Comparison of autofluorescence properties of sporogenous tissue in the six species of hornworts

Abstract

It has been pointed out that in hornworts, unique autofluorescence of the elaters observed under a fluorescence microscope. However, detailed information about the fluorescence properties was not provided. We observed the sporogenous tissue of six species of hornworts and confirmed that the distinctive autofluorescence of elaters of Phaeoceros laevis, Notothylas orbicularis, Dendroceros tubercularis, Megaceros flagellaris under a conventional epi-fluorescence microscope with ultraviolet (UV) and blue excitation light. Under UV excitation light, the autofluorescence of the elaters was yellow. In P. laevis and N. orbicularis, the autofluorescence of spores was yellowish, but in other species, the spores emitted strong blue-white autofluorescence. Although the elaters of P. laevis and N. orbicularis are “pseudoelaters” without a spiral thickening, they had the similar fluorescent properties as those of D. tubercularis and M. flagellaris with a spiral thickening. Observation using a confocal laser scanning microscope (CLSM) also confirmed that the elaters had autofluorescence with a unique wavelength. Interestingly, this characteristic autofluorescence was not detected in Anthoceros angustus and Folioceros fuciformis. The presence or absence of distinctive autofluorescence occurring in elaters may be an effective character to identify hornwort taxa. The fact that elater autofluorescence was not detected in liverworts may reflect the presence of cell wall components unique to the elaters of some hornworts.