Isolation and properties of lysosomes from dark-grown potato shoots

Histochemical and ultrastructural characterization of vacuoles and spherosomes as components of the lytic system in hyphae of the fungus Botrytis cinerea

An integrated approach to acid phosphatase (EC 3.1.3.2) histochemistry by the azo-dye and lead-capture ('Gomori') methods in phosphate-starved hyphae of the fungus Botrytis cinerea revealed strikingly different patterns of localization of activity staining. Reaction product formed with the azo-dye method was found in numerous small organelles (<0.5 microm diameter), which also accumulated the lipophilic dye Nile Red and mislocalized the formazan indicating mitochondrial succinate dehydrogenase activity. Such small organelles were stained only weakly and sporadically with the lead-capture method; instead, lead phosphate deposits were produced mainly in large vacuoles (up to 2.5 microm diam.), similar to those accumulating the vital dye Neutral Red. Additionally, acid phosphatase activity was detected in apical secretory vesicles with the lead-capture method but not with the azo-dye method. Ultrastructural studies by transmission electron microscopy confirmed the presence of large vacuoles which showed evidence of autophagic activity, and of small moderately osmiophilic organelles. The latter are considered to be spherosomes rather than lysosomes because of their weak reaction with the lead-capture method and their high lipid content. It is suggested that their apparently strong reaction with the azo-dye method is caused partly by false localization due to the lipophilic nature of the reaction product.

Ribosomes in the lutoïd fraction (=lysosomal compartment) from Hevea brasiliensis Künth. (Mull.-arg.) latex

Lutoïd ribosomes represent 11.9% of the total ribosomal content of latex from Hevea brasilensis. Their two high-molecular-weight RNA components are identified. When undegraded, their molecular weights are calculated to be 1.3×10(6) and 0.7×10(6). Their nucleotide base composition is determined. The occurrence of lutoïd membrane-bound ribosomes and the lability of the 1.3×10(6)RNA component are discussed in relation to the biological role of lutoïds, more generally of a lysosomal compartment in the cellular function.

Effect of freezing and thawing on the distribution of lysosomal hydrolases in leaves of Solanum tuberosum L

Density-gradient ultracentrifugation techniques showed that freezing and thawing of potato leaves resulted in a change in the density of subcellular particles containing acid phosphatase and acid ribonuclease (RNase). Gel filtration experiments were used to characterise the molecular forms of the hydrolases associated with the various cell fractions. Freezing and thawing promoted a release of a portion of the complement of acid phosphatase and RNase from the lysosomes to the supernatant fluid fraction of cell homogenates. The freezing treatment appeared to activate latent lysosomal RNase.

Arylsulphatase activity of corn (Zea mays L.) seedling roots

The crude lysosomal fraction of corn seedling root tips contains an arylsulphatase (E.C. 3.1.6.1) which hydrolysed p-nitrophenyl sulphate at pH 8.0 but had no activity towards p-nitrocatechol sulphate. The Km value for p-nitrophenyl sulphate was 1.24 mM. The hydrolysis of p-nitrophenyl sulphate was linear up to 2 h and the rate was proportional to the amount of enzyme added. The enzyme was strongly inhibited by cyanide, fluoride and phosphate ions and did not resemble the arylsulphatases of bacterial and animal origin.

The occurence of ribonucleic acid in the lutoïd fraction (lysosomal compartment) from Hevea brasiliensis Künth. (Müll.-Arg.) latex

The lutoïds from Hevea brasiliensis latex represent a polydisperse lysosomal compartment. They contain RNA which is resistant to RNase in conditions which maintain the integrity of the lutoïds but is hydrolyzed when these organelles are destabilized. This RNA appears to be a structural component of the lutoïds.

Changes in activity of lysosomal ribonuclease following mechanical damage to leaves of Solanum tuberosum L

Differential centrifugation experiments showed that the 13-fold increase in total acid ribonuclease (RNase) activity arising during the 48 h following mechanical damage to potato leaves was associated, in about equal proportions, with the sedimentable and supernatant fluid fractions of cell homogenates. Density gradient ultracentrifugation techniques revealed that the majority of the particulate activity of RNase was located in the lysosomal fraction of leaf homogenates. Although [(14)C]leucine was incorporated into leaf lysosomes during incubation following mechanical damage the various molecular forms of RNase purified from the organelles, one of which had a specific lysosomal location, contained negligible radioisotope. That form of the enzyme which did incorporate [(14)C]leucine was one of those confined to the supernatant fluid fraction of leaves.In addition to the massive quantitative changes in RNase activity which occurred subsequent to mechanical damage, extensive qualitative changes occurred in the complement of molecular forms of lysosomal RNase. The possible origins of these changes are discussed.

Katabolism of plant cytoplasmic ribosomes: A study of the interaction between ribosomes and ribonuclease

Ribosome preparations from several species of flowering plant were found to contain ribonuclease. It was predominantly latent in ionic conditions which maintained the integrity of the ribosomes but was activated by agents which disrupted ribosome structure by chelating their divalent cations. The ribonuclease was not a structural component of the ribosomes but was preferentially adsorbed by them upon disruption of cells. Adsorption took place onto both large and small ribosomal subunits, and onto monosomes and polysomes. These results are discussed in relation to possible mechanisms for the breakdown of ribosomal RNA in vivo.

Activation and de novo synthesis of ribonuclease following mechanical damage to leaves of Solanum tuberosum L

The pattern of changes in RNase activity in damaged potato leaves incubated in the presence of [(14)C]leucine followed closely that of leaves incubated in the absence of the radioisotope, but the levels of activity during time course experiments were consistently lower. Contributions of other nucleolytic enzymes to the increased capacity of damaged leaves to hydrolyse RNA were slight.Two peaks of RNase activity were isolated from leaves that had been damaged for 24 h. One of these peaks represented a form of the enzyme that occurred in undamaged leaves and which increased markedly in activity on damage. The second peak represented a novel form of the enzyme which still possessed appreciable radioactivity after further extensive purification. It is suggested that a component of this peak was due to de novo synthesis of enzyme. Several additional new peaks of RNase activity were resolved from homogenates of leaves which had been damaged for 48 h. None of these peaks contained a significant amount of radioactivity when final purification was attained. It was concluded that although some de novo synthesis of RNase may occur during the first 24 h following mechanical damage the majority of increased enzyme activity up to that point and thereafter is due to activation of pre-formed enzyme.