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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).
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.
Three-year-old `Valencia' orange [Citrus sinensis (L.) Osbeck] trees were exposed to air pollutants for 4. years in open-top field chambers to determine the chronic effects of ambient oxidants (primarily ozone) or sulfur dioxide (SO2) on fruit yield and quality and tree growth. Ozone concentrations averaged 0.012,0.040, and 0.075 ppm for 0800 to 2000 hr during April to October for filtered, half-ambient, and full ambient oxidant chambers. Sulfur dioxide was applied continuously at 0.09 ppm. Oxidant and SO2 effects were only marginally significant, as there was considerable variability in response among individual trees and between years. Across two “on” production years, yields were 31% lower with ambient oxidants, 11% lower with half-ambient oxidants, and 29% lower with sulfur dioxide compared to filtered air. Number of fruit per tree was reduced by ambient oxidants and SO2. Individual fruit weights were reduced by ambient oxidants, but no other fruit quality characteristics showed definite responses to ambient oxidants or SO2. Ambient oxidants had no effect on yield or quality of fruit during one “off' production year. Neither ambient oxidants nor SO, affected tree growth.