Seed catalogs are arriving, and gardeners are planning their vegetable gardens and flower beds. A seed is a miniature undeveloped plant embryo, with stored food and enclosed in a protective coating.
Lowe’s offers a good selection of seeds but lacks specialty options. They also have a good return policy.
Embryonic Development
The seed consists of three compartments, the embryo, endosperm, and seed coat, that originate from different cells within the ovule and have varying complements of maternal and paternal genomes (Bewley and Black 1994). In the early morphogenesis phase, the embryo develops its body plan by rearrangement of cells in the zygote known as gastrulation. During this process, the cells fold over each other and form three layers of tissues, namely the ectoderm, which produces the skin and nervous system; the mesoderm, from which develop the connective tissue, muscles, and bones; and the endoderm, which forms the digestive tract, lungs, and urinary system.
Our results indicate that the ap2 mutant has a major impact on seed mass, primarily because of alterations in the growth of the embryo and the endosperm. The ap2 mutant exhibits an extended period of rapid endosperm growth early in development that is associated with delayed endosperm cellularization and overgrowth of the central vacuole. The ap2 mutation also delays the onset of the maturation phase in the endosperm, as evidenced by persistent periclinal cell divisions at the periphery of cellularized syncytium.
Germination
Seed germination is the process of turning a seed into a seedling. It is an important biological phenomenon because it determines continuous plant production, which is critical for human survival. Seed germination can be stimulated by a variety of factors, including temperature, light, humidity, water, and nutrients.
Water uptake (imbibition) is the first step in germination, and is followed by radicle and plumule emergence from the seed. During this phase, metabolic processes that were suspended during dormancy resume and the seed’s structure is altered.
Priming seeds are pretreated with various chemicals before they are imbibed to enhance their germination capacity under stress. This involves reducing the lag phase of imbibition, increasing the activation of enzymes involved in germination, decreasing the accumulation of reactive oxygen species and lipid peroxidation, and accelerating osmotic adjustment and starch metabolism. Priming can also improve germination of halophytes by allowing them to tolerate higher salinity. However, it should be noted that priming agents are not effective under all conditions.
Imbibition
Water is absorbed by solid particles of the imbibant such as seeds or dried wood in the process of imbibition. A steep water potential gradient exists between the absorbing and imbibed material. Hence, the volume of the imbibant increases. Water absorbs more easily into protein and starch than into cellulose because of their hydrophilic nature. This is known as the imbibition potential of a substance or its matric potential.
Water absorbed during imbibition is used to hydrate the seed and initiate germination. The hydration of the seed is facilitated by abscisic acid (ABA) and gibberellins (GA), plant hormones. The expression levels of genes encoding for ABA synthesis and deactivation are important in determining seed dormancy and germination.
The hydration of the seeds is indicated externally by the wrinkles that develop in their seed coat. The wrinkling pattern correlates with the position of the cotyledons in the seed. The wrinkling of the seed is due to imbibition pressure, which is the force that pushes water molecules into the roots from the surface.
Drying
The amount of moisture present in seed is an important factor affecting its quality and storability during long term storage. Drying seed to 4-6% moisture content on wet basis decelerates the rate of seed deterioration exorbitantly.
Seeds are dried either naturally on trays or floors in open sun or artificially by bin drying with heated air. Sun drying is slow and prone to bird or rodent attacks while bin drying results in high initial costs, space limitations and mechanical mixtures.
To achieve low moisture contents without sacrificing seed germination, it is important to dry seed with dehumidified air. Bin drying with unheated air is not able to accomplish this since it is unable to remove the moisture from seeds at the recommended drying temperature. Bry-Air offers a system for moisture removal and sensible humidity control in conjunction with refrigeration equipment which is used extensively by seed processors around the world. This allows for consistent control preventing the adverse effects of humidity on the product and maintaining the integrity of the seed.
