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How does primary growth increase the length of roots and shoots?
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Plant
Grandidier's baobas (Adansonia grandidieri) in Madagascar.
Primary growth, which increases the length of roots and shoots, is driven by the activity of apical meristems—regions of actively dividing cells located at the tips of these organs.123
The process involves two main stages:
- Cell Division: Within the apical meristem, cells undergo mitosis to produce new cells. These cells are organized into primary meristems (protoderm, ground meristem, and procambium), which eventually differentiate into specialized tissues like the epidermis, ground tissue, and vascular system.12
- Cell Elongation: Following division, the daughter cells move into a region of elongation located just behind the meristematic center. In this zone, cells increase significantly in volume, primarily through the uptake of water into their central vacuoles. This water intake creates internal pressure that pushes against the elastic cell walls, causing the cells—and consequently the root or shoot—to lengthen.1452
While cell division provides the raw material, the actual increase in length is primarily the result of this subsequent cell enlargement.15