All authors contributed equally to this research.
HETEROSIGMA AKASHIWO (RAPHIDOPHYCEAE) RESTING CELL FORMATION IN BATCH CULTURE: STRAIN IDENTITY VERSUS PHYSIOLOGICAL RESPONSE 1,2
Article first published online: 23 NOV 2002
Journal of Phycology
Volume 38, Issue 2, pages 304–317, April 2002
How to Cite
Han, M.-S., Kim, Y.-P. and Cattolico, R. A. (2002), HETEROSIGMA AKASHIWO (RAPHIDOPHYCEAE) RESTING CELL FORMATION IN BATCH CULTURE: STRAIN IDENTITY VERSUS PHYSIOLOGICAL RESPONSE 1,. Journal of Phycology, 38: 304–317. doi: 10.1046/j.1529-8817.2002.01087.x
- Issue published online: 23 NOV 2002
- Article first published online: 23 NOV 2002
- 1 Received 8 May 2001. Accepted 11 December 2001.
- resting cells;
- toxic algae
In this study, we examined the impact of environmental perturbation on the movement of the toxic bloom-forming alga Heterosigma akashiwo (Hada) Hada ex Y. Hara et Chihara [syn. H. carterae (Hulburt) F.J.R. Taylor] between vegetative and resting cell phases of the life history. Resting state induction, in batch culture, was most effective when vegetative cells were subjected to low temperature (10° C) and darkness for extended time periods. Heterosigma cells in stasis had neither a cell wall nor scales but were surrounded by a calyx, most probably of polysaccharide composition. The resting cell was completely immobile, although both flagella remained attached. Heterosigma resting cells did not require a maturation period before successful activation to the vegetative state could occur. Cell division and motility were impacted sequentially during both the induction and activation phases of resting cell development. Our data show that Heterosigma had an obligate light requirement for resting cell activation. In replete medium, very low light fluences of 5 μmol photons·m−2·s−1 were as effective as 60 μmol photons·m−2·s−1 in the initiation of activation. Such sensitivity to extremely low light might give Heterosigma a competitive advantage for bloom formation in nature. Reduced nitrate levels significantly shortened the temporal transition of vegetative cells into the resting cell phase of the life history. Additionally, when resting cells induced in nitrate-limited medium were activated under nitrate-replete condition, the efficiency of the activation response was directly correlated to light availability. Both vegetative and resting cells maintained a haploid DNA complement. Rapid amplified polymorphic DNA (RAPD) analysis demonstrated variation in genetic identity among axenic Heterosigma strains. Strain identity influenced success in resting cell induction and survival in stasis. To date, no defined sexual cycle has been described. These observations are discussed in terms of population fitness. The data presented in this report provide a model algal system wherein the molecular events that govern long-term stasis in an obligately autotrophic organism can now be assessed.