Bacterial leaf glands in Styrax camporum (Styracaceae): first report for the family

In this study, we recorded, for the first time, the occurrence of leaf glands in a member of Styracaceae and their association with bacteria. Samples of Styrax camporum Pohl shoot apices and leaves at different developmental stages were prepared according to the conventional techniques for light and electron microscopy. Glands are emergences constituted by epidermal and parenchyma cells and are differentiated into a secretory body on a short nonsecretory stalk supplied with phloem. Actively secreting glands occur from leaf primordia to mature leaves and produce mucilage that accumulates inside schizogenous intercellular spaces. The epidermal secretory cells have abundant cytoplasm rich in hyperactive dictyosomes, an extensive endoplasmic reticulum, and modified plastids. Bacteria enter the gland via the intact surface and proliferate in the intercellular spaces of the glands. Once inside the intercellular spaces of the glands, bacteria enter the cells owing to the weakening of the anticlinal and inner periclinal cell walls and by phagocytosis. Strands of actin filaments occur near the endocytical vesicles containing degenerating bacteria. Accumulations of phenolic compounds and callose could explain the absence of bacteria in the stalk cells. The presence of bacteria inside the leaf glands of S. camporum is a regular and cyclic trait. The significance of the bacteria (not yet identified) and the type of interaction between these two organisms remain unknown.