Researchers from the University of Birmingham, Australian National University, Canberra, and James Cook University, Cairns, have discovered that certain plants, such as maize, sorghum, and proso millet, are able to survive stressful, dry conditions by controlling water loss through their leaves without relying on their usual mechanism of tiny pores known as ‘stomata’. This nonstomatal control of transpiration allows these C4 crops to maintain a beneficial microclimate for photosynthesis within their leaves, enabling them to absorb carbon dioxide and continue the growth process even in raised temperatures and increased atmospheric demand for water.
The study, published in PNAS, challenges traditional understanding of plant transpiration and photosynthesis under stressful and dry growing conditions by showing that nonstomatal control of transpiration limits water loss without compromising carbon gain. This revolutionary finding has significant implications for plant adaptation to climate change and agricultural practices in arid environments. By understanding this mechanism, new avenues for improving water-use efficiency in C4 crops can be explored, which are crucial for global food security.
The mechanism of nonstomatal control helps plants sustain photosynthesis by reducing water loss without significantly lowering intercellular CO2 levels for photosynthesis. This is essential for maintaining growth and ensuring that the crops continue to thrive, even when faced with stressful conditions. The study also suggests that nonstomatal control mechanisms may have evolved before the divergence of C3 and C4 photosynthetic pathways, indicating a shared evolutionary trait among different types of plants.
Photosynthesis is a vital process for plants as it allows them to use light and carbon dioxide to make sugars for growth through the enzyme Rubisco. While C3 plants rely solely on CO2 diffusion through their stomata for carbon gain, C4 plants have specialized leaf structures and enzymes that concentrate carbon dioxide around Rubisco, enhancing their photosynthetic performance and water-use efficiency. However, this benefit comes with a trade-off, as C4 plants are vulnerable to substantial photosynthesis reduction when the stomata close. Therefore, the nonstomatal mechanism plays a critical role in ensuring the success of these plants in controlling water loss while keeping their stomata open for carbon dioxide absorption.
The researchers found that C4 plants maintain reduced relative humidities in the substomatal cavity, down to 80% under vapour pressure deficit stress, which helps reduce water loss and emphasizes the importance of nonstomatal control in water-use efficiency. This alternative mechanism allows C4 plants to continue to grow and capture carbon dioxide, even when atmospheric water demand is high, challenging traditional assumptions about how these plants survive droughts. Understanding this unique mechanism can lead to new ways of improving water-use efficiency in C4 crops, which is crucial for global food security.
In conclusion, the discovery of nonstomatal control of transpiration in certain plants provides a new perspective on how these crops adapt to stressful and dry conditions. By challenging traditional understanding of plant transpiration and photosynthesis, this research opens up possibilities for improving water-use efficiency in C4 crops, which play a vital role in global food security. Understanding the mechanisms behind nonstomatal control can help researchers and farmers develop strategies to enhance crop resilience and productivity in changing environmental conditions brought about by climate change.
