橡胶树枝条初生乳管形态发育研究

Morphological Development of Primary Laticifers in Shoots of Hevea brasiliensis Muell. Arg

橡胶树的初生乳管主要存在幼嫩树干、枝条、叶片、花和果实中,其发育过程依然不清楚。本研究利用石蜡制片和改良的碱处理剥离2种方法研究了幼嫩枝条初生乳管的形态发育过程,发现碱处理剥离法能观察到乳管从起源到发育成熟的连续过程,优于石蜡制片。采用碱处理剥离法系统研究橡胶树枝条不同发育时期初生乳管形态特征。从古铜期枝条不同部位分离的乳管形态差异较大,顶端分生组织附近的乳管呈线性长管状、不分支、无隔,外凸结构不明显;距顶端7 cm左右的乳管具有明显的外凸结构或珠状结构;距顶端14 cm处的乳管明显增粗,相邻乳管间外凸结构联结贯通形成乳管桥,最终形成网状结构。稳定期枝条各部位的乳管形态趋同,外凸或珠状结构的密度和乳管桥的密度均显著高于古铜期枝条对应的部位,都形成了复杂的网络结构。同时发现初生乳管是多核的。本研究结果表明橡胶树枝条初生乳管为无节联结乳管,是一种新的乳管类型。本研究对植物乳管发育研究有重要意义。

The primary laticifers of Hevea brasiliensis Muell. Arg present mainly in young trunks, shoots, leaves, flowers, and fruits. However, its morphological development is unknown. Two methods, parafin section and modified alkali-treated stripping were used to study the development of the primary laticifers in this study, and the latter was found superior to the former by continuous observation of the whole developmental process. The morphological development of the primary laticifers of different stages was systematically investigated using the modified alkali-treated stripping method. The results showed that the laticifers isolated from different positions of the bronze-stage shoots were morphologically distinct. The laticifers close to the apical meristem were longtube-like linear structures without end-walls and branches, and protrusive growth was not obvious. The lacifers at 7 cm away from the apical meristem had obvious intrusive growth and bead-like structures, which resulting in increase in the diameter of laticifers. The laticifers at 14 cm away from the apical meristem were significantly enlarged in diameter, and contained more bead-like structures, and the bead-like structures between the neighboring laticifers were connected to form laticifer bridges, which resulting in the formation of a laticifer network. The laticifers isolated from different positions of the stable-stage shoots were morphologically similar, and the density of the protrusions or bead-like structures and the laticifer bridges was significantly higher than that in bronze-stage shoots, and complex laticifer networks were formed in the barks at all positions. The primary laticifers were proved to be multinuclear as well. The results of this study indicate that the primary laticifers in the rubber tree shoots are non-articulated and anastomosing, and belong to a novel type of laticifers. This study would play an important role in the fundamental research of the plant laticifer development.