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| − | [[image:Monocot vs dicot crop Pengo.jpg|thumb|Monocot (left) and dicot (right) seedlings]] | + | [[Image:Upload.png|thumb|[[Special:Upload|Upload image!]]]] |
| | + | A young plant raised from [[seed]]; a plant direct from seed without the intervention of [[graft]]ing of any kind.{{SCH}} |
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| − | A '''seedling''' is a young plant [[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 [[cotyledon]]s (seed leaves). The two classes of [[flowering plant]]s are distinguished by their numbers of seed leaves: [[Monocotyledon]]s (monocots) have one blade-shaped cotyledon, whereas [[dicotyledon]]s (dicots) have two round cotyledons. [[Gymnosperm]]s 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 [[acotyledon]]s.
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| − | == Germination and early seedling development ==
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| − | [[image:Acer seedling drawing.png|thumb|left|Development of an angiosperm (maple) seedling]]
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| − | {{main|Germination}} | |
| − | During germination, the young plant emerges from its protective seed coat with its radicle first, followed by the cotyledons. The radical orients towards gravity, while the hypocotyl orients away from gravity and elongates through cell expansion to push the cotyledons out of the ground.
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| − | == Photomorphogenesis and skotomorphogenesis ==
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| − | {{main|Photomorphogenesis}}
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| − | {{main|Etiolation}}
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| − | Dicot seedlings grown in the light develop short hypocotyls and open cotyledons exposing the [[epicotyl]]. This is also referred to as [[photomorphogenesis]]. In contrast, seedlings grown in the dark develop long hypocotyls and their cotyledons remain closed around the epicotyl in an ''apical hook''. This is referred to as skotomorphogenesis or [[etiolation]]. Etiolated seedlings are yellowish in color as [[chlorophyll]] synthesis and [[chloroplast]] development depend on light. They will open their cotyledons and turn green when treated with light.
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| − | In a natural situation, seedling development starts with skotomorphogenesis while the seedling is growing through the soil and attempting to reach the light as fast as possible. During this phase, the cotyledons are tightly closed and form the ''apical hook'' to protect the shoot [[apical meristem]] from damage while pushing through the soil. In many plants, the seed coat still covers the cotyledons for extra protection.
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| − | Upon breaking the surface and reaching the light, the seedling's developmental program is switched to photomorphogenesis. The cotyledons open upon contact with light (splitting the seed coat open, if still present) and become green, forming the first photosynthetic organs of the young plant. Until this stage, the seedling lives off the energy reserves stored in the seed. The opening of the cotyledons exposes the shoot apical meristem and the ''plumule'' consisting of the first ''true leaves'' of the young plant.
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| − | The seedlings sense light through the light receptors [[phytochrome]] (red and far-red light) and [[cryptochrome]] (blue light). [[Mutation]]s in these photo receptors and their [[signal transduction]] components lead to seedling development that is at odds with light conditions, for example seedlings that show photomorphogenesis when grown in the dark.
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| − | == Seedling growth and maturation ==
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| − | [[image:Pseudotsuga seed seedling.png|thumb|left|Development of a gymnosperm (Douglas fir) seedling]]
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| − | Once the seedling starts to [[Photosynthesis|photosynthesize]], it is no longer dependent on the seed's energy reserves. The apical meristems start growing and give rise to the [[root]] and [[shoot]]. The first "true" [[Leaf|leaves]] expand and can often be distinguished from the round cotyledons through their species-dependent distinct shapes. While the plant is growing and developing additional leaves, the cotyledons eventually [[Senescence|senesce]] and fall off.
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| − | ==Consumption of seedlings==
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| − | {{Unreferenced|date=March 2007}}
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| − | Seedlings are commonly eaten as a health food. These seedlings are usually labeled [[Sprouting|sprout]]s, but in a botanical sen
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| − | se are actually seedlings. There is controversy in whether seedlings, or sprouts, are really worth eating. These seedlings are used many times in organic foods and are eaten for their concentrations of certain vitamins the seedling naturally contains. This can be viewed out of proportion as the seedling is usually too small to contain enough vitamins or minerals to be in line with the amount they are claimed to obtain.
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| − | == Bibliography ==
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| − | {{wikibooks}}
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| − | *P.H. Raven, R.F. Evert, S.E. Eichhorn (2005): ''Biology of Plants'', 7th Edition, W.H. Freeman and Company Publishers, New York, ISBN 0-7167-1007-2
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| − | {{commons|Category:Seedlings}}
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| − | <gallery>
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| − | image:Seedling 2005-12-19.jpg|A seedling emerges
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| − | image:Sunflower seedlings.jpg|Three-day-old sunflower seedlings
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| − | image:Seekiefer (Pinus pinaster) 7d.jpg|Seven-day-old pine seedling
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| − | </gallery>
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| − | [[Category:Plant morphology]]
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| − | [[Category:Plant reproduction]]
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