Substrate restriction in entomophilous Splachnaceae: II. Effects of hydrogen ion concentration on establishment of gametophytes

The authors tested the hypothesis that establishment of Splachnum gametophytes is limited to neutral substrates by examining the effect of hydrogen ion concentration on spore germination, protonemal growth, and gametophore production in Splachnum ampullaceum, S. luteum, and S. sphaericum. Decreased germination was observed in S. sphaericum spores grown at pH 4 as compared to pH 7. Splachnum ampullaceum and S. luteum, however, exhibited no spore germination response to pH. Protonemal growth and gametophore production were inhibited at pH 4 compared to pH 7 in all taxa. Numbers of cells and protonemal branches per filament, chlorophyll a content, and total protein content were significantly reduced at pH 4. In addition, dark oxygen uptake was higher and light-dependent oxygen evolution was lower in protonema of S. ampullaceum grown at pH 4. In vivo [35S] sulfate-labelled protonema of S. ampullaceum grown at pH 4 and pH 7 produced generally similar polypeptide patterns on one-dimensional polyacrylamide gels, but four major differences were detected. Total [35S] sulfate uptake and incorporation into protein were reduced in protonema grown at pH 4. These observations are consistent with the neutrophilic hypothesis of substrate restriction in Splachnum