Abstract

We used lanthanum nitrate as an apoplastic tracer to examine possible mechanisms of retrieval nutrient in the epithem of laminar hydathodes of Ficus formosana Maxim. Cytochemical data showed that vesicles, of constant size about 100 nm, containing the precipitation of lanthanum were present in the cytoplasm and pericytoplasm. These lanthanum-containing vesicles were associated with the elongated profiles of endoplasmic reticulum (ER). Lanthanum deposits were also observed in other organelles such as mitochondria and peroxisomes. Lanthanum nitrate, an apoplastic tracer, can’t penetrate the plasmalemma hence its distribution in the vesicles was via endocytosis. In particular, we found that lanthanum precipitation was not present in the plasmolemmasomes, which are the structures of the fluid-phase endocytosis of plasmalemma. From SEM/EDX results, we proposed that the lanthanum ion (La3+) or calcium ion (Ca2+) was absorbed and transported into cell by the coated vesicles endocytosis, not through the fluid-phase endocytosis. The coated vesicle endocytosis, a selective pathway, is a possible mechanism for the uptake of metal ions, which then are further transported into other organelles.

Keyword: Calcium ion, Coated vesicle endocytosis, Epithem, Hydathodes, Fluid-phase endocytosis, Lanthanum nitrate.