STUDY ON THE PHYSIOLOGICAL MECHANISM OF BORON UTILIZATION EFFICIENCY IN RAPE CULTIVARS

Abstract

In order to uncover the mechanism of boron (B) utilization efficiency, B metabolism was studied through B forms and their balance of transformation. According to the reaction between B and some sugars in rape (Brassica napus L.), B was divided into free B, semi-bound B, and bound B using a sequential extraction procedure. One B-efficient rape cultivar (9589), one B-inefficient rape cultivar (95105), and the F₁ hybrid (95105 × 9589) were involved in this pot experiment, which was carried out during 1998–1999. Two externally applied B treatments (B₁: 0.05 mg kg⁻¹ and B₂: 0.25 mg kg⁻¹) were used, and in both B treatments, the results showed that the concentration of the three B forms differed between the different cultivars. The free B and bound B concentration in the B-efficient cultivar (9589) was significantly lower than that in the B-inefficient cultivar (95105), and the F₁ hybrid (95105 × 9589) was intermediate, but the semi-bound B concentration showed the opposite trend. Boron could react with some sugars which contained the vicinal group in cis position, which showed closely the relation between B and some sugar in plants. A significant difference of fructose content existed between cultivars. Using thin-layer chromatography and ultraviolet-scan analysis fructose was shown to react easily with B. From the close relationship between B and sugar, a hypothesis concerning the physiological mechanism of B utilization efficiency was formulated; a reaction constant k_m for the balance of B forms may indicate to some degree whether rape cultivars are B efficient.

ACKNOWLEDGMENTS

We thank Prof. Dr. Ronald G. Mclaren and Dr. Hong J. Di (Dept. of Soil Science, Lincoln University, New Zealand) for their critical review of this paper. In addition we also thank the National Natural Science Foundation (NSFC) for financial support.