Discovery on the road to better drought resistance across many crops
In this era of unprecedented risk of drought around the globe, the importance of making breakthroughs towards breeding much more drought-resistant crops has never been greater.
During hot days when their survival is potentially threatened, plants close tiny holes in their leaves (stomata) to prevent excessive water loss. However, this also puts a stop to photosynthesis (growth) because carbon dioxide (needed for photosynthesis) can no longer enter the leaves. Plant scientists have therefore been trying for a long time to determine if there is a way for plants to maintain CO2 uptake (and therefore continue to grow and produce higher yields at the end of the season) while water loss is prevented.
A huge discovery on this front as made not long ago by scientists from the Australian National University (ANU) and James Cook University (JCU), with their work published in the journal Nature Plants. They made the dream finding – a mechanism that exists in some plants which allows them to limit their water loss with little effect on CO2 intake.
Study leader Dr Suan Chin Wong from (ANU) and co-author Dr Diego Marquez (now a Research Fellow at the Busch Lab at University of Birmingham in the UK), believe that eventually, this water-preserving mechanism can be used in breeding much more water-efficient crops.
But first, they and their colleagues must better understand the mechanism.
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Inside the leaf
Marquez explains that the team is now working on three areas of research related to ‘non-stomatal control’ of transpiration in C3 plants, a plant group that includes most crops. One is the quest to understand how common the mechanism is among different plants groups and across what environments (ecological scale). Another is investigation of the cellular structures involved in the mechanism and the other is the internal plant signalling that controls the mechanism.
Dr Nicole Pontarin at ANU is examining the role of cellular structures, in collaboration with Dr Lucas Cernusac at JCU, who is also researching the ecological scale of the phenomenon. Marquez explains that “we know that the mechanism has to take place in the cell membrane but haven’t singled out the structure responsible for it. We still prioritise aquaporins as the most likely structure responsible.” Aquaporins are a family of small, integral membrane proteins that are found in animal and plant cells, consisting of helical segments, a narrow pore and others.
Process of transpiration
To explain a little more of what they’ve discovered about the mechanism, Marquez first reminds us that the process of transpiration is the movement of water from the soil drawn through the roots, upwards to the individual leaves and evaporating through the stomata out to the environment. Within the leaf, this water travels through the mesophyll (the cellular structure where photosynthesis occurs) with some water and CO2 being used in the photosynthesis process. Water that’s not used evaporates through the stomata. CO2 moves in the opposite direction, entering the stomata and moving into the mesophyll.
However, in the mechanism that Wong, Marquez and their colleagues found, water restriction somehow happens before water reaches the stomata. The ‘water exit path’ does not affect ‘the CO2 entry path’ if you will, and thus the plant can restrict water loss without closing the stomata (and without therefore restricting carbon gain and ceasing growth for the day).
Marquez says the reasons why the mechanism that restricts water loss but does not affect CO2 uptake will become clearer when the structures are responsible are clearly identified and investigated.
Identify the genes
And when the team can single out the structures and signals that allow the mechanism to function, they will then be able to take the next big step – to identify the genes involved in the expression of the trait.
“We think exploiting this mechanism in crop development may be possible,” says Marquez, adding that “it is in our minds to seek opportunities…either through variety selection or GMOs. However, more research and investment, public or private, are needed to pursue those ambitious objectives.”
As this mechanism research continues, Marquez has been working on whether non-stomatal control of transpiration occurs in C4 plant species of agricultural interest, and hopes to publish results in the next few months. He is also applying for funding to research focusing on the signalling and environmental triggers that control the phenomenon of non-stomatal transpiration control.
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