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Introduction to Plant Diversity Lecture 6 Spring 2014 1 What is a plant?? What is a plant?? • Land plants • Embryophytes – Embryo Fig. 29.4 2 Evolution of plants Plant traits shared with green algae • Chloroplast structure • Chlorophyll b • Store food as starch • Cell walls of cellulose 3 4 Evolution of plants Charophyceans Plant traits shared only with Charophyceans • Rosette shaped celluosesynthesizing complexes • Peroxisome enzymes • Structure of flagellated sperm • Formation of a phragmoplast • Molecular analysis Fig. 29.3 Fig. 29.2 The Move to Land Why move to land at all? Benefits from living on land • Sun • Abundant CO2 • Soil • Few herbivores or pathogens 5 Problems with moving to land 6 4 problems to solve 1. Preventing water loss from cells 2. Protection from ultraviolet radiation 3. Transporting water from tissues with access to water to tissues without access to water 4. Reproducing in dry conditions Problem #1: Preventing water loss Solution Evolution of cuticle • Problems w/cuticle? Solution • Evolution of stomata • Stomata trait of all land plants except liverworts 7 8 Problem #2: UV Radiation • Secondary compounds • Flavanoids Problem #3: Transporting water • Tissues needed to be in contact with water – Lack of rigidity Solution • Evolution of vascular tissue • Rigidity – Water pressure – Lignin rings Fig 35.10 9 10 Problem #3: Transporting water Problem #4: Reproducing in dry conditions 11 Alternation of generations • Alternation of multicellular haploid and diploid forms Fig. 29.13 Problem #4: Reproducing in dry conditions Changes in alternation of generation Fig. 30.2 12 Problem #4: Reproducing in dry conditions 13 Walled spores produced in sporangia • Sporopollenin • Transport in dry air Fig. 29.5 Problem #4: Reproducing in dry conditions Transporting gametes Bryophytes and seedless vascular plants • sperm swims to egg Solution • Pollen grain • Trait found in gymnosperms, angiosperms Pollen grain 14 Problem #4: Reproducing in dry conditions 15 Multicellular gametangia • Contained on gametophytes • Archegonium • Antheridium • Protection Fig. 29.5 Problem #4: Reproducing in dry conditions 16 Multicellular, dependent embryos • Embryophytes • Within gametophyte • Placental transfer cells Fig. 29.5 Derived traits of the Kingdom Plantae Traits present in plants but not in charophyceans • Alternation of generations • Walled spores produced in sporangia • Multicellular gametangia • Multicellular, dependent embryos • Apical meristems 17 Derived traits of the Kingdom Plantae Apical meristems • Localized regions of cell division • Cells differentiate Fig. 29.5 18 19 Evolution of plants • Nonvascular plants – Bryophytes • Vascular plants See Fig. 29.7 Evolution of plants 20 • Seedless vascular plants • Seed plants – Vascular tissue – Seeds See Fig. 29.7 21 Evolution of plants Gymnosperms Exposed seed Angiosperms Enclosed seed Diversity of plants 22 23 Diversity of plants Table 29.1 Major events in plant evolution First evidence of land plants 475 million years ago • Fossils 24 Major events in plant evolution Silurian-Devonian Explosion 410-360 million years ago • Fossils from most of major plant lineages • Adaptive radiation 25 26 Major events in plant evolution Carboniferous period - “age of the ferns” 320-290 million years ago Major events in plant evolution 27 • ~360 mya first seed plants (gymnosperms) appear • Climate change at end of Carboniferous period (320-290 mya) – gymnosperms (250 to 120 mya) Major events in plant evolution “Age of angiosperms” • 140-125 mya angiosperms appear • 65 mya major diversification 28