title: Diurnal Regulation of Leaf Water Status in High- and Low-Mannitol Olive Cultivars.
abstract: The role of mannitol and malic acid in the regulation of diurnal leaf water relations was investigated in 'Biancolilla' (high-mannitol) and 'Cerasuola' (low-mannitol) olive trees. Photosynthetic photon flux density (PPFD), vapor pressure deficit (VPD), stomatal conductance (gs), transpiration rate (T), relative water content (RWC), mannitol and malic acid were measured in 'Biancolilla' and 'Cerasuola' leaves during a dry and hot day of summer in Sicily. In general, leaves of 'Biancolilla' trees exhibited greater mannitol content, higher gs and T, but lower RWC than leaves of 'Cerasuola' trees. Differences in gs and T between the two cultivars were evident mainly in mid to late morning. 'Biancolilla' leaves accumulated mannitol at midday and again late in the evening. Stomatal responses to VPD were RWC dependent, and limited somewhat T, only in 'Biancolilla'. Mannitol was directly related to RWC, and may play an osmotic role, in 'Biancolilla' leaves, whereas 'Cerasuola' leaves remained well hydrated by just transpiring less and regardless of mannitol. A day-time accumulation and night-time utilization of mannitol in 'Biancolilla' leaves is proposed as an efficient mechanism to regulate water status and growth.
authors.affiliation: Dipartmento Scienze Agrarie e Forestali, Università degli Studi di Palermo, Viale delle Scienze 11, Palermo 90128, Italy. riccardo.lobianco@unipa.it.
authors.forename: Riccardo Lo
authors.initials: RL
authors.lastname: Bianco
authors.affiliation: Dipartimento Scienze e Tecnologie Biologiche Chimiche e Farmaceutiche, Università degli Studi di Palermo, Via Archirafi 32, Palermo 90123, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Avellone
keywords: malate; polyol; relative water content; stomatal conductance; transpiration; vapor pressure deficit