Tomato plants may hold one of their best drought defenses in a daily rhythm. New research from the Hebrew University of Jerusalem suggests that when plants use water may matter as much as how much water they use.
The study found that strong-performing tomato lines opened their microscopic leaf pores early in the morning. That timing helped them capture sunlight for growth before heat and dry air drove heavier water loss.
Led by Dr. Sanbon Chaka Gosa and Prof. Menachem Moshelion from the Faculty of Agriculture, the work points to a new way to breed drought-resilient crops. As climate change brings hotter and drier conditions, that kind of timing could help protect future food supplies.
Tomato plants cannot move into shade or seek water when drought arrives. They must survive by managing the small openings on their leaves.
These openings are called stomata. They let carbon dioxide enter the plant for photosynthesis, the process plants use to turn sunlight into energy.
But stomata also let water escape through transpiration. Every time a plant opens these pores, it gains carbon dioxide but risks losing moisture.
That tradeoff shapes growth, fruit yield and drought recovery. A plant that closes too soon may save water but lose growth. A plant that stays open too long may dry out.
The new study suggests the best plants do not simply save water. They use it with careful timing.
The strongest tomato lines showed an early-morning surge in stomatal activity. They opened their pores when sunlight was already strong but before the air became too hot and dry.
Researchers describe this period as a physiological “golden hour.” During this window, plants can gain carbon for growth while avoiding the worst water loss of the day.
“Plants don’t simply save water during drought, they manage it strategically,” said Moshelion. “Understanding these dynamic patterns gives breeders entirely new traits to target when developing crops that can thrive under increasingly unpredictable climate conditions.”
That idea changes how drought tolerance is often viewed. The goal may not be finding plants that use the least water. It may be finding plants that use water at the right time.
Many traditional plant studies rely on single-point measurements. A researcher may measure one leaf at one time and compare results across plants.
But real fields change constantly. Light, heat, humidity and soil moisture shift throughout the day. Plants respond minute by minute.
To capture that movement, the Hebrew University team used continuous whole-plant monitoring. Their greenhouse system weighed each potted plant and tracked tiny changes in water use.
This allowed researchers to see daily patterns instead of snapshots. It also helped them compare how different tomato lines responded before, during and after drought.
“Our work shows that a plant’s daily rhythm matters,” said Gosa. “By measuring how plants respond continuously rather than at a single moment, we can identify resilient varieties much earlier and with far greater precision.”
The study used tomato introgression lines. These plants carry genetic segments from the wild tomato relative Solanum pennellii in a cultivated tomato background called M82.
Wild relatives can carry useful traits that cultivated crops may have lost. In this case, the lines offered a wide range of water-use and yield patterns.
The researchers combined years of field performance data with advanced greenhouse testing. Field trials compared tomato lines under well-watered and drought conditions.
The team selected six lines for deeper study, along with M82. These lines represented different levels of yield, biomass, drought tolerance and recovery.
One line, IL5-2, stood out. It performed better than M82 across field categories under both wet and dry conditions.
A surprising result emerged from the study. Plants that used more water under favorable conditions often recovered better after drought.
That finding goes against a simple assumption. It might seem that drought-tolerant plants should always conserve water.
But high-performing lines showed a more flexible strategy. They used water actively when it helped growth, then adjusted when conditions became stressful.
IL5-2 and IL11-4 had high transpiration before drought. They also recovered quickly after watering resumed.
This matters because crops must do more than survive. Farmers need plants that keep producing fruit after stress passes.
The researchers applied drought carefully. Instead of cutting water the same way for every plant, they used feedback-controlled deficit irrigation.
Each plant received 80% of the water it had used the previous day. This helped create a fairer comparison across fast- and slow-transpiring lines.
During drought, some high-water-use plants reached stress sooner. The researchers described this as a kind of transpiration “flip-flop.”
A plant that drinks more under good conditions may face limits earlier when water declines. But the best lines adjusted and recovered strongly.
This shows why drought resilience depends on timing, response speed and recovery, not one static trait.
The team also studied stomatal density and opening size on tomato leaves. They looked at both the upper and lower leaf surfaces.
High-performing plants often had more stomata on the underside of their leaves. That lower surface is called the abaxial side.
But anatomy alone could not predict drought resilience. A plant’s number of stomata did not fully explain its performance.
The real clue came from behavior through the day. Strong lines opened and closed stomata in patterns that matched changing conditions.
That finding could help breeders move beyond simple structural traits. They may need to measure how plants behave, not just what their leaves look like.
Breeding drought-resilient crops takes time. Field trials can be expensive, and drought conditions vary from season to season.
Continuous monitoring may help scientists identify promising varieties earlier. A plant’s daily water-use rhythm could become a useful screening trait.
This approach could shorten the path from discovery to breeding. It may help researchers remove weak candidates before large field trials.
The strategy may also work beyond tomatoes. Many crops depend on stomatal control to balance growth and water loss.
If similar “golden hour” patterns exist in other plants, breeders could use them to improve food crops for warmer climates.
The study offers a more human way to think about plants. They are not passive victims of drought. They manage risk throughout the day.
The best tomato lines did not avoid water use. They spent water when it mattered most and protected themselves when conditions became harsher.
That kind of strategy may prove valuable as farms face heat waves, dry spells and less predictable rainfall.
A drought-resilient crop may need strong roots, good genetics and efficient leaves. But it may also need a good clock.
In this study, the morning hours became a hidden window of opportunity. For future crops, that window could help turn scarce water into stronger harvests.
This research could help breeders develop crops that handle drought without losing as much yield. By focusing on daily water-use patterns, scientists may identify strong plants earlier and more accurately.
The findings also show that drought resilience is not just about conserving water. Productive plants may need to use water boldly during favorable morning conditions, then reduce loss later in the day. That timing could help crops keep growing under water stress.
For agriculture, the approach could support faster breeding programs. Continuous plant monitoring may help researchers screen tomato lines and other crops before expensive field trials. This could save time as climate change increases pressure on food systems.
For humanity, the benefit is food security. Drought threatens farms around the world, especially in regions with rising heat and uncertain rainfall. Crops that use water more intelligently could help protect harvests, farmers and communities.
These resources provide broader scientific and agricultural context for understanding how crops respond to water stress and how plant physiology may help protect food production.
The State of Food and Agriculture 2020: Overcoming water challenges in agriculture: Examines growing agricultural water scarcity and strategies for improving water management and resilience across food-production systems. (Food and Agriculture Organization of the United Nations, 2020)
Climate Change 2022: Impacts, Adaptation and Vulnerability: Assesses how increasing heat, drought and water scarcity threaten agriculture and describes adaptation options for food systems worldwide. (Intergovernmental Panel on Climate Change, 2022)
Water for Sustainable Food and Agriculture: Explores how agriculture can increase productivity while using limited freshwater more efficiently under growing environmental pressure. (Food and Agriculture Organization of the United Nations, 2017)
Research findings are available online in the journal Plant Science.
The original story “Tomato study finds a ‘Golden Hour’ that could help crops survive drought” is published in The Brighter Side of News.
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