Gibson A, Bachelard E P
Department of Forestry, Australian National University, GPO Box 4, Canberra, ACT 2601, Australia.
Tree Physiol. 1986 Jun;1(1):67-77. doi: 10.1093/treephys/1.1.67.
At 15-20 degrees C, seeds of Eucalyptus sieberi L. Johnson need to maintain a water content equal to 30% or more of dry weight for approximately 60 h in order to germinate. Several shorter periods of imbibition at 30% water content separated by between 6 and 120 h desiccation were as effective as an unintenupted imbibition in bringing seeds to the point of germination. Even after 8 months' desiccation an earlier imbibition shortened the time required for the completion of germination, although it did not hasten the onset of germination. The water potential of seeds sufficiently hydrated to germinate was about -0.6 MPa, whereas that of the embryo was only about -4.5 MPa. The difference was caused by the inhibition of water uptake by the inner integument of the seed coat. During germination, reserve protein in a small group of cells above the collet was hydrolyzed. Subsequent expansion of these cells caused rupture of the inner integument thereby allowing further water uptake by the embryo. The balance of water absorption and evaporative loss by the outer integument was such that most seeds on a moist substrate but exposed to dry air (6.5-8 x 10(-4) MPa) did not maintain the 30% water content necessary for germination. Thus although able to germinate on seedbeds subject to intermittent drying, E. sieberi seeds have the capacity to avoid germination except under humid conditions.
在15 - 20摄氏度下，西氏桉（Eucalyptus sieberi L. Johnson）种子需要保持含水量等于或高于干重的30%约60小时才能发芽。在含水量为30%时进行几次较短时间的吸胀，每次吸胀之间间隔6至120小时的干燥处理，其促使种子达到发芽阶段的效果与不间断吸胀相同。即使经过8个月的干燥处理，提前吸胀仍能缩短完成发芽所需的时间，尽管它并未加速发芽的开始。充分吸水至可发芽状态的种子水势约为 -0.6兆帕，而胚的水势仅约为 -4.5兆帕。这种差异是由种皮内种被对水分吸收的抑制作用造成的。在发芽过程中，根颈上方一小群细胞中的贮藏蛋白被水解。随后这些细胞的膨胀导致内种被破裂，从而使胚能够进一步吸水。外种被的水分吸收与蒸发损失的平衡状况使得大多数放置在潮湿基质上但暴露于干燥空气（6.5 - 8×10⁻⁴兆帕）中的种子无法维持发芽所需的30%含水量。因此，尽管西氏桉种子能够在间歇性干燥的苗床上发芽，但它们有能力避免发芽，除非处于潮湿条件下。
