Am J Bot. 1998 Apr;85(4):449.
The feeding of spittlebug nymphs (Philaenus spumarius) from mature xylem vessels was studied by optical and cryo-analytical scanning electron microscopy. Feeding did not produce xylem embolisms and vessels remained liquid-filled during the day. Saliva secreted by the insect forms a hardened lining (salivary sheath) between the stylet bundle and the plant tissues. This sheath is continuous through the hole made by the stylets as they enter a vessel, and it extends into the vessel and along its periphery beyond the breach. The sheath is heterogeneous, with a thin outer layer adjoining the plant tissues and a thicker layer that contacts the stylet bundle. Both layers give positive histochemical reactions for proteins and, in fresh tissues, contain a red, strongly autofluorescent pigment, possibly condensed tannin derived from the plant (which is lost during tissue preparation), and other phenyl propanoid compounds, which are retained and which may produce the intense reaction of the periodic-acid-Schiff's-positive inner layer. It is concluded that the salivary sheath allows the insects to feed from functioning vessels without embolizing them or losing xylem fluid to the surrounding tissues. These findings and others in the entomological literature indicate low daytime tensions in the xylem conduits of the host plants.
利用光学和 cryo 分析扫描电子显微镜研究了沫蝉若虫（Philaenus spumarius）从成熟木质部导管中取食的情况。取食不会产生木质部栓塞，并且导管在白天保持充满液体的状态。昆虫分泌的唾液在喙束和植物组织之间形成坚硬的衬里（唾液鞘）。当喙进入导管时，鞘在由喙形成的孔中连续延伸，并延伸到导管内部及其周围的缺口处。鞘是异质的，与植物组织相邻的外层较薄，与喙束接触的内层较厚。这两层都对蛋白质进行阳性组织化学反应，并且在新鲜组织中含有红色、强烈自发荧光的色素，可能是来自植物的浓缩单宁（在组织准备过程中丢失）和其他苯丙烷化合物，这些化合物被保留下来，并可能产生强烈的周期性酸-Schiff 阳性内层反应。因此可以得出结论，唾液鞘使昆虫能够从功能正常的导管中取食，而不会使它们栓塞或使木质部液体流失到周围组织中。这些发现以及昆虫学文献中的其他发现表明，宿主植物木质部导管中的日间张力较低。
