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How do plants do it? Reproduction: from algae to flowering plants Plants come in all shapes and sizes Chara, Chlamydomonas, Pitcher plant, Giant Sequoia Plants and Biotechnology Howard Univ. Summer Workshop July 18, 2012 By Heven Sze & Dan Czerny University of Maryland, College Park, MD Fossil records indicate that higher plants evolved from algae Why are seed plants the most successful land plants? Seed Plants include recent 65 m 1. Gymnosperms (naked seeds) 200 m 2. Angiosperms or flowering plants (contained seed) 450 m Why? Most advanced and dominant, because of their reproductive features. •Embryo is protected and can survive harsh environment 600 m Years ago •Fertilization does not depend on water. Pollen and seeds are dispersed by wind or insect. •Plants have developed vascular tissues, so they can survive on land and reach great heights. The fossil records of some protist and plant groups. The width of the shaded space is an indicator of the number of species. Image from Purves et al., Life: The Science of Biology, 4th Ed. Algae is related to plants: evidence? Land plants evolved from an algal ancestor. • • Biologists hypothesized that green algae are closely related to plants. Why? b/c morphological traits, a) chloroplast b) cell wall. The green algae include species that are unicellular, colonial, or multicellular. Algae live in marine or freshwater habitats. Tiny alga: Ostreococcus lucimarinus. Fig 30-15. Water is essential for all life processes Green algae produce sperms and egg. Sperms swim to the egg. Egg (n) FE • Algae grow in marine environments and in fresh water. Take up minerals and water directly. • Mosses need moist environment and water for fertilization. Chara alga How do they reproduce? Moss developed organs to protect egg and sperms from drying. -Sperms swim to egg. ION Archegonium Haploid (n) Diploid (2n) FERTILIZATION MITO SI S Egg (n) Zygot e (2n) Eggs form in archegonia Developing sporophyte (2n) Sper m swim to egg Mature sporophyt e (2n) Sperm form in antheridia Developing sporophyte (2n) Spores (n) are produced in sporangia by meiosis, dispersed by wind Mature gametophyte (n) Mature gametophyte (n) MEIOS IS Diploid (2n) Sperm (n) Zygote (2n) (retained on parent) Multicellular adult (n) M MITO SIS O EI S SI R: unfertilized L: fertilized FIE promoter 1. Seed Germination Major stages in the life of a flowering plant 1. Seed germination 4. Seed formation Reproductive plant Heterotrophs Seedling 2. Development of the plant body 3. Development of the reproductive organs (flower) Vegetative Plant Autotrophs Alternation of generation? • 1. Surface to prevent drying out. [leaf cuticle] • 2. Pores for gas exchange [stomata] • 3. Support to give structure to plant body [cell wall] • 4. Plumbing system to distribute nutrients and water. [vascular tissues] • 5. Accomplish fertilization without an aqueous environment. How? • 6. Development of seed with dormant embryo. Physcomitrella patens Seed Haploid (n) Plants developed adaptations to survive on dry land Mosses: Gametophyte is large and long lived; sporophyte depends on gametophyte for nutrition. Spore (n) AT Spores (n) moss Developing MIT OSIS gametophyte RT ILI Z Gametes are produced in gametangia 2. Development of the vegetative plant body. 3. Development of the reproductive organs: a. formation of flowers 1. Sepal 2. Petal Plants develop appropriate structures to carry out special functions. Vegetative plant body is made of 3 organs: •leaf •Stem •root 3. Stamen: male organ 4. Pistil: female organ •Sperms & eggs are wellprotected •Separated by long distance •How do they find one another? Travel •How does one travel and not get dried out? Protection What are these parts? 4. Reproduction • Pollination: transfer of pollen grain to the pistil • Fertilization: fusion of the sperm with the egg. ? ? Insect or bird pollinated flowers are colored and fragrant. ? Inside Anther Pollen Mother Cell – > meiosis ->microspore pollen What is a pollen grain? A protective cell containing 2 sperms Pollination Transfer of pollen grain to the pistil How? Do sperms have flagella? No, they cannot swim. So how do they move? • How can they survive long hot journeys? • Successful pollination is landing on the right pistil. [compatible vs incompatible] David Twell’s Pollen website http://www.le.ac.uk/biology/research/pollen/pollen.html Answers Successful fertilization depends on pollen germination, tube growth & guidance • Fly: pollen is carried by wind, gravity carried by bees, insects, or other flying organisms. • Pollen wall is hard and thick. Some pollen grains can survive a few hours of heat and drought. 7 Fertilization: pH/osmotic shock of tube to discharge content Taken from Johnson & Lord 2006 Growing pollen tube Pollen tubes can sense signals from the female cells & then orient the tube to targeting the ovule Wild typeg Pollen chx 21/23 mutant A mutant pollen is completely clueless Pollen tubes grow into the stigma & transmitting tract Lu, Yongxian Pollen tube growth: videos • Ravi Palanivelu Lab: • http://ag.arizona.edu/research/ravilab/lab %20images&movies%20page.html See video 1: semi-in vivo pollen tube growth towards an ovule See video 2: tube is attracted to and enters an ovule Video 4: When one pollen tube enters ovule, other tubes are repelled. Video 15: in vitro pollen tube growth! Just like what you saw with tiger lily and other lilies. Lab. expt. • Form: What is a flower? What does each part do? Get acquainted with all the flower parts • Function: In vitro pollen germination & tube growth What nutrients are needed and why? Determine % germination and tube lengths of pollen in different test solutions.