Department of Biology, University of Kentucky, Lexington, KY 40546, USA.
Ann Bot. 2010 Jun;105(6):977-90. doi: 10.1093/aob/mcq078. Epub 2010 Apr 17.
Physical dormancy in seeds of species of Geraniaceae is caused by a water-impermeable palisade layer in the outer integument of the seed coat and a closed chalaza. The chalazal cleft has been reported to be the water gap (i.e. location of initial water entry) in innately permeable seeds of Geraniaceae. The primary aim of this study was to re-evaluate the location of the water gap and to characterize its morphology and anatomy in physically dormant seeds of Geraniaceae, with particular reference to G. carolinianum.
Length, width, mass, anatomy and germination of two seed types (light brown and dark brown) of G. carolinianum were compared. Location, anatomy and morphology of the water gap were characterized using free-hand and microtome tissue sectioning, light microscopy, scanning electron microscopy, dye tracking, blocking and seed-burial experiments.
Treatment with dry heat caused a colour change in the palisade cells adjacent to the micropyle. When placed in water, the 'hinged valve' (blister) erupted at the site of the colour change, exposing the water gap. The morphology and anatomy in the water-gap region differs from those of the rest of the seed coat. the morphology of the seed coat of the water-gap region is similar in G. carolinianum, G. columbinum, G. molle and G. pusillum and differs from that of the closely related species Erodium cicutarium.
Dislodgment of swollen 'hinged valve' palisade cells adjacent to the micropyle caused the water gap to open in physically dormant seeds of G. carolinianum, and it was clear that initial water uptake takes place through this gap and not via the chalazal opening as previously reported. This water gap ('hinged valve gap') differs from water gaps previously described for other families in morphology, anatomy and location in the seed coat.
天竺葵科植物种子的物理休眠是由种皮外种皮中的不透水栅栏层和封闭的合点层引起的。据报道，合点裂缝是天竺葵科固有可透性种子的水分间隙（即初始水分进入的位置）。本研究的主要目的是重新评估水分间隙的位置，并描述其形态和解剖结构在天竺葵科物理休眠种子中的特征，特别是对 G. carolinianum。
比较了 G. carolinianum 的两种种子类型（浅棕色和深棕色）的长度、宽度、质量、解剖结构和发芽情况。使用徒手和切片组织学、光镜、扫描电子显微镜、染色追踪、阻塞和种子埋藏实验，对水分间隙的位置、解剖结构和形态进行了描述。
干热处理导致与珠孔相邻的栅栏细胞颜色发生变化。当放入水中时，“铰链阀”（水疱）在颜色变化处爆裂，暴露出水分间隙。水分间隙区域的形态和解剖结构与种皮的其余部分不同。水分间隙区域种皮的形态在 G. carolinianum、G. columbinum、G. molle 和 G. pusillum 中相似，与亲缘关系密切的物种 Erodium cicutarium 不同。
毗邻珠孔的膨胀“铰链阀”栅栏细胞的移位导致 G. carolinianum 物理休眠种子中的水分间隙打开，显然初始水分吸收是通过这个间隙而不是以前报道的通过合点开口进行的。这个水分间隙（“铰链阀间隙”）在形态、解剖结构和种皮中的位置上与以前描述的其他科的水分间隙不同。
