Physiological and morphological studies on tapering blue-green algae

Abstract

A study was made of factors influencing hair development in 34 heterocystous and 2 non-heterocystous strains of Rivulariaceae. When grown with a high level of NO(_3)-N, 33 of the heterocystous strains lost their heterocysts; 19 became untapered, but I4 produced tapered trichomes which resembled those of Homoeothrix or Ammatoldea. One strain was unchanged in morphology. Hair development was reduced but not eliminated in the 3 strains with long hairs in the heterocystous state, and was unaffected in the 2 strains with short hairs. When one heterocystous strain was starved of Ng, heterocyst frequency increased, but tapering was unaffected and no hairs developed. These responses suggested that hair development and tapering in heterocystous Hivulariaceae are not necessarily directly related phenomena, and that neither is likely to be due solely to nitrogen deficiency in the apical cells. The influence of phosphate, iron, magnesium, calcium, molybdenum and sulphate deficiencies on hair development was examined, 12 of the heterocystous strains, and one Homoeothrix showed increased hair development under phosphate deficiency; 8 of these (heterocystous) strains also did so under iron deficiency, and one off the 3 did so under magnesium deficiency. The other deficiencies had no marked effect on hair formation. Several other morphological responses to nutrient deficiencies are also described. Hair development in deficient cultures preceded any degenerative changes, and did not appear to be merely a pathological symptom. The cells of hairs formed under phosphate deficiency were found to be capable of polyphosphate synthesis, indicating metabolic activity. The possibility is considered that the hairs of Rivulariaceae may have a functional significance, perhaps in the uptake of nutrients present at a low concentration. During the work some strains suddenly developed morphological abnormalities when grown in standard medium. Attempts to elucidate this phenomenon are described in the Appendix.