A seedling is a young plant sporophyte developing out of a plant embryo from a seed. All land plants and some Algae, have life cycles in which a haploid Gametophyte generation alternates with a Diploid sporophyte, the generation of a A seed (in some plants referred to as a kernel) is a small embryonic Plant enclosed in a covering called the seed coat usually with some stored Seedling development starts with germination of the seed. Germination is the process whereby growth emerges from a period of dormancy A typical young seedling consists of three main parts: the radicle (embryonic root), the hypocotyl (embryonic shoot), and the cotyledons (seed leaves). In Botany, the radicle is the first part of a Seedling (a growing plant Embryo) to emerge from the Seed during the process of Hypocotyl is a botanical term for a part of a germinating seedling of a Seed Plant. A cotyledon ("seed leaf" from Greek: κοτυληδών kotylēdōn, from κοτύλη ''kotýlē'', "cup bowl" The two classes of flowering plants are distinguished by their numbers of seed leaves: Monocotyledons (monocots) have one blade-shaped cotyledon, whereas dicotyledons (dicots) have two round cotyledons. The flowering plants or angiosperms ( Angiospermae or Magnoliophyta) are the most widespread group Monocotyledons or monocots are one of two major groups of Flowering plants (angiosperms that are traditionally recognised the other being Dicotyledons Dicotyledons, or "dicots", is a name for a group of Flowering plants whose Seed typically has two embryonic leaves or Cotyledons There Gymnosperms are more varied. Gymnosperm (Gymnospermae are a group of Spermatophyte seed-bearing Plants with Ovules on the edge or blade of an open Sporophyll, which are For example, pine seedlings have up to eight cotyledons. This article is about the tree For other uses of the term "pine" see Pine (disambiguation. The seedlings of some flowering plants have no cotyledons at all. These are said to be acotyledons. Acotyledon is used to refer to Seed plants or spermatophytes that lack cotyledons such as Orchids and Dodder.
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Germination and early seedling development
During germination, the young plant emerges from its protective seed coat with its radicle first, followed by the cotyledons. Germination is the process whereby growth emerges from a period of dormancy The radicle orients towards gravity, while the hypocotyl orients away from gravity and elongates through cell expansion to push the cotyledons out of the ground.
Photomorphogenesis and skotomorphogenesis
Dicot seedlings grown in the light develop short hypocotyls and open cotyledons exposing the epicotyl. In Developmental biology, photomorphogenesis is Light -mediated development Etiolation occurs when plants are grown in either partial or complete absence of light and is characterized by long weak stems smaller sparser leaves due to longer internodes and a In Plant physiology, the epicotyl is the embryonic shoot above the Cotyledons In most plants the epicotyl will eventually develop into the stem and the leaves This is also referred to as photomorphogenesis. In Developmental biology, photomorphogenesis is Light -mediated development In contrast, seedlings grown in the dark develop long hypocotyls and their cotyledons remain closed around the epicotyl in an apical hook. Hypocotyl is a botanical term for a part of a germinating seedling of a Seed Plant. This is referred to as skotomorphogenesis or etiolation. Etiolation occurs when plants are grown in either partial or complete absence of light and is characterized by long weak stems smaller sparser leaves due to longer internodes and a Etiolated seedlings are yellowish in color as chlorophyll synthesis and chloroplast development depend on light. Chlorophyll is a green Pigment found in most Plants Algae and Cyanobacteria. Chloroplasts are Organelles found in Plant cells and eukaryotic Algae that conduct Photosynthesis. They will open their cotyledons and turn green when treated with light.
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. A meristem is a tissue in all Plants consisting of undifferentiated cells ( meristematic cells) and found in zones of the plant where growth can take place In many plants, the seed coat still covers the cotyledons for extra protection.
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.
The seedlings sense light through the light receptors phytochrome (red and far-red light) and cryptochrome (blue light). Phytochrome is a Photoreceptor, a Pigment that Plants use to detect light Cryptochrome is a name used for the Blue Light Photoreceptors of Plants and Animals The word cryptochrome derives from Mutations 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. In biology mutations are changes to the Nucleotide sequence of the Genetic material of an organism In Biology, signal transduction refers to any process by which a cell converts one kind of signal or stimulus into another
Seedling growth and maturation
Once the seedling starts to photosynthesize, it is no longer dependent on the seed's energy reserves. Photosynthesis is a Metabolic pathway that converts Light Energy into Chemical energy. The apical meristems start growing and give rise to the root and shoot. ROOT is an object-oriented program and library developed by CERN. Shoots are new plant growth they can include stems, flowering stems with flower buds leaves The first "true" leaves expand and can often be distinguished from the round cotyledons through their species-dependent distinct shapes. In Botany, a leaf is an above-ground Plant organ specialized for Photosynthesis. While the plant is growing and developing additional leaves, the cotyledons eventually senesce and fall off. Senescence refers to the biological processes of a living Organism approaching an advanced age (i
Consumption of seedlings
Seedlings are commonly eaten as a health food. These seedlings are usually labeled sprouts, but in a botanical sense are actually seedlings. Sprouting is the practice of soaking draining and then rinsing seeds at regular intervals until they Germinate, or sprout 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.
Bibliography
- 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
 A seedling emerges |
 Three-day-old sunflower seedlings |
_7d.jpg/120px-Seekiefer_(Pinus_pinaster)_7d.jpg) Seven-day-old pine seedling |
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