Seed is the fertilized embryo enclosed by a protective covering (testa). Seeds have food reserves and multicellularity, which give them advantages over spores. Some seeds, such as those with hooks, barbs, or sticky hairs, stick to animal fur or feathers and drop off later.
Other seeds float and wash up on beaches. They may even be carried to distant places by rivers.
Origin
Seeds evolved as a way to help plants survive and thrive on land. They have become the dominant means of plant reproduction and dominate biological niches from forests to grasslands in hot and cold climates.
The appearance of seeds is a complex process that must be understood evolutionarily and developmentally. A defining feature of seeds is a pattern of alternation of generations that appears in all plants. Like a Russian doll, each generation is found inside the other.
Phylogenetic analyses show that the seed trait arose in bryophytes and pteridophytes (bryophytes) and in gymnosperms before angiosperms. Fossil records of pre-ovules in these groups suggest that they had one integument, which paleo-botanists call unitegmic (Fig. 2). Integuments are the maternal tissue that protects the ovule and forms the seed coat in seeds.
Function
Seeds serve several key functions for the plants that produce them. They nourish the embryo or young plant, disperse to a new location and provide dormancy during unfavorable conditions. Seeds are also a means of reproduction for the plants that create them, producing a remixing of genetic material and phenotype variability on which natural selection acts.
Most products that we eat come from seeds, including grains, vegetables and legumes, fruits, and some spices and beverages. Cecilia and her colleagues are learning more about the genes that direct seed development. The work has implications for improving crop performance.
Germination
Germination is the process by which a seed or spore sprouts and grows into a plant. It can be triggered by a number of factors, including water, temperature, and light. Different seeds require different conditions to germinate.
When environmental conditions are optimal, the seed begins to absorb water through a structure called the micropyle. This process is known as water imbibition and it causes the seed to swell until it ruptures. The radicle and plumule, the first root and shoot, then emerge from the seed.
After water imbibition, metabolic processes that were suspended during dormancy begin to accelerate. One of these is the glyoxylate cycle, where stored triacylglycerols are converted to glucose which is used as an energy source during germination. Another is the oxidative pentose phosphate (OPPP) pathway which is involved in supplying NADPH for cellular respiration [167]. Lastly, phytohormones such as auxins, gibberellins, cytokinins, abscisic acid (ABA), and salicylic acid (SA) are produced.
Perennation
Seeds are a very important part of many plants as they serve as the means of reproduction. They may lie dormant for long periods of time, especially during unfavorable conditions such as drought or winter. However, they germinate readily when the proper conditions are present.
Optimal temperature ranges for germination depend on the structure of the seed. A mature seed consists of two growing regions-a root portion (radicle) and a prospective shoot portion (plumule). Some seeds have one or two cotyledons; others, including those of Pinus and other gymnosperms, contain several cotyledons.
Seeds are a valuable source of food for animals and humans. They are also an efficient natural method of propagation in which plant genetic variation is increased. The loss of a single species can have profound impacts on connected ecosystems.
Dispersal
Seed dispersal is the movement of seeds away from the parent plant. It is an important process that helps reduce interspecific competition amongst plants and also facilitates genetic exchange between populations.
Seeds can be dispersed by gravity, wind, water, or animals. Animals are a key mode of seed dispersal, and many plants have developed special structures such as burs or barbs to make it easier for animals to transport the seeds.
Plants that produce fruit-eating animals like birds, mammals and reptiles are often effective dispersers of their seeds. They lure these animals to eat their fruits by making them tasty, and then the seeds are carried away in the animal’s digestive tract or regurgitated and then deposited in its feces. This is a form of seed dispersal called syn zoochory.
