Embryology of Petrosavia (Petrosaviaceae, Petrosaviales): evidence for the distinctness of the family from other monocots.
ABSTRACT The affinities of Petrosavia, a rare, leafless, mycoheterotrophic genus composed of two species indigenous to East to Southeast Asia, have long been uncertain. However, recent molecular analyses show that the genus is sister to Japonolirion osense. Japonolirion and Petrosavia comprise the Petrosaviaceae, which are now placed in its own order, Petrosaviales, distinct from other monocots based on molecular analyses. We conducted an embryological study of Petrosavia, comparing it to Japonolirion, as well as to basal monocots (Acorus and Araceae) and more derived monocots (Nartheciaceae, Velloziaceae, and Triuridaceae). Our results showed that Petrosavia is very similar in embryology to Japonolirion, with both genera sharing a glandular anther tapetum, simultaneous cytokinesis in microspore mother cells, anatropous and crassinucellate ovules, T-shaped tetrads of megaspores, ab initio Cellular-type endosperm, and a mature seed coat composed of the exotesta, endotesta, and endotegmen. The two genera of Petrosaviaceae are clearly distinct from Acorus, and all Araceae, Nartheciaceae, Velloziaceae, and Triuridaceae genera in various combinations of characters. Thus, both molecular and embryological evidence support the distinctness of the Petrosaviaceae from other monocots and its placement in its own order, Petrosaviales.
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ABSTRACT: Highlights ► We surveyed flavonoids in achlorophyllous plant, Petrosavia sakuraii (Petrosaviaceae). ► We identified isovitexin, vitexin, vicenin-2 and isorhamnetin 3-O-rutinoside, together with chlorogenic acid. ► Its flavonoid composition was compared with Japonolirion osense which is sister to the Petrosavia. ► Though flavonoid composition is similar between Petrosavia and Japonolirion, there are differences because of the presence of C-glycosylflavonols in the latter genus. ► The difference of the flavonoids may reflect difference of flavonoid function in the respective plants.Biochemical Systematics and Ecology 08/2011; 39(4):883-884. · 1.17 Impact Factor
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ABSTRACT: Dust seeds are the smallest existing seeds in angiosperms. This paper summarizes taxonomic distribution, phylogeny, ontogeny, morphology, and recruitment behavior of dust seeds, concluding with a general hypothesis on the evolution of dust seeds. Plants with dust seeds depend on external sources of organic carbon for seedling development and are thus parasitic during recruitment. Species with dust seeds are either mycoheterotrophic (fully or partially) or parasitic on plants. Dust seeds are a derived feature which has evolved independently in at least 12 families (Burmanniaceae, Corsiaceae, Orchidaceae, Triuridaceae, Petrosaviaceae, Ericaceae, Gentianaceae, Polygalaceae, Orobanchaceae, Rubiaceae, Buddlejaceae and Gesneriaceae). For the three latter families parasitic behavior during recruitment has not yet been described, and should be considered as a hypothesis. Many, but not all, dust seeds possess features that are likely to have been selected for increasing buoyancy in air or water. Selection for maximal fecundity at the expense of reducing maternal resources per seed is the probable driver of dust seed evolution. As endosperm was reduced, undifferentiated embryo evolved as a by-product due to endosperm mediated control of embryo development. Ultimately, seed size reduction passed a threshold where resource acquisition became dependent on external hosts. In order to embark on an evolutionary trajectory towards host dependence, facultative parasitism must have been established in ancestral lineages. Mycoheterotrophic and mixotrophic plants probably evolved along with the rise of angiosperm dominated tropical forests beginning in the Late Cretaceous. It is suggested that selection for increasing seed size associated with the expansion of modern type tropical forests spurred a competition/colonization trade-off initiating a reversed evolutionary trajectory towards smaller seeds. A different process is suggested for true parasites with dust seeds (Orobanchaceae), where the driver may have been the Mid-Tertiary expansion of grasslands, creating opportunities to exploit grasses and herbs. It is suggested that inequality and asymmetry in resource monopolization in ecosystems promote evolution of subordinate life strategies, and possession of dust seeds is considered as a subordinate strategy in plant communities dominated by other plant strategies. This escape route for ecological “losers” eventually promoted evolution of one of the most diverse groups of plants, the orchids.Perspectives in Plant Ecology Evolution and Systematics 05/2011; 13(2):73-87. · 3.32 Impact Factor
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ABSTRACT: Mycorrhizal fungi in roots of the achlorophyllous Petrosavia sakuraii (Petrosaviaceae) were identified by molecular methods. Habitats examined were plantations of the Japanese cypress Chamaecyparis obtusa in Honshu, an evergreen broad-leaved forest in Amami Island in Japan and a mixed deciduous and evergreen forest in China. Aseptate hyphal coils were observed in root cortical cells of P. sakuraii, suggesting Paris-type arbuscular mycorrhiza (AM). Furthermore, hyphal coils that had degenerated to amorphous clumps were found in various layers of the root cortex. Despite extensive sampling of P. sakuraii from various sites in Japan and China, most of the obtained AM fungal sequences of the nuclear small subunit ribosomal RNA gene were nearly identical and phylogenetic analysis revealed that they formed a single clade in the Glomus group A lineage. This suggests that the symbiotic relationship is highly specific. AM fungi of P. sakuraii were phylogenetically different from those previously detected in the roots of some mycoheterotrophic plants. In a habitat in C. obtusa plantation, approximately half of the AM fungi detected in roots of C. obtusa surrounding P. sakuraii belonged to the same clade as that of P. sakuraii. This indicates that particular AM fungi are selected by P. sakuraii from diverse indigenous AM fungi. The same AM fungi can colonize both plant species, and photosynthates of C. obtusa may be supplied to P. sakuraii through a shared AM fungal mycelial network. Although C. obtusa plantations are widely distributed throughout Japan, P. petrosavia is a rare plant species, probably because of its high specificity towards particular AM fungi.Mycorrhiza 03/2011; 21(7):631-9. · 2.99 Impact Factor