How to Improve Drought and Salinity Tolerance of Plants?

After years of experiments, scientists designed thale cress or Arabidopsis to behave like a succulent, to improve water-use efficiency, tolerate salinity and reduce the effects of drought. Tissue succulence engineering methods designed specifically for this small flowering plant can be used in other plants to improve drought and salt tolerance with the aim of applying this method to food and bioenergy crops.

"Water storage tissues are one of the most successful adaptations of plants, enabling them to survive prolonged drought. As global temperatures rise, this anatomical feature will become more important, thereby increasing the magnitude and duration of drought events in the 21st century," says John Cushman, a professor of Biochemistry and Molecular Biology at the University of Nevada and co-author of a new scientific paper on the plant tissue succulence published in the Plant Journal.

"These two adaptations complement each other," says Cushman of the University's College of Agriculture, Biotechnology & Natural Resources. "Our overall goal is to design CAM, but to do this effectively, we need to design a leaf anatomy that has cells that store malic acid accumulated in plants at night. The additional benefit is that these larger cells can also be used to store water to overcome drought and dilute salt and other ions absorbed by plants, making them more salt tolerant."

When a plant absorbs carbon dioxide, it absorbs it through the stomata on the leaves. They open stomata to allow carbon dioxide to enter and then fix it in sugars and all other compounds that support most of life on Earth. But when the stomata open, not only carbon dioxide enters, but also water vapor is emitted, and because plants cool down due to transpiration, they lose a lot of water."

The team of scientists at Cushman created transgenic Arabidopsis thaliana (A. thaliana), which has increased cell size, resulting in plants with more leaf thickness, more water storage capacity and fewer and less open stomatal pores, thus limiting leaf water loss due to gene overexpression, known by scientists as VvCEB1. This gene is involved in the cell expansion phase of berry development in wine grapes.

"Larger cells have larger vacuoles that store malic acid at night, which releases and fixes carbon sources of carbon dioxide through the so-called Rubiskozyme during the day behind the closed stomatal pores, thereby limiting photorespiration and water loss," Cushman said. "Moreover, the succulent tissue captures carbon dioxide released from decarboxylation of malate during the day and can therefore be repaired more efficiently by Rubisco."

One of the major benefits of VvCEB1 gene overexpression was the observed improvement in transient and integrated water use efficiency of whole plants, by 2.6- and 2.3-fold, respectively. Water use efficiency refers to the ratio of fixed carbon or biomass to plant transpiration or water loss. These improvements were related to leaf thickness and tissue succulence as well as lower stomatal pore density and reduced pore openings.

"We tried many candidate genes, but we only observed that the VvCEB1 gene had this dominant phenotype," Cushman said. "We usually investigate 10 to 30 independent transgenic lines and then breed them for 2 to 3 generations before detailed testing."

Arabidopsis is a powerful model for studying plant growth and developmental processes. It is a small weed-like plant with a short production time of approximately six weeks, and grows well under laboratory conditions and can produce large numbers of seeds.

Source: sciencedaily.com

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