Hexokinase: An Enzyme That Could Increase the Inherent Water Usage Efficiency of Field-grown Tobacco Plants

Researchers discovered that they could increase intrinsic water-use efficiency (iWUE) in field-grown tobacco plants without affecting photosynthetic rates or biomass output by overexpressing the sugar-sensing enzyme hexokinase.

Water use efficiency in agriculture

(Photo : JOEL SAGET/AFP via Getty Images)

According to a 2019 water study from the Food and Agriculture Organization (FAO) of the United Nations, water shortage is now one of the major problems restricting worldwide agricultural output, a condition that is further aggravated by global climate change, as per ScienceDaily.

To better adapt to water-scarce situations, experts from all over the world have been attempting to increase the water-use efficiency of crops.

Researchers from the University of Illinois, the Volcani Center (Agricultural Research Organization, Israel), and the University of Cambridge discovered that by overexpressing the sugar-sensing enzyme hexokinase in field-grown tobacco plants, they could increase intrinsic water-use efficiency (iWUE) without affecting photosynthetic rates or biomass production.

Their findings were recently published in the Journal of Experimental Botany.

Because it is very simple to deal with in the lab, greenhouse, and field, tobacco was chosen as a model crop.

Results in this crop may be observed much more quickly than in food crops, which require more effort and time to cultivate and change.

So, to see whether comparable effects could be demonstrated, tobacco was chosen as the first test crop.

The researchers can confidently replicate the advancements in food crops including cassava, cowpea, rice, and soybean after demonstrating success in the model crop.

According to field circumstances and a mild water restriction, this study shows that it is possible to produce plants that consume less water throughout the growing season without suffering a major yield hit.

This may help farmers use less irrigation and use less soil water during the growing season.

To absorb CO2 during photosynthesis, plants create microscopic holes in their leaves known as stomata.

However, water can also leave by transpiration when the pores are open. As a result, plants are forced to choose between losing too much water and absorbing CO2.

Liana Acevedo-Siaca, a postdoctoral researcher at Illinois who oversaw this work, explained that the guard cells that make up stomatal holes regulate the opening and closing of the pores.

Previous research has demonstrated that plants may change this trade-off by stimulating stomatal closure by genetic modification of signal components that cause stomatal movement, such as by overexpressing Arabidopsis Hexokinase 1 (AtHXK1) in the guard cells.

It has been demonstrated that guard-cell-targeted AtHXK1 expression can increase crops' WUE and resistance to salt stress and drought because hexokinase tells the pores there is enough sugar, preventing the need to fix additional CO2.

These earlier researches, however, only looked at crops produced in greenhouses or other controlled conditions.

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glucose and hexokinase

Through facilitated diffusion, which is facilitated by the glucose transporter (GLUT) protein family and permits monosaccharides to pass the cell membrane predominantly as a result of concentration gradients, glucose and other monosaccharides enter the cell, as per the National Library of Medicine.

Hexokinase enzymes phosphorylate the molecules as they enter the cell, thereby trapping the monosaccharide inside the cell since phosphorylated monosaccharides cannot pass through the GLUT.

Although sugars are the primary source of carbon and energy in cells, they may also function as signaling molecules that have an impact on the entire plant life cycle.

Because certain plant tissues may create sugars and send them to others, sugar signaling in plants is a very complicated process that involves components that can detect variations in sugar concentrations throughout various tissues, cell compartments, and developmental stages.

The effects of glucose (Glc) on plant regulation have received the greatest attention to date.

Hexokinase (HXK), which is presently acknowledged as a dual-function protein, was the first Glc sensor discovered in plants.

The expression of several photosynthetic genes can be suppressed by this enzyme in response to high internal Glc concentrations, in addition to its catalytic activity.

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