Dilated cisternae inCapparales—an attempt towards the characterization of a specific endoplasmic reticulum

Summary

Dilated cisternae (DC) of endoplasmic reticulum were found to be a typical component of stem-, hypocotyledon-, and root vascular parenchyma as well as root cap cells inBrassicaceae (14 species screened) andCapparaceae (7 species). In general, DC are very long, utricular organelles containing proteins and bound by a unit membrane which is studded with ribosomes. In aerial parts of the plants tested the proteins are tubular structures arranged parallel to the DC axis, in roots there ar filamentous proteins. In someBrassicaceae (e.g., Lunaria, Ptilotrichum, Schivereckia) DC are irregularly shaped and contain granular protein material. These forms are discussed to be leading to protein-containing vacuoles as found in companion cells ofTovaria. Since DC do occur in taxa which contain glucosinolates, an EM-cytochemical test for β-thioglucosidases (as first performed byIversen) was applied to some of the species. The results, however, did not prove a specific location of the enzyme inside DC. In addition to questions on the reliability of the method it is discussed whether it is likely that DC are a site of β-thioglucosidases while it is known thate.g., the glucosinolate-containingResedaceae do not contain this organelle. Also,Erythroxylum (Erythroxylaceae) andJacaranda (Bignoniaceae) gave the same precipitations when subjected to the cytochemical test (see “note added in proof”).