Alternation of Generations • Unlike animals, who have a direct life cycle, plants have two life stages – Sporophyte & Gametophyte Plant Life Cycles & Algae • One is haploid (gametophyte) • One is diploid (sporophyte) Alternation of Generations • Plants alternate between these generations • Each a distinct plant Life Cycle Terminology Gametophyte • Sporophyte (2n) • Gametophytes produce gametangia – Produces spores – Gamete-producing structures • Gametophyte (n) • Antheridia produce sperm – Produces gametes – Antheridium is singular • Meiosis produces spores (not gametes!) • Archegonia produce eggs – Spores germinate into gametophyte – Archegonium is singular – Gametophyte is already haploid • Mitosis produces gametes 1 Sporophyte Major Groups of Algae Based on Cellular Complexity • Sporophyte produces sporangia – Spore-producing structures • Prokaryotes – No nucleus; no organelles • Spore mother-cells undergo meiosis to produce haploid spores • Mesokaryotes – Primitive nucleus; organelles present • Spores are shed and develop into – Mitosis/meiosis weird or absent gametophytes • Eukaryotes • And so the cycle continues – highly evolved nucleus & organelles • Increasingly dominant phase in more • Only thing “algae” have in common is derived plants chlorophyll-a based photosynthesis! Cyanobacteria: miles away from Eukaryotic Tree the rest! From: Keeling, J.P. (2004). Diversity & evolution of plastids & their hosts, American Journal of Botany 91: 1481-1493 (available online via UNCW library for FREE) 2 Major Extant Eukaryotes with Plastids Endosymbiosis Plant cell organelles enclosed by a double membrane & contain internal membranes and vesicles Often involved with the synthesis & storage of sugars, fatty acids, terpenes, etc. E.g. chloroplast, leucoplasts, amyloplasts, & chromoplasts Plastid Endosymbiosis Prokaryotic Algae Cyanophyta (blue-greens) Prochloron (Prochlorophyta) 3 Mesokaryotes: Dinoflagellates Phylum Dinophyta Example of Dinoflagellate Life Cycle Biflagellated cell Amoeboid stage Amoeboid cyst Pfiesteria piscicida known life stages Ceratium tripoda Alexandrium (red tides) Spiniferites cyst Mesokaryotes: Euglenophyta Eukaryotes: Browns & Reds 4 Eukaryotes: Diatoms Eukaryotes: Greens & Goldens Chlorophyte Phylogeny Primitive Life Cycle 5 Advanced Life Cycle (Laminaria) 6.