Lecture 17 BIO 311D 2nd EditionOutline of Last Lecture I. Stomata experiment, what do we learn?II. Phloem loading and unloading, how?Outline of Current Lecture I. Plant signals (within a plant, for now)II. Seed germination Current LectureI. Plant signals (within a plant, for now)- What are two important plant functions that occur when stomata are open and not when the pores are closed?1. Gas exchanges (net intake of CO2 for photosynthesis to occur)2. Water evaporation (transpirational pull) - Light is the usual trigger for stomata to open- how could you tests what exact aspects of the light (wavelength, intensity, duration)? - What are some conditions under which stomata should open or close, regardless of whether it’slight or not?1. If the plant didn’t have enough water (little water in the soil, low water potential stressfulsituation for the plants)2. ABA (abscisic acid) – a hormone signal, a stress hormone 3. Plant opens stomata at night 4. Very low levels of CO25. Constant environment - What two ways do plant cells grow?1. Cytokinin (hormones) promotes growth by mitosis (cell division)2. Auxin (hormones) promotes growth by cell elongation - What are some things that happen when plant cells specialize? What causes their differentiation?Organelles, specialized proteins, root hairs - What happens to elongate a cell?Loosen the cell wall, turgor pressure expands cell size - Plant cells divide by mitosis and cytokinesis, elongate and then thicken their cell wall - Control of cell responses – signal transduction pathways - Receptors- Second messengers (i.e. Ca+ ions)- Kinases (phosphorylates proteins, makes it active) - Phosphatases (deactivates proteins) - Amplification (recruit more and more molecules)- The proton pump is activatedII. Seed germination - What should be in a seed?- Embryo- Nutrients (stored food)- Apical meristem - Seed coats (diploid, part of the maternal plant) - Seeds have one or two cotyledons = “seed leaves”- Dicots have two cotyledons- Monocots have one cotyledon - What is seed dormancy? What is an adaptive advantage of having a period of seed dormancy before germination?- Time germination with optimal season, give seed a rest period before growth - ABA hormone signal (promote dormancy) and giberrclins (GA- produced by the embryo)- Is in charge of promoting seed dormancy: Parent Plant- Is in charge of ending seed dormancy: Seed (embryo plant)- Experiment: look for the transport of proteins within the seed or look for the absence or presence of proteins in different areas of the seed, adding hormones at different states (stages) and track them - Maternal plant secretes a hormone into seeds that slow growth and triggers water loss from the seed, in final preparation for seed dormancy.- An environmental cue (different for different plants) triggers the end of dormancy. After that, water is imbibed, and the embryo releases hormones that trigger germination - What triggers break dormancy? – Changing day length, water conditions, varies with the plant - Ending seed dormancy, triggering imbibition fireweed and other end dormancy after afire. Smoke (NO) is the cue in many species - Seed dormancy is promoted by hormone abscisic acid (ABA), which promotes water loss,turning off metabolism in seed- Seed Germination: water imbibition stimulates embryo to secrete gibberellin hormone (GA), which stimulates target cells that release enzymes that digest nutrients for mobilization - After dormancy is broken by a change in environment, which of these happens first?- Water enters
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