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Science
Humanities and Social Sciences
multidisciplinary
摘要：
IN many families of flowering plants, exemplified by the Solanaceae (which includes the genera Nicotiana and Lycopersicon), self-pollination is prevented by a genetic system based on multiple alleles at what appears to be a single locus which is given the symbol S. Impressive progress towards the goal of discovering what the products of the S allele are and how they relate to each other in molecular terms has recently been made by two groups, first by J. B. Nasrallah etal. from Cornell University (Nature 318, 263; 1985) and now by Anderson et ai of Melbourne University and reported elsewhere in this issue (Nature 321,38; 1986).It is known that pollination is blocked only when the same allele is present in the germinating pollen grain and the style down which it is trying to grow. Because wild populations of outbreeding species usually have tens or even hundreds of S alleles, this system ensures that the great majority of random cross-pollinations are fertile. In some plant families, including the Cruciferae and its best-known genus Brassica, there is a variant system in which pollen expresses one or both of the S alleles present in the diploid plant which bore it, even though each pollen grain, as a haploid product of meiosis, retains only one allele. The difference between the two systems is presumably one of timing of S-locus expression - post-meiotic in the Solanaceae and pre-meiotic in the Cruciferae - and does not necessarily imply any fundamental difference in the functions of the products of the respective S loci. In each case, incompatibility evidently results from some kind of interaction between products of identical S *** is the mechanism of this self-recognition by S alleles? There are two possibilities. If one supposes that the S locus is really a single gene, encoding the same protein in pollen and style, one can think in terms of dimerization of similar protein monomers, located respectively on the cell surface of the pollen tube and in the c
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中文科技期刊
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