Unformatted text preview: Thoughts on some Interesting adaptations of Angiosperms Monotropa uniflora
(Indian pipe) In This No the blueberry family is an angiosperm ! chlorophyll heterotrophic This plant is a parasite... but it is parasitic parasite... on a fungus
A mycorrhyzal fungus associated with trees Not all non-photosynthetic plants are colorless non- Nearly 75% of parasitic plants are mistletoes ~ 3,000 species of such plants all angiosperms except for one liverwort 1 How do parasitic plants "steal" water and nutrients from hosts? steal" Nutrients What are the mechanics? Parasite e.g., and water are transported from the host by a "bridge" (haustorium) bridge" haustorium) connects its vascular system to that of the host (what about the "immune" system?) immune" seed lands on host plant
in a bird dropping Host Parasite "chemicals" stimulate germination chemicals" A lateral root of the growing parasite turns into the haustorium Chemotropic Root Parasite may then disable its own ability to photosynthesize (but not always) How??? ("control" genes?) ("control" attaches to host by forming a disc, which glues itself on Root tip "punches" into plant punches" Xylem/xylem and phloem/phloem connections Plants gotta "eat", too! eat" Nutritional Modes in Plants Photosynthesis Respiration vs. Stomata Transpiration Water use efficiency (ratio of CO2 taken up to water lost) A problem in some environments Photorespiration: Photorespiration: Plants have evolved three variations of photosynthesis high heat... heat... Under high light and C3 C4 CAM RUBISCO grabs oxygen instead of carbon dioxide Causes respiration to occur instead of photosynthesis Slows the production of sugars from photosynthesis 2 How C3 photosynthesis works CO2 C3 photosynthesis is first incorporated into a 3-carbon compound (G3P). Stomata are open during the day. RUBISCO (perhaps the most abundant enzyme on earth?) is the enzyme involved in the uptake of CO2. (see Fig. 10.18) Photosynthesis takes place throughout the leaf. Adaptive value of C3 photosynthesis More efficient than C4 and CAM plants under cool and moist conditions and under normal light because it requires less machinery (fewer enzymes and no specialized anatomy) plants are C3. C4 photosynthesis Most How C4 photosynthesis works CO2 Advantages of C4 photosynthesis
Photosynthesizes faster than C3 plants under high light intensity and high temperatures because the CO2 is delivered directly to RUBISCO, not allowing it to grab oxygen and undergo photorespiration. Has better Water Use Efficiency because PEP Carboxylase brings in CO2 faster and so does not need to keep stomata open as much (less water lost by transpiration) for the same amount of CO2 gain for photosynthesis. C4 plants include several thousand species in at least 19 plant families. is first incorporated into a 4-carbon compound. Stomata are open during the day. Uses PEP Carboxylase for the uptake of CO2.
This enzyme allows CO2 to be taken into the plant very quickly (PEP-C does not bind oxygen) Then it "delivers" the CO2 directly to RUBISCO for photosynthesis. Photosynthesis takes place in inner cells (requires special anatomy) 3 How CAM photosynthesis works CO2 CAM photosynthesis is stored in the form of an acid before use in photosynthesis. Stomata open at night (when evaporation rates are usually lower). The CO2 is converted to an acid and stored during the night. During the day, the acid is broken down and the CO2 is released to RUBISCO for photosynthesis Adaptive value of CAM photosynthesis Plant growth and light Plants Better Water Use Efficiency than C3 plants under arid conditions due to opening stomata at night when transpiration rates are lower May CAM-idle. When conditions are extremely arid, CAM plants can CAM- idle. just leave their stomata closed night and day. Oxygen given off in photosynthesis is used for respiration and CO2 given off in respiration is used for photosynthesis. Plant cannot CAM-idle forever. But CAM-idling does allow the plant to CAMCAMsurvive dry spells, and it allows the plant to recover very quickly when quickly water is available again (unlike plants that drop their leaves and go and dormant during dry spells). CAM plants include many succulents such as cactuses and agaves and also some orchids and bromeliads grown in high light environments grow "normally" for their species normally" Plants grown in low light environments are generally long, thin, and have long stem segments between sets of leaves Their growth form is altered in low light Young plants grown in a crowd should "race" each other upwards toward the light race" how do they know they are in a crowd when their leaves are getting lots of light? It is not the amount of light, it is the spectrum of the light
In particular, it is the ratio of red light to far-red farlight that plants use as a cue But... But... Chlorophyll absorbs red light more efficiently than far-red light, so more farneighbors means less red (lower ratio) Low red vs. far-red ratio triggers elongation far- 4 The important aspect is the ratio of the light reaching the stem... not stem... the leaves Evolution of flowers Evo-devo Evo Angiosperm ancestor had separate male (pollen-producing) and female (ovule(pollen(ovuleproducing) structures Female sporophylls became modified to form a flower... right? flower... Possibly wrong! A mutation may have caused ovules to be produced on the male sporophylls! sporophylls! 5 ...
View Full Document