated tissue produces then redifferentiate into a (possibly different) mature cell type once again; and, at the end of the cell's or the organ's functional life, it enters senescence -- a genetically programmed, orderly decline in metabolic activity, nutrient content and structural integrity -- which in due course leads to the death of that cell, organ, or (for an annual plant) the entire individual. …
Worked out. A short explanatory note box on plant developmental plasticity -- the ability of a plant to follow more than one distinct developmental pathway in response to its environment or its own stage of growth, producing structures of visibly different form from what is, genetically, the very same plant. Heterophylly, the production of differently shaped leaves at different stages or in different environments on one individual, is the clearest example: cotton and coriander produce simple, rounded juvenile leaves that are replaced by dissected, lobed mature-form leaves as the plant ages, while the buttercup (Ranunculus) growing partly submerged in water produces finely dissected, thread-like leaves underwater but broader, more typically leaf-shaped leaves in air. This plasticity is a normal, adaptive feature of plant development, not an abnormality, and is one of the clearest visible de …