PLANT PHYSIOLOGY
Az Agrármérnöki MSc szak tananyagfejlesztése
TÁMOP-4.1.2-08/1/A-2009-0010
Water status of plant,
influence of extreme water
supply
Overview
1. Plant water status
2. Water deficit in plant
3. Photosynthetic carbon fixation mechanisms
against water deficit
4. Excess of water
1. Plant water status
1.1. it can be measured by plant water potential
1.2. in leaves of well watered plant the value of water
potential is between -0.2 and -1 MPa
1.3. value of water potential depends on plant species
and variety
1.4. water potential shows short-term (diurnal)
variation
1.5. long-term decrease of water potential  start of
irrigation
Height profiles of xylem pressure at predawn (open symbols) and
midday (filled symbols) during the dry season for three trees
Source: Taiz L., Zeiger E. (2010): Plant Physiology. Web
material, http://5e.plantphys.net
The relationship between grain yield and stomatal conductance in
irrigated bread wheat
Source: Taiz L., Zeiger E. (2010): Plant Physiology. Web
material, http://5e.plantphys.net
2. Water deficit in plant
2.1. Physiological processes are affected by plant water
deficit
2.2. Solute accumulation helps cells maintain turgor and
volume
Sensitivity of various physiological processes to changes in water
potential under various growing conditions
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 81.
2.1. Physiological processes are affected by
plant water deficit
 water deficit leads to membrane damage
 photosynthesis is particularly sensitive to water
deficit
 stomata respond to water deficit
Dependence of leaf expansion on leaf turgor in sunflower plants
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 760.
Effects of water stress on photosynthesis and leaf expansion of
sunflower
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 765.
Relative effects of water stress on photosynthesis and translocation in
sorghum (Sorghum bicolor)
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 778.
Changes in water potential, stomatal resistance, and ABA content in
corn in response to water stress
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 676.
The leaves of young cotton (Gossypium hirsutum) plants abscise in
response to water stress
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 766.
3. Photosynthetic carbon fixation mechanisms
against drought stress
3.1. C4 plants are adapted to high temperature and water
deficit
3.2. Crassulacean acid metabolism (CAM) is an
adaptation to desert life
Inorganic carbon concentrating mechanisms: the C4 photosynthetic
carbon cycle
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 217.
Inorganic carbon-concentrating mechanisms: crassulacean acid
metabolism (CAM)
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 222.
4. Excess of water
4.1. Flooding and soil compaction cause O2 deficiency
for plant
4.2. Protective mechanisms of water plants
During episodes of anoxia, pyruvate produced by glycolysis is initially
fermented to lactate
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 777.
Summary
Plant water status can be measured by plant water
potential. Leaves of well watered plant have the value of
water potential between -0.2 and -1 MPa. Water potential
shows short-term (diurnal) and long-term variations.
Water deficit and excess are stress factors restricting
plant growth, biomass or agronomic yield production.
Drought resistance mechanisms vary with climate and
soil conditions. Stress caused by water deficit leads to
the expression of genes. Oxygen deficiency is typical of
flooded or waterlogged soils. Oxygen deficiency
depresses growth and survival of many species.
Questions
• What are the main characteristics of plant water status?
• A decrease or cessation of leaf expansion is an early
response to water stress. Provide a mechanism for this
response.
• Explain the role of the stomatal response to abscisic acid
in plant tolerance to water stress.
THANK YOU FOR YOUR ATTENTION
Next lecture:
Essential nutrients
Nutrient deficiencies
• Compiled by:
Prof. Vince Ördög
Dr. Zoltán Molnár