Sexual Reproduction in Plants: Higher Plants and Polyembryony Quiz

Sexual Reproduction in Plants: Focusing on Higher Plants and Polyembryony

Higher Plants

Sexual reproduction in plants, also known as meiosis, involves the fusion of two haploid gametes to form a diploid zygote. This process results in genetic variation in the offspring due to the mixing of genetic material from the two parents. Higher plants, such as flowering plants and conifers, undergo sexual reproduction to produce seeds, which are housed in fruits. The seeds then germinate to form a new plant.

Flowering Plants (Angiosperms)

Flowering plants, or angiosperms, are a diverse group of plants that reproduce sexually. They produce flowers, which are the reproductive structures of the plant. Flowers contain both male and female reproductive structures. The male structures, called stamens, produce pollen grains, while the female structures, called pistils, contain the egg cells. When pollen from one flower lands on the stigma of another flower, the pollen tube grows through the stigma and down the style to fertilize the egg cell. The resulting zygote develops into an embryo within the ovule, which eventually becomes a seed.

Conifers (Gymnosperms)

Conifers, or gymnosperms, are a group of plants that reproduce sexually by producing cones. The female cones contain the ovules, which are exposed and not enclosed in a seed. The male cones produce pollen, which is dispersed by wind or insects. When pollen lands on an ovule, it grows into a pollen tube, which fertilizes the ovule. The fertilized ovule then develops into a seed, which contains an embryo.

Polyembryony

Polyembryony is a phenomenon in which more than one embryo develops from a single fertilized egg. This process can occur in various species, including plants, invertebrates, and even humans. The embryos resulting from polyembryony are identical to one another but genetically diverse from the parents.

Polyembryony in Plants

In plants, polyembryony can occur through cleavage polyembryony, where the original zygote splits into many identical embryos. This process is influenced by genetics, the environment, and gene expression. For example, in the genus Citrus, some species undergo polyembryony, where multiple nucellar-cell-derived embryos exist alongside sexually-derived embryos. The genetic control of polyembryony in Citrus is determined by a shared locus, and the number of embryos that develop and the impact of the environment are factors that contribute to the expression of this phenomenon.

Polyembryony can also be found in mangoes and other plant species, and it is particularly useful for the propagation of certain species, such as citrus and mango, where adventive embryos are used to create genetically uniform seedlings.

Evolution of Polyembryony

The evolutionary advantages of polyembryony have been studied in various organisms, including parasitoid wasps and armadillos. In parasitoid wasps, polyembryony allows females to increase the number of potential offspring, potentially due to the mother not knowing the environmental conditions of her offspring or a constraint on reproduction. In the case of armadillos, the evolution of polyembryony may be related to the mother not knowing the environmental conditions of her offspring or a constraint on reproduction, as in the case of the nine-banded armadillo.

Comparison with Apomixis

While polyembryony is a form of sexual reproduction, apomixis is a form of asexual reproduction. Apomixis involves seed formation without the addition of gametes, while polyembryony refers to the emergence of multiple embryos from a single fertilized egg. Both processes contribute to the genetic diversity of offspring but differ in their modes of reproduction.