Background and aims The purpose of this study was to examine the developmental defects of cell walls and vessels at the ring sites of cotton petioles and thereby understand the effects of petiole rings on nutrient transport in cotton.
Methods Boric acid was applied as basal fertilizer in boron-deficient cotton field to verify the relationship between boron concentration and ring formation on cotton petioles. Petiole samples were taken from boron-deficient cotton plants to analyze the differences in cell wall properties and anatomical structure between the ring and non-ring sites.
Results Under boron deficiency stress, chloroplasts were deformed and slightly disintegrated at the ring sites of the petioles. The cell walls within the rings were irregularly thickened by 44.1%, while their mechanical strength was markedly reduced by 38.9% compared to those of the non-ring sites. There were also changes in the hydrogen bonding within carbohydrates and proteins and the structure of pectins along with cellulose accumulation in the cell walls at the ring sites. A large number of tiny vessels were formed in the petiole rings, resulting in the squeezing and rupture of vessels. Boron, magnesium, and manganese concentrations in various parts of the petioles varied substantially in the order of lower part > middle part > upper part.
Conclusions Boron application reduces the probability of ring formation on the petioles of cotton. The cell walls and vessels are destructed at the ring sites of the petioles, which impairs their mechanical support and mineral nutrient transport functions in boron-deficient cotton.