Berjak Patricia, Pammenter N W
School of Biological & Conservation Sciences, University of KwaZulu-Natal, Durban, South Africa.
Ann Bot. 2008 Jan;101(2):213-28. doi: 10.1093/aob/mcm168. Epub 2007 Aug 17.
Considered only in terms of tolerance of, or sensitivity to, desiccation (which is an oversimplification), orthodox seeds are those which tolerate dehydration and are storable in this condition, while highly recalcitrant seeds are damaged by loss of only a small proportion of water and are unstorable for practical purposes. Between these extremes, however, there may be a gradation of the responses to dehydration--and also to other factors--suggesting perhaps that seed behaviour might be best considered as constituting a continuum subtended by extreme orthodoxy and the highest degree of recalcitrance. As the characteristics of seeds of an increasing number of species are elucidated, non-orthodox seed behaviour is emerging as considerably more commonplace--and its basis far more complex--than previously suspected.
Whatever the post-harvest responses of seeds of individual species may be, they are the outcome of the properties of pre-shedding development, and a full understanding of the subtleties of various degrees of non-orthodox behaviour must await the identification of, and interaction among, all the factors conferring extreme orthodoxy. Appreciation of the phenomenon of recalcitrance is confounded by intra- and interseasonal variability across species, as well as within individual species. However, recent evidence suggests that provenance is a pivotal factor in determining the degree of recalcitrant behaviour exhibited by seeds of individual species. Non-orthodox--and, in particular, recalcitrant--seed behaviour is not merely a matter of desiccation sensitivity: the primary basis is that the seeds are actively metabolic when they are shed, in contrast to orthodox types which are quiescent. This affects all aspects of the handling and storage of recalcitrant seeds. In the short to medium term, recalcitrant seeds should be stored in as hydrated a condition as when they are shed, and at the lowest temperature not diminishing vigour or viability. Such hydrated storage has attendant problems of fungal proliferation which, unless minimized, will inevitably and significantly affect seed quality. The life span of seeds in hydrated storage even under the best conditions is variable among species, but is curtailed (days to months), and various approaches attempting to extend non-orthodox seed longevity are discussed. Conservation of the genetic resources by means other than seed storage is then briefly considered, with detail on the potential for, and difficulties with, cryostorage highlighted.
There appears to be little taxonomic relationship among species exhibiting the phenomenon of seed recalcitrance, suggesting that it is a derived trait, with tolerance having been lost a number of times. Although recalcitrant seededness is best represented in the mesic tropics, particularly among rainforest climax species, it does occur in cooler, drier and markedly seasonal habitats. The selective advantages of the trait are considered.
仅从对干燥的耐受性或敏感性方面考虑（这是一种过于简单的说法），传统种子是指那些能够耐受脱水并可在此条件下储存的种子，而高度顽拗性种子仅失去一小部分水分就会受到损害，实际上无法储存。然而，在这两个极端之间，对脱水以及其他因素的反应可能存在一个渐变过程，这或许表明种子行为最好被视为构成一个由极端传统性和最高程度的顽拗性所支撑的连续体。随着越来越多物种种子的特性被阐明，非传统种子行为正变得比以前所怀疑的更为常见，其基础也更为复杂。
无论单个物种种子的收获后反应如何，它们都是脱落前发育特性的结果，要全面理解各种程度的非传统行为的微妙之处，必须等待确定所有赋予极端传统性的因素及其相互作用。物种间以及单个物种在季节内和季节间的变异性使人们对顽拗性现象的认识变得复杂。然而，最近的证据表明，种源是决定单个物种种子表现出的顽拗行为程度的一个关键因素。非传统种子，尤其是顽拗性种子的行为不仅仅是干燥敏感性的问题：其主要原因是与处于静止状态的传统类型种子不同这些种子在脱落时具有活跃的新陈代谢。这影响了顽拗性种子处理和储存的各个方面。在短期到中期，顽拗性种子应在与脱落时相同的水合条件下储存，并在不降低活力或生活力的最低温度下储存。这种水合储存伴随着真菌繁殖的问题，除非将其降至最低，否则将不可避免地且显著地影响种子质量。即使在最佳条件下，水合储存的种子的寿命在不同物种间也存在差异，但会缩短（从几天到几个月），文中还讨论了试图延长非传统种子寿命的各种方法。然后简要考虑了通过种子储存以外的其他方式保护遗传资源的问题，重点介绍了低温储存的潜力和困难。
表现出种子顽拗性现象的物种之间似乎几乎没有分类学关系，这表明它是一种衍生性状，耐受性已经多次丧失。尽管顽拗性种子在湿润的热带地区最为常见，特别是在雨林顶极物种中，但它也确实出现在较凉爽、干燥和明显季节性的栖息地中。文中考虑了该性状的选择优势。
