Besides arable land, the factor that most hinders agricultural production in this increasingly dry region and increasingly hot world is the lack of clean water.
Now, scientists at Tel Aviv University (TAU) have succeeded in cultivating and characterizing tomato varieties with higher efficiency using irrigation water, and without compromising the yield. The researchers, using CRISPR genetic editing technology that allows scientists to quickly create cell and animal models, were able to grow tomatoes that absorbed less water while preserving the yield, quality, and taste.
The researchers explained that in light of global warming and the diminishing of freshwater resources, there is a growing demand for crops that consume less water without compromising the yield. Naturally, at the same time, because crops rely on water to grow and develop, it is particularly challenging to identify suitable plant varieties.
In a process called transpiration, plants evaporate water from their leaves. Concurrently, carbon dioxide enters the leaves and is assimilated into sugar by photosynthesis, which also takes place in the leaves. These two processes – transpiration and carbon dioxide uptake – occur simultaneously through special openings in the surface of the leaves called the stomata, that can open and close, serving as a mechanism through which plants regulate their water status.
The research was conducted in the labs of Prof. Shaul Yalovsky and Dr. Nir Sade and was led by a team of researchers from the School of Plant Sciences and Food Security at TAU’s Wise Faculty of Life Sciences.
The team included Dr. Mallikarjuna Rao Puli, a former postdoctoral fellow supervised by Yalovsky, and Purity Muchoki, a doctoral student jointly supervised by Yalovsky and Sade. Other students and postdoctoral fellows from the School of Plant Sciences and Food Security advanced the study as well. Researchers from Ben-Gurion University (BGU) of the Negev in Beersheba and from the University of Oregon also contributed to the research.
The researchers highlighted that under drought conditions, plants respond by closing their stomata, thereby reducing water loss by transpiration. The problem is that due to the inextricable coupling between the transpiration of the water and the uptake of carbon dioxide, the closing of the stomata leads to a reduction in the uptake of carbon dioxide by the plant. This decrease in carbon dioxide uptake leads to a drop in the production of sugar by the process of photosynthesis. Since plants rely on the sugar generated in this process as a vital energy source, a reduction in this process harms plant growth.
In crop plants, the decline in photosynthetic sugar production presents itself as a decline in both the quantity and quality of the harvest. In tomatoes, for example, the damage to the crop is reflected in a decrease in the number of fruits, their weight, and the amount of sugar in each fruit. Fruits with lower sugar content are less tasty and less nutritious.
In the present study, published in the renowned journal PLOS under the title “Null mutants of a tomato Rho of plants exhibit enhanced water use efficiency without a penalty to yield,” the team wrote: “we discovered that eliminating ROP9 by the CRISPR technology cause a partial closure of the stomata.
“This effect is particularly pronounced during midday when the rate of water loss from the plants in the transpiration process is at its highest. Conversely, in the morning and afternoon, when the transpiration rate was lower, there was no significant difference in the rate of water loss between the control plants and ROP9-modified plants.
“Because the stomata remained open in the morning and afternoon, the plants were able to uptake enough carbon dioxide, preventing any decline in sugar production by photosynthesis even during the afternoon hours, when the stomata were more closed in the ROP9-modified plants.”
To assess the impact of the impaired ROP9 on the crop, the researchers conducted an extensive field experiment involving hundreds of plants. The results revealed that although the ROP9-modified plants lose less water during the transpiration process, there is no adverse effect on photosynthesis, crop quantity, or quality (the amount of sugar in the fruits).
The study also identified a new and unexpected mechanism for regulating the opening and closing of the stomata that is related to the level of oxidizing substances known as reactive oxygen species in the stomata. This discovery holds significant implications for basic scientific knowledge as well, said Yalovsky.
Sade concluded by stating that “there is great similarity between the ROP9 in tomatoes and ROP proteins found in other crop plants such as pepper, eggplant, and wheat, so our discoveries could form the basis for the development of additional crop plants with enhanced water use efficiency, and for a deeper understanding of the mechanisms behind stomatal opening and closing.”