User:Anthere/What is an anther?
What is an anthere?
Anthère is the French word for the english "anther". That is a feminine gender word.
The anther is the terminal part of the en:stamen (or androecium), male reproductive component of the en:flower in en:angiosperms. It is connected to the other parts of the flower by a stalk called a filament.
The anther produces the en:pollen, which is responsible for fertilising the female part of the flower. When the anther matures, it opens, and release the pollen grains.
The pollen, male gametophyte, contains both a generative and a vegetative nucleus. It is derived from mother cells which undergo meiosis. Pollen grain is usually small and light enough to be carried by wind, water, or attached to the body of insects or birds. Pollen grains outer wall is made from exin, which is one of the most resistant biological material; they are not only very resistant but also very long-lasting, and they show a great diversity of forms, color, design.
When deposited on the stigma of the pistil (or carpel, female part of the flower), the pollen grain germinates, and forms a pollen tube which grows through "pores" in exin, from the style to the interior of the pistil. The ovary is located at the basal region of the pistil and contains the ovules. The pollen tube carries the male sperm nucleus to one of the ovules of the flower, where fertilisation can take place.
- Now, tell me, you mean, in French, the anthere is a feminine word, while it is the male component of the flower?
Well, yes. Just as le pistil is a masculine gender word, while the pistil is the female component of the flower! Go figure!
Diversity in angiosperms reproduction modes
There are, generally, two types of flowers.
- The imperfect flower has either male or female components, but not both at the same time (i.e. flowers can only be unisexual -- either male or female)
- the perfect flower has both male and female components. It is called an hermaphrodite or bisexual flower.
Modes of sexuality among flowers are amazingly various, from three levels: the individual flower level, the plant level (i.e., all the flower in a plant), and the population level (i.e., all the plants of a population).
Hermaphroditism is the most common mode in plants, about 70% of all flowering plants. Other rather common modes are dioecious (meaning unisexual male and female flowers are on different plants) and monoecious (meaning unisexual male and female flowers are on the same plant).
- So, is it possible that a dioecious plant fertilize itself?
Well, no, you need several plants in the population. Just "one plant", even with many many many flowers on it, can't be fertile, because no fertilisation can occur with only one sex.
Plant breeding, inbreeding depression and barrier to cross-fertilisation
As indicated above, hermaphrodism is the most common mode for flower plants. The problem is that hermaphrodite plants tend to be autogamous. In perfect flowers that do not have spatial separation of styles and anthers, autogamy or self-fertilisation can occur. Generation after generation, most plants will reproduce without crossing with neighboring plants. This can lead to inbreeding depression, another way to say accumulation of deleterious recessive alleles in genes.
Quite the opposite happen in dioecious flowers. In these flowers, it is not possible for selfing to occur. This promote outcrossing or cross-pollination and prevent inbreeding.
- Uh, I did not get what inbreeding depression is?
It can be defined as a reduction in fitness of offsprings resulting from self-fertilisation (inbreeding) compared to those resulting from cross-fertilisation (outbreeding). In short, that means plants will tend to be weaker and less fertile over time. Inbreeding depression in evolutionary biology is considered by many a major evolutionary force!
Barriers to genetic exchanges between two populations can prevent pollen of plants from one population from falling on stigmas of plants from another. Such barriers to cross-fertilisation can be :
- geographical (growth in two different places);
- ecological (populations not being similar enough to allow crossing);
- seasonal (different flowering time).