A Calcutta-born scientist is part of a research team that has discovered a hitherto unknown mechanism that plants utilise to carry out water and gaseous exchanges. The finding may transform the long-held understanding of how plants exchange water and gases, and is considered critical in this era of the Climatocene.
Sabyasachi Sen— a doctoral research scholar who did his schooling from Calcutta’s La Martiniere for Boys and BTech in mechanical engineering from IIT Kharagpur — was part of the research team along with other scientists from Cornell University, Harvard University, University of Illinois Urbana-Champaign in the US and Cambridge University in the UK. The discovery, published in Proceedings of the National Academy of Sciences or PNAS last November, has been based on studies of several plant species but the most robust evidence came from maize.
“Cornell researchers have discovered a previously unknown way plants regulate water that is so fundamental it may change plant biology textbooks — and open the door to breeding more drought-tolerant crops,” reads a November 20 communication from Cornell University. It describes for the first time how water regulation also occurs under the leaf’s surface, via the membranes of photosynthesising cells. The result was made possible thanks to AquaDust, a Cornell-developed nanoscale sensor that measures water status inside leaves.
Says Sen, who has been pursuing the research since 2020, “Leaves exchange water and carbon dioxide with the atmosphere, shaping both the water and carbon cycles that sustain life and, for decades, scientists believed that this delicate exchange was controlled solely by stomata.” Stomata are the microscopic pores on the surface of leaves that open and close to fulfil the plant’s need to take in carbon dioxide for photosynthesis.
“Using a new fluorescent technique developed at Cornell University, we peered inside living leaves to observe in real time how water moves through leaf tissues. What we found surprised us — the living cells within the leaf can dramatically reduce their internal conductance to water, effectively tightening the plant’s internal plumbing, without reducing the conductance to the carbon dioxide,” the researcher tells The Telegraph.
“The study is pathbreaking as it reveals a new layer of internal control over water loss in leaves. It may also help in understanding why C4 plants like sorghum and maize show high photosynthetic performance and water use efficiency at higher temperatures,” says Anshuman Das, an agroecologist with Welthungerhilfe, a Germany-based non-profit that fights global hunger and poverty. “This improved understanding could help scientists identify and develop crops better suited to water-scarce and hotter regions like in India,” he continues. C4 is one of three discovered photosynthetic pathways that plants use for carbon fixing.
“The 21st century confronts agriculture with an important constraint: producing more food with less water in an era of intensifying drought catered by rising global warming. Crop production consumes nearly 70 per cent of global freshwater withdrawals, meaning that even modest gains in water conservation — as possible through this secondary method — can yield significant benefits for food security, ecosystem resilience and long-term sustainability,” Sen says.
Through photosynthesis, vegetation acts as planetary regulators but this regulation comes at a cost. To assimilate carbon dioxide, plants must open stomata through which water is unavoidably lost. This fundamental trade-off between carbon gain and water loss forces plants to balance productivity against dehydration. Open stomata enable growth but accelerate water loss. Closed stomata conserve water but suppress carbon assimilation.
Sen explains how plants counter this uneasy trade-off as highlighted by the discovery. He says, “Our discovery of non-stomatal control of water loss fundamentally alters this paradigm. By decoupling water conservation from carbon assimilation, this mechanism enables plants to retain more water in soils and landscapes without sacrificing photosynthetic performance.”
Abraham D. Stroock is a professor at the Smith School of Chemical and Biomolecular Engineering in Cornell Engineering, a co-author of the paper and Sen’s guide. He says, “What we’ve discovered occurs within the last 100 microns of the long path that water follows during transpiration from the root to the site where it evaporates inside the leaves.”
“In other words, we uncovered a previously unknown mechanism that improves how efficiently plants use water, a vital trait as the world faces growing drought and water scarcity,” says Sen.
The discovery stands crucial in context to its impact on global environment and climate change.
According to Sen and other members of the research team, the finding can be seen as a game-changer in watershed sustainability, climate regulation and enhancing resilience of terrestrial ecosystems, particularly the agriculture sector within dry areas. “We have found that this phenomenon is more pronounced in water-deficient areas; hence it is clearly a climate adaptation,” says the scientist.
A quickly warming India, where nearly two-thirds of the 1.4 billion population depend on agriculture and allied activities, can be a major beneficiary of the research findings.
Anupam Pal, an agriculture expert and retired state government scientist, agrees that the discovery has brought a new insight and may be useful for promoting crops in India’s dry weather, but points out that the country already has several plants adapted to dry regions. These plants may already have the climate adaptation in place.