THE SHELL-FORMING MANTLE EPITHELIUM OF BIOPHALARIA GLABRATA (PULMONATA): ULTRASTRUCTURE, PERMEABILITY AND CYTOCHEMISTRY

In the freshwater snail Biomphalaria glabrata, the outer mantleepithelium and the transitional epithelium from the outer mantleepithelium to the belt are characterized by apical vesiclesof different electron density and vacuoles including lipid dropletsand fibrillar structures. Wide intercellular spaces predominatein the transitional epithelium. In addition to belt desmosomes,freeze fracture studies detect septate junctions as apical intercellularjunctions. The permeability of the septate junctions is testedby injecting anaesthetized snails with solutions containingperoxidase and lanthanum-nitrate. The septate junctions appearto be impermeable for the protein and inhibit permeation ofthe ion. Alkaline phosphatase is detected at the light microscope levelin the transitional and outer mantle epithelium. At the electronmicroscope level localization of alkaline phosphatase is restrictedto the apical and basal cell membranes of the same epithelia.An ATPase with low affinity to Ca²⁺ and Mg²⁺ ions is observedin the lumen of vacuoles in the proximal belt, the transitionaland the outer mantle epithelium. The possible role of the vacuolesas a site of synthesis or modification of the intercrystallinematrix is discussed. A high affinity Ca²⁺/Mg²⁺ ATPase is detectedwith the help of Electron Spectroscopic Imaging in the cellmembranes and in membranes of the rER. A model for solute transport through the epithelia to the extrapallialspace is proposed. (Received 18 August 1992; accepted 4 January 1993)     

Changes in mimosa epicotyl soluble nucleic acid patterns: Comparisons between changes related to growth rate and changes related to degree of maturation

Soluble nucleic acids from Albizzia julibrissin epicotyl tissueswere extracted and fractionated at different times during lategermination. Seedlings were grown on two different growth regimes,one with a relatively constant growth rate and an increasingpercentage of mature tissues, and a second with an increasinggrowth rate but relatively constant percentage of mature tissues.Consistent changes were observed in distribution of specificsoluble nucleic acid fractions with growth rate and stage ofdevelopment. Stability of terminal groups of soluble nucleicacid also were related to growth and developmental patterns.Finally, degree of amino acid acceptance by total tRNA decreasedwith stage of development, but did not relate to growth ratesor percentage of mature tissues. ¹Contribution from the Missouri Agricultural Experiment Station.Journal Series No. 5586. (Received February 3, 1969; )