Magnesium

Magnesium concentrations in plant tissues are usually high. This abundance indicates the number of functions in which it is involved, primarily as an activator of enzymatic reactions, such as RNA polymerase, responsible for the transcription of genetic messages. However, magnesium's importance lies in its role as the metallic nucleus of the chlorophyll molecule, responsible for photosynthesis and the pigment that gives plants their green color. Therefore, magnesium is essential for plant energy metabolism.
It intervenes in protein biosynthesis, in the formation of some hormones, in fertilization processes, and in the assimilation of nitrogen, phosphorus, and other elements.
And in crops with adequate magnesium levels, it induces better fruit sizes and helps them better tolerate the effects of low temperatures.

ABSORPTION
Magnesium is not usually a limiting factor for plants, except in very acidic or sandy soils. It is absorbed as the Mg+2 ion, and can be absorbed through the roots or leaves, the former being the most common in nature.

DEFICIENCIES

Magnesium deficiency commonly occurs in acidic, sandy soils in areas with moderate to high rainfall. This deficiency can be induced by high levels of Ca+2, K+, or Na+2 in the soil.

Magnesium is mobile in plants, so the first symptoms of magnesium deficiency appear in older leaves, when they turn yellow with green veins (interveinal chlorosis). In some plants, the lack of chlorophyll is followed by the appearance of other pigments.