龙须枣曲枝的解剖学观察

Anatomical Observation on the Tortuousness of Ziziphus jujuba var.tortuosa Branches

以龙须枣(Ziziphus jujuba Mill var.tortuosa)一年生枝条的扭曲枝段和直立枝段为试验材料,采用木材切片法和木材离析技术,观察比较枝条形态、解剖结构特点及导管分子特征。扭曲枝段和直立枝段解剖结构的差异主要表现在异常次生结构的数量、形态和分布上。与直立枝段相比较,扭曲枝段附加维管束数量较多,出现3个附加维管束相毗邻,相对集中于枝条内弯处;木间韧皮部的数量与直立枝段相差不多,其末端膨大,与直立枝段的略带弯曲的椭圆柱状不同,相对集中分布于枝条外弯处;髓维管束数量略微减少。从细胞水平看,扭曲枝段内弯处和外弯处导管分子均属于网纹导管、单穿孔,具有多种形态。其中,内弯处两端有尾和两端倾斜的导管分子数分别比其外弯处少28.0%和20.2%,两端无尾、一端倾斜和两端水平的导管分子数分别多17.9%、375.0%和200.0%,一端有尾导管分子数相同,导管分子端壁倾角比外弯处大10.1%,导管分子长度比外弯处的短16.4%,直径比外弯处的小18.6%。提出“异常结构—空间差异—相互协调”的假说。龙须枣的曲枝性可能是由附加维管束、木间韧皮部和髓维管束等3种异常次生结构的数量、机械拉力、同化产物的输导和利用在空间上的差异和相互协调所造成的枝条不同位置的生长速率和受力不均衡的结果。

Taking the twisted tortuous branch segment and twisted straight branch segment of annual branches in Ziziphus jujuba Mill. var. tortuosa as experimental materials,the morphological,anatomical and vessel characteristics of its branches were observed and compared by xylotomy and wood segregation techniques. The differences of anatomical structures between twisted tortuous branch segment and twisted straight branch segment were mainly manifested in the number,shape and distribution of abnormal secondary structures. Compared with the twisted straight branch segment,the number of auxillary bundles in twisted tortuous branch segments was more,and there were three auxillary bundles adjacent to each other,which were relatively concentrated in the inner bend of the segments;The number of interxylary phloem was about the same as that of the twisted straight branch segment,and its end expanded,which was different from the slightly curved elliptic columnar shape of the twisted straight branch segment,and relatively concentrated in the outer bend of the segments;The number of medullary vascular bundles was slightly reduced. At the cellular level,the vessel elements at the inner and outer bends of the twisted tortuous branch segments of the variety were all reticulate vessels with single perforation and various shapes. Among them,the number of vessel elements with tails at both ends and sloped at both ends at the inner bend were 28.0% and 20.2% less than those at the outer bend,respectively. The number of vessels without tails at either ends,sloped at one end and horizontal at both ends were 17.9%,375.0% and 200.0% more,respectively. The number of vessels with one tail at one end was the same. The end wall slope of end wall was 10.1% larger than that at the outer bend,and the length of vessel element was 16.4% shorter than that at the outer bend,while the diameter was 18.6% smaller than that at the outer bend. The hypothesis of "abnormal structure-spatial difference-coordination"was put forward. The tortuous branch traits of Z. jujuba var. tortuosa may be the result of the unbalanced growth rates and forces at different locations of the branches caused by the spatial difference and coordination of the number,the mechanical tension,the transport and utilization of the assimilated products of the three abnormal secondary structures,namely the auxillary bundle,interxylary phloem and medullary bundle.