Transcript Bio426Lecture35May1 - NAU jan.ucc.nau.edu web server

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
Facultative CAM switch to CAM during salt stress
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.
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
Corn roots develop large gas spaces when oxygen deficient.
Fig. 25.18
6. Air pollution
What are the major air pollutants?
What are their effects on plants?
What determines variation in sensitivity?
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.
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.
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W = S + P
W of xylem and phloem < 0
S < 0 if there are any solutes!
P of phloem > 0! “pressure flow”
Water moves passively from higher to lower w
Xylem
w =
w =
Phloem
w =
S=
p =
w =
S=
p =
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2.
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5.
W = S +  P
W of xylem and phloem < 0
S < 0 if there are any solutes!
P of phloem > 0! “pressure flow”
Water moves passively from higher to lower w
Xylem
w = -1.6
Phloem
w = -1.8
S= -2.8
p = 1.0
w = -1.0
w = - 1.2
S= -1.8
p = 0.8