Bruce D. Whitaker

Responses of early, mid and late season apple cultivars to postharvest application of 1-methylcyclopropene (1-MCP) under air and controlled atmosphere storage conditions

The potential for commercial application of 1-methylcyclopropene (1-MCP) to maintain quality of ‘McIntosh’, ‘Empire’, ‘Delicious’ and ‘Law Rome’ apples under air and controlled atmosphere (CA) storage conditions was investigated. These cultivars represent early, mid and late season apples with ripening rates ranging from fast to slow. 1-MCP gas concentrations used were 0.5, 1 and 2 m ll 1 , generated from measured amounts of Ethylbloc™ powder. Fruit of each cultivar were removed from storage at 6 week intervals during 30 weeks in air, or at 8 week intervals during 32 weeks in CA, and evaluated after 1 and 7 days at 20°C. Effects of 1-MCP were greater in CA than air storage. A dose response of internal ethylene concentrations and flesh firmness to 1-MCP was found in ‘McIntosh’ and ‘Law Rome’, but ‘Delicious’ and ‘Empire’ ripening was generally prevented by all 1-MCP concentrations. 1-MCP reduced superficial scald incidence, and accumulations of a-farnesene and conjugated trienols during air storage. The results indicate that the efficacy of 1-MCP is affected by cultivar and storage conditions, and that successful commercial utilization of the chemical will require understanding of these relationships.

A new liquid chromatography-mass spectrometry-based strategy to integrate chemistry, morphology, and evolution of eggplant (Solanum) species.

This study presents a strategy based on repeatable reversed-phase LC-TOF-MS methods and statistical tools, including untargeted PCA and targeted PLS/OPLS-DA models, to analyze 31 accessions representing 24 species in the eggplant genus Solanum (Solanaceae), including eight species whose metabolic profiles were studied for the first time. Sixty-two Solanum metabolites were identified after detailed analysis of UV absorbance spectra, mass spectral fragmentation patterns, NMR spectra, and/or co-injection experiments with authentic standards. Among these were two new 5-O-caffeoylquinic acid derivatives that were identified by analyzing their MS/MS fragmentation. Based on these results, a Solanum metabolic database (SMD) and a detailed biosynthetic pathway of Solanum metabolites were created. Results of analyses identified seven marker metabolites that distinguish four Solanum sections, and revealed species-specific chemical patterns. Combining LC-MS data with multivariate statistical analysis was proven effective in studying the metabolic network within the large genus Solanum, allowing for integration of complicated chemistry, morphology, and evolutionary relationships.

CHANGES IN LIPIDS OF TOMATO FRUIT STORED AT CHILLING AND NON-CHILLING TEMPERATURES

Mature green tomato fruits (Lycopersicon esculentum) were stored at non-chilling or chilling temperature (15 or 2°, respectively) for 2, 4, 8 or 12 days after harvest. Fruit stored at 15° had progressed to the pink stage of ripening after 12 days, whereas fruit stored at 2° had not ripened significantly. On a fresh weight basis, the phospholipid content of tomato pericarp tissue changed very little during storage at either 15 or 2°. Free fatty acids increased three-fold in fruit held at 15° and 1.2-fold in fruit held at 2°. Total sterol content increased during storage at both 15 and 2°. The increase in free sterols was greater in chilled compared to unchilled fruit, whereas the reverse was true for steryl esters. Chilling had no efrect on the amounts of free and acylated steryl glycosides. The stigmasterol: sitosterol ratio in all steryl lipids increased dramatically with storage at 15°, but only slightly with storage at 2°.

Calcium delays senescence-related membrane lipid changes and increases net synthesis of membrane lipid components in shredded carrots

The influence of Ca2+ on firmness and membrane lipid structural components was evaluated during storage of shredded (wound-stressed) carrot tissues (Daucus carota L. ‘Caropak’). During 10 days of storage at 10 °C and 95% RH, Ca2+ treatment (applied as 1% w/v CaCl2 upon shredding) provided 6–16% greater firmness retention than did a water control treatment. Calcium accentuated net increases in total phospholipid and monogalactosyldiacylglycerol concentrations after 4 and 10 days of storage, and in acylated steryl glycoside concentrations after 4 days of storage. Calcium partially counteracted a net reduction in steryl glycoside concentration which occurred following 4 days of storage, and prevented an increase in the free sterol : phospholipid ratio following 10 days of storage. Calcium preserved membrane integrity of carrot shreds not only by delaying senescence-related membrane lipid changes, but also by apparently augmenting membrane restructuring processes.

Cell wall composition of calcium-treated apples inoculated with Botrytis cinerea

Abstract The role of calcium in maintaining cell wall integrity was investigated in cortical tissue of apple fruit. Carbohydrate, phenolic, protein and mineral element composition were determined in cell walls of high- and low-calcium content fruit inoculated with Botrytis cinerea . Cell walls in fungal-infected tissue of low-calcium fruit showed a decrease in non-cellulosic polysaccharides containing galacturonosyl, rhamnosyl, arabinosyl, xylosyl and galactosyl moieties and increases in cellulose, wall-bound phenolics, protein and mineral elements. In infected tissue of high-calcium fruit, the compositional changes in the cell wall were generally smaller compared with those observed in the low-calcium treatment. The results of this investigation indicate that the effect of calcium in reducing decay is associated with maintaining cell wall structure by delaying and/or modifying chemical changes in cell wall composition.

Steryl esters in the elaioplasts of the tapetum in developing Brassica anthers and their recovery on the pollen surface

The tapetum cells in the developing anthers of Brassica napus contained abundant elaioplasts, which had few thylakoid membranes but were packed with globuli of neutral esters. Of the neutral esters, the major ester group possessed mainly 24-methylenecholesterol, 31-norcycloartenol, 24-dehydropollinastanol, and pollinastanol esterified to 18∶3 and other unsaturated and saturated fatty-acyl moieties. The minor ester group had a dominant component tentatively identified as 12-dehydrolupeol esterified to mostly 18∶0, 16∶0, and 20∶0 fatty-acyl moieties. The elaioplasts also contained a high proportion (16% w/w of total lipids) of monogalactosyldiacylglycerols (MGDG). This is the first report of plastids having steryl esters as the predominant lipids. We propose that the globuli contain steryl esters and are stabilized by surface MGDG and structural proteins. The tapetosomes, the other abundant lipid-containing organelles in the tapetum, possessed tricylglycerols (TAG) as the predominant lipids. At a late stage of anther development, the minor group of neutral esters and MGDG of the elaioplasts, as well as the TAG of the tapetosomes, were degraded. Steryl esters similar to those of the elaioplasts were recovered from the pollen surface and were the major lipids of the pollen coat. The pollen coat steryl esters and proteins could be extracted with moderately polar or nonpolar solvents. These proteins, which were mostly fragments of oleosins derived from the tapetosomes, had a high proportion of lysine (13 mol %). The possible functions of the steryl esters and the proteins on the pollen surface are discussed.

A reassessment of heat treatment as a means of reducing chilling injury in tomato fruit

Abstract Recent studies have indicated that heat treatment administered prior to chilling reduces the incidence and severity of chilling injury in tomato fruit and other plant organs. Partial ripening of tomato and other fruits has also been shown to reduce chilling sensitivity. To test the relative merits of these “treatments”, tomato fruit (cv. ‘Rutgers’) were harvested when mature-green, held 3 days at ripening or heat-stress temperature (20 or 38°C, respectively), chilled for 20 days at 5°C, and assessed for ripening and injury over 7 subsequent days at 20°C. Based on chromaticity ( a ∗ ) values, lycopene content, rates of CO2 and ethylene evolution, and visible injury (pitting on shoulders), heat-treated (38°C) fruit sustained more chilling injury and ripened much more slowly than the partially-ripened (20°C) controls. Membrane lipids extracted from outer pericarp tissue from 0 day, 3 day control, and 3 day heat-treated fruits were also analyzed. Lipid changes after 3 days at 20°C were typical of early ripening, whereas several anomalous changes occurred during 3 days at 38°C, most notably, a drop in steryl esters, large increases in phospholipids and cerebrosides, and a decrease in fatty-acid unsaturation in galacto- and phospholipids. These results show that, under certain conditions, heat treatment of tomato fruit may not reduce chilling injury as effectively as partial ripening.

Quantitative high-performance liquid chromatography analysis of plant phospholipids and glycolipids using light-scattering detection

Application of the evaporative light-scattering principle to quantitative high-performance liquid chromatography (HPLC) analyses of plant membrane lipids has received little study. Light-scattering detection response curves were generated for nine classes of plant membrane phospholipid and glycolipids. Quantitative results obtained by HPLC/light-scattering detection and conventional lipid analytical methods (thin-layer chromatography and lipid-P assay) were in close agreement, confirming the reliability of HPLC/evaporative light-scattering detection (ELSD) analyses. Only three of the nine plant lipid classes gave linear detector response functions above 10 μg injected lipid mass. This finding contradicts earlier precepts involving light-scattering detection of lipids. At a given mass, appreciable variation in ELSD signal intensity and detection limit was found to exist among the various plant membrane lipid classes. The variation in detector response among plant lipid classes is an important consideration in achieving accurate quantitative results in plant lipid analyses.

Characterization of a calcium/calmodulin- regulated SR/CAMTA gene family during tomato fruit development and ripening

BackgroundFruit ripening is a complicated development process affected by a variety of external and internal cues. It is well established that calcium treatment delays fruit ripening and senescence. However, the underlying molecular mechanisms remain unclear.ResultsPrevious studies have shown that calcium/calmodulin-regulated SR/CAMTAs are important for modulation of disease resistance, cold sensitivity and wounding response in vegetative tissues. To study the possible roles of this gene family in fruit development and ripening, we cloned seven SR/CAMTAs, designated as SlSRs, from tomato, a model fruit-bearing crop. All seven genes encode polypeptides with a conserved DNA-binding domain and a calmodulin-binding site. Calmodulin specifically binds to the putative targeting site in a calcium-dependent manner. All SlSRs were highly yet differentially expressed during fruit development and ripening. Most notably, the expression of SlSR2 was scarcely detected at the mature green and breaker stages, two critical stages of fruit development and ripening; and SlSR3L and SlSR4 were expressed exclusively in fruit tissues. During the developmental span from 10 to 50 days post anthesis, the expression profiles of all seven SlSRs were dramatically altered in ripening mutant rin compared with wildtype fruit. By contrast, only minor alterations were noted for ripening mutant nor and Nr fruit. In addition, ethylene treatment of mature green wildtype fruit transiently stimulated expression of all SlSRs within one to two hours.ConclusionsThis study indicates that SlSR expression is influenced by both the Rin-mediated developmental network and ethylene signaling. The results suggest that calcium signaling is involved in the regulation of fruit development and ripening through calcium/calmodulin/SlSR interactions.

Temperature Preconditioning Increases Tolerance to Chilling Injury and Alters Lipid Composition in Zucchini Squash

Summary Temperature preconditioning at 15°C for 2 d effectively delayed the development of chilling injury in zucchini squash ( Cucurbita pepo L., cv. ‹Ambassador›) storage at 5°C. Chilling at 5°C resulted in loss of phospholipids, including PC, PE, PG, and PI. These losses were reduced by temperature preconditioning treatment. The degree of fatty-acid unsaturation of phospholipids declined during storage, but was higher in treated squash than in the controls. Temperature preconditioning treatment also reduced losses of the galactolipids MGDG and DGDG during the cold storage. Spinasterol and Δ 7 -stigmastenol were the two predominant sterols, constituting more than 75 % of both the free sterol and steryl ester fractions. The ratio of free sterol/total phospholipids increased during the cold storage. The increase of this ratio was suppressed by the temperature preconditioning treatment. These results may indicate that acclimation to chilling storage temperatures involves protection of membranes from chilling-induced degradation of glycerolipids.