The UK is currently experiencing a heatwave. We all know the potential risks unusually high temperatures can pose to humans and animals but what about plants?
In all organisms high temperatures can alter cell properties. The phospholipid membranes surrounding the cell and internal organelles (nucleus, ER etc.) become more fluid (1). Not only can this make the membranes less stable, it can also make them more permeable and affect the ability of other molecules such as signalling proteins to interact with them. High temperatures also alter the rates of chemical reactions within the cell and can lead to unfolding or misfolding of proteins. Ultimately these changes can lead to cell death so are best avoided!
Unlike animals, plants cannot avoid the heat by moving to a cooler place so they rely on strategies that enable them to tolerate the high temperatures. An increase in membrane fluidity and/or unfolded proteins leads to the activation of heat shock responses. These include the alteration of membrane composition to reduce fluidity and the up-regulation of Heat Shock Proteins (HSPs), a family of chaperone proteins that assist protein folding and increase protein stability (1).
High temperatures can also affect the efficiency of photosynthesis (capture of light energy to fix carbon dioxide into high-energy carbon compounds). It can lead to the inactivation of proteins in the light harvesting complexes and reduce the efficiency of the fixation of carbon dioxide into glycerate-3-phosphate by the enzyme RuBisCO (1). RuBisCO activity is a rate-limiting step in photosynthesis and many plants that are adapted to live in hot climates use a different mechanism of photosynthesis (known as C4) that is able to maintain a higher rate of carbon fixation by RuBisCO at higher temperatures.
The ability of plants to be able to defend against pathogens can also be affected by high temperatures. A plant that is suffering from heat stress may be more vulnerable to pathogen infection and crop varieties can have resistance to a pathogen at a low temperature but be susceptible at higher temperatures (2,3,4). On the other hand there are some resistance genes that confer resistance to diseases only at higher temperatures. For example, wheat plants expressing the gene Yr36 are resistant to stripe rust (caused by the fungus Puccinia striiformis) when grown at 25-35 °C, but are susceptible when grown at lower temperatures (5).
With global temperatures on the rise, understanding how plants sense and respond to high temperatures and how it impacts on their responses to other stresses such as pathogen attack are important areas of research. Recently, scientists at the John Innes Centre have identified Arabidopsis thaliana mutants that are more resilient to climate in terms of disease resistance. Identifying the genes involved may enable the breeding of crop plants in the future that maintain disease resistance over a larger range of temperatures.
Something to think about next time you relax in the shade under a tree!
Image Credit: Photograph by Dako99 distributed by a CC BY-SA 3.0 licence.
- Wahid et al. (2007). Heat tolerance in plants: an overview. Environmental and Experimental Botany
- Sugiyama et al (2009). Effect of temperature on symptom expression and viral spread of Melon yellow spot virus in resistant cucumber accessions. Journal of General Plant Pathology.
- Navar et al. (2003). Temperature dependent brown rust resistance in wheat cv. PBW343. Plant Disease Research (Ludhiana).
- Roderick et al. (2000) Temperature-dependent resistance to crown rust fungus in perennial ryegrass, Lolium perenne. Plant Breeding.
- Fu et al. (2009) A kinase-START gene confers temperature-dependent resistance to wheat stripe rust. Science.
- Resistance gene found against Ug99 wheat stem rust pathogen (phys.org)
- Factors affecting photosynthesis (ellemedit1234.wordpress.com)