Plant reproduction

Source: Wikipedia, the free encyclopedia.

Plant reproduction is the production of new offspring in plants, which can be accomplished by

mutations
occur.

Asexual reproduction

See also: Asexual reproduction

Asexual reproduction does not involve the production and fusion of male and female gametes. Asexual reproduction may occur through

vegetative propagation
.

Asexual reproduction is a type of reproduction where the offspring comes from one parent only, thus inheriting the characteristics of the parent. Asexual reproduction in plants occurs in two fundamental forms, vegetative reproduction and agamospermy.[1] Vegetative reproduction involves a vegetative piece of the original plant producing new individuals by budding, tillering, etc. and is distinguished from apomixis, which is a replacement of sexual reproduction, and in some cases involves seeds. Apomixis occurs in many plant species such as dandelions (Taraxacum species) and also in some non-plant organisms. For apomixis and similar processes in non-plant organisms, see parthenogenesis.

Natural vegetative reproduction is a

ramet, or apparent individual, of a clonal colony is genetically identical to all others in the same colony. The distance that a plant can move during vegetative reproduction is limited, though some plants can produce ramets from branching rhizomes or stolons that cover a wide area, often in only a few growing seasons. In a sense, this process is not one of reproduction but one of survival and expansion of biomass of the individual. When an individual organism increases in size via cell multiplication and remains intact, the process is called vegetative growth. However, in vegetative reproduction, the new plants that result are new individuals in almost every respect except genetic. A major disadvantage of vegetative reproduction is the transmission of pathogens from parent to offspring. It is uncommon for pathogens to be transmitted from the plant to its seeds (in sexual reproduction or in apomixis), though there are occasions when it occurs.[2][page needed
]

Seeds generated by apomixis are a means of asexual reproduction, involving the formation and dispersal of seeds that do not originate from the fertilization of the

Kentucky blue grass (Poa pratensis) all use this form of asexual reproduction. Pseudogamy occurs in some plants that have apomictic seeds, where pollination is often needed to initiate embryo growth, though the pollen contributes no genetic material to the developing offspring.[3] Other forms of apomixis occur in plants also, including the generation of a plantlet in replacement of a seed or the generation of bulbils
instead of flowers, where new cloned individuals are produced.

Structures

A

polypody, iris, couch grass and nettles
.

Prostrate aerial stems, called runners or stolons, are important vegetative reproduction organs in some species, such as the strawberry, numerous grasses, and some ferns.

Adventitious buds form on roots near the ground surface, on damaged stems (as on the stumps of cut trees), or on old roots. These develop into above-ground stems and leaves. A form of budding called suckering is the reproduction or regeneration of a plant by shoots that arise from an existing root system. Species that characteristically produce suckers include elm (Ulmus)[4]: 299  and many members of the rose family such as Rosa,[4]: 285–296  Kerria[4]: 206  and Rubus.[4]
: 258 

Bulbous plants such as

narcissi and tulips reproduce vegetatively by dividing their underground bulbs into more bulbs. Other plants like potatoes (Solanum tuberosum) and dahlias reproduce vegetatively from underground tubers. Gladioli and crocuses reproduce vegetatively in a similar way with corms
.

Club mosses such as Huperzia lucidula .[5] They are also found in some higher plants such as species of Drosera
.

Usage

The most common form of plant reproduction used by people is seeds, but a number of asexual methods are used which are usually enhancements of natural processes, including: cutting, grafting, budding,

stooling
.

In horticulture, a cutting is a branch that has been cut off from a mother

rooting liquid or powder containing hormones. When a full root has formed and leaves begin to sprout anew, the clone is a self-sufficient plant,[7]
genetically identical.

Examples include cuttings from the stems of

Nurseries offer for sale trees with grafted stems that can produce four or more varieties of related fruits, including apples. The most common usage of grafting is the propagation of cultivars onto already rooted plants, sometimes the rootstock is used to dwarf the plants or protect them from root damaging pathogens.[8]

Since vegetatively propagated plants are clones, they are important tools in plant research. When a clone is grown in various conditions, differences in growth can be ascribed to environmental effects instead of genetic differences.[7]

Sexual reproduction

Main article:
Sexual reproduction of plants
Part of a series on
Sex
Biological terms
Sexual reproduction
Sexuality
Sexual system

Sexual reproduction involves two fundamental processes:

diploid number. In between these two processes, different types of plants and algae vary, but many of them, including all land plants, undergo alternation of generations, with two different multicellular structures (phases), a gametophyte and a sporophyte. The evolutionary origin and adaptive significance of sexual reproduction are discussed in the pages Evolution of sexual reproduction and Origin and function of meiosis
.

The gametophyte is the multicellular structure (plant) that is

haploid, containing a single set of chromosomes in each cell. The gametophyte produces male or female gametes (or both), by a process of cell division, called mitosis
. In vascular plants with separate gametophytes, female gametophytes are known as mega gametophytes (mega=large, they produce the large egg cells) and the male gametophytes are called micro gametophytes (micro=small, they produce the small sperm cells).

The fusion of male and female gametes (fertilization) produces a diploid zygote, which develops by mitotic cell divisions into a multicellular sporophyte.

The mature sporophyte produces spores by meiosis, sometimes referred to as reduction division because the chromosome pairs are separated once again to form single sets.

In mosses and liverworts, the gametophyte is relatively large, and the sporophyte is a much smaller structure that is never separated from the gametophyte. In ferns, gymnosperms, and flowering plants (angiosperms), the gametophytes are relatively small and the sporophyte is much larger. In gymnosperms and flowering plants the megagametophyte is contained within the ovule (that may develop into a seed) and the microgametophyte is contained within a pollen grain.

History of sexual reproduction of plants

Main article: Evolution of sexual reproduction

Unlike animals, plants are immobile, and cannot seek out sexual partners for reproduction. In the evolution of early plants, abiotic means, including water and much later, wind, transported

gametes
for protection of the sperm during the process of transfer from the male to female parts.

It is believed that insects fed on the pollen, and plants thus evolved to use

Ginkgophyta
, which have flagella.

Flowering plants

Further information: Plant reproductive morphology

Flowering plants, the dominant plant group,[9]: 168  reproduce both by sexual and asexual means. Their distinguishing feature is that their reproductive organs are contained in flowers. Sexual reproduction in flowering plants involves the production of separate male and female gametophytes that produce gametes.

The

germinate
and grow into the next generation.

Pollination

An orchid flower

Plants that use insects or other animals to move pollen from one flower to the next have developed greatly modified flower parts to attract pollinators and to facilitate the movement of pollen from one flower to the insect and from the insect to the next flower. Flowers of wind-pollinated plants tend to lack petals and or sepals; typically large amounts of pollen are produced and pollination often occurs early in the growing season before leaves can interfere with the dispersal of the pollen. Many trees and all grasses and sedges are wind-pollinated.

Plants have a number of different means to attract pollinators including color, scent, heat, nectar glands, edible pollen and flower shape. Along with modifications involving the above structures two other conditions play a very important role in the sexual reproduction of flowering plants, the first is the timing of flowering and the other is the size or number of flowers produced. Often plant species have a few large, very showy flowers while others produce many small flowers, often flowers are collected together into large inflorescences to maximize their visual effect, becoming more noticeable to passing pollinators. Flowers are attraction strategies and sexual expressions are functional strategies used to produce the next generation of plants, with pollinators and plants having co-evolved, often to some extraordinary degrees, very often rendering mutual benefit.

Flower heads showing disk and ray florets.

The largest family of flowering plants is the orchids (

Orchidaceae), estimated by some specialists to include up to 35,000 species,[10] which often have highly specialized flowers that attract particular insects for pollination. The stamens are modified to produce pollen in clusters called pollinia, which become attached to insects that crawl into the flower. The flower shapes may force insects to pass by the pollen, which is "glued" to the insect. Some orchids are even more highly specialized, with flower shapes that mimic the shape of insects to attract them to attempt to 'mate' with the flowers, a few even have scents that mimic insect pheromones
.

Another large group of flowering plants is the Asteraceae or sunflower family with close to 22,000 species,[11] which also have highly modified inflorescences composed of many individual flowers called florets. Heads with florets of one sex, when the flowers are pistillate or functionally staminate or made up of all bisexual florets, are called homogamous and can include discoid and liguliflorous type heads. Some radiate heads may be homogamous too. Plants with heads that have florets of two or more sexual forms are called heterogamous and include radiate and disciform head forms.

Ferns

Ferns typically produce large diploids with stem, roots, and leaves. On fertile leaves

archegonia. After rains or when dew deposits a film of water, the motile sperm are splashed away from the antheridia, which are normally produced on the top side of the thallus, and swim in the film of water to the antheridia where they fertilize the egg. To promote out crossing or cross-fertilization the sperm is released before the eggs are receptive of the sperm, making it more likely that the sperm will fertilize the eggs of the different thallus. A zygote is formed after fertilization, which grows into a new sporophytic plant. The condition of having separate sporophyte and gametophyte plants is called alternation of generations. Other plants with similar reproductive strategies include Psilotum, Lycopodium, Selaginella and Equisetum
.

Bryophytes

Main articles:
Bryophyte life cycle

The

one sex while other species may be monoicous, producing both antheridia and archegonia on the same gametophyte which is thus hermaphrodite.[12]

Dispersal and offspring care

Main article: Seed dispersal

One of the outcomes of plant reproduction is the generation of seeds, spores, gemmae and other vegetative organs that allow plants to move to new locations or new habitats.[citation needed]

Plants do not have nervous systems or any will for their actions. Even so, scientists are able to observe mechanisms that help their offspring thrive as they grow. All organisms have mechanisms to increase survival in offspring.[citation needed]

Offspring care is observed in the Mammillaria hernandezii, a small cactus found in Mexico. A cactus is a type of succulent, meaning it retains water when it is available for future droughts. M. hernandezii also stores a portion of its seeds in its stem, and releases the rest to grow.[13] This can be advantageous for many reasons. By delaying the release of some of its seeds, the cactus can protect these from potential threats from insects, herbivores, or mold caused by micro-organisms. A study found that the presence of adequate water in the environment causes M. Hernandezii to release more seeds to allow for germination. The plant was able to perceive a water potential gradient in the surroundings, and act by giving its seeds a better chance in this preferable environment.[14] This evolutionary strategy gives a better potential outcome for seed germination

There are similar reproductive strategies found in both mammals and plants. A divergence between the two is that in harsh environmental conditions, mammals produce fewer and larger offspring,[citation needed] whereas plants produce more seeds.[15]

See also

References

  1. ISBN 978-0-226-03816-2
    .
  2. ISBN 978-0-226-26554-4
    .
  3. ^ "Why apomixis is genetic gold - Australian Life Scientist". Archived from the original on 2009-10-26. Retrieved 2009-10-25.
  4. ^
    ISBN 978-1-5272-2630-2
    .
  5. ^ "Ferns and Fern Allies of Wisconsin". University of Wisconsin. Retrieved 8 March 2022.
  6. ISBN 978-1-4018-4188-1
    .
  7. ^
    ISBN 978-0-85092-394-0
    .
  8. ISBN 978-0-7668-1567-4
    .
  9. ISBN 0-87893-403-0
    .
  10. ^ Orchidaceae in Flora of North America @ efloras.org
  11. ^ Asteraceae in Flora of North America @ efloras.org
  12. ^ Lovett Doust, Jon, and Lesley Lovett Doust. 1988. Plant reproductive ecology: patterns and strategies. New York: Oxford University Press. P 290.
  13. PMID 23345416
    .
  14. ISSN 2296-701X
    .
  15. S2CID 59143904
    .

External links
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