Corn silk is a common name for Stigma maydis, the shiny, thread-like, weak fibers that grow as part of ears of corn (maize); the tuft or tassel of silky fibers that protrude from the tip of the ear of corn. The ear is enclosed in modified leaves called husks. Each individual fiber is an elongated style, attached to an individual ovary. [1] The term probably originated sometime between 1850 and 1855. [1]
Up to 1000 ovules (potential kernels) form per ear of corn, each of which produces a strand of corn silk from its tip that eventually emerges from the end of the ear. The emergence of at least one strand of silk from a given ear of corn is defined as growth stage R1, and the emergence of silk in 50% of the plants in a corn field is called "mid-silk". The silk lengthens from the basal ovules during the 10 to 14 days previous to growth stage R1; this is due to a change of shape of existing cells rather than their replication. The elongation progresses at 1.5 inches per day at first but gradually slows as the full length is approached. Elongation of a corn silk strand stops soon after a grain of pollen is captured or due to senescence of the silk 10 days after its emergence. [2]
If an ovule is successfully fertilized, the corn silk will detach from it two or three days later. Otherwise, the silk will remain attached indefinitely, and fertilization remains possible (with decreasing chances of success) for 10 days after silk emergence. For this reason, it is possible to sample developing ears of corn from a field, husking them gently with a sharp knife, then shaking them to assess the progress of pollination based on how much of the corn silk falls away. [3]
Corn silk is part stigma and part style, providing a female flower surface to which pollen grains can adhere and defining the path through which the pollen must travel. [4] The stigma is the very tip of the corn silk, which has a larger number of hairs to help pollen to adhere to it. [5] Kernel formation in the cob requires pollination of the external corn silk by wind or insects. Usually several grains of pollen adhere, but only one will successfully participate in fertilization of the ovule to form a corn kernel.
For the pollen grain, the male gametophyte, to transmit its genetic material to the ovule, it must germinate and form a pollen tube that extends down nearly the full length of the corn silk strand. [3] Typically 400 to 600 kernels are successfully formed in this way. [2] The pollen tube extends at a rate of over 1 centimeter per hour, requiring only 24 hours to create a foot-long pathway within the intercellular space of the corn silk through which the sperm cells (the gametes) pass to join the female gametophyte within the ovule. The pollen tube is produced by the single vegetative cell in the pollen grain, which passes its cytoplasm, nucleus and two sperm cells into the tube. The tube extends itself at the apex only, in an actin polymerization dependent process, and the direction in which the apex progresses responds to cyclic AMP levels, including cAMP cyclization by a pollen signalling protein (PSiP). [6]
Corn silk can control the types of pollen that an ear of corn will accept through expression of certain forms of the Gametophyte Factor 1 gene. Many races of popcorn, of the everta type, will greatly slow the development of pollen tubes from any pollen that does not carry a similar form of Ga1-S or Ga1-M, thereby preventing the ingression of genes (natural or engineered) from other types of corn. The popcorn remains free to donate its genes via its own pollen to other types of corn. The effectiveness of this restriction can be measured by planting the popcorn beside purple dent corn; the xenia effect would cause the formation of purple aleurones if kernels permitted themselves to be fertilized by pollen from outside the group. [7] Organic farmers are pursuing the transfer of some of these mechanisms into non-popcorn strains for purposes of preventing inadvertent pollination by GMO corn, which under U.S. regulations can cause their product to be rejected as organic corn, and for which they have no recourse against GMO growers. [8]
The moisture of freshly emerged corn silk sometimes attracts insects, which can cause silk clipping, which can interfere with kernel formation. [9]
Corn silk contains a variety of pharmacologically-active compounds and as such is used in many types of folk medicine, including as a diuretic [10] and as an inhibitor of melanin production. [11]
In many studies, corn silk has been claimed to have antioxidant and healthcare properties, as well as acting as a diuretic agent that reduces hyperglycemia and works as an antidepressant and anti-fatigue agent. Corn silk is also used in teas and supplements for treating urinary problems. [12] The antioxidant and hematoprotective effect of corn silk protein hydrolysate have been experimentally demonstrated. [13] Potential antioxidant peptides in the hydrolysate have also been identified. [14]
A gamete is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. The name gamete was introduced by the German cytologist Eduard Strasburger in 1878.
A gametophyte is one of the two alternating multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has one set of chromosomes. The gametophyte is the sexual phase in the life cycle of plants and algae. It develops sex organs that produce gametes, haploid sex cells that participate in fertilization to form a diploid zygote which has a double set of chromosomes. Cell division of the zygote results in a new diploid multicellular organism, the second stage in the life cycle known as the sporophyte. The sporophyte can produce haploid spores by meiosis that on germination produce a new generation of gametophytes.
Fertilisation or fertilization, also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a zygote and initiate its development into a new individual organism or offspring. While processes such as insemination or pollination, which happen before the fusion of gametes, are also sometimes informally referred to as fertilisation, these are technically separate processes. The cycle of fertilisation and development of new individuals is called sexual reproduction. During double fertilisation in angiosperms, the haploid male gamete combines with two haploid polar nuclei to form a triploid primary endosperm nucleus by the process of vegetative fertilisation.
Pollen is a powdery substance produced by most types of flowers of seed plants for the purpose of sexual reproduction. It consists of pollen grains, which produce male gametes. Pollen grains have a hard coat made of sporopollenin that protects the gametophytes during the process of their movement from the stamens to the pistil of flowering plants, or from the male cone to the female cone of gymnosperms. If pollen lands on a compatible pistil or female cone, it germinates, producing a pollen tube that transfers the sperm to the ovule containing the female gametophyte. Individual pollen grains are small enough to require magnification to see detail. The study of pollen is called palynology and is highly useful in paleoecology, paleontology, archaeology, and forensics. Pollen in plants is used for transferring haploid male genetic material from the anther of a single flower to the stigma of another in cross-pollination. In a case of self-pollination, this process takes place from the anther of a flower to the stigma of the same flower.
Sweet corn, also called sweetcorn, sugar corn and pole corn, is a variety of corn grown for human consumption with a high sugar content. Sweet corn is the result of a naturally occurring recessive mutation in the genes which control conversion of sugar to starch inside the endosperm of the corn kernel. Sweet corn is picked when still immature and prepared and eaten as a vegetable, rather than field corn, which is harvested when the kernels are dry and mature. Since the process of maturation involves converting sugar to starch, sweet corn stores poorly and must be eaten fresh, canned, or frozen, before the kernels become tough and starchy.
Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds. Pollinating agents can be animals such as insects, for example beetles or butterflies; birds, and bats; water; wind; and even plants themselves. Pollinating animals travel from plant to plant carrying pollen on their bodies in a vital interaction that allows the transfer of genetic material critical to the reproductive system of most flowering plants. When self-pollination occurs within a closed flower. Pollination often occurs within a species. When pollination occurs between species, it can produce hybrid offspring in nature and in plant breeding work.
Corn smut is a plant disease caused by the pathogenic fungus Mycosarcoma maydis. One of several cereal crop pathogens called smut, the fungus forms galls on all above-ground parts of corn species such as maize and teosinte. The infected corn is edible; in Mexico, it is considered a delicacy, called huitlacoche, often eaten as a filling in quesadillas and other tortilla-based dishes, as well as in soups.
Gametogenesis is a biological process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid gametes. Depending on the biological life cycle of the organism, gametogenesis occurs by meiotic division of diploid gametocytes into various gametes, or by mitosis. For example, plants produce gametes through mitosis in gametophytes. The gametophytes grow from haploid spores after sporic meiosis. The existence of a multicellular, haploid phase in the life cycle between meiosis and gametogenesis is also referred to as alternation of generations.
A pollen tube is a tubular structure produced by the male gametophyte of seed plants when it germinates. Pollen tube elongation is an integral stage in the plant life cycle. The pollen tube acts as a conduit to transport the male gamete cells from the pollen grain—either from the stigma to the ovules at the base of the pistil or directly through ovule tissue in some gymnosperms. In maize, this single cell can grow longer than 12 inches (30 cm) to traverse the length of the pistil.
In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. It consists of three parts: the integument, forming its outer layer, the nucellus, and the female gametophyte in its center. The female gametophyte — specifically termed a megagametophyte — is also called the embryo sac in angiosperms. The megagametophyte produces an egg cell for the purpose of fertilization. The ovule is a small structure present in the ovary. It is attached to the placenta by a stalk called a funicle. The funicle provides nourishment to the ovule. On the basis of the relative position of micropyle, body of the ovule, chalaza and funicle, there are six types of ovules.
Plant reproductive morphology is the study of the physical form and structure of those parts of plants directly or indirectly concerned with sexual reproduction.
Self-incompatibility (SI) is a general name for several genetic mechanisms that prevent self-fertilization in sexually reproducing organisms, and thus encourage outcrossing and allogamy. It is contrasted with separation of sexes among individuals (dioecy), and their various modes of spatial (herkogamy) and temporal (dichogamy) separation.
Gynoecium is most commonly used as a collective term for the parts of a flower that produce ovules and ultimately develop into the fruit and seeds. The gynoecium is the innermost whorl of a flower; it consists of pistils and is typically surrounded by the pollen-producing reproductive organs, the stamens, collectively called the androecium. The gynoecium is often referred to as the "female" portion of the flower, although rather than directly producing female gametes, the gynoecium produces megaspores, each of which develops into a female gametophyte which then produces egg cells.
Corn kernels are the fruits of corn. Maize is a grain, and the kernels are used in cooking as a vegetable or a source of starch. The kernel comprise endosperm, germ, pericarp, and tip cap.
Double fertilization or double fertilisation is a complex fertilization mechanism of angiosperms. This process involves the fusion of a female gametophyte or megagametophyte, also called the embryonic sac, with two male gametes (sperm). It begins when a pollen grain adheres to the stigmatic surface of the carpel, the female reproductive structure of angiosperm flowers. The pollen grain begins to germinate, forming a pollen tube that penetrates and extends down through the style toward the ovary as it follows chemical signals released by the egg. The tip of the pollen tube then enters the ovary by penetrating through the micropyle opening in the ovule, and releases two sperm into the embryonic sac (megagametophyte).
Plant reproduction is the production of new offspring in plants, which can be accomplished by sexual or asexual reproduction. Sexual reproduction produces offspring by the fusion of gametes, resulting in offspring genetically different from either parent. Asexual reproduction produces new individuals without the fusion of gametes, resulting in clonal plants that are genetically identical to the parent plant and each other, unless mutations occur.
Megagametogenesis is the process of maturation of the female gametophyte, or megagametophyte, in plants. During the process of megagametogenesis, the megaspore, which arises from megasporogenesis, develops into the embryonic sac, which is where the female gamete is housed. These megaspores then develop into the haploid female gametophytes. This occurs within the ovule, which is housed inside the ovary.
Maize, also known as corn in North American English, is a tall stout grass that produces cereal grain. It was domesticated by indigenous peoples in southern Mexico about 9,000 years ago from wild teosinte. Native Americans planted it alongside beans and squashes in the Three Sisters polyculture. The leafy stalk of the plant gives rise to male inflorescences or tassels which produce pollen, and female inflorescences called ears. The ears yield grain, known as kernels or seeds. In modern commercial varieties, these are usually yellow or white; other varieties can be of many colors.
Stenocarpella maydis (Berk.) Sutton is a plant pathogenic fungus and causal organism of diplodia ear and stalk rot. Corn and canes are the only known hosts to date. No teleomorph of the fungus is known.
Gametophytic selection is the selection of one haploid pollen grain over another through the means of pollen competition, and that resulting sporophytic generations are positively affected by this competition. Evidence for the positive effects of gametophytic selection on the sporophyte generation has been observed in several flowering plant species, but there are is still some debate as to the biological significance of gametophytic selection.
