Organization of the tonoplast in frozen-etched root tips

Lysosome and proteasome pathways are distributed in laticifers of Euphorbia helioscopia L

At present, the lysosome pathway (LP) and proteasome pathway (PP) are known as major clearance systems in eukaryotic cells. The laticifer, a secretory tissue, degrades some cytoplasm during development. In this study, we investigated the distribution of LP and PP in non-articulated laticifers of Euphorbia helioscopia L. Electron microscopy revealed that, plastids, mitochondria and some cyotsol were degraded in the late development laticifers, where there were numerous vesicles originated from dicytosomes. Accordingly, some key proteins in LP and PP were detected in E. helioscopia latex using isobaric tags for relative and absolute quantitation (iTRAQ) proteomics. Further immunohistochemistry analysis revealed that the clathrin heavy chain (CHC) belonging to LP and the ubiquitin-mediated proteasome degradation increases gradually as the laticifer develops. Immuno-electron microscopy revealed that the cysteine protease, CHC and AP-2 complex subunit beta-1 belonging to LP were mainly distributed in vesicles deriving from dicytosomes, which we called lysosome-like vesicles. Ubiquitin was widely distributed in the cytosol, and proteasome activity was significantly reduced when various concentrations of the inhibitor MG132 were added to the latex total protein. We hypothesize that LP and PP are distributed in E. helioscopia laticifers; and it was speculated that LP and PP might be involved in the degradation of organelles and some cytoplasmic matrix in E. helioscopia laticifers.

Ultrastructure and cytochemical localization of acid phosphatase of laticifers in Euphorbia kansui Liou

Acid phosphatase (AcPase) activities are involved in the degeneration process of cytoplasm in plants. In this study, acid phosphatase was detected by the method of lead nitrate and cytochemical electron microscopy during the development of nonarticulated laticifers in Euphorbia kansui Liou. The most important feature in the differentiation of the laticifers in E. kansui is that the development of small vacuoles arises from endoplasmic reticulum (ER). The mature laticifers possess a thin layer of electron-dense peripheral cytoplasm in which the organelle cannot be distinguished and a large central vacuole filled with latex particles. AcPase cytochemistry studies show AcPase reaction products congregated into heaps are distributed along the tonoplast of central vacuole and around the mitochondria and plastids. Some small vacuoles which develop at later developmental stages of laticifers contain AcPase reaction products. As a result, the central vacuole is formed by cellular autophagy and fusion of small vacuoles which apparently arises from ER.

Organization of frozen-etched Thelohania bracteata (Strickland, 1913) (Microsporida, Nosematidae) emphasizing the fine structure of the posterior vacuole

This study examines the ultrastructure of the posterior vacuole in frozen-etched spores of Thelohania bracteata (Nosematidae), a microsporidian infecting the fat body of larval black-flies (Simuliidae). This organelle, considered important in providing intrasporal pressure for sporoplasm extrusion through the polar filament, has a double membrane with particles on its internal faces as revealed by the freeze-etching technique. The size and pattern of these particles differ from those in membranes of the polar filament and nucleus, and this difference may have functional significance. The posterior vacuole, and also the polaroplast, may originate from expanded sacs that occur in the immature spore. There is evidence from this study that there are many basic ultrastructural similarities between spores of different microsporidian species and that at least some reported differences are the result of varying techniques.

We gratefully acknowledge the freeze-etching facilities provided by the Department of Pathology, Faculty of Medicine, McMaster University. The research was supported by Grant A-130 from the National Research Council of Canada.

The lysosome-concept in plants : II. Location of acid hydrolases in maize root tips

The sedimentability of eight acid hydrolases in an homogenate from root tips of Zea mays (L.) varied between 13% (α-glucosidase) and 46% (β-N-acetylglucosaminidase) of the total activity. Between 20% and 30% of total activity of the majority of acid hydrolases examined was sedimentable.High specific activities of acid hydrolases (up to ten times the sedimentable or soluble activities) were associated with the cell walls, and considerable amounts of this activity (20-60%, depending on the enzyme) could only be released by cellulase treatment.Mitochondria-free membrane fractions isolated from the 8000 g, 25000 g and microsomal fractions contained acid hydrolase activities. The membranes could be separated into two bands on Ficoll gradients, but acid hydrolase activities were present in both bands.The 25000 g fraction was incubated with glucose-6-phosphate and lead nitrate to label the vesicles containing neutral phosphatase with lead phosphate. The labelled vesicles were separated from the remaining vesicles by density grandients. The majority of acid phosphatase, β-glucosidase, β-galactosidase and peroxidase activities were associated with the unlabelled fraction. Phosphodiesterase was present in both fractions. The peroxidase isozyme thought to be tonoplast-associated (Parish, 1975) was found in the unlabelled vesicles.It was concluded that sedimentable acid hydrolases are associated with a specific class or classes of membrane.More than 60% of the sedimentable acid hydrolase activities were strongly bound to membranes. A membrane model of lysosome action is proposed.The isozymes of acid phosphatase and β-galactosidase present in the cell wall, sedimentable fractions and the supernatant were examined.A number of tentative conclusions are drawn concerning "lysosomes" and acid hydrolases in plant cells.

Ultrastructure of barley aleurone cells as shown by freeze-etching

Aleurone tissue from non-germinated or germinating barley seeds, as well as from isolated aleurone layers imbibed with water or gibberellic acid, was frozen directly in Freon and investigated by the freeze-etching technique. Aleurone grains remained spherical under all conditions, although the volume increased on hydration. They contained both protein crystalloids and globoids (phytin or lipid) embedded in the matrix. Globoids appeared to be membrane-enclosed. Spherosomes were evidently enclosed within a normal membrane, and they were in close contact with the membrane of aleurone grains, covering the surfaces of the latter. A highly-ordered particle structure was seen on some preparations of the plasmalemma. During germination no alterations were observed in membrane structure.