BIO3082 Lecture Notes - Lecture 6: Dissolved Load, Apoplast, Water Potential
Lecture 6 – Other Stresses
Salinisation
• Disproportionally affects Australia
o Concentrated in Western Australia and Murray-Darling Basin
• Due to high salt concentration, dry soils and high groundwater salinity
• Due to agricultural intensification
• Consequences:
o Reduces freshwater supply
o Decreases agricultural productivity
o Endangers native species
▪ Inhibits growth and survival of plants, microorganisms and
invertebrates
• Causes
o Land clearing → Water cycling becomes unbalanced → increased
ground water levels due to surface run off → saline ground water rises
and reaches surface → salt accumulation kills plants and facilitates soil
erosion
o Irrigation has similar effects – mild saline
o Salts being concentrated → evaporation and transpiration
• Salinity is soil is measured by electrical conductivity
• Plant salt injury – reduced growth
o Osmotic effects
▪ High NaCl concentrations → negative soil water potential
▪ Stomatal closure, decreased photosynthesis
o Ionic effects
▪ Na+ accumulation → direct toxicity effects
▪ Inactivate enzymes, inhibits photosynthesis → micronutrient
imbalances
o But some plants are highly salt tolerant
• Halotolerant plants have usual salt levels in leaves – reduces leaf salt
concentrations
o Filtration
▪ Plants regulate internal salt load through ultrafiltration at
transport barriers
▪ Salt accumulates at roots and is restricted from leaves
▪ E.g. coastal mangrove keeps leaf NaCl concentration at 9 mM
o Dilution
▪ Some plants increase water content to dilute intracellular salt
concentrations
▪ Linear relationship between chloride concentration and water
content in leaves
• Cellular Mechanisms excluse salt from cytosols
o Salinity stress activates a calcium importer and induces SOS stress
signal transuction pathway
o Cells upregulate sodium-proton antiporters: transport Na+ from
cytosol to vacuole and apoplast
o NaCl concentration in Sueada: 4x higher in vacuole than cytosol and
chloroplast
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