Plant Diversity Posted on web 2 28 07 at 5 30 pm Ecol 182 3 8 2007 Summary from last time We talked about Figure 29 10 The Evolution of Today s Plants The Seed Plants Seed plants are the most derived tracheophytes Gymnosperms such as pines and cycads four phyla Angiosperms flowering plants one phyla Big evolutionary innovations Evolution of a seed Reduction in gametophyte generation The haploid gametophyte is attached to and nutritionally dependent on the diploid sporophyte Figure 35 14 A Woody Twig Gymnosperms Naked Seeds Gymnosperms except Gnetophyta have only tracheids and simple phloem Tracheids are simple xylem that conduct water throughout the plant body Tracheids undergo apoptosis and operate as empty cells cell walls remain Phloem are alive and transport carbohydrates and other materials throughout the plant The Angiosperms Flowering Plants Phylum Angiospermae 257 000 species Angiosperm means enclosed seed The angiosperms are the most derived form of the tracheophytes the sporophyte generation is larger and has greater independence from the gametophyte the gametophyte is smaller and more dependent on the sporophyte The Angiosperms Flowering Plants A number of synapomorphies or shared derived traits characterize the angiosperms They have double fertilization upcoming figure They produce triploid endosperm Their ovules and seeds are enclosed in a carpel modified leaf They have flowers modified leaves They produce fruit at minimum mature ovary and seed Their xylem contains vessel elements specialized H2O transport and fibers structural integrity Their phloem contains companion cells assists with metabolic issues associated with transport The Angiosperms Flowering Plants Double fertilization two male gametes participate in fertilization events within the megagametophyte One sperm combines with the egg to produce a diploid zygote The other sperm combines with two other haploid nuclei of the female gametophyte to form a triploid nucleus Results in endosperm tissue that nourishes the embryonic sporophyte Figure 30 11 The Life Cycle of an Angiosperm The Angiosperms Flowering Plants All the parts of a flower are modified leaves Stamens filament bearing anthers containing pollenproducing microsporangia Pistil one or more carpels with a swollen base ovary containing megasporangia Style is the apical stalk of the pistil terminal surface receiving pollen is called the stigma The Angiosperms Flowering Plants Specialized leaves petals and sepals are important for attracting pollinators Many angiosperms are animal pollinated increasing the likelihood of outcrossing in exchange for nectar or pollen Coevolution has resulted in some highly specific interactions but most plant pollinator systems are not highly specific Evolutionarily ancient angiosperms have a large and variable number of floral structures petals sepals carpels and stamens Evolutionary trend within the group reduction in number of floral organs differentiation of petals and sepals changes in symmetry and fusion of parts Figure 30 8 Inflorescences The Angiosperms Flowering Plants Perfect flowers have both microsporangia and megasporangia Imperfect flowers have either but not both Monoecious species produce both types of imperfect flowers on the same plant In dioecious species a plant produces either megasporangiate or microsporangiate flowers but not both Developing embryos consists of an embryonic axis and one or two cotyledons seed leaves which metabolize endosperm and may become photosynthetic Figure 35 1 Monocots versus Eudicots Figure 35 2 Vegetative Organs and Systems Organs of the Angiosperms Two main types of root system taproot and fibrous root Many eudicots have a taproot system a single large deepgrowing primary root with smaller lateral roots Monocots and some eudicots have a fibrous root system composed of numerous thin roots roughly equal in diameter A fibrous root system holds soil in place very effectively Some plants have adventitious roots which arise from points along the stem where roots would not usually occur Figure 35 3 Root Systems Angiosperm vascular systems Xylem in angiosperms consists of vessel elements in addition to tracheids Vessel elements also conduct water and are formed from dead cells Vessel elements are generally larger in diameter than tracheids and are laid down end to end to form hollow tubes Sieve tube elements Phloem in Angiosperms are stacked similar to xylem Have adjacent companion cells that retain all organelles Companion cells may regulate the performance of the sieve tube members through their effects on active transport of solutes Figure 35 9 Plant Cell Types Part 3 Why is a greater diameter a big deal for the evolution of plants Figure 35 10 Evolution of the Conducting Cells of Vascular Systems Figure 35 11 Sieve Tubes Angiosperms Flowering Plants Monocots a single embryonic cotyledon grasses cattails lilies orchids and palms Eudicots two cotyledons and include the majority of familiar seed plants Additional clades water lilies star anise and the magnoliid complex Big question in plant evolution what is the basal angiosperm Uptake and Movement of Water and Solutes Transport of Water and Minerals in the Xylem Transpiration and the Stomata Translocation of Substances in the Phloem General problem in plant function Need for H2O for photosynthesis Solute transport temperature control internal pressure for growth Plants obtain water and minerals from the soil via the roots in turn roots extract carbohydrates and other important materials from the leaves Water enters the plant through osmosis but the uptake of minerals requires transport proteins Uptake Movement of Water Solutes in Plants Osmosis is the diffusion of water through a membrane primary means of water transport in plants Osmotic potential or solute potential determines the direction of water movement across a membrane Potential refers to the potential energy contained in the system measured Dissolved solutes have the effect of lowering the concentration of water changing the potential energy Greater solute concentration results in a more negative solute potential and a greater the tendency of water to diffuse to the solution Uptake Movement of Water Solutes in Plants Water potential is the tendency of a solution to take up water from pure water Water potential of a system is the sum of the negative solute potential s and the usually positive pressure potential p s p Solute potential pressure potential and water