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Lecture Quiz 3 Lycophytes and Ferns Ques5on 1-‐Lycophytes (4 pts) You are given germinated spores of Selaginella and you are asked to describe them. ADer observing under the microscope, you find: A. One type of spore B. No visible gametophytes aLached to the spores C. Hermaphrodi5c gametophytes germina5ng from spores D. Smaller (micro-‐) and bigger (mega-‐) spores E. A and C F. B and D Ques5on 2 (4 pts.) In fern sporophytes: A. Eusporangia are ancestral, while leptosporangia are derived and more widespread B. Sporangia are organized in sori, which are always covered by a membrane (indusium). C. Leaves are megaphylls, they are Euphyllophytes. D. Some ferns have microphylls, others have megaphylls E. All of the above. F. A and C are correct G. B and D are correct. Meristems “Plant growth by shoot apical meristems is rather like having numerous small, 5ghtly-‐ controlled cancers at the extremi5es” Quen5n Cronk 2010 Apical growth in land plants Chara Prigge M J , Bezanilla M Development 2010;137:3535-3543 Growth of Gametophyte (Non-vascular Plants) Apical cell Cutting faces 1 division 2 divisions Apical cell continues to divide Outer cell – forms leaf or side stem Cells enlarge Inner cell – forms stem tissue Division forming an inner and outer cell hLp://www.anbg.gov.au/bryophyte/case-‐studies/apical-‐cells.html Apical Meristems consisting of a single apical cell: Moss Gametophyte Physcomitrella patens gametophyte initials. Prigge M J , Bezanilla M Development 2010;137:3535-3543 Liverwort Shoot Apical Meristems: single apical cell Leafy Porella stem single apical cell Leaf primordia are generated at the meristem's flanks Thalloid Apical cell denoted by * Location of apical meristem Fern Sporophyte Apical Meristems: single apical cell trichome root cap stem long. section hLp://www.sbs.utexas.edu/mauseth/weblab/webchap6apmer/6.8-‐1a.htm hLp://www.sbs.utexas.edu/mauseth/weblab/webchap6apmer/chapter_6.htm hLp://www.sbs.utexas.edu/mauseth/weblab/webchap6apmer/6.3-‐1.htm root long. section Equisetales Sporophyte Meristems hLp://www.botany.hawaii.edu/faculty/webb/bot201/equisetu/equi-‐98.html Lycophyte Sporophyte Apical Meristems: multicellular Selaginella bifurca5ng meristem Mul5cellular LP = leaf primordia SAM = shoot apical meristem hLp://www.botany.hawaii.edu/faculty/webb/Bot201/Lycopodium/lycophyta3.htm Eudicot Shoot Apical Meristems: Mul5layered Tunica-‐corpus organiza5on tunica corpus Rib zone PZ = peripheral zone hLp://www.sbs.utexas.edu/mauseth/weblab/webchap6apmer/6.3-‐4.htm KEY GENES IN SHOOT APICAL MERISTEM DEVELOPMENT THE KNOX GENE SHOOTMERISTEMLESS (STM) Maintains stem cell fate in the SAM Expression of the STM:GUS Reporter in Wild-Type Arabidopsis embryos WT Stm mutant Cronk 2010 Jurkuta R J et al. Plant Cell 2009;21:1957-‐1971 ©2009 by American Society of Plant Biologists The WUSCHEL (WUS)-‐CLAVATA (CLV) Gene Network WT wus WUSCHEL Promotes cell division of ini5als, prevents their differen5a5on. T Laux, KF Mayer, J Berger and G Jurgens, Development 122 (1) 87-‐96, 1996 CLAVATA Represses cell division of ini5als, promotes their differen5a5on Steve Clark Lab, University of Michigan The SAM Gene Network Cronk 2010 Lecture review (2 pts) Based on the meristem genes we just discussed, the stem over-‐prolifera5on mutant shown below could be due to: A. A loss of func5on (LOF) allele of STM (shootmeristemless) B. A gain-‐of-‐func5on (GOF) allele in WUS (WUSCHEL) C. A LOF muta5on in CLV (CLAVATA) D. All of the above E. None of the above F. B or C G. A or C Shoot/flower meristem Fascia5on mutants! Seed Plant Root Apical Meristems RAM Trends in Plant Science Volume 14, Issue 7 2009 399 -‐ 408 Main gene-‐players in root development SCARECROW::GFP PLETHORA in situ Protein expression gene expression MODEL Vocabulary • SHOOTMERISTEMLESS (STM), WUSCHEL (WUS), CLAVATA 1-‐3 (CLV1-‐3) • SCARECROW (SCR), PLETHORA (PLT) • GFP fusions (for protein localizaMon), in situ hybridizaMon (for RNA localizaMon=gene expression) • Apical cell • Tunica, corpus, an5clinal/periclinal cell divisions • Fascia5on mutants • Organizing center, apical ini5als, peripheral zone, rib zone • Quiescent center, root cap Embryos: Liverwort Embryo Marchantia Isoetes- What is it? hLp://www.plantsystema5cs.org/imgs/robbin/r/Isoetaceae_Isoetes_riparia_36073.html Fern Embryo Selaginella Embryo The seed plant embryo becomes dormant and is dispersed within the seed Gymnosperm seed (Pinus) Angiosperm Seed fruit + seeds Capsella hLp://www.botany.hawaii.edu/faculty/webb/bot201/angiosperm/OnionEmb-‐6-‐02.jpg Young Angiosperm Sporophyte
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