The Earth is getting hotter as a result of climate change and high temperatures lead to unusual fluctuations, most notably prolonged, multi-seasonal droughts, which exacerbate the phenomenon of acute food insecurity in various regions around the world, due to their direct effects on crops.
With increasing periods of drought, plants face a major challenge because they depend on water to perform all their basic functions, including photosynthesis and growth. But when there is not enough water, plants are forced to adapt to survive. Plants have to be flexible to survive environmental changes, and the adaptive methods they deploy must often be as changeable as the shifts in climate and conditions to which they adapt.
Secret in the roots
The roots are one of the most important means used by plants to cope with drought. They produce a water-repellent polymer called suberin that blocks water from flowing up towards the leaves, where it would quickly evaporate. Without suberin, the resulting water loss would be like leaving the tap running.
In some plants, suberin is produced by endodermal cells that line the vessels inside the roots. But in others, like tomatoes, suberin is produced in exodermal cells that sit just below the skin of the root.
The role of exodermal suberin has long been unknown, but a new study by researchers at the University of California, published January 2 in Nature Plants, shows that it serves the same function as endodermal suberin, and that without it, tomato plants are less able to cope with water stress.
In the new study, the researchers tested exodermal suberin's role in drought tolerance by exposing tomato plants to a ten-day drought. They identifyed all of the genes that are actively used by root exodermal cells, and how are these genes affected by the hormones that control the plants’ response to drought.
After disabling these genes in tomato plants, the researchers found that these plants lost their ability to produce suberin and became more prone to drought. The plants also showed unstable response to drought, which indicates that suberin plays a key role in helping plants to adapt to the lack of water.
“Suberin plays an important role in plants’ resistance to drought. It helps prevent water loss by acting as a barrier between root cells and the surrounding environment, to maintain plants’ moisture, help them survive longer, and adapt to drought,” Siobhan Brady, lead author and professor in the University of California’s Department of Plant Biology, told Asharq Al-Awsat.
“Our study showed that tomato root cells have an external barrier that is resistant to drought, unlike other plants, and this discovery provides us with a better understanding of how tomato plants deal with drought,” she added. “Using this knowledge, we can develop new tomato varieties that are more drought-resistant, which is especially important as climate change increases.”
Brady hoped that these results will lead to the development of new technologies to improve tomato production in areas suffering from water shortages, saying the team is currently testing the ability of suberin to resist drought in the field, to try to make tomatoes more able to withstand drought.
Various techniques to preserve water
Research has shed light on the complex mechanisms behind many of the natural means plants use to adapt to drought, most notably reducing transpiration.
Transpiration is the process of losing water through the surfaces of leaves. Despite the importance of this process in regulating the temperature of plants and maintaining water balance, transpiration can be harmful to plants, especially in drought conditions.
During drought, plants reduce transpiration to control the loss of water through the leaves. Smaller leaves, fewer and smaller pores (stomata), and thicker cuticles (waxy layers) reduce evaporation. For example, the aloe vera plant has needle-like leaves that reduce its surface area, while it stores water in its fleshy, thick-skinned leaves to utilize this reserve for as long as possible in long drought periods.
In severe drought conditions, some plants, such as oaks, strategically drop their leaves to greatly reduce water loss.
There are also natural techniques to maximize water absorption through deep roots. Plants such as desert shrubs develop extensive and deep root systems that reach deep into the soil, tapping into hidden water reserves that shallow-rooted plants cannot access. As climate change causes floods and heavy rains, the area of lands vulnerable to severe drought is also expected to increase, according to the United Nations.
Since 2000, the cases and duration of droughts have increased by 29 percent, the agency reports. More than 2.3 billion people already face water stress, while most drought-related deaths have occurred in Africa.
Scientists can use their understanding of drought adaptation to improve the ability of plants to tolerate dry conditions, and this could lead to the development of more drought-resistant crops, as well as helping ensure the sustainability of food security in the future.
