Studies on water transport through the sweet cherry fruit surface: V. Conductance for water uptake

Rain-induced cracking of sweet cherry (Prunus avium L.) fruit is thought to be related to water absorption through the fruit surface. Conductance for water uptake (g(tot.uptake)) through the fruit surface of 'Sam'sweet cherry was studied gravimetrically by monitoring water penetration from a donor solution of deionized water through segments of the outer pericarp, into a polyethyleneglycol (PEG) containing receiver solution. Segments consisting of cuticle plus five to eight cell layers of epidermal and hypodermal tissue were mounted in stainless steel diffusion cells. Conductance was calculated from flow rates of water across the segment and the difference in osmotic potential between donor and receiver solution. Flow rates were constant up to 12 hours and decreased thereafter. A log normal distribution of g(tot. uptake) was observed with a median of 0.97 x 10(-7) m.s(-1). Further, g(tot uptake) was not affected by storage duration (up to 71 days) of fruit used as a source of segments, thickness of segments (range 0.1 to 4.8 mm), or segment area exposed in the diffusion cell. Osmolality of the receiver solution in the range from 1140 to 3400 mmol.kg(-1) had no effect on g(tot uptake) (1.45 +/- 0.42 x 10(-7) m.s(-1)), but g(tot uptake) increased by 301 % (4.37 +/- 0.46 x 10(-7) m.s(-1)) at 300 mmol.kg(-1). g(tot uptake) was highest in the stylar sear region of the fruit (1.44 +/- 0.16 x 10(-7) m.s(-1)) followed by cheek (1.02 +/- 0.21 x 10(-7) m.s(-1)), suture (0.57 +/- 0.17 x 10(-7) m.s(-1)) and pedicel cavity regions (0.22 +/- 0.09 x 10(-7) m.s(-1)). Across regions, g(tot-uptake) was related positively to stomatal density. Extracting total cuticular wax by dipping fruit in chloroform/methanol increased g(tot uptake) from 1.18 +/- 0.23 x 10(-7) m.s(-1) to 2.58 +/- 0.41 X 10(-7) m.s(-1), but removing epicuticular wax by cellulose acetate stripping had no effect (1.59 +/- 0.28 x 10(-7) m.s(-1)). Water flux increased with increasing temperature (range 20 to 45 degreesC). Conductance differed between cultivars with 'Hedelfinger' sweet cherry having the highest g(tot. uptake) (2.81 +/- 0.26 x 10(-7) m.s(-1)), followed by 'Namare' (2.68 +/- 0.26 x 10(-7) m.s(-1)), 'Kordia' (0.96 +/- 0.14 x 10(-7) m.s(-1)), 'Sam' (0.87 +/- 0.15 X 10(-7) m.s(-1)), and 'Adriana' (0.33 +/- 0.02 x 10(-7) m.s(-1)). The diffusion cell system described herein may be useful in analyzing conductance in water uptake through the fruit surface of sweet cherry and its potential relevance for fruit cracking.