Boron-Efficient Sugar Beet ( Beta Vulgaris L.) Cultivar Improves Tolerance to Boron Deficiency by Improving Leaf Traits

Crop nutrient-efficient cultivars are more adapted to the nutrient-deficient environment. However, the physiological tolerance mechanisms of boron (B)-efficient sugar beet cultivars in response to B deficiency are unclear. Therefore, the B-efficient and B-inefficient sugar beet cultivars were used as test materials and cultured at two B levels (B deficiency and normal) to investigate the changes in the sugar beet leaf morphology, cell wall composition, and related gene expression under B-deficient conditions. The results indicated that B deficiency distorted the cell wall structure, altered cell wall components, and adversely affected leaf morphology. However, compared with the B-inefficient cultivar, the B-efficient sugar beet cultivar allocated more B concentration in the cell wall under B-deficient conditions. In B-efficient sugar beet cultivar leaves, the chelator-soluble pectin contents were remarkably increased while the alkali-soluble pectin content decreased, and the KDOPS expression was less upregulated. The B-efficient sugar beet cultivar accumulated more leaf biomass, a larger leaf area, and was less affected by B deprivation. In conclusion, the B-efficient cultivar responded efficiently in cell wall composition, gene expression, and leaf morphology, thus demonstrating better resistance to B-deficient stress.