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In hot, dry weather, plants sacrifice their leaves to cool and protect flowers, which contain their sexual organs. The strategy could be harnessed to defend crop yields against climate change.

Plants lose nearly all the water they absorb through evaporation via pores known as stomata. This process, known as transpiration, cools the plant and helps them suck up more nutrient-filled water from the ground, like drinking through a straw.

When the weather is hot, the stomata open to release water and heat. But when water is scarce, stomata stay closed, preserving moisture but raising the temperature. The combination of heat and drought can disrupt complex reproductive processes and devastate crop yields.

at the University of Missouri in Columbia and his colleagues studied soya bean plants (Glycine max) grown under artificial conditions. When the plants began to flower, some of them were subjected to excess heat, drought, or a combination of both, while others grew in ideal conditions. After 10 days, the team measured inner flower and leaf temperatures, whether stomata were open, and transpiration.

Plants facing heat and drought were hotter and drier than all other groups. They also developed higher densities of stomata in the flowers and leaves.聽 In their leaves, these plants closed their stomata and transpiration levels fell. Yet surprisingly to the researchers, they opened stomata in the flowers, and transpiration remained high. This suggests that the plants prioritised where cooling was taking place.

By repeating the experiment and preventing transpiration, the researchers found the behaviour cooled the inner flower by between 2 and 3掳C. They also repeated the experiment with tobacco plants (Nicotiana tabacum) and found a similar pattern.

鈥淩eproduction is by far the most temperature-sensitive process,鈥� says at Michigan State University in East Lansing. 鈥淭he excess heating of the leaves may be tolerated while the cooling of the reproductive organs could be critical for maintaining yield.鈥�

The strategy is probably most useful in plants that fertilise when the flower is closed. But other plants, particularly those in ecosystems facing droughts and heatwaves, may be using it too, says Mittler.

Manipulating crop plants to develop more or larger stomata in the flowers, or to keep them open for longer, could bolster crop yields, says Mittler. 鈥淲e have a grasp of what鈥檚 required to cool the flower. Now we can manipulate it, to try to improve on nature,鈥� he says.

Reference: BioRxiv,

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