Photosynthesis of Grass Species Differing in Carbon Dioxide Fixation Pathways

Publisher Website
Google Scholar
Abstract
Panicum spp. of the Laxa group were investigated in a series of published reports and possessed C4, C3 and intermediate photosynthetic characteristics. Taxonomic and other relationships among these plants are not clear. It was the objective of this investigation to document chromosome number, metaphase I chromosome behavior and mode of reproduction, including abnormalities in the embryo sac, for these species. Chromosome counts showed a basic number (x) of 10 and ploidy levels of diploid (2n = 2x = 20), tetraploid (2n = 4x = 40) and hexaploid (2n = 6x = 60) in this group of Panicum. One diploid and one tetraploid accession of the C4 species, P. prionitis Griseb., were obtained. Of the intermediate species, P. milioides Nees ex Trin. was diploid, P. schenckii Hack. was hexaploid, and P. decipiens Nees, ex Trin. possessed 2 ploidy levels, 1 accession being diploid and the other accession being hexaploid. All C3 species, which included 2 accessions of P. laxum Sw., 3 accessions of P. hylaeicum Mez. and 1 accession of P. rivulare Trin., were tetraploid. Meiosis was regular with primarily bivalent pairing at metaphase I in all species except the tetraploid accession of P. prionitis which possessed from 4-10 tetravalents. Stainable pollen was high in all species, ranging from 70-99%. Embryo sac analyses showed a single sac in all plants except the tetraploid accession of P. prionitis, which possessed an additional sac at anthesis. An additional sac was also observed in some ovaries of the P. schenckii accession. Self-pollinated seed set was high in all accessions except the diploid accession of P. prionitis and one accession of P. laxum where no seed was set under bagged conditions. This information establishes, within the limits of this collection, a base for future studies on genetic, taxonomic, photosynthetic and evolutionary relationships among these plants. Possession of the same basic chromosome number, regular meiotic pairing, a high degree of stainable pollen and good seed set in most plants studied indicate possible success in making hybrids for a genetic study of photosynthetic pathways in Panicum.