Search Results
Abstract
Large differences in abscisic acid (ABA) concentrations were found among persisting fruit of ‘Winter Nelis’, seeded ‘Bartlett’ and parthenocarpic ‘Bartlett’ pear (Pyrus communis L.) even though fruit set and fruit growth rates were similar. Concentration of ABA was positively correlated with rate of fruit and seed growth in these 3 pear types. The concentration of ABA was greater in the seed than in fruit flesh, and in the integuments plus endosperm than in the embryo.
Abstract
Analysis for hormones in plant material received impetus from the early studies of Went (4). Since that time, scientists have used living plant materials to estimate the presence of specific hormones. Among the advantages of the bioassay are sensitivity to the nanogram and in some cases, picogram range, ease of use, functionality with high levels of contaminants, and low cost of operation. The disadvantages include lack of specificity, variable response, and, in most instances, the need to use a species foreign to the one under examination.
Abstract
Flowers of caged ‘Winter Nelis’ pear (Pyrus communis L.) set parthenocarpic fruit that persisted until maturity after a single treatment with the gibberellin GA3, GA3 + CaCl2 or the pear gibberellin GA45. Cytex (a zeatin-like cytokinin), abscisic acid (ABA), GA9, GA17 and GA25 were ineffective. The persisting fruits treated with GA3 or GA3 + CaCl2 were significantly smaller than the controls and the GA3 + CaCl2 treated fruits were significantly smaller than those treated with GA45.
Abstract
Olive (Olea europaea L.) leaves are characterized by their ability to respond to exogenous ethylene by a 100- to 400-fold enhanced ethylene production irrespective of leaf age or time of year when sampled. The autoenhancement of ethylene production from intact or detached leaves is positively correlated with the concentration of external ethylene. A lag time of 72 to 120 hr occurred before the autoenhancement of ethylene production could be observed. An autoinhibition of ethylene production was usually observed during the first 24 to 48 hr. The effect was, however, much less pronounced. This autoinhibition of ethylene production apparently does not involve wound ethylene. Olive fruit normally produce only negligible amounts of ethylene, and the enhanced ethylene evolution, which was observed after the fruits were exposed to exogenous ethylene, was found to be exogenous ethylene that was trapped by the fruit tissue during its exposure to ethylene. In leaves, however, autoenhancement of ethylene production evidently is a physiological response that may induce a senescing process in the leaves rather than abscission.
Abstract
At “June drop”, the abscission zone occurs predominantly between the fruit and the receptacle. The abscising fruits had low levels of a growth promoter and high levels of a growth inhibitor, tentatively identified as ABA. Persisting fruits had higher levels of the growth promoter and lower levels of the growth inhibitor than did abscising fruit. Treatment of immature fruits with the chemical thinners 3-CPA or ethephon induced levels of growth regulators in the abscising fruits equivalent to those in abscising non-treated fruits.
Olive (Olea europaea L.) field experiments involving natural flower and fruit populations are fraught with variability, resulting in large coefficients of variation. We provide evidence that coefficients of variation can be reduced successfully by judiciously selecting four experimental twigs per tree and using only those twigs with an internodal growth ≥2 cm, two inflorescences per node, and that are selected from trees with near-maximum bloom density. Although counting flowers at full bloom may establish the population uniformity, only a single node; e.g., node 5, is needed for analysis. Increasing the number of trees will reduce variance more than increasing the number of twigs or nodes.
Abstract
Concentration of abscisic acid (ABA), abscisic acid-glucose ester (ABA-GE), indoleacetic acid (IAA), zeatin (Z), zeatin riboside (ZR) and gibberellic acid (GA) were measured in ‘Winter Nebs’ pear (Pyrus communis L.) receptacles from anthesis to 12 days thereafter. Concentration of GA or IAA may signal subsequent growth rate for GA3-treated and pollinated receptacles. No correlations with growth were evident for Z or ZR. ABA-GE began massive accumulation prior to the senescence and abscission of control receptacles.
Abstract
Withholding irrigation of walnut trees (Juglans regia L. cv. Ashley) for one growing season significantly reduced trunk growth and kernel weight. Tree survival and return cropping were unaffected. When irrigation was resumed kernel weight was significantly heavier than that from trees irrigated the previous year.
Early fall (September) defoliation and late spring (early June) shading of “off” and “on” pistachio trees were used to test two hypotheses: that 1) fall defoliation would reduce carbohydrate storage sufficiently to suppress spring growth and 2) spring shading would reduce carbohydrate status and increase inflorescence bud abscission. Defoliation suppressed initial leaf area expansion the following spring on current year shoots of “off” but not “on” trees respectively. Suppression of leaf size was correlated with the initial low concentration of carbohydrates in organs of individual branches of the tree. Fruiting and artificial shading in June had more dramatic effects on growth parameters than defoliating. Shading “off” trees for 14 days in early June accelerated abscission of inflorescence buds, reduced dry mass of individual leaves, buds, current year and 1-year-old shoots. Shading also reduced the concentration of total nonstructural carbohydrates (TNC) of these organs in “off” and “on” trees. Fruiting suppressed leaf size and leaf dry mass by 20% and 30% among individual branches of undefoliated and defoliated trees respectively. Low carbohydrate concentrations in individual branches and inflorescence buds following shading were closely correlated with the abscission of inflorescence buds.
The objective of this investigation was to determine the dynamics of carbohydrate use as revealed by soluble sugar and starch concentration in leaves, inflorescence buds, rachises, nuts, current and 1-year-old wood, and primary and tertiary scaffold branches and roots (≤10 mm in diameter) of alternate-bearing `Kerman' pistachio (Pistachia vera L.) trees that were in their natural bearing cycles. Two hypotheses were tested. First, carbohydrate concentration is greater early in the growing season in organs examined from heavily cropping (“on”) than light cropping (“off”) trees. This hypothesis was affirmed as judged by soluble sugar and starch concentration in leaves, inflorescence buds, rachises, nuts, current and 1-year-old wood, and primary and tertiary branches and roots of “on” compared to “off” trees. Second, carbohydrate concentration remains high in “on” tree organs as the first wave of inflorescence bud and nut abscission occurs early in the growing season. This hypothesis was also affirmed. In fact, soluble sugars and starch remained high in “on” trees through full bloom FB + 60 days (FB + 60) as inflorescence bud and nut abscission occurred. In the persisting “on” tree inflorescence buds, sharp decreases in soluble sugars and starch were evident by the final sample date when “off” tree inflorescence buds contained a 13 times greater concentration of soluble sugars and starch than “on” tree buds. At that time, “off” tree inflorescence buds contained 50% more dry mass than “on” tree inflorescence buds. After FB + 60, “on” tree soluble sugars and starch declined in all organs as nut growth occurred. During the same time period, organs of “off” trees began to accumulate greater concentrations of soluble sugars and starch and exceeded concentrations measured in organs of “on” trees.