Constraints on floral water status of successively blossoming Mediterranean plants under natural conditions

The water relations of showy laminar floral tissues (petals and tepals) were studied in 20 Mediterranean plants successively blossoming under ambient conditions. The water potential and osmotic potential of floral tissues decline according to the succession of the median day of flowering of the selected plant species. The highest (least negative) value of floral water potential (–0.32 MPa), among the examined species, was measured in petals of Anemone coronaria in March, and the lowest value (–1.25 MPa) in petals of Coridothymus capitatus in June. Low values of water potential of floral tissues coincided with constraints in declining values of osmotic potential at the onset of the dry period in the Mediterranean region; this apparently resulted in a reduction of turgor of floral tissues of Mediterranean plants subjected to water shortage. The reduced osmotic potential was correlated with enhanced soluble sugar content of floral tissues, presumably contributing to the expansion and water status of flowers under water scarcity, by decreasing water requirements.