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4. Salinity stress

4. Salinity stress. Two kinds of problems due to high soil salinity 1. Osmotic stress 2. Specific ion effects of high [Na +] , [Cl - ], [SO 4 -2 ] inactivate enzymes, inhibit protein synth. Plant Strategies 1. Osmotic adjustment to allow water uptake use inorganic ions, organic solutes

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4. Salinity stress

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  1. 4. Salinity stress • Two kinds of problems due to high soil salinity • 1. Osmotic stress • 2. Specific ion effects of high [Na+], [Cl-], [SO4-2] • inactivate enzymes, inhibit protein synth. • Plant Strategies • 1. Osmotic adjustment to allow water uptake • use inorganic ions, organic solutes • 2. Salt exclusion or compartmentation to • deal with ion effects. • prevent entry at roots • prevent transport to shoot • keep away from sensitive organelles • vacuolar compartmentation • extrude salt into glands

  2. Facultative CAM switch to CAM during salt stress

  3. 5. O2 deficiency Typically only a problem in flooded soils or heavily compacted soils. O2 diffusion to roots is inhibited. Flooding sensitivity and tolerance vary greatly and are related to anatomical and biochemical differences.

  4. Hypoxia and root function growth inhibition active transport reduced Flooding sensitive plants Flooding tolerant plants Soil conditions associated with anoxia toxic forms of some ions, e.g. Fe+2 H2S from SO4-2

  5. Corn roots develop large gas spaces when oxygen deficient. Fig. 25.18

  6. 6. Air pollution What are the major air pollutants? What are their effects on plants? What determines variation in sensitivity?

  7. Ozone enters leaves through stomata during normal gas exchange. As a strong oxidant, ozone (or secondary products resulting from oxidation by ozone such as reactive oxygen species) causes several types of symptoms including chlorosis and necrosis. It is almost impossible to tell whether foliar chlorosis or necrosis in the field is caused by ozone or normal senescence. Several additional symptom types are commonly associated with ozone exposure, however. These include flecks (tiny light-tan irregular spots less than 1 mm diameter), stipples (small darkly pigmented areas approximately 2-4 mm diameter), bronzing, and reddening. Ozone symptoms usually occur between the veins on the upper leaf surface of older and middle-aged leaves, but may also involve both leaf surfaces (bifacial) for some species. The type and severity of injury is dependent on several factors including duration and concentration of ozone exposure, weather conditions, and plant genetics. One or all of these symptoms can occur on some species under some conditions, and specific symptoms on one species can differ from symptoms on another. With continuing daily ozone exposure, classical symptoms (stippling, flecking, bronzing, and reddening) are gradually obscured by chlorosis and necrosis.

  8. EPA estimates an agricultural crop loss of $2 billion to $3 billion dollars per year attributable to ozone exposure; the extent of forest damage is currently being studied. Heagle, A.S. 1989. Ozone and crop yield. Annual Review of Phytopathology 27:397-423.

  9. YW = YS + YP YW of xylem and phloem < 0 YS < 0 if there are any solutes! YP of phloem > 0! “pressure flow” Water moves passively from higher to lower Yw Xylem Phloem w = S= p = w = S= p = w = w =

  10. YW = YS + YP YW of xylem and phloem < 0 YS < 0 if there are any solutes! YP of phloem > 0! “pressure flow” Water moves passively from higher to lower Yw Xylem Phloem w = -1.8 w = -1.6 S= -2.8 p = 1.0 w = -1.0 S= -1.8 w = - 1.2 p = 0.8

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