Lipoxygenase activity in the oomyceteSaprolegnia is dependent on environmental cues and reproductive competence

Saprolegnia ferax grows vegetatively when not nutrient limited; however, when starved, it switches to sexual reproduction.Saprolegnia parasitica does not show this reproductive competence in response to starvation. This study examined lipoxygenase activity inS. ferax andS. parasitica during starvation. Lipoxygenase activity in starved cultures ofS. ferax decreased in a time-dependent manner, reaching less than 20% of initial levels by 72 h and decreasing to less than 10% by 192 h, the onset of reproductive structures.S. ferax showed no decline in peroxidase activity over 72 h of starvation.S. parasitica had initial lipoxygenase activity 50% greater thanS. ferax and showed no decline in lipoxygenase activity during 72 h of starvation and only a small decline at 192 h. StarvedS. ferax cultures resumed vegetative growth after transfer back to rich medium, and lipoxygenase activity returned to 70–80% of initial levels after 24 h in rich medium.S. ferax cultures transferred to full-strength medium maintained initial lipoxygenase activity levels for 48 h, then showed a sharp decrease between 48 and 72 h, the time at which nutrients become limiting. Cultures transferred to 40 and 20% strength media showed more rapid declines in lipoxygenase activity. These data demonstrate that starvation, an environmental cue that initiates sexual reproduction, depresses lipoxygenase activity in the reproductively competentS. ferax but not in the reproductively recalcitrantS. parasitica. These data are consistent with the hypothesis that lipoxygenase products are associated with vegetative growth but not sexual reproduction.