摘要
【目的】研究合欢种皮结构及其对种子吸水的影响,探索种子的吸水机制,为硬实性种子休眠的解除提供理论依据。【方法】以籽粒饱满、无病虫害的合欢种子为试材,利用体视显微镜和扫描电镜观察种皮结构,并结合染色法和凡士林密封试验,探究合欢种皮结构对吸水的影响。【结果】合欢种子的种皮具有不透水性,采用始温60、70、80℃的热水浸种处理均能有效解除其硬实性,但种子生活力随热水温度的升高而降低。合欢种子呈不规则的扁椭圆形,种皮坚硬,黄褐色,背腹面各有一条向外突出且长轴与种子侧缘平行的椭圆形棱。扫描电镜结果表明,椭圆形棱是种皮表面的一道较宽的裂痕。合欢种子种皮由外到内依次为:表皮层、栅栏层、骨状石细胞层、厚壁细胞层、薄壁细胞层。种子表面有许多大小、形状及深度不同的裂缝。种孔和种脊紧闭,种脐被致密的蜡质所覆盖,维管束由种脐开始平行于种皮表面向其深处延伸。热水处理后,种孔开启,种脊处细胞开裂,种脐处的蜡质减少。凡士林密封实验发现,解除硬实性后,种子各部位均可吸水,但子叶末端区域的吸水量始终最低。吸水4h时,种脐部位的吸水量最大,显著高于其他处理;随后中间部位吸水加快,吸水至24h,种脐部位和中间部位的吸水率差异不显著,均高于子叶末端部位,该差异趋势一直保持至种子吸水饱和。苯胺蓝染色发现,种皮有3种吸水途径:水分最先由种脊进入种皮并沿其内的维管束移动;随后种孔和种脐处也有水分进入;水分还可以透过表皮层,但没有继续向内穿过栅栏层进入种子内部。TTC染色发现,种子的胚根端最先吸水并被染成红色,随后水分由胚根端向种子另一端即子叶末端迁移,在同一水平位置水分由子叶侧缘向中间渗透。【结论】解除合欢种子硬实性的最佳方法是始温70℃的热水处理5min。种脊是合欢种子的初始吸水部位,随后水分也由种孔和种脐进入种胚,并由胚根端向子叶末端迁移。种皮的栅栏层、明线、厚壁细胞层、覆盖于种脐表面的蜡质层和填充于种皮维管束中的蜡质可能均与合欢种子的硬实性有关。
【Objective】 The seeds of Albizia julibrissin,collected from Suqian of Jiangsu Province,were used to identify the main water entry sites during imbibition.The structure of seed coat of A.julibrissin and the relationship with water uptake were studied to explore the mechanism of dormancy breaking of A.julibrissin seeds.【Method】 Taking the healthy full seeds without pest and disease as material,the structure of seed coat of A.julibrissin was observed by a stereo microscopy and a scanning electron microscopy (SEM).The effect of seed coat structure on water absorption was studied by dye-tracking and vaseline sealing experiments.【Result】 The seed coat of A.julibrissin is impervious to water.Soaking treatment with hot water at different temperatures (60 ℃,70 ℃,80 ℃) was able to ef ciently break the hardness of the seeds,however the seed viability decreased with the increase of hot water temperature.Structural characteristics of the seed coat were also examined.A.julibrissin seeds were irregular flat ellipse and had a hard and opaque seed coat with a yellowish-brown colour.There was a protruding oval-shaped edge which was a large fissure in the seed coat parallel to the macroaxis of seed.SEM images showed that from exterior to the interior the seed coat consisted of five layers: the epidermal layer,the palisade layer,the osteosclereid layer,the stereid layer,and the parenchymal cell.There were many cracks with different size,shape and depth in the seed coat.Micropyle and lens were closed and its hilum was covered by wax,vascular bundles extended parallel to the surface of the seed coat from the hilum.Morphological changes during dormancy breaking were also evaluated.Micropyle opened,the thickness of wax layer in hilum reduced,and a large crack appeared in the lens after the hot water treatment.Blocking experiments showed that all parts of treated seeds could absorb water,but the quantity of water uptake at the end of cotyledon was always the lowest.After incubation for 4 h,the most of water was imbibed by the hilum region.Subsequently,water uptake in the middle of seeds quickly increased.It was notable that water absorption was not significantly different between treatments exposing the hilum region and the middle part of seeds,but these two treatments had significantly higher water absorption values than the treatment exposing the cotyledons extremities after 12 h steeping conditions.The difference trend remained until the water absorptivity of A.julibrissin seeds reached saturation.Aniline blue staining showed that the seed coat could absorb water in 3 ways: 1) crack at lens,2) gaps in the micropyle and hilum,and 3) the epidermis layer of the seed.Water first entered the seed coat from the lens and moved along the vascular bundles within it.Then there was water entering the seed through micropyle and hilum.After that,water also permeated through the epidermal layer which was the outermost layer of seed coat.However,palisade layer hindered the further entry of water into the seed.The first red staining appeared in the radicle afteR2 h of soaking in TTC solution,then water moved to the end of cotyledon.In horizontal direction,water penetrated from the edge of the cotyledons to the middle.【Conclusion】 Treated in water at 70 ℃ for 5 minutes was the optimum method to break dormancy of A.julibrissin seeds.The series experiments indicated that nondormant seeds could absorb water throughout the entire seed coat,but the initial site of water absorption was the lens followed by the micropylar and hilum.After water entered the embryo it moved from the radicle to the terminal cotyledon.The hardness of seeds possibly relates to the structures of palisade layer,light line,parenchymal cell and the wax which covered the hilum and filled in vascular bundle.
作者
陈丽
代松
马青江
邓先静
朱铭玮
李淑娴
Chen Li;Dai Song;Ma Qingjiang;Deng Xianjing;Zhu Mingwei;Li Shuxian(Co-Innovation Center for Sustainable Forestry in Southern China,Nanjing Forestry University Nanjing 210037;Tongren Academy of Sciences Tongren 554300;Forestry Seedling Station of Qinghai Xining 810008)
出处
《林业科学》
EI
CAS
CSCD
北大核心
2019年第5期46-54,共9页
Scientia Silvae Sinicae
基金
国家自然科学基金项目(31270711)
江苏省青蓝工程创新团队
江苏高校优势学科建设资助项目(PAPD)
关键词
合欢
吸水机制
种皮结构
TTC染色
苯胺蓝染色
Albizia julibrissin
mechanism of water uptake
seed coat structure
TTC staining
aniline blue staining
