A cereal is a grass cultivated for its edible grain. Cereals are the world's largest crops, and are therefore staple foods. They include rice, wheat, rye, oats, barley, millet, and maize. Edible grains from other plant families, such as buckwheat and quinoa are pseudocereals. Most cereals are annuals, producing one crop from each planting, though rice is sometimes grown as a perennial. Winter varieties are hardy enough to be planted in the autumn, becoming dormant in the winter, and harvested in spring or early summer; spring varieties are planted in spring and harvested in late summer. The term cereal is derived from the name of the Roman goddess of grain crops and fertility, Ceres.
In botany, a seed is a plant embryo and food reserve enclosed in a protective outer covering called a seed coat (testa). More generally, the term "seed" means anything that can be sown, which may include seed and husk or tuber. Seeds are the product of the ripened ovule, after the embryo sac is fertilized by sperm from pollen, forming a zygote. The embryo within a seed develops from the zygote and grows within the mother plant to a certain size before growth is halted.
Vernalization is the induction of a plant's flowering process by exposure to the prolonged cold of winter, or by an artificial equivalent. After vernalization, plants have acquired the ability to flower, but they may require additional seasonal cues or weeks of growth before they will actually do so. The term is sometimes used to refer to the need of herbal (non-woody) plants for a period of cold dormancy in order to produce new shoots and leaves, but this usage is discouraged.
Germination is the process by which an organism grows from a seed or spore. The term is applied to the sprouting of a seedling from a seed of an angiosperm or gymnosperm, the growth of a sporeling from a spore, such as the spores of fungi, ferns, bacteria, and the growth of the pollen tube from the pollen grain of a seed plant.
Dormancy is a period in an organism's life cycle when growth, development, and physical activity are temporarily stopped. This minimizes metabolic activity and therefore helps an organism to conserve energy. Dormancy tends to be closely associated with environmental conditions. Organisms can synchronize entry to a dormant phase with their environment through predictive or consequential means. Predictive dormancy occurs when an organism enters a dormant phase before the onset of adverse conditions. For example, photoperiod and decreasing temperature are used by many plants to predict the onset of winter. Consequential dormancy occurs when organisms enter a dormant phase after adverse conditions have arisen. This is commonly found in areas with an unpredictable climate. While very sudden changes in conditions may lead to a high mortality rate among animals relying on consequential dormancy, its use can be advantageous, as organisms remain active longer and are therefore able to make greater use of available resources.
Plant hormones are signal molecules, produced within plants, that occur in extremely low concentrations. Plant hormones control all aspects of plant growth and development, including embryogenesis, the regulation of organ size, pathogen defense, stress tolerance and reproductive development. Unlike in animals each plant cell is capable of producing hormones. Went and Thimann coined the term "phytohormone" and used it in the title of their 1937 book.
Gibberellins (GAs) are plant hormones that regulate various developmental processes, including stem elongation, germination, dormancy, flowering, flower development, and leaf and fruit senescence. GAs are one of the longest-known classes of plant hormone. It is thought that the selective breeding of crop strains that were deficient in GA synthesis was one of the key drivers of the "green revolution" in the 1960s, a revolution that is credited to have saved over a billion lives worldwide.
The endodermis is the innermost layer of cortex in land plants. It is a cylinder of compact living cells, the radial walls of which are impregnated with hydrophobic substances to restrict apoplastic flow of water to the inside. The endodermis is the boundary between the cortex and the stele.
The endosperm is a tissue produced inside the seeds of most of the flowering plants following double fertilization. It is triploid in most species, which may be auxin-driven. It surrounds the embryo and provides nutrition in the form of starch, though it can also contain oils and protein. This can make endosperm a source of nutrition in animal diet. For example, wheat endosperm is ground into flour for bread, while barley endosperm is the main source of sugars for beer production. Other examples of endosperm that forms the bulk of the edible portion are coconut "meat" and coconut "water", and corn. Some plants, such as orchids, lack endosperm in their seeds.
Plant embryonic development, also plant embryogenesis is a process that occurs after the fertilization of an ovule to produce a fully developed plant embryo. This is a pertinent stage in the plant life cycle that is followed by dormancy and germination. The zygote produced after fertilization must undergo various cellular divisions and differentiations to become a mature embryo. An end stage embryo has five major components including the shoot apical meristem, hypocotyl, root meristem, root cap, and cotyledons. Unlike the embryonic development in animals, and specifically in humans, plant embryonic development results in an immature form of the plant, lacking most structures like leaves, stems, and reproductive structures. However, both plants and animals including humans, pass through a phylotypic stage that evolved independently and that causes a developmental constraint limiting morphological diversification.
In developmental biology, photomorphogenesis is light-mediated development, where plant growth patterns respond to the light spectrum. This is a completely separate process from photosynthesis where light is used as a source of energy. Phytochromes, cryptochromes, and phototropins are photochromic sensory receptors that restrict the photomorphogenic effect of light to the UV-A, UV-B, blue, and red portions of the electromagnetic spectrum.
The ground tissue of plants includes all tissues that are neither dermal nor vascular. It can be divided into three types based on the nature of the cell walls. This tissue system is present between the dermal tissue and forms the main bulk of the plant body.
- Parenchyma cells have thin primary walls and usually remain alive after they become mature. Parenchyma forms the "filler" tissue in the soft parts of plants, and is usually present in cortex, pericycle, pith, and medullary rays in primary stem and root.
- Collenchyma cells have thin primary walls with some areas of secondary thickening. Collenchyma provides extra mechanical and structural support, particularly in regions of new growth.
- Sclerenchyma cells have thick lignified secondary walls and often die when mature. Sclerenchyma provides the main structural support to a plant.
Florigens are proteins capable of inducing flowering time in angiosperms. The prototypical florigen is encoded by the FT gene and its orthologs in Arabidopsis and other plants. Florigens are produced in the leaves, and act in the shoot apical meristem of buds and growing tips.
Gibberellic acid (also called gibberellin A3 or GA3) is a hormone found in plants and fungi. Its chemical formula is C19H22O6. When purified, it is a white to pale-yellow solid.
The secondary cell wall is a structure found in many plant cells, located between the primary cell wall and the plasma membrane. The cell starts producing the secondary cell wall after the primary cell wall is complete and the cell has stopped expanding.
In enzymology, a NDP-glucose—starch glucosyltransferase is an enzyme that catalyzes the chemical reaction
Fruits are the mature ovary or ovaries of one or more flowers. They are found in three main anatomical categories: aggregate fruits, multiple fruits, and simple fruits.
Plants depend on epigenetic processes for proper function. Epigenetics is defined as "the study of changes in gene function that are mitotically and/or meiotically heritable and that do not entail a change in DNA sequence". The area of study examines protein interactions with DNA and its associated components, including histones and various other modifications such as methylation, which alter the rate or target of transcription. Epi-alleles and epi-mutants, much like their genetic counterparts, describe changes in phenotypes due to epigenetic mechanisms. Epigenetics in plants has attracted scientific enthusiasm because of its importance in agriculture.
The coleorhiza or root sheath is a protective layer of tissue that surrounds the radicle in monocotyledon seeds. During germination, the coleorhiza is the first part to grow out of the seed, growing through cell elongation. Soon afterwards, it is pierced through by the emerging primary root and then remains like a collar around the root base. Also the adventitious roots have a coleorhiza.
Photoblasticism is a mechanism of seed dormancy. Photoblastic seeds require light in order to germinate. Once germination starts, the stored nutrients that have accumulated during maturation start to be digested which then supports cell expansion and overall growth. Within light-stimulated germination, Phytochrome B (PHYB) is the photoreceptor that is responsible for the beginning stages of germination. When red light is present, PHYB is converted to its active form and moves from the cytoplasm to the nucleus where it upregulates the degradation of PIF1. PIF1, phytochrome-interaction-factor-1, negatively regulates germination by increasing the expression of proteins that repress the synthesis of gibberellin (GA), a major hormone in the germination process. Another factor that promotes germination is HFR1 which accumulates in light in some way and forms inactive heterodimers with PIF1.
