Ginkgo biloba retains functions of both type I and type II flowering plant phytochrome

Differential response of Scots pine seedlings to variable intensity and ratio of red and far-red light

We investigated the response to increasing intensity of red (R) and far-R (FR) light and to a decrease in R:FR ratio in Pinus sylvestris L. (Scots pine) seedling. The results showed that FR high-irradiance response for hypocotyl elongation may be present in Scots pine and that this response is enhanced by increasing light intensity. However, both hypocotyl inhibition and pigment accumulation were more strongly affected by the R light compared with FR light. This is in contrast to previous reports in Arabidopsis thaliana (L.) Heynh. In the angiosperm, A. thaliana R light shows an overall milder effect on inhibition of hypocotyl elongation and on pigment biosynthesis compared with FR suggesting conifers and angiosperms respond very differently to the different light regimes. Scots pine shade avoidance syndrome with longer hypocotyls, shorter cotyledons and lower chlorophyll content in response to shade conditions resembles the response observed in A. thaliana. However, anthocyanin accumulation increased with shade in Scots pine, which again differs from what is known in angiosperms. Overall, the response of seedling development and physiology to R and FR light in Scots pine indicates that the regulatory mechanism for light response may differ between gymnosperms and angiosperms.

Light and temperature regulation of greening in dark-grown ginkgo (Ginkgo biloba)

The last steps of chlorophyll (Chl) biosynthesis were studied at different light intensities and temperatures in dark-germinated ginkgo (Ginkgo biloba L.) seedlings. Pigment contents and 77 K fluorescence emission spectra were measured and the plastid ultrastructure was analysed. All dark-grown organs contained protochlorophyllide (Pchlide) forms with similar spectral properties to those of dark-grown angiosperm seedlings, but the ratios of these forms to each other were different. The short-wavelength, monomeric Pchlide forms were always dominating. Etioplasts with small prolamellar bodies (PLBs) and few prothylakoids (PTs) differentiated in the dark-grown stems. Upon illumination with high light intensities (800 micromol m(-2) s(-1) photon flux density, PFD), photo-oxidation and bleaching occurred in the stems and the presence of (1)O(2) was detected. When Chl accumulated in plants illuminated with 15 micromol m(-2) s(-1) PFD it was significantly slower at 10 degrees C than at 20 degrees C. At room temperature, the transformation of etioplasts into young chloroplasts was observed at low light, while it was delayed at 10 degrees C. Grana did not appear in the plastids even after 48 h of greening at 20 degrees C. Reaccumulation of Pchlide forms and re-formation of PLBs occurred when etiolated samples were illuminated with 200 micromol m(-2) s(-1) PFD at room temperature for 24 h and were then re-etiolated for 5 days. The Pchlide forms appeared during re-etiolation had similar spectral properties to those of etiolated seedlings. These results show that ginkgo seedlings are very sensitive to temperature and light conditions during their greening, a fact that should be considered for ginkgo cultivation.

Phytochrome-mediated development in land plants: red light sensing evolves to meet the challenges of changing light environments

Phytochromes are photoreceptors that provide plants with circadian, seasonal, and positional information critical for the control of germination, seedling development, shade avoidance, reproduction, dormancy, and sleep movements. Phytochromes are unique among photoreceptors in their capacity to interconvert between a red-absorbing form (absorption maximum of approximately 660 nm) and a far-red absorbing form (absorption maximum of approximately 730 nm), which occur in a dynamic equilibrium within plant cells, corresponding to the proportions of red and far-red energy in ambient light. Because pigments in stems and leaves absorb wavelengths below about 700 nm, this provides plants with an elegant system for detecting their position relative to other plants, with which the plants compete for light. Certain aspects of phytochrome-mediated development outside of flowering plants are strikingly similar to those that have been characterized in Arabidopsis thaliana and other angiosperms. However, early diverging land plants have fewer distinct phytochrome gene lineages, suggesting that both diversification and subfunctionalization have been important in the evolution of the phytochrome gene family. There is evidence that subfunctionalization proceeded by the partitioning among paralogues of photosensory specificity, physiological response modes, and light-regulated gene expression and protein stability. Parallel events of duplication and functional divergence may have coincided with the evolution of canopy shade and the increasing complexity of the light environment. Within angiosperms, patterns of functional divergence are clade-specific and the roles of phytochromes in A. thaliana change across environments, attesting to the evolutionary flexibility and contemporaneous plasticity of phytochrome signalling in the control of development.

Form, function and environments of the early angiosperms: merging extant phylogeny and ecophysiology with fossils

The flowering plants--angiosperms--appeared during the Early Cretaceous period and within 10-30 Myr dominated the species composition of many floras worldwide. Emerging insights into the phylogenetics of development and discoveries of early angiosperm fossils are shedding increased light on the patterns and processes of early angiosperm evolution. However, we also need to integrate ecology, in particular how early angiosperms established a roothold in pre-existing Mesozoic plant communities. These events were critical in guiding subsequent waves of angiosperm diversification during the Aptian-Albian. Previous pictures of the early flowering plant ecology have been diverse, ranging from large tropical rainforest trees, weedy drought-adapted and colonizing shrubs, disturbance- and sun-loving rhizomatous herbs, and, more recently, aquatic herbs; however, none of these images were tethered to a robust hypothesis of angiosperm phylogeny. Here, we synthesize our current understanding of early angiosperm ecology, focusing on patterns of functional ecology, by merging recent molecular phylogenetic studies and functional studies on extant 'basal angiosperms' with the picture of early angiosperm evolution drawn by the fossil record.

Phytochrome Evolution in Green and Nongreen Plants

Photoreceptors are critical molecules that function at the interface between organism and environment. Plants use specific light signals to determine their place in time and space, allowing them to synchronize their growth, metabolism, and development to the environments in which they occur. Thus, innovation in light sensing mechanisms is expected to coincide with adaptation and diversification. Three studies involving the well-characterized phytochrome photoreceptor system in plants indicate that much work is yet needed to test this expectation. In early diverging flowering plants, episodic positive selection influenced the evolution of phytochrome A, but little of the functional data needed to link molecular adaptation with a change in gene function are available. In the model plant Arabidopsis thaliana, known functional differences between a recently duplicated gene pair remain difficult to characterize at the sequence level. In parasitic plants, patterns of development that in autotrophs are under the control of light signals are highly modified, suggesting that phytochromes and other photoreceptors function differently in nonphotosynthetic plants. Analyses of phytochrome A coding sequences indicate that they are evolving under relaxed constraints in nonphotosynthetic Orobanchaceae, consistent with the expectation of functional change. Further work is needed to determine which of the processes mediated by phyA may have been altered, a line of investigation that may improve our understanding of divergence points in downstream signaling pathways.