Specificity of leaf terminal phloem in Gentianaceae species

摘要

The structure of leaf terminal phloem in 17 species of Gentianaceae family has been studied by electron microscopy. Structure of terminal phloem of studied species was described and analyzed. Structural row observed in this family was compared with well-known primitive and advanced structural variants of terminal phloem. As a result the range of Gentianaceae structural variations is described as a sequence of apoplastic type evolutionary development. Terminal phloem of Swertia obtusa is the most primitive and probably the most related to ancestral (0) type. Terminal phloem of another 12 species studied - Anagallidium dichotomum, Blackstonia perfoliata, Centaurium sp., Gentiana azurea, G.decumbens, G.fischeri, G.macrophylla, G.tenella, Gentianopsis ciliata, Halenia corniculata, Lomatogonium carrintianum, Lisianthus sp. - is comparable with primitive apoplastic type (2A). Other 4 species-Gentiana algida, G.squarrosa, G.uniflora, G.aquatica-have a special advanced feature numerous cell wall ingrowths in companion cells. Development of cell wall ingrowths is connected with intensity of phloem loading from the apoplast. These species are the most advanced on this feature among Gentianaceae. In spite of the progress in establishment of cell wall ingrowths specific for apoplastic species, the terminal phloem of these species seems to be rather primitive.