野生黄瑞香种子的休眠机制与破除方法

The Mechanisms of Seed Dormancy of Wild Daphne giraldii and Methods for Dormancy Breaking

【目的】祁连山野生的黄瑞香生长在海拔2 500~2 600 m左右的半荫半阳的缓坡地带,为适应祁连山寒冷的冬季和凉爽的夏季气候,黄瑞香种子具有较强的休眠特性。探寻破除黄瑞香种子休眠的方法,可为其种子人工繁殖提供理论依据与技术支持。【方法】采用种子萌发抑制物的生物学鉴定、激素溶液浸种、低温层积、干藏等不同处理方法对黄瑞香种子的休眠类型、休眠原因及其破眠方法进行研究。【结果】1)新采收的黄瑞香种子生活力为84.6%,但不萌发,具有显著的休眠现象。种子吸水过程符合Logistic曲线,其种皮对种子吸水无严重阻碍作用。2)黄瑞香种子种皮和胚的醇提液、水提液对白菜种子的发芽率和胚根长均有不同程度的抑制作用。外种皮的水提液对白菜种子萌发和胚根长的抑制作用在相同浓度条件下比醇提液明显;种胚的醇提液和水提液在0.1,0.15 g·m L^(-1)的浓度下完全抑制白菜种子萌发,在0.05 g·m L^(-1)浓度下种胚的水提液对白菜种子萌发和胚根长的抑制作用显著低于醇提液;内种皮的醇提液在低浓度条件时已对白菜种子的萌发和胚根的伸长产生极其明显的抑制作用,但内种皮的水提液无论浓度高低对白菜种子的萌发抑制作用均较小。这些结果说明黄瑞香种子外种皮中存在的水溶性萌发抑制物、种胚中溶于有机溶剂和水的萌发抑制物、内种皮中溶于有机溶剂的萌发抑制物的共同作用是其种子休眠的主要原因。3)黄瑞香种皮的电镜结构显示未处理的种子的种皮表面细胞排列较规则紧密,种皮中长柱状细胞构成栅栏组织;经5℃温度条件下层积90天后,种皮表面已出现较多的"蚁穴"状孔洞,有利于种子萌发。【结论】将新采收的黄瑞香种子进行GA3和6-BA溶液浸种、低温干藏和暖温干藏处理,均不能有效提高黄瑞香种子的萌发,经5℃湿沙层积90天后黄瑞香种子萌发率近80%。新采收的黄瑞香种子为综合性休眠。

【Objective】Wild shrub Daphne giraldii mainly grows on half-shaded half-sunlighted gentle slope with an altitude from 2 500 to 2 600 m of Qilian Mountains. In order to adapt to cold winter and cool summer in Qilian Mountains,the seeds of D. giraldii have developed a strong dormancy. This study was intended to explore methods of breaking the seed dormancy and improving germination rate of the D. giraldii seeds,therefore to provide theoretical basis and technical support to the propagation from seeds. 【Method】Different seed treatments such as biological identification of germination inhibitors of D. giraldii seeds,immersing seeds in GA3 and 6-BA solution,low temperature sand stratification and dry storage were employed to study the types of and the causes for dormancy,and methods of breaking dormancy of D. giraldii seeds were investigated in this study.【Result】The results indicated that： 1） The viability of newly collected D. giraldii seeds were 84. 6%,but not germination at all,indicating that there was obvious dormancy phenomenon in freshlycollected D. giraldii seeds. The process of water absorption,including quick soaking,stable soaking and saturated soaking stages,of D. giraldii seeds was in line with the Logistic curve,and the seed testa had no serious impact on water absorption of the seeds. 2） Alcohol extract and water extract of seed testa,endotesta and embryo had different degree of inhibitory activity on seed germination rate and radicle length of Chinese cabbage（ Brassica pekinensis） seeds. The water extract of testa had more obvious inhibition effects than alcohol extract on the germination and the radicle length of Chinese cabbage seeds under the same condition. The alcohol and water extract of embryo completely inhibited the germination of Chinese cabbage seeds at the concentrations of 0. 1 g·m L^（-1）and 0. 15 g·m L^（-1）,however the inhibitory effect of water extract of embryo were significantly lower than alcohol extract at the concentration of 0. 05 g·m L^（-1）,showing significantly inhibition in germination and radicle length. The alcohol extract of endotesta had extremely significant inhibition in germination and radicle length of Chinese cabbage seeds, but the water extract had less inhibition at all concentrations. These indicated that the main reason of the seed dormancy of D. giraldii might result from the joint effect of water-soluble germination inhibitory substances in seed testa,both water-soluble and alcoholsoluble germination inhibitory substances in embryo and alcohol-soluble germination inhibitory substances in endotesta.3） The scanning by electron microscopic showed that the surface cells of the control seeds were smoother and the shape was more regular,the longer columnar cells constituted the palisade tissue,but some holes were found on the surface cells of the seeds after the low temperature sand stratification at 5 ℃ for 90 days,favorable for seeds to germinate.【Conclusion】Soaking seeds in GA3 and 6-BA solutions,low and warm temperature dry storage all could not obviously improve the germination of newly collected D. giraldii seeds,but sand stratification at 5 ℃ for 90 days could break seed dormancy effectively and the germination rate could reach about 80 %. The dormancy of newly collected D. giraldii seeds is a type of comprehensive dormancy.