Green light-mediated photomorphogenesis in a dinoflagellate resting cyst

Abstract

Developmental responses to light are well known and ubiquitous among higher plants¹, but examples of such responses among the algae are less common. Those responses which have been reported in this group are generally photoperiodic or require prolonged light exposures; most involve macrophytes². We now report a non-photosynthetic, low-threshold, photomorphogenic response in a unicellular alga, the dinoflagellate Scrippsiella trochoidea (Stein) Loeblich. In contrast to the reported behaviour of most other dinoflagellate species, resting cysts of S. trochoidea require light to germinate. This requirement is satisfied to a large extent by low photon fluences delivered in exposures as short as 1 second. Green light is most effective in eliciting the response. Given the importance of dinoflagellates as primary producers in many aquatic ecosystems and the potential role of resting cysts in controlling the dynamics of natural dinoflagellate populations, the present observations are of obvious ecological significance. The primitive phylogenetic standing of dinoflagellates³, and the relative rarity of green light-mediated photomorphogenic responses in eukaryotes generally^4,5,suggest that this phenomenon may also hold considerable evolutionary and photophysiological interest.