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  • Author or Editor: L. Carl Greve x
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Abstract

A simple procedure for synthesizing and purifying the [14C]ethyl ester of IAA (Et-IAA) is described. This auxin has been found to stimulate parthenocarpic fruit set in day-neutral strawberries (Fragaria × ananassa Duch. ‘Fern’), which are non-responsive to various other auxins. Et-IAA may prove useful in eliciting physiological responses in systems shown previously to be auxin-nonresponsive. Chemical name used: 1H-indole-3-acetic acid (IAA).

Open Access

Discs from outer pericarp of mature green (MG) and light red (LR) tomatoes were incubated with 13C6-glucose as precursor to cell wall constituents, to determine biosynthetic capacity of the outer 2mm (including cuticle) and adjacent inner 2mm of tissue. Cell wall material was fractionated into pectic and hemicellulosic classes by sequential extraction, and alditol acetates and partially-methylated alditol acetates were prepared. Neutral sugars (NS), glycosidic linkage compositions and incorporation of label were determined by GC-FID and GC-MS. Rhamnose, arabinose and galactose accounted for ca. 90% of both labeled and total NS in the pectic fractions (sugar ratios within ripeness stage were the same for labeled and total NS). Xylose and glucose accounted for ca. 70% of both labeled and total NS in the hemicellulosic fraction (sugar ratios within ripeness stage were different between labeled and total NS). In the crude cell wall, galactose and glucose contents were significantly higher in the inner than in outer tissues for both MG and LR tomatoes. Loss of galactose during ripening was higher from outer tissues. These results show compositional differences between inner and outer tissues, and suggest that ripening-related wall synthesis may give rise to pectic polymers similar in NS composition to existing polysaccharides, and hemicellulosic polymers which may differ in composition.

Free access

Acid hydrolysis-generated pectic oligomers have been shown to affect ripening of tomato fruit by inducing both acceleration of reddening and increased ethylene biosynthesis (Campbell & Labavitch, 1991 Plant Physiol 97:706-713). In the present work, homogeneous size classes of these oligomers were demonstrated to have different impacts on ethylene production of tomato fruit pericarp discs. Endogenous oligomeric material of the same size classes was isolated from ripening tomato tissues and also tested for biological activity. They promoted some aspects of ripening as shown by increased ACC and ethylene production, which suggests that pectic oligomers are potential regulators of the ripening process in tomatoes. A metabolic origin for these oligomers is suggested by the fact that they are produced by in vitro polygalacturonase I treatment of polygalacturonic acid or tomato pectin.

Free access

Abstract

Intact almond fruits [Prunus dulcis (Mill.) D.A. Webb.] showed a transient increase in ethylene production at the time of gum duct initiation. Treatment with ethylene promoted gum duct formation if applied 1 week before natural duct initiation, but had no effect when applied earlier. Silver thiosulfate, applied either as a spray or through bark-feeding, was found to delay natural duct initiation. AO A also delayed duct initiation when applied through bark-feeding, but not when applied as a spray. Chemical name used: aminooxyacetic acid (AOA).

Open Access

Abstract

Cell wall-degrading enzymes were extracted from the cell wall free space of mesocarp tissue from immature almonds [Prunus dulcis(Mill.)D.A. Webb, ‘Nonpareil’]. The activities of several of these enzymes were found to correlate with the development of gum ducts in this tissue. Polygalacturonase (EC 3.2.1.15) and 1,3-β-D-glucanase (EC 3.2.1.39) activities rose sharply at, or just prior to, the early schizogenous stage of duct initiation, while increases in α-galactosidase (EC 3.2.1.22), β-galactosidase (EC 3.2.1.23), α-arabinosidase (EC 3.2.1.55), and α-mannosidase (EC 3.2.1.24) activities were correlated with the later lysigenous stage of duct formation. Cell wall analysis of almond mesocarp tissue sampled the week preceding gum duct formation determined that the predominant noncellulosic sugars present in the mesocarp cell walls are arabinose, galactose, xylose, and glucose, with smaller amounts of rhamnose and mannose also present. The walls also contain a high percentage of galacturonic acid and trace amounts of glucuronic acid. Methylation analysis of the cell walls confirmed that many of the specific glycosidic linkages that are cleaved by the enzymes tested are present in the mesocarp cell walls immediately prior to gum duct formation.

Open Access

α-l-Arabinofuranosidases (α-Af) are plant enzymes that have the capacity to release terminal arabinofuranosyl residues from a wide variety of pectic and hemicellulosic polymers, as well as different glycoconjugates. Our interest in α-Af is related to its potential role in ripening-related loss of arabinose from tomato fruit cell walls. Using both control (cv. VF 36) and ACC synthase antisense (A11.1) tomatoes (Lycopersicon esculentum Mill.), we demonstrate that tomato α-Af activity is present during the entire ontogeny of the fruit. Immature 10-day-old fruit displayed 6-fold more α-Af activity on a per gram fresh weight basis, than mature green fruit. In VF 36 fruit, α-Af activity increased 45% from mature green 4 (48 days post anthesis) to light red stages (55 days) when fruit ripened on the vine. In contrast, no similar increase was detected in ACC synthase antisense fruit that do not ripen in the same time frame. However, when A11.1 fruit were detached at 48 days after anthesis and treated continuously with 100 mL·L-1 ethylene the fruit ripened and α-Af increased, as in ripening normal fruit. The α-Af activity pattern is similar to that reported for tomato β-galactosidases. The increasing α-Af activity during ripening and the decreased activity in antisense ACC synthase fruit after reaching the mature green stage suggest a role for ethylene in the ripening-related synthesis or activation of this enzyme.

Free access

The variation in polyunsaturated fatty acid content of walnut (Juglans regia L.) oils was determined by analysis of samples isolated from specimens growing in four germplasm collections [California (55 cultivars), Washington (64 seedlings), China (12 cultivars), and France (20 cultivars)]. In addition, the impact of within-state geographic differences on oil composition was examined by comparing samples from three California cultivars (`Ashley', `Hartley', and `Franquette') grown in three locations. Local environmental effects on oil composition of `Chico' were also examined by comparing 1) samples collected from shaded and sun-exposed locations of the same trees and 2) samples collected from trees subjected to three irrigation regimes. Polyunsaturated fatty acid content, as a percentage of total fatty acids, ranged from 47.2% in nuts from PI 142323 from France to 81.0% in `Ashley' from California. However, our data indicate that environment, genotype, nut maturity, and their interactions all contribute significantly to variation in the degree of unsaturation of walnut oil.

Free access