MACROBLASTS: CHARACTERISTICS AND SCIENTIFIC IMPORTANCE - BIOLOGY - 2025

The long shoots are known botanically as long branches, characterized by a significant increase in the entrenudos area, whereby the sheets are far apart from each other. These branches differ from the brachyblasts, which are short branches with little internode growth, so the leaves are very close to each other.

In cell biology, on the other hand, macroblasts, macrocytes or megaloblasts, are nucleated cells of the bloodstream that derive from an abnormal formation or maturation of erythrocytes. And they can be observed in human pathologies such as megaloblastic and pernicious anemias.

Macroblasts in Brunfelsia australis. Taken and edited from: Photo by David J. Stang.

Both terms will be considered in this article, where various aspects of macroblasts will be analyzed both from the botanical point of view and from the cellular biology.

Preliminary considerations

Botany

In plants, the structures that we commonly call branches are considered by botanists as shorter stems attached to the main, longer stem.

On the other hand, the stem is defined as an elongated, cylindrical or sub-cylindrical supporting organ whose function is to give mechanical support to other organs such as leaves, flowers and fruits.

The stem also facilitates the transport of water and nutrients from the root to these organs. Shorter stems (branches) will emerge from the main stem, which will support a greater number of leaves, flowers and fruits, and in many species they will be the only ones to do so.

The branches can be classified into macroblasts and brachyblasts, which, as already noted, are differentiated by their internode growth and the arrangement of the leaves.

Cell biology

Blood macroblasts or macrocytes are abnormal erythrocytes. Erythrocytes are blood cells also called red blood cells and are responsible, when mature, for the transport of gases in vertebrates.

In mammals, they are characterized by lacking a nucleus and by their biconcave shape, with diameters that range between 5 and 7 microns, sometimes more. They are also about 1 micrometer thick.

The cell when it is immature is large, with abundant cytoplasm and a large nucleus that later loses along with the mitochondria when maturing.

characteristics

Botany

Macroblasts are long branches with unlimited growth, which have a prolonged growth between nodes, resulting in leaves with long separations from each other. They arise from the stem.

Cell biology

Macroblasts are formed by abnormal development of erythrocytes and are characterized by being large, nucleated, abnormal cells with specific chromatin alterations. What could be interpreted as a young cell that did not reach its normal development.

Development

Botany

Both macroblasts and brachyblasts are considered by many authors as secondary stems, high branches and / or second class branches (depending on the taxon of the plant).

In a developing plant, stem growth occurs because the apical meristem lengthens the stem (primary growth), in addition to developing leaves that will join the trunk in certain places called nodes. Just above that junction an axillary bud is formed.

The apical meristem inhibits the growth of the axillary buds by means of a hormone called auxin. As the trunk grows, the apical meristem moves away from the bud, thereby decreasing the auxin concentration and unblocking the growth of the axillary bud.

In a first phase, the apical growth of the bud occurs due to the multiplication of cells of the meristem, in this way foliar primordia are developed separated by very short internodes.

While the bud continues to develop, the stem lengthens by intercalary growth of internodes, the basal ones growing first and then the apical ones. This development or growth of secondary branches occurs mainly by elongation of existing cells and not so much by cell division.

Cell biology

Red blood cells in mammals are formed in the bone marrow, at sites called erythroblastic islands, in the long bones, the sternum, and in the ribs. In other vertebrates they are formed in the kidneys and in the vessel.

The formation of erythrocytes involves several processes, ranging from cell proliferation to the maturation of red blood cells, passing through various stages of cell differentiation. During this process, the cells undergo mitotic divisions, so their size and that of the nucleus decrease.

Later they lose the nucleus and other organelles (such as mitochondria) and will enter the circulatory system in a process that takes between 5 and 6 days approximately.

Generally, when the concentrations of folic acid and cobalamin are very low, the nuclear genetic material of the precursor cells of red blood cells cannot be synthesized, so they are not capable of mitosis.

On the other hand, the cytoplasmic volume becomes larger, a phenomenon called macrocytosis, resulting in a very large cell that is the so-called macroblast or macrocyte (other authors call it megaloblast).

Macroblasts, macrocytes, or magaloblasts, in a patient with magaloblastic anemia. Taken and edited from: Prof. Osaro Erhabor.

Scientific importance

Botany

The study of macroblasts is a tool used in botanical systematics and taxonomy, due to the fact that characteristics of these structures, as well as of the brachyblasts, vary from one plant taxon to another.

For example, one of the defining characteristics of gymnosperms of the genus Pinus is that the leaves present in the macroblasts are scaly and non-photosynthetic, while those of the brachyblasts present acicular forms, are photosynthetic and are arranged in fascicles.

The use of this tool has been relevant for phylogenetic analysis and even for the description of new species.

Cell biology

Macroblasts are of clinical importance, because the formation of megaloblastic cells or macroblasts originate a variety of blood diseases that are called macroblastic anemias, the most common of which is called pernicious anemia.

This pathology arises mainly because vitamin B12 cannot be absorbed by the small intestine. Other causes can be diseases of the digestive system, alcoholism, poorly balanced diets and even some medicines.

Symptoms of this type of anemia include abnormally pale body coloration, a tendency to be irritated, poor appetite, frequent and watery stools, headaches, motor problems, muscle weakness, and mouth and tongue ulcers.

For weak or mild anemias, no treatment is required, however, sometimes they can be controlled by supplying vitamin complexes (preferably in injections) or folic acid. Severe anemias in some cases require blood transfusions.

References

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