The well-known and perhaps most important role of boron in plants is cross-bonding with Rhamnogalacturonan-II (RG-II), a pectic polysaccharide in cell walls. With this interaction with Rhamnogalacturonan-II, boron directly affects the stability of cell walls, mechanical properties and physiological function in growth. Studies show that about 90% of RG-II in plant cell walls is bound by boron. Rhamnogalacturonan-II is a complex pectin substance located in cell walls and directly affects the stability and functions of the cell wall with the bonds it makes with boron. The main reason why dicot plants need more boron than monocots is based on the fact that dicot plants contain much more pectin. The amount of uronic acid, which can be considered as an indicator of pectin, is generally 2-3 times higher in dicotyledonous plant tissues than in monocotyledonous plants. Studies reveal that there is a very close relationship between the amount of pectin and the need of plants for boron. Boron deficiency leads to a decrease in the B-RG-II complex, leading to significant deterioration in the structural and functional integrity of the cell walls, and this causes a slowdown of cell elongation and growth in plants, to the point of stopping.
Boron has a decisive role on the stability of cell membranes as well as in the cell wall. In boron deficiency, the stability of cell membranes deteriorates very rapidly and gains a very permeable/leaky character. Due to this membrane destruction, the secretion (exudation) of organic compounds such as sugars and amino acids from root and leaf cells increases. These organic compounds secreted from the cell serve as nutrients for the proliferation of pathogens. In fact, it is known that boron deficiency makes plants susceptible to diseases. Another reason for this is that the cell walls lose their ability to detect physical barriers against pathogens in boron deficiency. As the cell walls gain a weak structure and lose stability in boron deficiency, the pathogen enters/penetrates the plant tissue and infects the plant.