| B deficiency in rape(Brassica Napus L.) is a common micronutrient deficiency phenomenon in field. But the cultivate response to low B varied widely. So it is possible to get ideal B efficient rape cultivars through methods of breeding and molecular biology. To achieve this goal, it is essential to make clear the mechanisms of efficiency. Recently studies showed that pectin content of plant cell wall may be the main factor to determine plant B efficient. In this stud), two B efficient rape cultivars and two B inefficient rape cultivars, which were screened by Wang Yunhua et al(1995) in our laboratory, were used to study B functions and distribution laws in the wall, and the differences of these respects among the cultivars. The main results as follow:1. 0.001Bmg/L~0.005Bmg/L B content range can be used as critical B content to screen different B efficient rape cultivars in seedling stage in Hoagland nutrition culture system. The growing conditions and root activities in this range were distinguished difference in different B-efficient cultivars. In addition, the root was more sensible to B deficiency than the shoot, which can looked on as a main index to judge B efficient cultivars.2. The constitution of wall were significantly different in different organs and cultivars and it was controlled by genetic and organ differentiation. The cellulose content in root is higher than that in leaf, pectin content is lower than that in leaf, and little difference exists in hetnicellulose. Cultured cells had the lowest cellulose content and the highest hemicellulose content The content of total pectin, cellulose and hemicellulose had little differences between B-efficient and B-inefficient cultivars. However, the dictation soluble pectin content was much higher and the alkaline soluble pectin content was much lower in B-efficient cultivars than in B-inefficient cultivars.3. B had little effect on the constitution of root and leaf wall, but B deficiency could significantly decrease the cellulose content in cultured cell and significantly increases the SDS extractants.4. It is proved that cell wall and pectin were the main sites combining B and Ca, and the Mg concentration in wall was very low, those were in agree with the other researcher's result.4.1. Under normal B condition, about more than 50% of root B was found in the wall; about 30% in upper leaf and about 20% in lower leaf. And the wall B content was more stable in different B conditions than the organs. So the ratio of wall B was significantly increased in B deficient conditions.4.2. More than 80% B in root wall and more than 90% B in leaf wall was found in pectin's.4.3.The B concentration in root wall and in the pectin was distinguished lower than that in leaf. 4.4.The Ca concentration in cell wall and its distribution in cell wall constitutions were influenced by growth stages and vitro boron concentration, its capability of combining with cell wall pectin is not strong.5. Through pectinase decomposition and DEAE- Sepharose chromalography methods, a B-complexe was separated for the first time in rape. And proved that this complexes may be B-RG-II.6. Boron is proved to be an essential element in cell wall formation through the method of protoplast breeding.7. New suggestions were put forward on mechanism of boron efficiency in rape cultivars.7.1. B-efficient cultivars had lower B content in root and old leaf wall and the ratio of free boron was higher under B deficiency condition, which meaned stronger capability of transportation of B upward.7.2. The B content needed in the protoplast wall rebuilding in B-efficient cultivars was much lower that that in B-inefficient cultivars. Therefore, the wall of B-efficient cultivars can form and grow normally under certain lower boron concentration.7.3. Lower polymerization of the pectin in upper leaves was founded in B-efficient cultivars, which might be advantageous for the cultivator to adapt to the change of outside environment.
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