Frequently asked questions about in vivo chlorophyll fluorescence: practical issues.

The aim of this educational review is to provide practical information on the hardware, methodology, and the hands on application of chlorophyll (Chl) a fluorescence technology. We present the paper in a question and answer format like frequently asked questions. Although nearly all information on the application of Chl a fluorescence can be found in the literature, it is not always easily accessible.

Auxin regulation of axial growth in bryophyte sporophytes: its potential significance for the evolution of early land plants.

To identify developmental mechanisms that might have been involved in the evolution of axial sporophytes in early land plants, we examined the effects of auxin-regulatory compounds in the sporophytes of the hornwort Phaeoceros personii, the liverwort Pellia epiphylla, and the moss Polytrichum ohioense, members of the three divisions of extant bryophytes. The altered growth of isolated young sporophytes exposed to applied auxin (indole-3-acetic acid) or an auxin antagonist (p-chlorophenoxyisobutyric acid) suggests that endogenous auxin acts to regulate the rates of axial growth in all bryophyte divisions. Auxin in young hornwort sporophytes moved at very low fluxes, was insensitive to an auxin-transport inhibitor (N-[1-naphthyl]phthalamic acid), and exhibited a polarity ratio close to 1.

Evolutionary patterns in auxin action.

This review represents the first effort ever to survey the entire literature on auxin (indole-3-acetic acid, IAA) action in all plants, with special emphasis on the green plant lineage, including charophytes (the green alga group closest to the land plants), bryophytes (the most basal land plants), pteridophytes (vascular non-seed plants), and seed plants. What emerges from this survey is the surprising perspective that the physiological mechanisms for regulating IAA levels and many IAA-mediated responses found in seed plants are also present in charophytes and bryophytes, at least in nascent forms. For example, the available evidence suggests that the apical regions of both charophytes and liverworts synthesize IAA via a tryptophan-independent pathway, with IAA levels being regulated via the balance between the rates of IAA biosynthesis and IAA degradation.