Sporophyte: Sporo means spores and phyte means plants. The generation of plants that produce spores is called sporophyte. Algae, bryophytes, angiosperms and gymnosperms all of these make spores. A spore is a tiny structure that leads to a new plant after its germination. Spores can be of two types, namely mitotic spore and meiotic spore. Mitosis and meiosis are types of cell divisions which lead to the formation of these spores.
Mitotic spores are asexual spores and meisotic spores are called sexual spores. Sporophyte can make both kinds of spores; algae is a simplified organism and forms mitotic or asexual spores, similarly chlamydomonas also form asexual spores. Bryophytes form meiotic or sexual spores, homosporous pteridophytes form same size of spores from spore mother cell and heterosporous pteridophytes form two different kinds of spores, namely microspore from microspore mother cell and megaspore from megaspore mother cell.
Similarly, heterosporous gymnosperms and angiosperms form their spores. Alternation of generations is a life cycle that includes both haploid and diploid multicellular stages. It is divided into two parts N haploid and 2n diploid. It was discovered by Strasburger. It is the conversion of gametophyte generation into sporophyte generation and vice versa. The male conifer gametophyte exists as pollen, which is wind-dispersed.
For flowering plants such as fruit trees and flowers, female gametophytes contain a few cells and reside inside the ovary of the flower; the male exists as pollen. The small gametophytes of vascular plants only live for a season.
Vascular plants that make two kinds of spores and gametophytes are called heterosporic. Non-vascular plants such as bryophytes which include mosses, liverworts and hornworts display different characteristics for their gametophytes and sporophytes. Bryophytes comprise the oldest land plants on the planet, having existed for over million years. They require wetter locales for their reproductive success. Their sporophytes are not visibly dominant.
However, their gametophyte generation is the noticeable, photosynthetic part of the plant like green moss that attaches to substrates via rhizoids rather than the diploid sporophyte. In fact, their sporophytes are not as long-lived as in vascular plants.
The sporophyte forms from a fertilized egg inside the flask-like archegonium and attaches to the gametophyte via a penetrating foot. The sporophyte receives nourishment from the gametophyte.
The sporophyte forms a very small stalk called a seta and a single sporangium. A protective covering called a calyptra surrounds this embryonic sporophyte. Single-celled spores travel via wind and germinate only in a moist area; water is required for fertilization. Then they form a new gametophyte plant, which creates more spores in the sporophyte cycle. Because they make just one type of spore and gametophyte, these non-vascular plants are called homosporic. Scientists continue to learn more alternating generations in plants.
Genetic studies of mosses reveal that a group of proteins called KNOX help drive development of sporophytes. In the angiosperm Arabidopsis thaliana , the PKL gene is needed for maternal sporophytes to promote male and female gametophyte development.
The haploid stage, in which a multicellular haploid gametophyte develops from a spore and produces haploid gametes, is the dominant stage in the bryophyte life cycle. The mature gametophyte produces both male and female gametes, which join to form a diploid zygote. The zygote develops into the diploid sporophyte, which extends from the gametophyte and produces haploid spores through meiosis.
Once the spores germinate, they produce new gametophyte plants and the cycle continues. Tracheophytes are plants that contain vascular tissue; two of the major classes of tracheophytes are gymnosperms conifers and angiosperms flowering plants.
Tracheophytes, unlike bryophytes, have developed seeds that encase and protect their embryos. The dominant phase in the tracheophyte life cycle is the diploid sporophyte stage. The gametophytes are very small and cannot exist independent of the parent plant. The reproductive structures of the sporophyte cones in gymnosperms and flowers in angiosperms , produce two different kinds of haploid spores: microspores male and megaspores female.
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