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Environmental and Stress Physiology

Abscisic Acid Metabolism in Salt-Stressed Cells of Dunaliella salina

Possible Interrelationship with -Carotene Accumulation

Department of Botany, Schönland Botanical Laboratories, Rhodes University, Grahamstown 6140, South Africa, Department of Biochemistry and Microbiology, Goldfields Biotechnology Laboratory, Rhodes University, Grahamstown 6140, South Africa

The interrelationship between abscisic acid (ABA) production and -carotene accumulation was investigated in salt-stressed cells of the halotolerant green alga Dunaliella salina var bardawil. Cells were supplied with either R-[2-¹⁴C]mevalonolactone or [¹⁴C] sodium bicarbonate for 20 hours and then exposed to increased salinity (1.5 to 3.0 molar NaCl) for various lengths of time. Incorporation of label into abscisic acid and phaseic acid and the distribution of [¹⁴C]ABA between the cells and incubation media were monitored. [¹⁴C]ABA and [¹⁴C]phaseic acid were identified as products of both R-[2-¹⁴C]mevalonolactone and [¹⁴C]sodium bicarbonate metabolism. ABA metabolism was enhanced by hypersalinity stress. Actinomycin D, chloramphenicol, and cycloheximide abolished the stress-induced production of ABA, suggesting a role for gene activation in the process. Kinetic analysis of both ABA and -carotene production demonstrated two stages of accelerated -carotene production. In addition, ABA levels increased rapidly, and this increase occurred coincident with the early period of accelerated -carotene production. A possible role for ABA as a regulator of carotenogenesis in cells of D. salina is therefore discussed.