Department of Neurological, Neurosurgical and Behavioral Sciences, Section of Pharmacology G. Segre, University of Siena, Strada delle Scotte 6, 53100 Siena, Italy.
J Exp Bot. 2011 Nov;62(15):5267-81. doi: 10.1093/jxb/err154. Epub 2011 Aug 9.
In most species, arrest of growth and a decrease in water content occur in seeds and pollen before they are dispersed. However, in a few cases, pollen and seeds may continue to develop (germinate). Examples are cleistogamy and vivipary. In all other cases, seeds and pollen are dispersed with a variable water content (2-70%), and consequently they respond differently to environmental relative humidity that affects dispersal and maintenance of viability in time. Seeds with low moisture content shed by the parent plant after maturation drying can generally desiccate further to moisture contents in the range of 1-5% without damage and have been termed 'orthodox'. Pollen that can withstand dehydration also was recently termed orthodox. Seeds and pollen that do not undergo maturation drying and are shed at relatively high moisture contents (30-70%) are termed 'recalcitrant'. Since recalcitrant seeds and pollen are highly susceptible to desiccation damage, they cannot be stored under conditions suitable for orthodox seeds and pollen. Hence, there are four types of plants with regard to tolerance of pollen and seeds to desiccation. Orthodoxy allows for dispersal over greater distances, longer survival, and greater resistance to low relative humidity. The advantage of recalcitrance is fast germination. Orthodoxy and recalcitrance are often related to environment rather than to systematics. It has been postulated that certain types of genes are involved during presentation and dispersal of pollen and seeds, since molecules (sucrose, polyalcohols, late embryogenic abundant proteins, antioxidants, etc.) that protect different cell compartments during biologically programmed drying have been detected in both.
在大多数物种中，种子和花粉在散布之前会停止生长并减少水分含量。然而，在少数情况下，花粉和种子可能会继续发育（发芽）。例如闭花受精和胎生现象。在所有其他情况下，种子和花粉在散布时具有不同的含水量（2-70%），因此它们对影响散布和维持活力的环境相对湿度的反应不同。母植物成熟干燥后释放的含水量低的种子通常可以进一步干燥到 1-5%的水分含量而不会受损，并被称为“正常型”。能够耐受脱水的花粉最近也被称为正常型。未经成熟干燥而在相对较高含水量（30-70%）下散布的种子和花粉被称为“顽拗型”。由于顽拗型种子和花粉极易受到干燥损伤，因此不能在适合正常型种子和花粉的条件下储存。因此，就花粉和种子对干燥的耐受性而言，植物有四种类型。正常型允许更远距离的散布、更长的存活期和更高的抗低相对湿度能力。顽拗型的优势是快速发芽。正常型和顽拗型通常与环境有关，而与系统发育无关。有人假设，在花粉和种子的呈现和散布过程中涉及某些类型的基因，因为在两者中都检测到了在生物程序干燥过程中保护不同细胞区室的分子（蔗糖、多元醇、晚期胚胎丰富蛋白、抗氧化剂等）。
