Martin J. Bukovac

Ion exchange properties of isolated tomato fruit cuticular membrane: Exchange capacity, nature of fixed charges and cation selectivity.

SummaryIsolated tomato fruit cuticular membrane, free of extractable materials, was titrated potentiometrically using various bases. Three dissociable groups were observed in the pH ranges 3–6 (0.2 meq g-1), 6–9 (0.3 meq g-1) and 9–12 (0.55 meq g-1). The first group was tentatively assigned to-COOH groups of pectic materials and protein embedded in the membrane, the second to nonesterified-COOH groups of the cutin polymer and the third to phenolic-OH groups, such as non-extractable flavenoids present in the membrane, and to a small amount of-NH3+groups of proteins. The cuticular membrane exhibited a behavior typical of highly cross-linked, high-capacity ion exchange resins of the weak-acid type. Ion exchange capacity increased with increasing pH and neutral salt concentration. At constant pH and salt concentration, the exchange capacity increased with increasing counter ion valence and decreasing crystal radius, e.g. [tris (ethylenediamine) Co]3+≥Ca2+>Ba2+>Li+>Na+>Rb+>N(CH3)4+. The cutin polymer exhibited a pronounced selectivity for Ca2+ over Na+ which increased with increasing neutralization of fixed charges. The large trivalent [Co(en)3]3+ was preferred only at low equivalent ionic fractions in the polymer. These results are discussed in relation to the structure and function of cuticular membranes.

Rheological Properties of Enzymatically Isolated Tomato Fruit Cuticle

Rheological properties were determined for cuticular membranes (CMs) enzymatically isolated from mature tomato (Lycopersicon esculentum Mill. cv Pik Red) fruit. The cuticle responded as a viscoelastic polymer in stress-strain studies. Both CM and dewaxed CM expanded and became more elastic and susceptible to fracture when hydrated, suggesting that water plasticized the cuticle. Dewaxing of the CM caused similar changes in elasticity and fracturing, indicating that wax may serve as a supporting filler in the cutin matrix. Exposure of the cuticle to the surfactant Triton X-100 did not significantly affect its rheological properties.

Preferential polar pathways in the cuticle and their relationship to ectodesmata

SummaryEctodesmata-like structures, referred to here as mercurous or mercury precipitates (MP) and considered to be identical to precipitates observed after treatment of leaf tissue with Gilson solution for demonstration of ectodesmata, were demonstrated with cuticle enzymatically isolated from Allium bulb scales and leaves mounted on ascorbic acid-enriched agar or gelatin. The MP distribution patterns obtained with isolated cuticle, in the absence of a cell wall, were identical to those observed with living tissue. Since the distribution in either the presence or absence of the cell wall was similar, the distribution pattern must be determined by the cuticle and not by the cell wall. Disruption of the physical arrangement of epicuticular wax by brushing or removal with chloroform altered the distribution pattern and increased the frequency of MP. This was interpreted to mean that epicuticular wax plays an important role and also that the necessary reductant was not localized in specific structures in the cell wall. Based on this evidence, it appears that ectodesmata, as demonstrated with Gilson solution, are not specific cell-wall structures, whether plasmic or not plasmic. More likely, the MP observed in the cell wall reflect areas in the cuticle permeable to mercuric chloride and undoubtedly to other polar compounds. The presence of such pathways in the cuticle, long established as the prime barrier to penetration of polar compounds, has marked implications in foliar uptake and excretion.

Studies on water transport through the sweet cherry fruit surface : characterizing conductance of the cuticular membrane using pericarp segments

Abstract. Water conductance of the cuticular membrane (CM) of mature sweet cherry fruit (Prunus avium L. cv. Sam) was investigated by monitoring water loss from segments of the outer pericarp excised from the cheek of the fruit. Segments consisted of epidermis, hypodermis and several cell layers of the mesocarp. Segments were mounted in stainless-steel diffusion cells with the mesocarp surface in contact with water, while the outer cuticular surface was exposed to dry silica (22 ± 1 °C). Conductance was calculated by dividing the amount of water transpired per unit area and time by the difference in water vapour concentration across the segment. Conductance values had a log normal distribution with a median of 1.15 × 10−4 m s−1 (n=357). Transpiration increased linearly with time. Conductance remained constant and was not affected by metabolic inhibitors (1 mM NaN3 or 0.1 mM carbonylcyanide m-chlorophenylhydrazone) or thickness of segments (range 0.8–2.8 mm). Storing fruit (up to 42 d, 1 °C) used as a source of segments had no consistent effect on conductance. Conductance of the CM increased from cheek (1.16 ± 0.10 × 10−4 m s−1) to ventral suture (1.32 ± 0.07 × 10−4 m s−1) and to stylar end (2.53 ± 0.17 × 10−4 m s−1). There was a positive relationship (r2=0.066**; n=108) between conductance and stomatal density. From this relationship the cuticular conductance of a hypothetical astomatous CM was estimated to be 0.97 ± 0.09 × 10−4 m s−1. Removal of epicuticular wax by stripping with cellulose acetate or extracting epicuticular plus cuticular wax by dipping in CHCl3/methanol increased conductance 3.6- and 48.6-fold, respectively. Water fluxes increased with increasing temperature (range 10–39 °C) and energies of activation, calculated for the temperature range from 10 to 30 °C, were 64.8 ± 5.8 and 22.2 ± 5.0 kJ mol−1 for flux and vapour-concentration-based conductance, respectively.

Ontogenetic variations in the composition of peach leaf wax

Abstract The composition of the epicuticular waxes from the adaxial and abaxial surfaces of peach leaves varies considerably during one seasons growth. Triterpenoid acids are major components 84–95% of the waxes from the youngest leaves but the proportions of these constituents decrease as the leaves expand. The waxes from the abaxial surfaces of fully expanded leaves consist primarily of hydrocarbons (C 22–C34 ) and triterpenoid acids, whereas the adaxial surface waxes also contain large proportions of primary alcohols (C 26 -C 34 ) and esters (C 42 -C 52 ). The latter include sitosteryl esters of hexacosanoic, octacosanoic and eicosanoic acids. Variations were also noted between fully expanded leaves of different ages, the abaxial surface waxes of the oldest leaves containing the highest proportions of hydrocarbons, whilst the wax from the adaxial surface of the corresponding leaves contained the largest amounts of esters, sitosterol and hydrocarbons.

Using a videographic system to assess spray droplet impaction and reflection from leaf and artificial surfaces

A video motion analysis system was used with two different monodisperse droplet generators to quantify droplet impaction and any consequent reflection. By using different magnification/droplet generator combinations, droplet impaction was detailed at various stages. Low (7×) magnification, together with a generator that produced a spray cloud, allowed determination of the height and numbers of droplets reflected from plant surfaces. Higher (15×) magnification and a single-drop generator enabled the trajectory, and changes in velocity, of a rebounding droplet to be followed. By using high (90×) magnification and the single-drop generator, detailed measurements of a droplet deforming on impact could be made. Examples of how these techniques could be used are given.

Histochemical changes in the developing abscission layer in fruits of Prunus cerasus L.

SummaryAbscission layer formation in the sour cherry (Prunus cerasus L.) during fruit maturation occurred in the transition zone between the fruit and the pedicel. The abscission layer, consisting of 5–8 rows of cells, was first identified by its low affinity for haematoxylin. The walls of cells in the abscission layer contained less total polysaccharides than adjacent cells. The pectins were degraded and the cellulose was partially broken down resulting in cell separation. The Ca level in the abscission zone decreased and Ca and Mg were lost from the walls of cells in the layer during abscission. After the abscission layer formed, cells associated with the layer had a lower capacity to bind 45Ca than cells distal or proximal to the layer.

Effect of spray volume and time of NAA application on fruit size and cropping of Redchief ‘Delicious’ apple

Abstract The effect of naphthaleneacetic acid (NAA) thinning sprays on fruit size of Redchief ‘Delicious’ apple was studied in relation to spray application volume and time of application. A constant dose of NAA resulted in similar fruit size at harvest when applied in varying spray volumes from high (near full retention, Vx) to V x 8 . NAA applied as a high volume spray (15 mg l−1) at various stages of fruit development (4.6 to 22.5 mm king fruit diameter, KFD), indicated that the maximum amount of small fruit was produced following applications at about 11 mm KFD. NAA did not consistently affect growth rate of king fruit immediately after treatment when fruit competition was minimized. NAA reduced fruit size at harvest by about 11% when two competing fruits were present on the same spur, but did not significantly reduce fruit size when a single fruit was permitted to develop per spur.

The nature of precipitates formed in the outer cell wall following fixation of leaf tissue with Gilson solution

SummaryThe nature of precipitates formed in the outer cell walls of leaf tissue fixed in Gilson solution, used extensively to demonstrate ectodesmata, is described. Electron-microbe X-ray analysis established that the crystalline precipitates contained both mercury and chlorine. Based on solubility in water and ethanol, birefringence and ratio of mercury to chlorine, the chemical form is probably mercurous chloride. Further treatment of the leaf tissue with potassium iodide caused the crystalline precipitate to turn black and lose birefringence when viewed with plane-polarized light. Analysis of this precipitate showed the presence of only mercury, chlorine having been lost.

Cuticular Penetration of Abscisic Acid

SummaryPenetration of 2-14C abscisic acid (ABA) through enzymatically isolated cuticles from tomato fruit and from the upper epidermis of apricot, pear and orange leaves was assessed. Penetration was linear with time, greater as the undissociated than the dissociated ion, and greater through dewaxed than non-dewaxed cuticles. Significantly less (3–6 times) (2-14C)ABA penetrated the tomato fruit cuticle than NAA or 2,4-D. The leaf cuticles were less permeable than the tomato fruit cuticle. There was no evidence that the ABA was altered during transfer across the cuticle.