Fruit and Seed Formation Without Fertilization: Formation and Development

Introduction To Fruit And Seed Formation

A fundamental phenomenon in the process of reproduction of a plant, the formation of fruit and seed, typically takes place after fertilisation, through which the ovary of the flower is transformed into fruit and the fertilized ovules are matured into seeds. This process starts with the fertilisation of the ovule with the help of the pollen that forms a zygote. The fruit protects the seeds and helps their dispersal. Thus, it is important to comprehend this process, as it allows species of plants to continue, provides aid in seed dispersion, and becomes a contributor to the plant diversity and adaptation of the plant.

Types Of Asexual Reproduction In Plants

Asexual reproduction in plants is explained below-

Apomixis

Apomixis is a mode of asexual reproduction in which the seeds are formed without the act of fertilisation. Its offspring has the same genetic makeup as the parent plant. Hence, by this process, the plants increase in number without pollination or fertilisation and can perpetuate specific characteristics.

Types of Apomixis:

Gametophytic and Sporophytic: In gametophytic apomixis the embryo originates from the unreduced gametes, and in sporophytic apomixis from the somatic cells of the ovule. In both types, the development of seeds occurs without genetic contribution from male gametes.

Examples in Nature

The dandelion, Taraxacum officinale, which commonly propagates by apomixis, and some graminaceous examples, for example, species of Paspalum, are examples that can propagate by sexual means as well as by apomictic.

Parthenocarpy

Parthenocarpy is defined as the phenomenon that fruit develops in the absence of the fertilisation of the ovary, giving rise to seedless fruits. It can be manipulated or naturally occurring taken account of and is often used to provide fruit crops that are far more acceptable for eating.

Natural vs. Artificial Parthenocarpy

Natural parthenocarpy occurs on its own in some plant species under the influence of genetic factors, whereas artificial parthenocarpy comes about through treatment—for example, hormonal application. The former examples are naturally found in plants like bananas, and Musa spp., whereas the latter includes seedless grapes and some cucumbers.

Examples and Applications

Some of the common examples of parthenocarpic fruits include bananas and seedless oranges. The applications herein are the improvement of the quality and marketability of fruits, plus the shelf life of the produce.

Mechanisms Of Apomixis

The mechanism of apomixis is explained below-

Detailed Mechanisms

In apomixis, seeds are formed without fertilisation. In general, both forms of seeds are similar to each other in their structure, but in the case of gametophytic apomixis, embryos are formed through the female gametophyte, whereas in the second case, embryos are formed from the ovule's somatic cells.

Gametophytic Apomixis

It is a type of apomixis in which embryos are developed autonomously from the unreduced egg cells or other cells of the gametophyte. This avoids the process of fertilisation, which, upon maturity, will lead to offspring that are genetic replicas of the mother plant.

Sporophytic Apomixis

In sporophytic apomixis, the embryos arise from the somatic cells of the ovule, such as the nucellus or integuments, and do not go through meiosis or fertilisation. It is a system that can give rise to clonal progeny from the mother plant.

Genetic And Molecular Basis

According to this, apomicts are due to several functional genes involved in the process, like meiosis and embryo development. Molecular pathways participate in regulating cell divisions as well as the formation of embryos, allowing the normal sexual reproduction process to be bypassed.

Role of Specific Genes

Genes that have been associated with apomixis are usually those that regulate seed development and cell differentiation. These include genes that control the formation of unreduced gametes and the maintenance of the diploid genetic state of progeny.

Molecular Pathways Involved

Molecular pathways for apomixis mainly involve signal vehicle networks that link the control of embryo development with and without fertilisation. Hormonal regulation and genetic expression mechanisms are also involved in these pathways.

Mechanisms Of Parthenocarpy

The mechanism of parthenocarpy is explained below-

Detailed Mechanisms

Parthenocarpy is the formation of fruit from an ovary that has not been fertilised. This state can be brought about by hormonal changes or genetic changes. It skips over the fertilization stage and goes straight to forming seedless fruit.

Hormonal Control

Two very important hormones in the induction of parthenocarpy are auxins and gibberellins. They are responsible for promoting fruiting through stimulation without fertilization. Even the presence of cytokinins will further increase cell division and fruit set.

Genetic and Environmental Influences

Genetic factors decide the potential of a plant to grow parthenocarpic fruits, whereas environmental conditions, for instance, temperature and light, may—for now, or then—influence the result of the application of hormonal treatments. Application of environmental stress may also cause certain species of plants to exhibit natural parthenocarpy.

Methods To Induce Parthenocarpy

Parthenocarpy in crops can be induced by chemical treatments, like the application of synthetic auxins and gibberellins. Parthenocarpic varieties have also been developed through genetic engineering techniques by targeted genetic manipulations.

Chemical Treatments

The application of chemicals like gibberellic acid (GA) and auxin analogues to foster fruit development has been practised. These treatments can be applied directly to plants to enhance fruit set and quality.

Genetic Engineering Techniques

Genetic engineering has advanced to produce genetically modified plants with regulated hormones that result in parthenocarpic fruit. These techniques contain gene editing and introduction/transformation to develop more in-depth parthenocarpic traits.

Advantages and Disadvantages

The advantages and disadvantages are explained below-

Advantages

The asexual reproduction techniques have many advantages, like apomixis and parthenocarpy, including crop uniformity, seedless fruit, increased shelf life, better recovery cost in the market, and reduced frequency of replanting seeds.

Disadvantages

The aforementioned major disadvantages include loss of genetic diversity in crops, and less resistance to environmental changes, and diseases. Besides, all these require high human intervention and very good technicality, which might increase production costs and complexities.

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