Study On B-efficient Physiology And Cell-wall Properties Of Rape (Brassica Napus L.) Cultivars

Boron (B) is an essential microelement in higher plants, and B deficiency always causes the decrease of the crop yield and quality. B deficiency in rape ( Brassica Napus L.) is a conmon micronutrent deficiency phenomenon in the field of China, but the cultivars respond very differently to low B stress. So, to get the high efficient rapeseed genotype by the molecular biology and breeding technology is a good measure to solve the problem of the absence of China's boron rock resource, and to reduce the damage to the environment, and to increase the crop yield and the quality. There were 8 high B efficiency cultivars and 2 low B efficiency cultivars which had been identified and screened from 211 cultivars of rapeseed by Wang Yunhua since 1991. In this study, the typical high efficiency cultivar of QingYou 10 (95090) and the typical low efficiency cultivar of Bakow (9141) were used to study on the relationships among the different B efficiency varieties of the rapeseed (Brassica Napus L.). The results were as the followings.1. In the low B condition of the soilless culture, rapeseed seedlings were short of B, the seedlings were short and the leaves were malformed and the weight of the shoots decreased, the branch roots were fewer and snuff color, the weight of roots decreased, and the length of root and the ratio of shoot/root decreased, too. However, the high B- efficiency type of rapeseed had the a great ability to the low B stress, the growth of shoots and roots were better than the low efficiency, and the B concentration range of the rapeseed varieties which responded to the B scarce was 0.001 mg/L to 0.01 mg/L. In the bolting time and blooming time, B deficiency mainly influenced on the growth of the propagative organ of rapeseed ( Brassica Napus L.), the agronomic character was similar to the seedlings, and the B concentration range of the rapeseed varieties which responded to the B scarce was 0.005 mg/L to 0.25 mg/L.2. B deficiency influenced the chlorophyll content of the rapeseed cultivars. In the condition of abundant B, the content of chlorophyll in the top leaves was higher than that of the below leaves, in the leaves of the typical low efficiency cultivar of Bakow (9141) was higher than that of the typical high efficiency cultivar of QingYou 10 (95090). In the seedlings time, the content of chlorophyll decreased by the deficiency of B, but the content of chlorophyll in the high efficiency cultivar decreased slowly than that of the low efficiency cultivar. This suggested that the leaves of the high efficiency cultivar can capture more light energy and the photosynthetic rate of the high efficiency cultivar decreased slowly. In the bolting time and blooming time, after two weeks of B deficiency treatment, the content of chlorophyll in the top leaves of the high efficiency cultivar decreased, and in the late time, the content of chlorophyll decreased slowly. But, the content of chlorophyll in the bellow leaves of the two cultivars had little changes. The reason may be that B in the high efficiency cultivar distributed to the propagative organ in the late growth, and the leaves were short of B.3. At the different levels of B, the results of the cell ultrastructure of root tip suggested that the cell wall thickened and the amount of plasmodesmata decreased by the deficiency of B. And the development and formation of the sieve tube elements of the different cultivars were influenced by the different levels of B: the sieve tube elements of the two cultivars were not formed at the level of 0.001mg/L; At the level of 0.01mg/L, the sieve tube elements of the high efficiency (Qingyou 10) cultivar could be formed, but the structure of the sieve tube elements was not complete, and the abruption and differenciation of the sieve tube elements of the low efficiency cultivar (Bakow) were inhibited, they were not formed; At the level of 0.01mg/L, the sieve tube elements of the two cultivars were formed. And the amount of organelles and cell ultrastructure were different at different levels of B.4. In the condition of the soilless culture, the extraction rate of the cell wall of the cultivars and the content of B, Ca and Mg in the cell wall of the cultivars suggested that the extraction rate increased by the lack of B, but, the extraction rate of the high efficiency cultivar was less than that of the low efficiency cultivar. The content of B in the cell wall decreased with the descent of B levels. But in the late time, the degressive extent of the content of B in the high efficiency cultivar was decreased slowly. B deficiency caused the increase of Ca content in the cell wall, but at the very low level of B, the content of Ca in the cell wall decreased, and the content of Ca in the roots cell wall decreased more slowly than that in the leaf cell wall. The Ca/B ratio was great statistic difference in the different times and parts. In the condition of lack of B, the changes of the content of Mg in the two cultivars was alike the Ca content changes, but the former was more complex.