构树次生韧皮部细胞组成与形态的季节性变化
Seasonal Changes of Cell Types and Morphology in Secondary Phloem of Broussonetia papyrifera

采用光学显微切片技术和组织解离的方法，得出构树次生韧皮部解剖构造特征，确定主要细胞尺寸并总结其季节变化规律。结果表明，构树的次生韧皮部由纤维细胞、薄壁细胞、筛管、乳汁管和韧皮射线等细胞类型组成。在一个生长界限内韧皮部细胞排列不规整，顺序为：乳汁管-韧皮薄壁细胞-筛管-韧皮纤维-筛管-韧皮薄壁细胞-乳汁管。整个韧皮部中，具输导功能的区域比例较小，具有明显的季节规律。筛管长度平均值为245.3~281.6 μm，随生长季先减小后增大；筛管直径平均值42.8~67.2 μm，生长季内呈先减小后增大的规律，3-9月直径逐渐增加至最大，11月略有降低。韧皮纤维量大，细胞壁厚，形似木质部胶质木纤维。纤维长度平均值6 377.9~7 889.3 μm，3-11月中，呈先减小再增大后减小的模式，3月和7月达到最大值，5月最小；纤维宽度平均值13.91~19.54 μm，在整个生长季中，呈先增大后减小的趋势，9月直径最大，3月最小。韧皮部包括大量晶体，多存在于薄壁细胞中，并且具有季节规律。乳汁管平均数量14~28个，呈现季节差异，为揭示构树皮发育及其高效利用提供理论依据。
Secondary phloem anatomy characteristics and cell morphology of Broussonetia papyrifera (BP) and its seasonal changes were investigated.The results showed that BP phloem consisted of fiber cell,sieve tube,parenchymal cell,laticifer and ray cells.Different type cells were misarranged in one growth area and were in the order of laticifer-parenchymal-sieve tube-fiber-sieve-parenchymal-laticifer.In the whole phloem,conducting phloem accounted small proportion and presented significant seasonal changes.The average length of sieve tube was 245.3-281.6 μm and decreased in July and September,but slightly increased in November.The average diameter of sieve tube was 42.8-67.2 μm,increased from March,reached the peak value at September.More fibers were found in phloem which had thick cell wall and looked like gelatinous fiber.The average length of fiber was 6 377.9-7 889.3 μm and changed as circuitous line in growth season but the width of fiber increased from March to the peak value at September.The average width of fiber was 13.91-19.54 μm and increased from March to September,and then slightly decreased in November.A large number of crystals were observed in phloem parenchymal tissues.The average amount of laticifer was 14-28 and its distribution also changed seasonally.This work would provide foundation to reveal the development and efficient utilization of BP phloem