Heat stress is an unlikely topic for an article as we feel our way through the depths of winter. That said, we have had to deal with this issue in two of the past three seasons.
Steroids are commonly used in human medication and now it seems that they can also play a part in a plant’s response to excess heat.
While not a common problem in Ireland, we have seen incidences in recent years where some crops such as beans may have suffered more from heat stress than from moisture stress.
The past few decades have seen increased incidences of heat waves, with record high temperatures reported around the globe.
“Heat stress can negatively affect plants in their natural habitats and destabilise ecosystems, while also drastically reducing crop harvests, thereby threatening our food security,” says Professor Brigitte Poppenberger from the Technical University of Munich (TUM).
Heat stress protection
Plants, like other organisms, can be severely affected by high temperature heat stress, but they cannot move into the shade or get out of the heat for protection.
To help combat heat stress, Professor Poppenberger tells us that plants activate their heat shock response, a molecular pathway that is also used by human and animal cells to help protect them against stress.
Now the researchers at TUM have discovered that plant steroid hormones can promote this response in plants.
To help them survive short periods of heat stress, plants activate a molecular pathway called the heat-shock response. This helps to protect cells from the damage inflicted by proteotoxic stress, which can damage essential proteins. This type of stress can also result from exposure to certain toxins, UV light or soil salinity.
Professor Poppenberger explains that the heat-shock response protects cells in various ways, one of them being production of so-called heat-shock proteins. These serve as a type of molecular shield that protect other proteins by preventing misfolding of their structure.
In plants, hormones frequently act as chemical messengers and these have also been found to be involved in the heat-shock factors, along with other molecular players.
Among the hormones that are involved in this process in plants are brassinosteroids. These hormones primarily regulate plant growth and development and the researchers at TUM found that they also confer enhanced ability to increase heat stress resistance in plants.
They found that brassinosteroids help to regulate a specific transcription factor - a special protein which is responsible for switching certain sections of the DNA on or off.
This transcription factor, called BES1, can interact with heat shock factors, thus enabling genetic information to be targeted to increase the synthesis of heat shock proteins.
The TUM research found that when BES1 activity is increased, plants become more resistant to heat stress and vice versa. They also demonstrated that BES1 is activated by heat stress and that this activation is stimulated by brassinosteroids.
“While these results were found using the model plant Arabidopsis thaliana, they have potential for practical application in agriculture and horticulture,” according to Professor Poppenberger.
Some bio-stimulants contain brassinosteroids and these can now be assessed for their ability to increase heat stress resistance in plants.
Brassinosteroids are natural products that are already approved for use in organic farming.
Alternatively, plant breeders may begin to target BES1 production in plant varieties to make them more resistant to heat stress for warmer climates and thus provide improved yield stability in future heat waves.