Auxospores are specialised

cells Cell most often refers to: * Cell (biology), the functional basic unit of life * Cellphone, a phone connected to a cellular network * Clandestine cell, a penetration-resistant form of a secret or outlawed organization * Electrochemical cell, a d ...

diatom A diatom (Neo-Latin ''diatoma'') is any member of a large group comprising several Genus, genera of algae, specifically microalgae, found in the oceans, waterways and soils of the world. Living diatoms make up a significant portion of Earth's B ...

s that are produced at key stages in their

cell cycle The cell cycle, or cell-division cycle, is the sequential series of events that take place in a cell (biology), cell that causes it to divide into two daughter cells. These events include the growth of the cell, duplication of its DNA (DNA re ...

or life history. Auxospores typically play a role in growth processes,

sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...

dormancy Dormancy is a period in an organism's Biological life cycle, life cycle when growth, development, and (in animals) physical activity are temporarily stopped. This minimizes metabolism, metabolic activity and therefore helps an organism to conserv ...

.Hoek, C. van den, Mann, D. G. and Jahns, H. M. (1995).
Algae : An introduction to phycology
', Cambridge University Press, UK.

Mechanism

Auxospores are involved in re-establishing the normal size in diatoms, as successive

mitotic Mitosis () is a part of the cell cycle in eukaryotic cells in which replicated chromosomes are separated into two new nuclei. Cell division by mitosis is an equational division which gives rise to genetically identical cells in which the t ...

cell division Cell division is the process by which a parent cell (biology), cell divides into two daughter cells. Cell division usually occurs as part of a larger cell cycle in which the cell grows and replicates its chromosome(s) before dividing. In eukar ...

s leads to a decrease in cell size. This occurs because each daughter cell produced by cell division inherits one of the two valves that make up the

frustule A frustule is the hard and porous cell wall or external layer of diatoms. The frustule is composed almost purely of silica, made from silicic acid, and is coated with a layer of organic substance, which was referred to in the early literature on ...

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundant f ...

cell wall A cell wall is a structural layer that surrounds some Cell type, cell types, found immediately outside the cell membrane. It can be tough, flexible, and sometimes rigid. Primarily, it provides the cell with structural support, shape, protection, ...

), and then grows a smaller valve within it. Consequently, each division cycle decreases the average size of diatom cells in a population. When its size becomes too small, a dividing diatom cell produces an auxospore to expand its cell size back to that which is normal for

vegetative cells Vegetative describes vegetation. Vegetative may also refer to: *Vegetative reproduction, a type of asexual reproduction for plants *Persistent vegetative state, a condition of people with severe brain damage *Plant community A plant community is ...

. Auxospores can also play a role in sexual reproduction in diatoms, and may be formed after

haploid Ploidy () is the number of complete sets of chromosomes in a cell (biology), cell, and hence the number of possible alleles for Autosome, autosomal and Pseudoautosomal region, pseudoautosomal genes. Here ''sets of chromosomes'' refers to the num ...

gamete A gamete ( ) is a Ploidy#Haploid and monoploid, haploid cell that fuses with another haploid cell during fertilization in organisms that Sexual reproduction, reproduce sexually. Gametes are an organism's reproductive cells, also referred to as s ...

s fuse to form a

diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Here ''sets of chromosomes'' refers to the number of maternal and paternal chromosome copies, ...

zygote A zygote (; , ) is a eukaryote, eukaryotic cell (biology), cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individ ...

. Finally, auxospores can be produced by diatoms to act as dormant stages, sometimes referred to as "resting spores." These are used to survive periods of time that are unfavourable to growth, such as the low-light period of winter or while nutrients are depleted.

Structure

The auxospore is covered by a flexible cell wall called perizonium, which replace the thin zygotic membrane when the auxospore originates from a zygote, and doesn't restrict cell growth. A few species don't form a perizonium, and has a wall of scales and imperforate silica instead. Usually the auxospore is photosynthetic and depends on light to grow, but with sufficient accumulated storage material before its formation, it can be formed formed without any further supply of energy. After maximal size has been reached, a new diatom with a rigid frustule, a so-called initial cell that is significally larger than its parent cells, is formed inside the auxospore which it eventually breaks free from.

References

Diatom biology {{Diatom-stub