Study On The Relationship Between Boron Efficience And Cell Wall Consitituents Of Brassica Napus

Boron (B) is one of the essential micronutrient elements for plants. As an important cash crop in China, rapeseeds (Brassica napus) are more sensitive to low-B stress. B deficiency always causes the decrease of crop yield and quality in the area of the middle and lower reaches of Yangtze River. So, using the knowledge of genetics and molecular biology to screen the high efficient rapeseed cultivar and studying with the mechanism of B efficiency are very important methods for us to change the situation of the absence of B resource and to raise the rapeseed yield and quality. In this study, we chose the typical B-efficient rapeseed cultivar QY10 (BEC) and the typical B-inefficient cultivar Westar10 (BIC) which were screened and identified by our laboratory. Using these cultivars, pot and solution experiment were conducted to systematically study on the difference in the constituents and development of the cell wall and B efficiency between the two rapeseed cultivars, and then the relationship between cell wall properties and B efficiency was discussed. The main research results obtained as follows:1 Differences in boron uptake, transport and utilization in Brassica napus cultivars with different B efficiencyB-efficient cultivar QY10 and B-inefficient cultivar WestarlO were used to study boron uptake, transport and utilization in Brassica napus. The results obtained from pot experiment showed that there were obvious differences in response to low-B stress between the two cultivars with different B efficiency. Under low-B stress, BEC had higher biomass production and stronger capability for transporting B to young tissues than BIC, and the B concentration in stems of BEC were higher than BIC in both seedling stage and bolting stage. Under the condition of sufficient B, the B accumulation in BIC was higher than BEC, indicating that BIC needs more B, but the uptake and distribution capability of B was weak.2 Relationship between cell wall properties and B efficiencyB-efficient cultivar QY10 and B-inefficient cultivar WestarlO were used to study the differences in cell wall concentration, cell wall constituents and boron distribution. The results from nutrient solution culture showed:Firstly, the cell wall extraction of leaf was higher than root in Brassica napus, and low-B stress resulted in an increase in cell wall extraction. Under low-B stress, the cell wall extraction of leaf and root in BIC were basically higher than BEC, which was same to the total pectin and pectin II; Secondly, pectin of cell wall was the main sites combined with B. Under the sufficient B condition, about 40% of plant B was found in cell wall, and the proportion in root was much higher than leaf at low-B stress, which reached about 70%-90% of plant B; Thirdly, the cell wall B was more stable than organ B on different B treatments; the proportion of cell wall B was increased significantly under low-B stress, and the ascensional range of BIC was greater than BEC. The B concentration in cell wall was significantly and positively correlated with the B concentration of pectin (especially in pectinâ…¡); finally, the main differences between two cultivars were that BIC needs more B. But the B distribution in cell wall and pectin in BIC was less, and equivalent B was difficult to meet the demand for its normal growth compared with that happened in BEC. So the growth of BIC was keep down, and B deficiency symptom was obvious and the seed yield was lower.3 Effects of boron on microstructure and ultrastructure of roots and leaves in Brassica napusB-efficiency cultivar QY10 and B-inefficiency cultivar WestarlO were used to study the microstructure and ultrastructure of roots and leaves by plant microtechnique, it showed that low-B stress caused the inhibition of root growth, epidermal injury, root tip swell, cell disorganization, and root surface, root volume and root tips were distinct decreased. Due to the deficiency of B, the meristematic tissue cell structure of root tips turned to be disordered, and the number and volume of vacuoles increased; the activity of nucleolus decreased, chromatin shrinked, nucleolus became deformed; the cell wall became thickening, and the cell wall of BIC was broken accompanied with cytoplasm spilled out. At the same time, the cell of leaf became unusual, the cell wall of leaf thickened, the structure of chloroplast and its grana lamellae turned to be incomplete and unclarity by the deficiency of B. In particular, the effects of low B on BIC were greater than BEC.4 Effects of B on the expression of the cell wall synthesis related gene KDOPSB-efficient cultivar QY10 and B-inefficient cultivar WestarlO were used to study the expression of KDOPS by real-time PCR technology. The results indicated:KDOPS expressed in root, old leaf and young leaf of Brassica napus, but the expression of KDOPS has significant differences for both B treatments and cultivars. Firstly, the expression in young leaf was much greater than others; secondly, the increased expression of KDOPS was detected in both, and BIC was significantly increased than the other one; in the end, the expression of KDOPS in BIC was higher than in BEC.