For plants, periods of drought and intense sunlight often mean excessive water loss. To control the exchange of air and water vapor, plant leaves have microscopic pores on their surface that act like vents. The plant hormone abscisic acid (ABA) is mainly responsible for closing these pores. To activate the guard cells, the cysteine synthase complex in the chloroplasts, which consists of two enzymes, evaluates a number of signals. Among these are the sulfate nutrient signal and a small protein molecule that are both transported from the roots into the shoots when the soil dries up. The researchers at Heidelberg University also discovered a particular plant hormone induced by strong light intensity.

“When the cysteine synthase complex in the chloroplasts is activated by one of these stress signals, it stimulates ABA biosynthesis in the guard cells and ensures that the pores on the leaves close. In this way, the plant conserves water,” explain Prof. Dr Rüdiger Hell and Dr Markus Wirtz from the “Molecular Biology of Plants” research group at the COS. “Our results show that chloroplast metabolism not only provides building blocks through photosynthesis but also actively responds to stress signals, thereby fine-tuning plant responses to environmental conditions like drought.” Based on these findings, the researchers were able to generate an Arabidopsis plant – a molecular biology model organism of the Brassicaceae family – that withstands soil dehydration more effectively while maintaining growth. For the researchers, this is an approach to developing new strategies to improve crop resilience in the face of climate change.

The research was carried out in cooperation with partners at Nanjing Agricultural University (China). The German Research Foundation funded the research. The results were published in the journal “Nature Communications”.