Exogenous putrescine enhances fruit set and yield in tomato under drought through improved water status and antioxidant defense

Tomatoes are a global favorite, a staple in kitchens from Mumbai to Munich, prized for their vibrant color and nutritional value. Yet, for the plants that produce them, life is often a precarious balancing act. When water becomes scarce, a tomato plant does not simply wilt; it undergoes a cascade of internal failures. The lack of water triggers a buildup of harmful molecules within the cells, essentially causing the plant to rust from the inside out. This oxidative damage tears apart cell membranes and disrupts the delicate machinery needed to turn sunlight into food. As the plant struggles to survive, it often sacrifices its future, dropping flowers and failing to set fruit, leaving farmers with empty vines. For decades, scientists have searched for ways to help crops withstand these dry spells, looking for substances that could act as a shield, stabilizing the plant's internal chemistry when the environment turns hostile.

In a recent study, researchers explored a specific solution: a natural compound called putrescine. Found naturally in all living things, putrescine is a small molecule that helps cells maintain their structure and manage stress. The scientists wondered if spraying this compound onto tomato plants just as they began to flower could help them survive a drought. To test this, they grew tomato plants in a controlled greenhouse environment. They selected a specific variety known as 'Kashi Anupam' and allowed them to grow until they reached the flowering stage, a critical moment when the plant decides whether to keep its flowers or drop them. At this point, the researchers subjected the plants to a severe water shortage, reducing the moisture in the soil to a level that would normally cause significant damage.

The experiment was designed to see if different amounts of putrescine could reverse the damage. The team sprayed the leaves of the drought-stricken plants with solutions containing varying concentrations of the compound, ranging from a very small amount to a much higher dose. They also kept a group of plants under normal watering conditions as a baseline, and another group that received no spray at all to see how bad the drought would get without help. Over the course of six days, the researchers watched closely, measuring everything from how tall the plants grew to how many fruits they managed to produce. They also dug deep into the plant's biology, checking the health of the leaves, the amount of water held inside the cells, and the activity of the plant's internal defense systems.

The results were striking. The plants that suffered from drought without any treatment suffered greatly. They grew shorter, lost a significant number of leaves, and their ability to hold water dropped sharply. Most critically, their reproductive success collapsed; the number of flowers that turned into fruit plummeted, and the total harvest was reduced by more than three-quarters compared to healthy, well-watered plants. The cells in these stressed plants were leaking, their membranes damaged by the toxic buildup of harmful molecules. However, the plants treated with putrescine told a different story. The spray acted as a powerful buffer against the stress. The plants that received the highest dose of the compound, ten millimoles per liter, looked and performed much closer to the healthy, well-watered plants than to the untreated, drought-stricken ones.

The treated plants held onto their water much better, keeping their leaves turgid and green when others were wilting. Inside their cells, the damage was far less severe. The spray helped the plants maintain the integrity of their cell membranes, preventing the leakage that signals cellular death. It also boosted the plant's natural defense mechanisms. The researchers found that the treated plants produced higher levels of protective enzymes, which act like a cleanup crew, neutralizing the harmful molecules that accumulate during stress. This internal cleanup was so effective that the plants could continue to photosynthesize and grow, even while the soil around them was dry.

Perhaps the most significant finding was the impact on the harvest. While the untreated drought plants produced very few fruits, the plants treated with the highest concentration of putrescine managed to set nearly twice as many fruits. The number of tomatoes per plant increased dramatically, and the fruits themselves were heavier. In terms of total yield, the treated plants produced nearly three times as much fruit as the untreated, drought-stressed plants. The spray essentially allowed the plant to ignore the signal to give up, keeping its reproductive processes running despite the lack of water. The study suggests that this effect is dose-dependent, meaning that higher concentrations of the spray generally led to better results, with the ten-millimole dose providing the most robust protection.

The researchers also looked at the genetic level to understand how this was happening. They found that the spray did not just passively protect the plant; it actively turned on the genes responsible for making those protective enzymes. The plant's internal instructions were rewritten to prioritize defense, ensuring that the machinery needed to fight off stress was produced in large quantities. This suggests that putrescine works by communicating with the plant's genetic code, telling it to switch on its survival mode. The study indicates that this approach is particularly effective when applied at the flowering stage, a time when the plant is most vulnerable and most likely to abort its fruit.

This work offers a promising glimpse into how agriculture might adapt to a drier future. It demonstrates that a simple, naturally occurring compound can be used to bolster a crop's resilience, turning a failing plant into a productive one even under severe water stress. While the study was conducted in a controlled greenhouse setting, the findings point toward a practical method for farmers to protect their tomato crops. By spraying the plants with the right amount of putrescine at the right time, it may be possible to secure a harvest that would otherwise be lost to drought. The research confirms that with the right chemical support, tomato plants can maintain their water balance, protect their cells, and continue to produce food even when the rain does not come.