ORIGINAL ARTICLE Moritz Knoche á Stefanie Peschel á Matthias Hinz Martin J. Bukovac Studies on water transport through the sweet cherry fruit surface: II. Conductance of the cuticle in relation to fruit development Received: 23 November 2000 / Accepted: 14 February 2001 / Published online: 17 May 2001 Ó Springer-Verlag 2001 Abstract Water conductance of the cuticular membrane CM) of sweet cherry Prunus avium L. cv. Sam) fruit during stages II and III 31±78 days after full bloom, DAFB) was investigated by gravimetrically monitoring water loss through segments of the exocarp. Segments were mounted in stainless-steel diusion cells, ®lled with 0.5 ml of deionized water and incubated for 8 h at 252 °C over dry silica. Conductance was calculated by dividing the amount of water transpired per unit surface area and time by the dierence in water vapor concen- tration across the segment 23.07 g m ±3 at 25 °C). Fruit mass and fruit surface area increased 4.9- and 2.8-fold between 31 and 78 DAFB, respectively. However, CM mass per unit area decreased from 3.9 to 1.5 g m ±2 , and percentage of total wax content remained constant at about 31%. Stomatal density decreased from 0.8 to 0.2 mm ±2 31±78 DAFB). Total conductance of the CM on the fruit cheek g tot. ) remained constant during stage II of development approx. 1.38´10 ±4 ms ±1 from 31 to 37 DAFB), increased to 1.73´10 ±4 ms ±1 during early stage III of fruit growth 43±64 DAFB) then de- creased to 0.95´10 ±4 ms ±1 at maturity 78 DAFB). Partitioning g tot. into cuticular g cut. ) and stomatal con- ductance g sto. ) revealed that the relative contribution of g cut. to g tot. increased linearly from 30% to 87% of g tot. between 31 and 78 DAFB, respectively. On a whole-fruit basis, g tot. and g cut. consistently increased up to 64 DAFB, and decreased thereafter. A signi®cant negative linear relationship was obtained between g cut. and CM thickness, but not between the permeability coecient p) and CM thickness. Further, p was positively related to strain rate, suggesting that strain associated with expansion of the fruit surface increased p. Keywords Cracking cherry fruit) á Cuticle á Prunus fruit) á Stoma á Transpiration á Strain á Water permeability Abbreviations A fruit : fruit surface area á CM: cuticular membrane á DC: driving force for diusion á DAFB: days after full bloom á d sto. : number of stomata per unit area á F: ¯ow rate of water per unit time á g cut. : con- ductance of CM between stomata á g sto. : stomatal con- ductance á g' sto. : stomatal conductance at d sto. =1 mm )2 á g tot. : total conductance á J: ¯ux of water per unit area and time á p: permeability coecient of CM of unit thickness á R: fruit surface area expansion rate á S: strain rate Introduction The cuticular membrane CM) covers all above-ground organs in terrestrial plants and serves as the primary barrier to transport across the plant surface Franke 1967). Signi®cant progress has been made in the last two decades in analysing and understanding transport characteristics of the CM for recent reviews, see SchoÈnherr and Riederer 1989; Bukovac and Petracek 1993; Kerstiens 1996; Baur 1998). Most of ourunder- standing is based on studies using well-developed CMs isolated from astomatous surfaces of fruit and fully ex- panded leaves. Relatively little information has been generated using delicate or stomatous CMs isolated from mature fruit, and limited dataare available on transport characteristics and CM properties of devel- oping fruit. While many characteristics such as composition, structure and wettability etc. are common to CMs of both leaves and fruit, there are distinct dierences. First, stomata,if present, occur in signi®cantly lower densities and are often nonfunctional on fruit compared with the Planta 2001) 213: 927±936 DOI 10.1007/s004250100568 M. Knoche &) á S. Peschel á M. Hinz Institut fuÈr Acker- und P¯anzenbau, Martin-Luther-UniversitaÈt Halle-Wittenberg, 06099 Halle Saale), Germany E-mail: knoche@landw.uni-halle.de Fax: +49-345-5527543 M.J. Bukovac Department of Horticulture, Michigan State University, East Lansing, MI 48823, USA