Abstract:
The structure of the Royal Anne cherry cuticle (Prunus avium
L.) and its penetration by a SO₂-calcium bisulfite brine was determined. The structural features of the cuticle are interpreted in the
light of its possible significant to cuticular penetration.
The morphology of the cuticle was determined by standard
histological and histochemical techniques. The surface structure of
the cuticle was studied with a scanning electron microscope.
Enzymatically isolated cuticles were used to evaluate the effect of
the cuticle on the penetration of the various components of brine.
The surface of the cuticle was found to have a smooth to granular
sheet or layer of surface wax which when removed revealed a
porous sponge-like surface. The surface wax was found to be
intermittently birefringent which increased as the fruit matured.
Ectodesmata (MP) were found to occur over anticlinal walls and in
guard cells on both sides of the fruit with more on the side opposite the suture. Both sides, were stomatous with more occurring on the
suture side. Secondary bleaching was found to alter the structure and
permeability of the cuticle.
Removing the wax was found to increase percent weight loss as
well as increasing cuticular penetration. Ion penetration was found to
be generally greater from the outside to the inside than the inside to
the outside surface and was greater from the side opposite the suture
than the suture side. Potassium from potassium bitartrate was found
to penetrate rapidly while SO₂, Ca⁺⁺, and H⁺ were delayed.
It was concluded from this study that calcium penetration
entered by a different route than SO₂; the major penetrating species of
SOp in water and brine would seem to be molecular SCX and bisulfite
ion; stomatal pores were not the sites of entry; ectodesmata were
probably the sites for polar entry; the guard cells were more important
for potassium penetration while ectodesmata in astomatous regions
were more important for SO₂ penetration; and one of the major
factors involved in penetration of brine is the waxy layer on the cuticle.
Causes, preventative measures and recommendations for the structural
defect known as "solution pockets" are discussed in light of the structure
and penetration data.
