BIOL 420 1st Edition Lecture 17External Factors, Plant Growth and DefensesText References: Pages 665-680 (External factors and plant growth)Text References: pages 57, 30-35, 685, 610, 554-555, 497 (plant defenses)- External Factors and plant GrowthCircadian rhythms – follow an approximately (22-29) 24 hour cycle; these cycles will general continue even when environmental conditions are kept constant Among the plant responses that follow a circadian rhythm:Photosynthetic activity: independent whether there is sunlight or notSeed germinationEnzyme and auxin production - hormoneStomatal opening: guard cells independent of daylight/darkFlower opening: some flower close or open during the night Cell division and elongationLeaf movements – the leaf moves outward during the day and closer to the stem at night to conserve heatCharacteristics of circadian rhythms:Endogenous – internal to the cell, a built in “oscillator” generates. 3 separate parts:1. A central oscillator that generates rhythmic behavior2. Input pathways that carry environmental information to synchronize the central oscillator3. Output pathways that regulate physiological and biochemical processesCircadian clockCircadian clocks are “free-running” – synchronized by the environment – instrinsic, or natural period These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Entrainment: some stimulus that causes the rhythm to be synchronized in a cycle by a certain period of light that the plant is set to. Process by which a periodic repetition of light and dark causes a circaidian rhythm to synchronize with the same cycle as the entraining factorPhotoperiodism: phenomenon that the plants can detect the time of the year to flower (bloom). Plants that flower only in certain daylenght conditions; biological response to a change in the proportions of light and dark in a 24hour dcycle. Short-day plants: cockleburg - fall or early spring – Chrysanthemum. Critical growth period in the night time. Must have a light period that is shorter than a critical lenghtLong-day plants: inenbane – late spring, during the summer months. The link of darkness links to the ability to grow – spinach. Flower if the light periods are longer than a critical lengthDay-neutral plants: flower without respect to daylenght. Ex: cucumber, sunflower, rice, maize, and graden pea. Phytochrome red (Pr ): once it is exposed to red light it immediately converts to far red. Absorbs red light; biologically inactive Phytochrome far-red ( Pfr): the active form of the process, then at night consisting to converting it back to red, the longer the night more conversion of red; biologically activeOne second burst of light resets the light and all goes back to far-red loosing trackof timeEtiolationWhere the seed germinates and the shoot is really long and looks pale and sickly looking.Not healthy and is unable to grow for a long time; in response to not being able to receive the right amount of light. The energy goes into the stretching the stem. Without light, chlorophyll isn’t going to matter, once it detects light it was start to grow upward and start looking like a normal plant.Shade Avoidance:Plants can tell when they are being shaded and the type of shading. Response is determined on if they are shaded by another plant, chlorophyll absorbs in blue and red, much of the red is already being absorbed so the bottom leaf is absorbing more of the red, changes the ratio of the red:far-red is much lower. Much longer plant and greater node distance, trying to grow more than the plant above; if it keeps growing in this low ratio then it will grow prematurely. Floral StimulusFlorigen: a hormone that its chemically and produce by genes, stimulates the flowering in the flowering plant.Vernalization: involves with either the seed or the entire plat, blub – often subject the seed or the bulb or entire plant into a cold period before it can turn into a seed, Dormancy: a plant or a seed requires some kind of environmental cue to break the dormancyStratification: Drying requirement in order for it not to grow prematurely, a lot of seeds have to go through this in order to absorb water. Series of cues that can happen in order for the seed to germinateScarification: where the seed coat is scared or torn, sometimes its happen in the soil and its particals, subjective to enough of that to germinate it. Fruit containing the seed passing through the animal’s body. Birds would swallow bits of sand in order to get the germination and causes it to scar. Acclimation: involves to the explosion to cold and things that happen to the plant to prepare for the winter. In the fall when the plant is exposed to the cold bud scales start to form and protect the buds.Nastic movements: you can see it, sensitive plant (venus fly trap). Cell elongation is faster than division. In response to a stimulus but the reaction to the stimulus is not positive or negative, completely different in response. Involve row of cells that can quickly get rid or absorb water. The whole organ of NyctinasticPulvinus: whole organ of the leaf, vascular tissue runs through it. Potassium is the same mechanism that allows guard cells and is transported in the vascular tissue that pulls water into the arms of the pulvinus and increases water pressure and is going to open the leaves up. If you want to close it you’ll open the potassium pumps and releases the water and it then closes the leavesThigmosnasticMimosa (Sensitive plant): fold its leaves, the advantage is to make it less obvious to the herbivore. Lost or gain to a turger response,Dionaea (Venus flytrap): has to be fast enough to trap insects, the mid vein has adapted tothe same thing of the potassium. Fly traps - the upper epidermal cells loose water (shrinking), lower can quickly gain water (expanding). There are hair cells in the leaves, 2 of the cells have to be stimuluated for it to trigger, if more than one is trigger the plant will sense how big the insect is because it takes a lot of energy to do this. Very quick and selectiveThigmomorphogenesis: thigmo (touch). By touching it can cause difference in the growth patterns. Mechanical, the one on the left was touched twice a day, by touching plants can cause the plants to grow more shorter, stalkier, thicker. If not touched, long and spinly. Wind, rain, animals can cause it to effect with