Guard cell photorespiration controls stomata behavior and development

Photorespiration is often seen as a burden because it is diminishing photosynthetic efficiency. However, it is essential for safeguarding the Calvin–Benson-Bassham cycle from inhibitory byproducts of Rubisco oxygenation and highly intertwined with overall plant primary metabolism. Here we show that targeted manipulation of the entry enzyme 2-phosphoglycolate (2-PG) phosphatase (PGLP1) in Arabidopsis guard cells consistently influences growth, photosynthesis, carbohydrate allocation, and stomatal movement. Altered PGLP1 expression triggered guard cell-specific starch and H ₂ O ₂ accumulation patterns under photorespiratory conditions and affects stomata size, a response replicated by 2-PG feeding to Arabidopsis wildtype. These results reveal that efficient photorespiratory metabolism is essential for guard cell function and critical for acclimation to external CO ₂ /O ₂ ratios. By uncovering a direct metabolic link between photorespiration and stomatal behavior, our work highlights an unexpected role of this ancient pathway in shaping gas exchange and photosynthesis and opens a new avenue in optimizing plant yield and resilience.