Susceptibility of sweet cherry (Prunus avium L.) fruit to rain cracking increases toward maturity and is
thought to be related to increases in both tissue pressure (Yfruit
P ) and cell pressure (Ycell
P ). Furthermore, at a given
water potential (Yfruit ), one might expect the increase in Yfruit
P and theYcell
P to balance the decrease in osmotic potential
(Yfruit
P ). The objectives of our study were to quantify Yfruit
P and Ycell
P in developing sweet cherry using vapor
pressure osmometry (VPO), compression plate (CP), and the cell pressure probe (CPP). In addition, the tissue water
potential Ytissue was determined by quantifying the bending of strips of fruit skin and the change in projected area of
discs excised from the flesh when incubated in a range of sucrose solutions of varying osmotic potentials (Ysolution
P ). Fruit
growth followed a sigmoid pattern with timewith the Stage II/Stage III transition occurring at’55 days after full bloom
(DAFB). The Ytissue and the Yfruit
P were constant up to ’55 DAFB but decreased to –2.8 MPa at maturity. The Ycell
P
calculated by subtracting the Y fruit
P from Ytissue averaged ’350 kPa up to 48 DAFB and then decreased at a decreasing
rate to ’21 kPa toward maturity. The Ytissue determined from bending assays using excised skin strips or from water
uptake of excised flesh discs was essentially constant up to ’48 DAFB, then decreased until ’75 DAFB and remained
constant thereafter. TheseYtissue values were in good agreementwith those determined by VPO. TheYfruit
P as determined
by CP passed through a transient peak at ’41 DAFB, then decreased until ’63 DAFB and remained constant and low
until maturity. Similarly, Ycell
P by CPP increased from 27 to 48 DAFB, remained constant until ’55 DAFB, and then
decreased until maturity.Our data demonstrate a consistent decrease inYfruit
P andYcell
P that coincides with a decrease in
Yfruit
P of sweet cherry during Stage III. BecauseYfruit
P and Ycell
P are low relative toYfruit
P , the change inYfruit parallels that
inYfruit
P . The reason for the low turgor most likely lies in the accumulation of apoplastic solutes. These prevent a catastrophic
increase in pressure that would otherwise lead to the bursting of individual cells and the cracking of entire fruit.