Exudation of phloem sap into EDTA (ethylenediaminetetraacetic acid) solutions has been found to be a successful technique for qualitatively determining translocated assimilates in many plants. Mature Chysanthemum leaves were excised under a solution of 10 mM EDTA (pH 7.0). The petioles of these leaves were placed in EDTA, and leaf exudate was collected at intervals for 24 h. Soluble carbohydrates were determined with HPLC. While numerous sugars were present in the leaf, sucrose was the only sugar found in the EDTA solutions. The greatest rate of sucrose exudation occurred in the first two h after excision. Diurnal fluctuations of soluble sugars in Chrysanthemum leaves were also monitored in greenhouse-grown plants (late winter in Arizona). Sucrose exhibited a clear diurnal fluctuation, and nearly doubled in concentration (to appx. 25 mg/g DWT) in the afternoon relative to the low in the morning. Other leaf carbohydrates, including glucose, starch, and fructans showed diurnal variations as well.
Susan E. Trusty and William B. Miller
Monte L. Nesbitt, J. Benton Storey, D. Lyda, and L.J. Grauke
Rootstock resistance to soil-borne phytopathogenic fungi, such as Phymatotrichum omnivorum (Shear) Duggar, is an important factor in disease control. Measurement of natural rootstock resistance is often based on plant survival/mortality percentage, and /or growth data. Fungal colonization of host roots in disease screening experiments may not be uniform for many reasons, causing variability in host response. Quantification of fungal colonization is needed in order to better understand rootstock performance. Ergosterol, a structural sterol in cell membranes of fungi, is not found in higher plants, and can thus be a measure of fungal colonization. Ergosterol was extracted from roots of pecan seedlings artificially inoculated with P. omnivorum and grown in an environmental growth chamber. Analysis of extracts with HPLC revealed that seedlings which were killed in screening, or had low root performance ratings, had increased levels of ergosterol. Non-inoculated controls also contained Ergosterol. indicating contamination and possible competition by other fungi.
Jorge H. Siller-Cepeda, Leslie Fuchigami, and Tony H. H. Chen
Many seeds of woody plants require low temperature or other treatments to overcome dormancy. Changes in catalase activity and glutathione has been proposed to be associated with the breaking of dormancy. We examined the level of glutathione and catalase activity of cherry seeds (Prunus mahaleb cv. Lambert) exposed to several dormancy breaking agents. Seeds imbibed in water for 24 hrs. were either stratified at 4°C or at 25°C for up to 12 weeks, or exposed to other dormancy breaking agents. Germination test, glutathione and catalase activity were determined weekly and/or after treatment. Analysis of levels and state of glutathione were performed by high pressure liquid chromatography (HPLC), and catalase activity was assayed spectrophotometrically. Total glutathione in dry and imbibed seeds were similar, but, ratio between the reduced and oxidized form were different. Low temperature stratification for 12 weeks increased the reduced form of glutathione six-fold, while percent germination increased up to 94%.
John R. Stommel
Sugar accumulation throughout fruit development in the cultivated tomato (Lycopersicon esculentum) and a wild green-fruited species (L. peruvianum) are being examined. Results obtained using HPLC demonstrate that the fruit of L. peruvianum accessions accumulate the disaccharide, sucrose, in addition to the monosaccharides, glucose and fructose, common to L. esculentum. When detectable, sucrose in the L. esculentum cultivar FM6203 was present at very low levels throughout development. Analysis of mature fruit of L. esculentum var. cerasiforme, L. pimpinellifolium, and L. cheesmanii accessions indicate glucose and fructose as the primary storage sugars. Similar to L. peruvianum, mature fruit of the green-fruited species, L. hirsutum f. typicum and L. hirsutum f. glabratum, accumulate sucrose in addition to glucose and fructose.
Teryl R. Roper and Marianna Hagidimitriou
Carbohydrate concentration may be important for flower initiation and fruit set in cranberry (Vaccinium macrocarpon Ait.). Fruit set has been shown to be a major limiting factor in yield component analysis. The objective of this research was to identify carbohydrate concentrations in cranberry tissues at various stages of development under field conditions. Samples of two cranberry cultivars, `Stevens' and `Searles' were collected during the 1989 season using a 13 cm diameter probe. Samples were divided into fruit, uprights, woody stems and roots. Carbohydrates were quantified by HPLC. Nonstructural carbohydrates were primarily sucrose, glucose, fructose and starch. Soluble carbohydrate concentration was stable throughout the season in tissues analyzed, while starch content was high early in the season then decreased during blossom and fruit set. This work shows that starch reserves in leaves and stems apparently are remobilized to support fruit set in cranberry.
Shahid N. Chohan and Terence A. Brown
HPLC was used to measure nucleotide pools in tomato seeds during the 3 h following imbibition in water. In dry seeds, nucleotides were predominantly in the form of monophosphates. During the first 2 h post-imbibition, the monophosphate levels declined and there were sharp increases in the amounts of diphosphates, followed by triphosphates. Between the 2nd and 3rd h, the di- and triphosphate levels continued to increase and the monophosphate levels began to recover, especially in the case of UMP—presumably the result of degradation of unwanted mRNAs left over from the maturation phase of seed development. The adenylate energy charge increased during imbibition and, within 3 h, reached a value close to that of normal active tissue.
M.S. Padda and D.H. Picha
Sweetpotatoes may be potentially high in concentration of certain phytochemical compounds, including phenolics. Low temperature stress-induced phenolic compounds may enhance the nutraceutical value of sweetpotatoes. However, extended exposure to low temperature results in chilling injury. Cured and non-cured roots of `Beauregard' sweetpotatoes were exposed to low temperature storage (5 °C) for up to 4 weeks. The total phenolics and individual phenolic acid contents were determined at weekly intervals using Folin-Denis reagent and reversed-phase HPLC, respectively. Total phenolics and individual phenolic acids increased with length of low temperature exposure. Non-cured roots had a higher phenolic content than cured roots after 4 weeks. A 3-day exposure period to room temperature (22 °C) following removal from low temperature storage typically resulted in increased phenolics. In a comparison of different tissue locations, the highest phenolic content was found in peel tissue and the lowest in the pith tissue. The major individual phenolic acid in all root tissues was chlorogenic acid.
Claire Hébert and Claude Willemot
Plant antioxidants have gained considerable interest because of their importance for the preservation of produce and also because of their therapeutic properties. There is increasing evidence that these compounds protect plant tissues from stress and that they delay senescence. Seven strawberry cultivars were analyzed to investigate the possible relationship between their antioxidant potential and fruit shelf-life. The antioxidant defense systems studied were free radical scavenging enzymes (SOD, catalase, glutathione reductase, GSH, ascorbate peroxidase, ascorbate free radical reductase), ascorbic acid, and ellagic acid. Enzyme assays were performed using spectrophotometric kinetic measurements. Ascorbic acid and ellagic acid were determined by HPLC. The antioxidant potential of the tissues had an incidence on fruit quality and shelf-life. The impact of these antioxidative parameters will be discussed with respect to breeding criteria for reduced perishability of strawberries.
Isa Bertline and Carol J. Lovatt
Tryptophan is known to be a precursor of IAA in plants. The amount of IAA available for the development of avocado fruit might be a limiting factor for its growth. It is well known that IAA is not transported into developing fruit along its strictly basipetal transport route. Therefore, IAA present in fruit must be synthesized in situ. We investigated the possibility that tryptophan or its metabolites are transported from leaf to fruit.
An HPLC method was developed to quantitatively isolate and measure tryptophan and all well known intermediates in the synthesis of IAA. Avocado leaves were fed L-[side chain-3-14C] tryptophan and its transport and metabolism to IAA within the leaf and within the fruit were monitored over time. Significant movement of tryptophan or a metabolite from leaf to fruit occurs in 24 h.
Fernando De Villena, Vincent Fritz, Jerry Cohen, and William Hutchison
Gluconasturtiin (2-phenylethyl glucosinolate), an aromatic glucosinolate, was used to evaluate the response of Chinese cabbage (Brassica campestris L. ssp. pekinensis) cv. Green Rocket to three and five cabbage looper (Trichoplusia ni Hubner) larvae per plant. Plants were harvested 0, 10, and 17 days after infestation. The change in gluconasturtiin content due to decreased light and leaf area removed was also studied. All samples were assayed for gluconasturtiin content using high performance liquid chromatography (HPLC). The gluconasturtiin content of plants subjected to five larvae/plant had a 59% increase, compared to noninfested plants 10 days after infestation. The effect of larval feeding was also dependent on harvest time. The levels of gluconasturtiin increased by 52% from the first harvest (prior to infestation) to the second harvest (10 days after infestation) in both larval feeding densities. Seventeen days after infestation (final harvest), gluconasturtiin content experienced a nonsignificant 6% decrease, compared to the previous harvest.