AKINETE GERMINATION IN ANABAENA CIRCINALIS (CYANOPHTA)

Akinetes of a clonal culture of Anabaena circinalis Rabenhorst from Mt. Bold reservoir (eutrophic), South Australia, were isolated and the effects of light, phosphorus, and nitrogen availability on their germination were investigated. Light was required but there was no significant difference in percentage of germination after 72 h if akinetes were incubated in ASM‐1 medium at irradiances of 15, 30, or 50 μmol.m ‐2 .s ‐1 . Maximum akinete germination occurred by 48 h. Nitrogen was not required, as 88% of akinetes germinated in the flasks without combined nitrogen added to the medium and without N 2 in the air. NH 4 + ‐N at 28 mg N.L ‐1 completely suppressed germination, whereas 28 mg NO 3 N.L ‐1 had no effect relative to the controls without nitrogen. Phosphorus was required, and at 48 h percentage of germination in the flasks with 0.6 mg P.L ‐1 added (78%) was significantly greater than in the flasks with 0.06 P.L ‐1 (58%) and 0 mgP.L ‐1 (24%) added. Germlings in the 0 mg P.L ‐1 flasks were only 2–4 cells long and stunted in appearance, whereas germlings at all other P concentrations were 8–16 cells long. It is likely that the isolation process exposed some akinetes to intracellular phosphorus released from lysing vegetative cells, but this was insufficient to allow normal development in the 0 mg P.L ‐1 flasks. The plot of percentage of germination vs. initial phosphorus concentration, in the medium showed a relationship analogous to Michaelis‐Menten nutrient uptake kinetics, suggesting that a specific membrane‐bound enzyme system(s) is involved, with phosphorus as the substrate. The half saturation value (K S ) for germination was 50 μg P.L ‐1 .