Circadian rhythms of leaf and stomatal movements in gymnosperm species

It is generally accepted that various physiological, morphological and gene expression phenomena are under the control of a circadian clock, and that this time keeping mechanism is universally present. Although such endogenou sly regulated phenomena have first been documented in plants more than 250 years ago and much work has been accumulated particularly in the past 70 ye ars, it was not obvious from the literature whether such time keeping mecha nisms exist in gymnosperms. Two prominent parameters were investigated in several gymnosperm species wh ich have been demonstrated to be under the control of a circadian clock in many plants: (i) leaf movement and (ii) stomata movement. In young plants o f Pinus sylvestris, Picea abies, Taxus baccata, Araucaria angustifolia, Ara ucaria heterophylla and Ginkgo biloba leaf oscillations could be recorded f or about 5 days. However, compared to angiosperm. plants, the amplitude was small. The period length under free running conditions (constant temperatu re and continuous light) was characteristic for the species. Stomatal movement was observed in Ginkgo biloba leaves by electron microsco py. Stomata were open at noon and closed at midnight under normal day/night conditions (LD) as well as under constant light conditions (LL), indicatin g that stomatal aperture is under circadian control in the gymnosperm Ginkg o biloba. Online recordings of stomata conductance however, exhibited diurn al but not circadian oscillations of net CO2-exchange in G. biloba leaves. Our results show that a circadian clock controls leaf and stomatal movement s in gymnosperm species indicating that endogenous time keeping mechanisms are present.