Plant interaction with environmentHow does a plant find out about its surroundings and react to them?MechanismsSlide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10How does a plant know the ‘right kind” of light is presentSlide 12Slide 13Slide 14Slide 15Slide 16Other IssuesSlide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Plant interaction with environmentHow does a plant find out about its surroundings and react to them?Needs to know•When is water present•When is sun (good wavelength)present•Season of the year.Mechanisms•Environmental sensors – without a nervous system = chemical reactions sensitive to environment•Hormones – to regulate growth.How does a plant (organism) tell time?, like when it is Spring?Animal pattern of activity.Why is inaccurate?Circadian clock = 24hr cycle.Entrainment = resetting.Plants; length of day vs night to tell seasons (temperate climate)Plant measures length of night – animals do also – so can change flowering time with a flash of light (change night length) cat breeding.Basis of system: Chemical change based on light vs dark periods – accumulation of something to a certain level stimulates plantHow does a tropical plant tell time?? If day length always the same?In tropics, time of sunrise varies, even though day length constantAlso, position of sunrise varies, north to south.How does a plant know the ‘right kind” of light is present•Right kind = proper wavelength for photosysthesis•If in shade of a tree, this light is absorbed by the tree – does not reach the plant below.Phytochromes (bluish pigment – absorbs red – converted by light wavelengthDifferent wavelengths of light affect growth.Far red light stops growth - far red light absorbed by green leavesSo no growth if in shadeFar red light does not penetrate ground very far, so no growth if buried deepSo what does a seed to if it senses proper wavelength not present?• wait; many seeds can wait a long time• grow but put all energy into elongation, not leaves – try to reach the sun.Plant growth regulated by hormones. Gibberellin favors stem growth vs leaf growth = all effort put into getting tall, vs building photosynthetic surface area – good if you are under someone – need to reach sun – but how do you know? = light quality.How does a plant sense water?? How does it tell if there is enough water?1. Water can be absorbed by seeds and plants2. How to tell amount?Two possibilities? - if seed coat scratched (washed down a stream bed- there is lots of water- Only germinate 10% of seeds in response to water. If not enough, other seeds wait till next time. A major feature of agriculture; selection of synchronous germination.Other Issues•How to tell which way is up, down? response to gravity, sunlight.•Can you be sensitive to temperature? do you need to be?• Can you respond to being eaten? • •Mechanism: nearly all plant growth mediated by hormones.Mechanism of hormone action.0. Small molecules, soluble in water, move through vascular system and between cells.1. Secreted in some area – caused by environmental or internal stimulation2. Diffuses or transported to target cells3. Either enters these cells or interacts with cell membranes to cause a response.How to study hormones 1. remove hypothesized secretory area – see if you can eliminate effect2. Capture the substance secreted3. Replacement – can you get the effect back with addition of substance.4. Chemical analysisTypical plant hormones, - water soluble, fairly smallMay need transport system to cross membrane.Darwin and Darwin 1880: Classic experiment to discover auxin; comes from tip of plantFritz Went: substance isolated; replacement therapy restores action.Auxin moves in response to light (negative – away from)And in response to gravity (positive – towards)Note: pleiotropy – one hormone can do many different things in different areas of a plant. Mechanisms = complicated biochemicalHow does stem know to go up, root to go down??Low level of auxin – root grows downHigh level of auxinStep grows up.Auxin is actively transported cell to cellAuxin stimulates cell lengthening = elongation of stem.NOTE: Pleiotropic effects = same hormone can affect different parts of the plant in different ways.Sensitivity to water-When should a seed germinate??•In presence of water in deserts – how do you know there is enough??In presence of light? – how do you sense it??When there is no one above you – shadeAfter winter – in Spring – how do you know it is spring??Plus – how does a seedling know which way is up?otherOther hormones in plants:defense – secreted in response to injury – stimulate toxin secretionor wall off invader = plant galls, leaf drop – deciduous trees – stimulated by cold, lack of waterripening of fruit – ethylene – artificially stimulated by farmersMost systems have an opposing effect – can stimulate or inhibit fruiting, leaf growth, stem elongation, leaf abcissionEither absence of the positive effect hormone or presence of an opposing hormone.Plant options: a. be toxic: wasteful if no predator b. secrete toxin in response to injury which is best?? predator strategies: eat only young leaves eat very few leaves and then move on be able to detoxify.When to germinate or flower?New England = cold winter, plenty of water; based on cold shock to avoid fall developmentClaremont = not very cold winter, very seasonal water; based on water presenceWe have some trees, ornamentals from the east that get ‘fooled’ every year as they flower in the winter after a cold shock.What should a desert plant do? – very rare water.need abrasion – flood water = lots of wateror only 10% of seeds germinate – avoid not having enough water. (farmers hate this – select for 100% germination = early domestication of plants = selecting for synchronous germination)Major issue for plants: be an annual or be a perennialAnnual: advantages: don’t have to worry about bad conditions, live only when things are good. Need to sense this.tend to behave like r species; short life, small size, lots of offspring.disadvantages: need to grow from seed = takes time. Must reproduce very quickly, when there is a lot of competition.Perennial: advantages; already big when conditions become good – head start at competition for light,