What are Meristems?
Plants’ fundamental structural basis is made up of several sorts of tissues. Plant tissues may be divided into two categories based on their ability to divide: permanent tissues and meristematic tissues. Meristematic tissues’ cells, unlike those of permanent tissues, do not lose their ability to divide.
They don’t differentiate in order to acquire a permanent form, size, or function; instead, they stay tiny, immature, and cytoplasmically dense, with high respiration rates. Meristematic tissues are divided into two categories based on their origin: primary and secondary meristems.
The primary meristematic tissues are generated directly from the embryonic meristems, whereas the secondary meristematic tissues are dedifferentiated from the permanent tissues. There are three forms of primary meristematic tissue dependent on the tissue’s location.
Apical, Intercalary, and Lateral are the three types. With the assistance of the “Apical Meristem,” we can explain that it happens at apices (both root and shoot apices). It takes place in the plant body’s internodes with the aid of the “Intercalary Meristem.” With the aid of the “Lateral Meristem,” it happens together with the girth of the plant body.
To help identify and differentiate intercalary meristem, see the figure below. Meristematic tissues are composed of cells that are actively dividing. Plants with uncertain growth are caused by them. Permanent plant tissues such as vascular tissues, epidermis, phellem, ground tissues, and so on are produced by them.
The three forms of meristematic tissue are (1) apical meristem (terminal parts), (2) intercalary meristem (at the nodes of some monocots), and (3) lateral meristem (at the nodes of certain monocots) (toward or from the sides).
Intercalary Meristem Definition
A kind of meristematic tissue that may be seen at the base of monocot nodes and leaf blades. The term comes from the fact that intercalary meristem is a form of meristematic tissue that grows in length at the midway position.
This layer comprises of meristematic cells that divide mitotically in the stem at the base of nodes and leaf blades. Intercalary growth is the term for the growth that occurs at this moment. This is important for these plant groupings because it acts as an adaptation against herbivory.
These plants may compensate for herbivore eaten plant sections by rapidly regrowing leaves and elongating stems thanks to intercalary growth. Intercalary meristematic tissue; intercalary growth tissue are synonyms.
What is Intercalary Meristems?
An intercalary meristem is a type of primary meristematic tissue that aids in vertical growth by increasing the length of a plant or tree. Small, totipotent, thin-walled, and protoplasm-filled cells make up this meristematic area. The following are the distinguishing characteristics of the intercalary meristem:
1. Divergence in nature
2. Primary by origin (originating straight from an embryo)
3. Positional intercalary (between permanent tissues)
Because it is mitotically (dividing) active, the intercalary meristem contributes to the plant’s vertical or intercalary growth, earning its name. The intercalary meristem, unlike the other basic meristematic tissues, has a limit; it will ultimately reach a limit and develop into permanent tissues.
The intercalary meristem is really implanted meristematic tissue in the mature tissue, according to certain scientific literature. In this view, the apical meristem is the source of the intercalary meristem. After insertion, the apical tissue is said to be divided into a number of intercalary sections, which eventually form a number of intercalary meristems, by progressively produced nodes.
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Sources of Intercalary Meristems
Two sources of intercalary meristem may be found far behind the shoot and root tips. One is the subapical meristem, which is located at the base of the apical meristem and helps to generate the intercalary meristem “directly.” Another way is by the dedifferentiation of mature tissues, which “indirectly” leads to the development of the intercalary meristem later in the plant’s life.
1. Subapical Meristem This occurs when division activity is gradually restricted to any area of the internode/floral axis/spike axis where it is very lengthy and contributes considerably to internodal tissues.
2. Dedifferentiation of Mature Tissues Although the intercalary meristem develops into developed tissues, some of it is “silently retained” after maturation. This quiescent tissue dedifferentiates when it is triggered by an environmental, growth, or developmental situation.
The transition of cells from a highly differentiated state to a less differentiated or stem cell-like state is known as dedifferentiation of mature tissues. It contributes to division activity for a long period through this pathway, and it is generally the primary contributor to longitudinal growth in the later stages of plant life.
Presence of Intercalary Meristems in Different Plant Lineages
Intercalary meristems have been found in thallophytes (algae), bryophytes (mosses), pteridophytes (ferns), gymnosperms (conifers, cycads), and angiosperms (monocots and dicots) across a variety of plant lineages. Although the position and functions of intercalary meristems vary greatly throughout the spectrum, their importance in plant growth and development stays constant.
Monocots have the intercalary meristem, which is typical among angiosperms. However both monocots and dicots have a shoot apical meristem, it divides throughout development in monocots but not in dicots, resulting in an additional meristem below the apex known as the intercalary meristem. This process continues until blooming begins, resulting in the formation of intercalary meristems in grass nodes.
Pinus has been shown to have an intercalary meristem among gymnosperms. The intercalary meristem is important in the formation of Pinus cataphyll (reduced gymnosperm leaves).
Intercalary meristems have been found in the lamina of kelps (Phaeophyta/Brown algae) among thallophytes/algae. In kelps, an intercalary meristem exists between the stipe and the blade to lengthen the thallus.
Horsetails have been shown to have an intercalary meristem among pteridophytes/ferns (Equisetum spp.). Intercalary meristems are found in aerial shoots of Equisetum spp., but there is no information on their existence in rhizomes.
How Intercalary Meristem Helps in Vegetative Growth of Equisetum Spp. Shoots?
The events that lead to the development of the intercalary meristem in Equisetum spp. are described here. The intercalary meristem, in combination with the apical meristem, assists in the vegetative development of Equisetum spp.
1. In the vegetative shoot, apical cells divide, resulting in the development of “merophytes.”
2. These merophytes operate in unison, resulting in the formation of units known as “phytomers.”
3. A phytomer can be subdivided into two different levels.
- A. The basal internodal tier is referred to as
- B. a higher nodal tier
4. The meristematic activity of Equisetum spp. is maintained by the basal internodal tier, which leads to the development of the intercalary meristem.
Functions of Intercalary Meristems
Intercalary meristematic tissue, like organs and tissues in mammals, may perform a variety of roles in various lineages, genera, and species; similarly, intercalary meristematic tissue serves a variety of roles in plants.
It satisfies several essential necessities of a plant to live and proliferate, ranging from vertical (longitudinal) growth to grazing tolerance to gynophore development. The following are some of the most significant functions of the intercalary meristem:
1) It helps to re-establish fallen cereal plant stems.
2) It aids in the regeneration of lawn grass that has been grazed by animals or mowed repeatedly.
3) It promotes bamboo height development by elongating the internodes.
4) It has a significant impact on grasses’ developmental morphology and physiology. When grasses grow, the entire leaf primordium has meristematic activity at initially, but later, only the intercalary meristem has cellular division.
Intercalary meristematic activity inside the blade ends after ligule development. Intercalary meristematic activity within the sheath stops when the ligule is revealed. As a result of the basal position of the intercalary meristematic tissue inside the two primary components of grasses—blade and sheath—leaf elongation can occur without replacement of the leaf tip following defoliation/grazing/repeated mowing.
When we examine the meristematic activity of different meristems in grasses, we may deduce two important points: the intercalary meristem grows replacement grass leaves at the quickest pace, while the axillary meristem grows replacement grass leaves at the slowest rate.
As a result, grass meristem is commonly referred to as intercalary meristem. Intercalary Meristem > Apical Meristem > Axillary Meristem Intercalary meristems are short-lived, but axillary buds provide perenniality to the plant.
5) In culmed grasses such as sorghum, millet, and sugarcane, the intercalary meristem is important for culm elongation.Culm is an essential component of the malt product produced from these grasses. The more elongated the culm, the greater the amount of malt that may be extracted. They are also utilised as healthy animal feeds due to their great nutritional content.
6) In peanuts (Arachis hypogea), the presence of an intercalary meristem in the ovarian stalk causes gynophore development near the ovary.Only after pollination and successful fertilisation does the intercalary meristem become active. The fertilised ovary is buried deep into the soil by the intercalary meristem.
7) The intercalary meristem in kelps (Phaeophyta/Brown algae) aids in thallus lengthening.
Intercalary Meristems Examples
The following autotrophs and their locations, in summary, exemplify intercalary meristems:
1. Grasses and grains belong to the Poaceae family (at the base of internodes and above the nodes).
2. Present in a mint container (below the nodes)
3. Possible in Pinus (at the base of the leaves)
4. Exhibit in bamboo (in internodes)
5. It’s found in sugarcane (at the base of the several uppermost internodes)
6. Assembled in Equisetum (located above each node)
7. Arachis hypogea is present (in ovarian stalk)
8. Present in kelps, Chorda filum (in both vegetative and sporophytic phases)
Intercalary Meristems References
Mechanisms for Growth: https://forages.oregonstate.edu/
intercalary meristem: http://www.sbs.utexas.edu/