Departamento de Botânica, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil.
Plant Biol (Stuttg). 2012 Mar;14(2):347-53. doi: 10.1111/j.1438-8677.2011.00505.x. Epub 2011 Sep 2.
Temperature and humidity are the main factors influencing seed viability, dormancy and longevity of buried seeds. Unfortunately, very little is known about such processes in species of tropical regions, where temperature does not show major seasonal variations. The extent to which germination capacity, phytohormones and vitamin E levels were altered after burial of seeds of Xyris bialata and X. peregrina (Xyridaceae), two species endemic to rupestrian fields of Brazil, was examined. After 2 months of burial, seed germination capacity remained constant, which is associated with decreases in ABA and IAA content in both species. During this period, zeatin levels also decreased in X. bialata, but not in X. peregrina, the latter showing much lower levels of ABA. During the summer (rainy season), seeds of both species experienced a progressive, but severe, decrease in germination capacity, which reversed at the end of the winter (dry season), thus suggesting secondary dormancy. This dormancy appeared to be caused by drastic decreases in GAs, rather than increases in ABA. Levels of GA(4) decreased to non-detectable values during dormancy in both species. Furthermore, zeatin levels decreased in X. bialata but not in X.peregrina during this period. Both species accumulated γ-tocopherol as the major vitamin E form, and levels of this antioxidant remained constant or even increased during seed burial; however, X. bialata seeds showed a significant decrease in α-tocopherol during seed burial and dormancy. It is concluded that in X. peregrina and X. bialata, (i) burial causes significant changes in the phytohormone levels of seeds; (ii) secondary dormancy is induced in seeds; (iii) a GA(4) decrease, rather than an ABA increase, seems to be involved in the induction of secondary dormancy; and (iv) reductions in α-tocopherol in buried seeds are not necessarily indicative of reduced germination capacity.
温度和湿度是影响种子活力、休眠和寿命的主要因素。然而，对于热带地区的物种，由于温度没有明显的季节性变化，人们对这些过程知之甚少。本研究考察了巴西岩生植被特有种叉柱花（Xyris bialata）和羽芒叉柱花（X. peregrina）（鸢尾科）种子在埋藏后的萌发能力、植物激素和维生素 E 水平的变化。埋藏 2 个月后，种子的萌发能力保持不变，这与两种植物 ABA 和 IAA 含量的降低有关。在此期间，X. bialata 中的玉米素水平也下降，但 X. peregrina 中的玉米素水平没有下降，后者的 ABA 水平较低。在夏季（雨季），两种植物的种子萌发能力逐渐严重下降，但在冬季（旱季）结束时又恢复，表明存在次生休眠。这种休眠似乎是由赤霉素（GA）水平的急剧下降引起的，而不是 ABA 水平的增加。在两种植物中，休眠期间 GA(4) 的水平降低到无法检测的水平。此外，在此期间，X. bialata 中的玉米素水平下降，但 X.peregrina 中的玉米素水平没有下降。两种植物都积累 γ-生育酚作为主要的维生素 E 形式，在种子埋藏期间，抗氧化剂水平保持不变甚至增加；然而，X. bialata 种子在种子埋藏和休眠期间α-生育酚显著减少。研究结论认为，在叉柱花和羽芒叉柱花中：（i）埋藏会导致种子中植物激素水平发生显著变化；（ii）种子会产生次生休眠；（iii）GA(4) 的减少，而不是 ABA 的增加，似乎参与了次生休眠的诱导；（iv）埋藏种子中 α-生育酚的减少并不一定表明萌发能力降低。
