[Intracellular localization and function of hydrolytic enzymes in tobacco].

1. Four acid hydrolases are partially sedimentable from cell free extracts of tobacco seedlings; these enzymes have the following pH-optima: acid protease pH 3,5; acid RNase pH 6,2; acid phosphatase pH 5,4 and 5,8 and acid unspecific esterase pH 5,5. 2. After differential centrifugation of cell free extracts the sedimentable hydrolases are recovered in the mitochondrial and microsomal fractions. 3. Treatments of the sedimentable material which destroy cytoplasmic membranes result in the solubilization of the acid hydrolases. 4. Isopycnic centrifugation in sucrose-gradients revealed the presence in cell free extracts of two particulate fractions carrying hydrolases; the relative densities of these particles are 1,11 and 1,09g cm(-3). 5. The lighter fraction consists mainly of spherosomes, as can be demonstrated by fluorescence microscopy of the particles stained with berberine sulfate. The heavier fraction probably consists of so-called prospherosomes. 6. The hydrolases from isolated spherosomes are able to digest isolated mitochondria in vitro. 7. The total activities as well as the quantity of sedimentable fractions are highest in seedlings and decrease markedly during ontogenesis of the plant. 8. The isolation of mature leaves causes the mobilization of the cytoplasm of the mesophyll cells within a few days; the chlorophyll disappears completely within 6 days whereas protein and lipid disappear gradually over a period of 16 days. 9. Immediately after the isolation of the leaves new sedimentable protease and esterase activity is formed; new RNase is synthesized a few days later. Soon after their formation these enzymes appear in the soluble fraction. 10. Treatment of detached leaves with kinetin delays the mobilization of chlorophyll, lipid and protein markedly. In addition the synthesis of acid hydrolases is suppressed almost completely. 11. The spherosomes are viewed as organelles of the plant cells equivalent to the lysosomes of animal cells. The intracellular localization and significance of the hydrolases occuring in the soluble fraction of cell free extracts is discussed. 12. The events taking place in mature detached leaves are interpreted as a catabolic mobilization of the cytoplasm due to the action of the spherosomal enzymes.