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Understanding the Effects of Stresses on Plants

This course explores the effects of various stresses on plants and their implications. Topics include phytoremediation, plant products, biofuels, seed germination, nutrient deprivation, climate change, non-coding RNAs, biotechnology, plant movements, stress responses, plant signaling, flowering, hormones, plant pathology, plant tropisms, root growth responses, metal toxicity, circadian rhythms, effects of magnetic fields, and effects of different colors of light on plant growth.

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Understanding the Effects of Stresses on Plants

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  1. Course Plan • We will study effects of stresses on plants and see where it leads us • Phytoremediation • Plant products • Biofuels • Effects of seed spacing on seed germination • Effects of nutrient deprivation • Effects of stresses • Climate/CO2 change • Non-coding RNAs • Biotechnology • Plant movements: flytraps, mimosa, soybeans • Carnivorous plants • Stress responses/stress avoidance • Plant signaling (including neurobiology) • Flowering? • Hormones? • Plant pathology? • Plant tropisms and nastic movements • Root growth responses • Metal toxicity? • Circadian rhythms? • Effects of magnetic fields? • Effects of different colors of light on plant growth?

  2. We will study effects of stresses on plants and see where it leads us • Learn about plant stress • Pick some stresses to study • Decide which plants to study and how to assay the stress effects • What to measure? • Biomass • Yield • Proteins, pigments • Secondary products • Responses to stimuli • Solar tracking • Leaf closing • Tropisms • Flowering

  3. Plant Stress • Won Senator Proxmire’s “Golden Fleece” award for wasteful government spending • Water? • Nutrients? • Environment? • Temp? • pCO2? • Pollution? • Ozone, other gases? • Herbicides, eg Round-Up, Atrazine? • Light? • Insects and other herbivores? • Pathogens = bacteria, viruses, fungi

  4. Mineral Nutrition Studied by soil-free culture in nutrient solutions:

  5. Mineral Nutrition • Soil-free culture • Sand culture • Hydroponics: immerse roots in nutrient solution • Slanted film maintains [nutrients] &O2 • Aeroponics spraysnutrient solution on roots

  6. Mineral Nutrition • Macronutrients • CHOPKNS • CHOPNS make biopolymers

  7. Mineral Nutrition • Macronutrients • CHOPNS make biopolymers • N deficiency • mobile in plant, so old leaves go yellow first

  8. Mineral Nutrition • P deficiency • mobile in plant, so shows first in old leaves which turn dark green or purple

  9. Mineral Nutrition • S deficiency • mobile in plant, so shows first in old leaves which turn yellow

  10. Mineral Nutrition • K deficiency • mobile in plant, so shows first in old leaves which go yellow at edges.

  11. Mineral Nutrition • Ca deficiency • immobile in plant, so shows first in young leaves which show blotches of necrotic tissue • Crucial role in water- • splitting!

  12. Mineral Nutrition • Fe deficiency • immobile in plant, so shows first in young leaves which turn yellow while veins stay green

  13. Mineral Nutrition • Mg deficieincy • mobile in plant, so shows first in old leaves which brown off at edges

  14. Mineral Nutrition • Mg deficieincy • mobile in plant, so shows first in old leaves which brown off at edges • One/ chlorophyll and also cofactor for many enzymes

  15. Mineral Nutrition • Micronutrients: BNaCl • B: cell elongation. NA metabolism • immobile in plant, so shows first in young leaves

  16. Mineral Nutrition • Micronutrients: BNaCl • B: cell elongation. NA metabolism • Na: PEP regeneration in C4, K substitute • mobile in plant, so shows first in old leaves

  17. Mineral Nutrition • Micronutrients: BNaCl • B: cell elongation. NA metabolism • Na: PEP regenerationin C4, K substitute • Cl: water-splitting, osmotic balance • mobile in plant, so shows first in old leaves

  18. Mineral Nutrition • Micronutrients: BNaCl others include Cu, Zn, Mn • B: cell elongation. NA metabolism • Na: PEP regeneration, K substitute • Cl: water-splitting, osmotic balance • Cu: cofactor • immobile in plant, so shows first in young leaves

  19. Mineral Nutrition • Micronutrients: BNaCl others include Cu, Zn, Mn • Mn: cofactor for many enzymes, especially water splitting enzyme • Immobile in plants so shows first in young leaves

  20. Mineral Nutrition • Commercial fertilizers mainly supply NPK

  21. Plant food • 2.6% ammoniacal nitrogen • 4.4% nitrate nitrogen • 9% phosphorus • 5% potassium • calcium (2%) • magnesium (0.5%) • sulfur (0.05%) • boron (0.02%) • chlorine (0.1%) • cobalt (0.0015%) • copper (0.05%) • iron (0.1%) • manganese (0.05%) • molybdenum (0.0009%) • nickel (0.0001%) • sodium (0.10%) • zinc (0.05%)

  22. Nutrient excesses More infrequent since plants control nutrient uptake

  23. Nutrient excesses • More infrequent since plants control nutrient uptake • Na stress: frequently occurs in areas that have been irrigated or are near oceans

  24. Effects of excess Sodium • Reduced turgor due to lower Ys • Reduced growth rate • Plasmolysis

  25. Effects of excess Sodium • Reduced turgor due to lower Ys • Enzyme inhibition • [Na] > 100 mM inhibit enzymes of all spp • Even spp that live in 5 M NaCl

  26. Effects of excess Sodium • Reduced turgor due to lower Ys • Enzyme inhibition • Accumulation in old leaves to • toxic levels

  27. Mechanisms of Sodium Tolerance • Exclusion • negative correlation with HKT1 (unloads Na from xylem)and salt tolerance in Arabidopsis • Accumulation of Na+ in leaf promotes Na tolerance!

  28. Mechanisms of Sodium Tolerance • Exclusion • Compartmentalization in vacuoles • Some plants make salt glands • that excrete salt

  29. Mechanisms of Sodium Tolerance • Exclusion • Compartmentalization in vacuoles • Osmotic tolerance • Mechs not fully understood; sometimes involve accumulation of organics such as trehalose in vacuole • Reason weak HKT1 • promotes Na tolerance?

  30. Mineral Nutrition • Soil nutrients • Amounts & availability vary • PSU extension Text

  31. Mineral Nutrition • Soil nutrients • Amounts & availabilityvary • Many are immobile, eg P, Fe

  32. Mineral Nutrition • Soil nutrients • Amounts & availability vary • Many are immobile, eg P, Fe • Mobile nutrients come with soil H2O

  33. Mineral Nutrition • Soil nutrients • Amounts & availability vary • Many are immobile, eg P, Fe • Mobile nutrients come with soil H2O • Immobiles must be “mined” • Root hairs get close

  34. Mineral Nutrition • Immobile nutrients must be “mined” • Root hairs get close • Mycorrhizae get closer

  35. Mineral Nutrition • Immobile nutrients must be mined • Root hairs get close • Mycorrhizae get closer Solubility varies w pH

  36. Mineral Nutrition • Solubility varies w pH • 5.5 is best compromise

  37. Mineral Nutrition • Solubility varies w pH • 5.5 is best compromise • Plants alter pH @ roots to • aid uptake

  38. Mineral Nutrition • Nutrients in soil • Plants alter pH @ roots toaid uptake • Also use symbionts • Mycorrhizal fungi help: especially with P

  39. Mineral Nutrition • Also use symbionts • Mycorrhizal fungi help: especially with P • P travels poorly: fungal hyphae are longer & thinner

  40. Mineral Nutrition • Also use symbionts • Mycorrhizal fungi help: especially with P • P travels poorly: fungal hyphae are longer & thinner • Fungi give plants nutrients

  41. Mineral Nutrition • Also use symbionts • Mycorrhizal fungi help: especially with P • P travels poorly: fungal hyphae are longer & thinner • Fungi give plants nutrients • Plants feed them sugar

  42. Mineral Nutrition • Also use symbionts • Mycorrhizal fungi help: especially with P • P travels poorly: fungal hyphae are longer & thinner • Fungi give plants nutrients • Plants feed them sugar • Ectomycorrhizae surround root: only trees, esp. conifers

  43. Mineral Nutrition • Ectomycorrhizae surround root: only trees, esp. conifers • release nutrients into apoplast to be taken up by roots

  44. Mineral Nutrition • Ectomycorrhizae surround root: trees • release nutrients into apoplast to be taken up by roots • Endomycorrhizae invade root cells: Vesicular/Arbuscular • Most angiosperms, especially in nutrient-poor soils

  45. Mineral Nutrition • Endomycorrhizae invade root cells: Vesicular/Arbuscular • Most angiosperms, especially in nutrient-poor soils • May deliver nutrients into symplast

  46. Rhizosphere • Endomycorrhizae invade root cells: Vesicular/Arbuscular • Most angiosperms, especially in nutrient-poor soils • May deliver nutrients into symplast • Or may release them when arbuscule dies

  47. Rhizosphere • Endomycorrhizae invade root cells: Vesicular/Arbuscular • Most angiosperms, especially in nutrient-poor soils • Deliver nutrients into symplast or release them when arbuscule dies • Also find bacteria, actinomycetes, protozoa associated with root surface = rhizosphere

  48. Rhizosphere • Also find bacteria, actinomycetes, protozoa associated with root surface = rhizosphere • Plants feed them lots of C!

  49. Rhizosphere • Also find bacteria, actinomycetes, protozoa associated with root surface = rhizosphere • Plants feed them lots of C! • They help make nutrients available

  50. Rhizosphere • Also find bacteria, actinomycetes, protozoa associated with root surface = rhizosphere • Plants feed them lots of C! • They help make nutrients available • N-fixing bacteria supply N to many plant spp

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