Seasonal pattern of mannitol and malate accumulation in leaves of two manna ash species (Fraxinus ornus L. and F. angustifolia Vahl) growing in Sicily

ABSTRACT

The content of mannitol and malate was assayed enzimatically during spring, summer and autumn, in leaves of two species of ash, Fraxinus ornus L. and Fraxinus angustifolia Vahl, traditionally cultivated in Sicily for the extraction of manna. Both species contain high levels of mannitol and show, on a dry weight basis, a 65–80% increase in the summer content of this polyol. The malate content differs in the two species: in F. ornus it shows a summer increase, but it is relatively low (65–115 µmol g^-1 DW), while in F. angustifolia it is higher (275–318 µmol g^-1 DW), but remains more or less constant throughout the year. The results suggest that in these species, under the local field conditions, mannitol has a more relevant role than malate in the response to summer drought.

KEY WORDS:

• Fraxinus
• malate
• manna ash
• mannitol
• seasonal variation