10-20 Colonization and Plant Diversity

10-20 Colonization and Plant Diversity - Plant evolution...

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10/19/2010 1 Colonization of the land & plant diversity First 3 billion years of Earth’s history, single cell aquatic, 1.2 by, Colonization of the land Plant evolution Land plants evolved from green algae What is the evidence? Key characteristics shared with protists Multicellular, eukaryotic, photoautrophs, cellulose walls, chlorophylls a & b Distinctive traits of charaphytes : cellulose synthesizing sites (Rosettes in PM), Peroxisomes, flagellated sperm, phragomatoplast in dividing cells Fig. 29-1 Seedless and seed plants 1 st 100 million years: seedless Charophytes share with plants: 1) Peroxisome enzymes reduce photorespiration, 2) cellulose synthesizing rosettes of proteins complexes, 3) flagellated sperm 4) phragmatoplast: microtubles involved in cell wall formation & division 5) genetic evidence
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10/19/2010 2 Sporopollenin Key molecule protects plant against desiccation-1 st in Charaphytes transitioning the H 2 O/ air barrier add structure, access to CO 2 and mineral nutrients on land 1.2 billion yrs thin coat of cyanobacterial mat on land Last 500 million small plants developed along with fungi & animals 370 million taller forms Now 290, 000 land plants worldwide except in some extreme environments Contribute stability, food and O 2 Fig. 29-4 ANCESTRAL ALGA Red algae Chlorophytes Charophytes Embryophytes Viridiplantae Streptophyta Plantae Plant fossil materials
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10/19/2010 3 Fig. 29-2 30 nm Sporopollenin Chemically, enzymatically resistant to hydrolysis. Recalcitrant Contain mainly long chain fattyacids , phenylpropanoids , phenolics and traces of carotenoids Reduce desiccation and promote dispersal Fig. 29-3 40 μm 5 mm Chara species, a pond organism Coleochaete orbicularis, a disk-shaped charophyte that also lives in ponds (LM ) Alternation of generations Life Cycle of all land plants alternate between two generations of multicellular organisms: gametophyte s and sporophyte s. Multicellular haploid & multicellular diploid organisms Gametophyte produces, via mitosis , haploid eggs & haploid sperm w/ fuse to form diploid zygote Mitotic divisions of zygote produces Sporophyte & meiosis produces haploid spores that develop to haploid organism The 5 generalized steps of alternation of generations
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10/19/2010 4 Fig. 29-5a Gametophyte ( n ) Gamete from another plant n n Mitosis Gamete FERTILIZATION MEIOSIS Mitosis Spore n n 2 n Zygote Mitosis Sporophyte (2 n) Alternation of generations Embryos from zygote Develop within tissues of female parent plant placental cell provided protection & aa & sugars as nutrients Multicellular, dependent embryo a key trait of land plants embryophytes Fig. 29-5b Embryo Maternal tissue Wall ingrowths Placental transfer cell (outlined in blue) Embryo (LM) and placental transfer cell (TEM) of Marchantia (a liverwort)
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