Co-occurring heat and drought stresses challenge crop performance. Stomata open to promote evaporative cooling during heat stress, but close to retain water during drought stress, which resulted in complex stomatal regulation under combined heat and drought. We aimed to investigate stomatal regulation in leaves and flowers of perennial, indeterminate cultivars of tomatoes subjected to individual and combined heat and drought stress followed by a recovery period, measuring morphological, physiological, and biochemical factors involved in stomatal regulation. Under stress, stomata of leaves were predominantly affected by drought, with lower stomatal density and stomatal closing, resulting in significantly decreased photosynthesis and higher leaf temperature. Conversely, stomata in sepals seemed affected mainly by heat during stress. The differential patterns in stomatal regulation in leaves and flowers persisted into the recovery phase as contrasting patterns in stomatal density. We show that flower transpiration is regulated by temperature, but leaf transpiration is regulated by soil water availability during stress. Organ-specific patterns of stomatal development and abscisic acid metabolism mediated this phenomenon. Our results throw light on the dual role of stomata in heat and drought tolerance of vegetative and generative organs, and demonstrate the importance of considering flower surfaces in the phenotyping of stomatal reactions to stress.

Centre of the Region Haná for Biotechnological and Agricultural Research Department of Genetic Resources for Vegetables Medicinal and Special Plants Crop Research Institute Šlechtitelů 29 78371 Olomouc Czech Republic

College of Horticulture Nanjing Agricultural University Nanjing 210095 China

Czech Advanced Technology and Research Institute Palacky University Šlechtitelů 27 78371 Olomouc Czech Republic

Department of Food Science Plant Food and Climate Aarhus University Agro Food Park 48 DK 8200 Aarhus N Denmark

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