Seedling
Young sporophyte developing from a seed embryo.
A seedling is a young sporophyte developing out of a plant embryo from a seed. Seedling development starts with germination of the seed. A typical young seedling consists of three main parts: the radicle (embryonic root), the hypocotyl (embryonic shoot), and the cotyledons (seed leaves). The two classes of flowering plants (angiosperms) are distinguished by their numbers of seed leaves: monocotyledons (monocots) have one blade-shaped cotyledon, whereas dicotyledons (dicots) possess two round cotyledons. Gymnosperms are more varied. For example, pine seedlings have up to eight cotyledons. The seedlings of some flowering plants have no cotyledons at all; these are said to be acotyledons.
- field
- Botany
- known_for
- Early developmental stage of plants from seed germination through photosynthesis
- key_characteristics
- Consists of radicle, hypocotyl, and cotyledons; exhibits photomorphogenesis or skotomorphogenesis depending on light
Lore & Background
Seedling development begins with germination, producing a radicle, hypocotyl, and cotyledons. The plumule, part of the seed embryo, develops into the shoot bearing the first true leaves. In epigeal germination, the plumule grows after cotyledons emerge above ground; in hypogeal germination, the plumule grows upward while cotyledons remain below. Seedlings sense light through phytochrome and cryptochrome receptors. In darkness, they undergo skotomorphogenesis (etiolation), developing long hypocotyls and closed cotyledons in an apical hook. Upon light exposure, they switch to photomorphogenesis, opening cotyledons and turning green.
Reader's Guide
Seedlings are critical in plant life cycles, transitioning from seed reserves to photosynthesis. Their growth is influenced by light, temperature, photoperiod, carbon dioxide, and nitrogen supply. First-year seedlings often experience high mortality, primarily from drought, though in some habitats frost heave and competition become major factors. Seedlings are vulnerable to pests and diseases such as damping off, cutworms, and slugs. Transplanting typically occurs when the first pair of true leaves appear, and a vitamin hormone concentrate may be used to avoid transplant shock. Understanding seedling development informs agriculture, forestry, and horticulture practices.
Did You Know?
- Pine seedlings can have up to eight cotyledons.
- Etiolated seedlings are yellowish because chlorophyll synthesis depends on light.
- Seedlings sense light through phytochrome (red and far-red) and cryptochrome (blue) receptors.
- A photoperiod shorter than 14 hours causes seedling growth to stop.
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