CALIPTRA: FEATURES AND FUNCTIONS - BIOLOGY - 2024

Caliptra is a term used primarily in botany to define various types of protective tissues. The word derives from the ancient Greek καλύπτρα (kaluptra) which means to cover, veil or cover.

The term caliptra is used to define, in bryophyte plants, a thin, bell-shaped tissue that protects the sporophyte during development; in flowering and fruiting plants, it is a cap-shaped covering that protects such structures, and at the root it is a protective layer of the apical system.

Caliptra of the moss Physcomitrella patens. Taken and edited from: Ralf Reski

In zoology, on the other hand, the term caliptra is used to define a small well-defined membranous structure, located on top of the second pair of modified wings (halteres) of flies and mosquitoes, and which has high taxonomic interest. In this article, only the botanical meaning of the term will be considered.

History

The use of the term caliptra dates back a long time, to more than 1800 years ago, in the writings of the Roman grammarian Sixth Pompey Festus, who used it in his work De Significatione Verborum.

Between the V and XV centuries (Middle Ages), on the other hand, the term was used to name the covers of some types of seeds. Starting in the 18th century, botanists of the time used it to designate the remnant of the archegonium of mosses.

At the end of the 19th century the famous French mycologist and botanist Philippe Édouard Léon Van Tieghem used the term to define a thick membrane of the parenchyma that protects the area of ​​radical apical growth of vascular plants, what today in botany they also call Coping.

characteristics

Source: Apical meristem of onion root (»Allium cepa») covered by the caliptra. Madrid, 2007-03-25. Photography: Luis Fernández García {{cc-by-sa-2.5-es}}

The caliptra is made up of living cells of the parenchyma tissue. It usually contains special amyloplasts with starch granules. It has cells of medium to short life that when dying are replaced by the radical meristem.

These cells are distributed in radial rows. In central cells of Gymnospermae of the genera Pinus and Picea (for example), they form an axis called columella and the meristem is of the open type, and in other groups of plants the cells are arranged in longitudinal rows.

In bryophytes, it is used to define the enlarged part of the multicellular sexual organ (archegonium), which contains the ovule or female gamete of the moss, while in some spermatophytes with flowers, it is the protective tissue of the stamens and pistils.

The term cap is a synonym for caliptra, and both are used to describe the tissue that covers the apical region of the roots, which is found at the end of the root and has the appearance of a cone.

Training

The calyptra originates from different places on plants.

Pteridophytes

In ferns (Pteridophyta) both in the root and in the stem there is a tetrahedral apical cell that produces cells by division on each of its four faces. These cells grow outward to form the caliptra and other tissues through further division.

Spermatophytes

In gymnosperm plants and angiosperms, their formation in general is not very clear. However, it is known that in gymnosperms the apical meristem does not present an apical meristematic cell, and instead there are two groups of initial cells (internal and external group).

The internal group is in charge of forming the main mass of the root body through alternate anticline and expert divisions, while the external group is in charge of producing the cortical tissue and the caliptra.

In angiosperms, on the other hand, there is a stratified formation center of initial groups of independent cells at the apical end of the root. Different adult tissues are formed from this center, such as the caliptra and the epidermis, among others.

The initial training structure may vary in some cases. In monocotyledonous plants such as grasses, it forms in a meristematic layer called a caliptrogen.

This outer layer (caliptrogen), is united with the protodermis (which produces the superficial tissue of the root) as well as the underlying meristematic layer, forming a unique initial group from which the cortical tissue comes.

In most dicotyledonous plants, caliptra is formed in caliptrodermatogen. This occurs by anticline divisions of the same initial group that also forms the protodermis.

Features

The main function of the caliptra is to provide protection. In mosses, it is responsible for protecting the sporophyte, where spores are formed and mature, while in spermatophyte plants it forms a protective layer or tissue on pistils and stamens.

At the root, it is the protective coating of the meristematic structure, it provides mechanical protection when the root grows and develops through the substrate (soil). The cells of the caliptra are constantly renewed since root growth involves a lot of friction and cell loss or destruction.

Caliptra participates in the formation of mucigel or mucilage, a gelatinous, viscous substance mainly composed of polysaccharides that covers the newly formed meristem cells and lubricates the passage of the root through the soil. Caliptra cells store this mucigel in Golgi apparatus vesicles until it is released into the medium.

Large cell organelles (statoliths) are found in the columella of the caliptra that move within the cytoplasm in response to the action of gravitational force. This indicates that the caliptra is the organ in charge of controlling the georeaction of the root.

End of a root, seen at 100x magnification. Legend: 1) meristem, 2) columella of the caliptra (statocytes with statoliths), 3) lateral portion of the root, 4) dead cells of the caliptra detaching, 5) from the elongation zone. Taken and edited from: SuperManu.

Geotropism and hydrotropism

Plant roots respond to Earth's gravity, which is called geotropism (or gravitropism). This answer is positive, that is, the roots tend to grow downwards. It has a great adaptive value because it determines the correct anchoring of the plant to the substrate, and the absorption of water and nutrients present in the soil.

If an environmental change, such as a landslide, causes a plant to lose its underground verticality, positive geotropism causes the overall root growth to reorient downward.

Aminoblasts, or plastids containing starch grains, act as cellular gravity sensors.

When the tip of the root is directed to the side, these plastids settle on the lower lateral wall of the cells. It appears that calcium ions from aminoblasts influence the distribution of growth hormones in the root.

For its part, the caliptra columella plays an important role in both geotropism and positive hydrotropism (attraction to regions of the soil with higher concentrations of water).

Scientific importance

From the phylogenetic and taxonomic point of view, the study of the caliptra has been a useful tool, since its type of development, as well as the structures that this tissue protects differ depending on the group of plants.

Other relevant investigations in relation to the calyptra are on the geotropism, georeaction and gravitropism of the root. Where various studies have shown that the caliptra has cells and also organelles (amyloplasts or statoliths) that transmit gravitational stimuli to the plasma membrane that contains them.

These stimuli are translated into movements of the root, and will depend on the type of root and the way it grows. For example, it has been found that when roots grow vertically, statoliths are concentrated in the lower walls of central cells.

But, when these roots are placed in a horizontal position, the statoliths or amyloplasts move downwards and are located in the areas that were previously vertically oriented walls. In a short time the roots are reoriented vertically and thus the amyloplasts return to the previous position.

References

1. Calyptra. Recovered from en.wikipedia.org.
2. Caliptra. Morphological botany. Recovered from biologia.edu.ar.
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5. Caliptra etymology. Recovered from etimologias.dechile.net.
6. Coping (biology). Recovered from pt.wikipedia.org.
7. The root system and its derivatives. Recovered from britannica.com.
8. Caliptra. Recovered from es.wikipedia.org.
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10. J.-J. Zou, Z.-Y. Zheng, S. Xue, H.-H. Li, Y.-R. Wang, J. Le (2016). The role of Arabidopsis Actin-Related Protein 3 in amyloplast sedimentation and polar auxin transport in root gravitropism. Journal of Experimental Botany.