PLANT PHYSIOLOGY

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

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 81.

Sensitivity of various physiological processes to changes in water potential under various growing conditions

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

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 760.

Dependence of leaf expansion on leaf turgor in sunflower plants

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 765.

Effects of water stress on photosynthesis and leaf expansion of sunflower

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 778.

Relative effects of water stress on photosynthesis and translocation in sorghum (Sorghum bicolor)

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 676.

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. 766.

The leaves of young cotton (Gossypium hirsutum) plants abscise in response to water stress

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

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 217.

Inorganic carbon concentrating mechanisms: the C₄ photosynthetic carbon cycle

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 222.

Inorganic carbon-concentrating mechanisms: crassulacean acid metabolism (CAM)

4. Excess of water

4.1. Flooding and soil compaction cause O₂ deficiency for plant

4.2. Protective mechanisms of water plants

Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 777.

During episodes of anoxia, pyruvate produced by glycolysis is initially fermented to lactate

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