How plants survive through heat
WHAT happens to a plant when the thermometer tops 40 degrees Celsius? As the temperature rises, heat may damage labile macromolecular complexes and impair the vital biological functions of plants.
Photosynthesis is one of the most remarkable biochemical processes on earth and allows plants to use sunlight to make food from water and carbon dioxide.
But at temperatures above 40 degrees Celsius, the enzymes that carry out photosynthesis lose their shape and functionality.
A garden or farm that provides optimum light and water but gets too hot will be less vigorous. Tomatoes, for example, will drop blossoms and not set fruit if temperatures are too high.
Even plants that endure high heat can be stunted, weakened and attract pests and diseases, even if water is available.
Plants do have natural systems that respond to heat problems. Some plants are better at this than others.
Plants can cool themselves by pumping water out through the leaves for a kind of swamp cooler effect. They can also make “heat-shock” proteins which reduce problems from overheating.
Plants have a heat shock response (HSR), which is activated via fluidity changes in the plasma membrane and heat-responsive cyclic nucleotide-gated ion channels (CNGCs), which use Ca2+ and reactive oxygen species (ROS) as messengers to mediate a signaling pathway, leading to the upregulation of heat-induced mRNA in minutes, and to the accumulation of protective heat shock proteins (HSPs) and metabolites in hours.
Unfortunately, all these strategies do take resources away from a plant’s other needs like growth, flowering and fruiting.
What happens to plants in high temperatures?
Scientists at Yale University and Tao Chen Huazhong Agricultural University in China say they have discovered the precise way in which heat causes plant defences to fail.
The research team experimented with a plant called thale cress, a member of the mustard family, which is commonly used in scientific lab tests.
The scientists studied a plant defence hormone known as salicylic acid.
When plants are threatened by disease or pests, the levels of salicylic acid increase by up to seven times. This boosts the plant’s immune system and helps fend off the attack.
At particularly high temperatures, however, plants are unable to increase their salicylic acid levels leaving them defenceless in the face of pathogens or insects.
The scientists found this to be the case even during short periods of intense heat.
Mitigating extreme heat
Whether in the presence or absence of adequate soil moisture in the soil profile, heat stress can be an important risk and/ or limitation to plant growth and development.
While some crops are more susceptible to heat stress during critical growth stages (e.g pollination for maize and flowering stage for soybean), both plants are susceptible to extreme heat and water stress during early vegetative stages.
Therefore monitoring soil moisture during heat wave periods is critical. Maintaining adequate moisture in the soil profile is crucial to reducing the impact of heat stress on crops.
Research shows that in reduced or no-till fields, soil temperatures in the surface soil layers tend to be lower than in disk-tilled fields. Reducing soil temperature during heat waves can greatly help to mitigate the impact of heat stress on plants.
Additional residue on the soil surface in reduced and no-till fields can also minimize the heat exchange between the soil and surrounding microclimate. This reduces soil temperature. Reducing soil temperature is beneficial for enhancing root growth and water and nutrient uptake during heat wave periods.− www.pressbanner.com