Flowers T J
School of Biological Sciences, University of Sussex, Falmer, Brighton, Sussex BN1 9QG, UK and School of Plant Biology, 35 Stirling Highway, Crawley, Western Australia 6009, Australia.
J Exp Bot. 2004 Feb;55(396):307-19. doi: 10.1093/jxb/erh003. Epub 2004 Jan 12.
Salinity is an ever-present threat to crop yields, especially in countries where irrigation is an essential aid to agriculture. Although the tolerance of saline conditions by plants is variable, crop species are generally intolerant of one-third of the concentration of salts found in seawater. Attempts to improve the salt tolerance of crops through conventional breeding programmes have met with very limited success, due to the complexity of the trait: salt tolerance is complex genetically and physiologically. Tolerance often shows the characteristics of a multigenic trait, with quantitative trait loci (QTLs) associated with tolerance identified in barley, citrus, rice, and tomato and with ion transport under saline conditions in barley, citrus and rice. Physiologically salt tolerance is also complex, with halophytes and less tolerant plants showing a wide range of adaptations. Attempts to enhance tolerance have involved conventional breeding programmes, the use of in vitro selection, pooling physiological traits, interspecific hybridization, using halophytes as alternative crops, the use of marker-aided selection, and the use of transgenic plants. It is surprising that, in spite of the complexity of salt tolerance, there are commonly claims in the literature that the transfer of a single or a few genes can increase the tolerance of plants to saline conditions. Evaluation of such claims reveals that, of the 68 papers produced between 1993 and early 2003, only 19 report quantitative estimates of plant growth. Of these, four papers contain quantitative data on the response of transformants and wild-type of six species without and with salinity applied in an appropriate manner. About half of all the papers report data on experiments conducted under conditions where there is little or no transpiration: such experiments may provide insights into components of tolerance, but are not grounds for claims of enhanced tolerance at the whole plant level. Whether enhanced tolerance, where properly established, is due to the chance alteration of a factor that is limiting in a complex chain or an effect on signalling remains to be elucidated. After ten years of research using transgenic plants to alter salt tolerance, the value of this approach has yet to be established in the field.
盐分对作物产量始终构成威胁，在那些灌溉对农业至关重要的国家尤其如此。尽管植物对盐渍条件的耐受性各不相同，但作物品种通常无法耐受海水中三分之一浓度的盐分。通过传统育种计划提高作物耐盐性的尝试收效甚微，原因在于该性状的复杂性：耐盐性在遗传和生理方面都很复杂。耐受性通常表现出多基因性状的特征，在大麦、柑橘、水稻和番茄中已鉴定出与耐受性相关的数量性状位点（QTL），在大麦、柑橘和水稻中还发现了与盐渍条件下离子转运相关的QTL。在生理上，耐盐性也很复杂，盐生植物和耐受性较差的植物表现出多种适应方式。提高耐受性的尝试涉及传统育种计划、体外选择的应用、综合生理性状、种间杂交、将盐生植物用作替代作物、标记辅助选择的应用以及转基因植物的使用。令人惊讶的是，尽管耐盐性很复杂，但文献中普遍声称转移单个或几个基因就能提高植物对盐渍条件的耐受性。对这些说法的评估表明，在1993年至2003年初发表的68篇论文中，只有19篇报告了植物生长的定量估计。其中，有四篇论文包含了六个物种的转化体和野生型在适当施加盐分和不施加盐分情况下反应的定量数据。所有论文中约有一半报告了在几乎没有或没有蒸腾作用的条件下进行的实验数据：此类实验可能有助于深入了解耐受性的组成部分，但不能作为在整个植物水平上声称耐受性增强的依据。耐受性增强（如果确实确立）是由于复杂链条中限制因素的偶然改变还是对信号传导的影响，仍有待阐明。经过十年利用转基因植物改变耐盐性的研究，这种方法在田间的价值尚未确立。
