In plants, very different morphological and physiological changes manifest themselves with the occurrence of Boron (B) deficiency stress. These changes occur primarily in the fastest growing parts of plants, particularly roots. Root growth is much more affected than green part growth during the vegetative growth process. In some trials, it has been known that root growth stops abruptly within hours after plants are transferred from conditions of sufficient boron nutrition to a nutritional medium where boron is completely deficient. A similar condition occurs under Calcium (Ca) deficiency conditions, and the aforementioned dramatic decreases in root growth are associated with the very low in-plant portability of boron in the vast majority of plant species. In other words, when there is a boron deficiency in the soil, the existing boron in the plant cannot be transported to areas with high boron demand, such as root tips or flower organs.
As seen in the Canola plant below, significant reductions in root growth have been found under boron deficiency conditions before a marked reduction in foliage growth or any sign of boron deficiency in the leaves. Naturally, such a problem is not easy for producers to see or understand under field conditions. For this reason, it is useful to make leaf analyzes from time to time and to perform analyses on the youngest leaves of the plants.
Physiologically, several factors play a decisive role behind the dramatic negative effect of boron on the root growth. As above, the best known function of boron in plants is related to cell walls. In boron deficiency, deterioration and destruction of the stability, mechanical properties and resistance of the cell walls and physiological functions occur, and these changes have an inhibitory effect on the cell elongation and growth. The fact that the amount of free oxygen radicals, which have a very high toxic effect, accumulates in high amounts at the root growth tips and causes cell destruction in boron deficiency is another reason why root growth is sensitive to boron deficiency.
It is stated that it has an important role in the transport of photosynthesis products from the leaves to the growth points (meristematic organs) in the roots and green parts. If photosynthesis products are transported to the roots in boron deficiency, a significant decrease in root growth is also likely. In addition, the accumulation of ethylene hormone, which has a growth arresting effect on the root tips in boron deficiency, and the decrease in the root tips of indolacetic acid (auxin hormone), which is a growth hormone, contribute to explaining why the negative effects of boron deficiency occur on the root growth.