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Michael Wisniewski and Les Fuchigami

During autumnal leaf senescence, leaf nitrogen is translocated to bark and root tissues for storage. By definition, proteins that accumulate in large amounts in winter and are absent in summer are called storage proteins. These storage proteins are believed to play an important role in spring growth and helping trees to tolerate and/or recover from both abiotic and biotic stress. Little knowledge exists regarding storage proteins in apple, their physiological function, or how management practices impact them. Our objectives in this research was to characterize seasonally regulated proteins in apple, develop knowledge about their physiological function, and determine how they are affected by management practices. Results of the first-year studies have identified four major proteins that exhibit a seasonal pattern of accumulation in bark tissues of apple. One of these is a pathogenesis-related protein, meaning that it plays a role in disease resistance. Another of these proteins is a stress-related protein important in the use of carbohydrates under stress conditions. A third protein is a vegetative storage protein serving as a reserve for nitrogen. The last protein has not been completely identified. Greatest seasonal fluctuation of these proteins occurred in current season and 1-year-old bark tissues. Experimental studies that achieved varying levels of nitrogen in shoot tissues of young Fuji apple trees were examined for the effect on the accumulation of these proteins. Results indicated that despite a significant increase in total nitrogen, increases in the accumulation of these proteins were only slight. Instead, it appears that most of the nitrogen was present as free amino acids rather than stable proteins. These data indicate that more knowledge is required to determine the benefits and feasibility of elevating the levels of specific proteins in dormant apple trees or trying to manipulate the type of amino acids that accumulate.

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Lawford Baxter and Luther Waters Jr.

Okra (Abelmoschus esculentus L. Moench) pods stored In a controlled atmosphere (CA) of 5% O2 and 10% CO2 at 11 ± 1C and in air at the same temperature (RA) were compared to determine the effects of the two storage environments on changes in sugars, organic acids, proteins and amino acids, and ascorbic acid contents within the tissue. Pods were sampled at 3-day intervals for 12 days. CA-stored pods generally had greater retention of sugars, soluble proteins, and amino acids than RA-stored pods. Citric, malic, and ascorbic acids contents of CA pods also declined more slowly than those of RA pods.

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Gregory A. Lang and Jiaxun Tao

We have previously demonstrated that a protein of ∼62 kD decreases in response to temperature during the final stages of chilling unit accumulation in dormant peach flower buds (Lang and Tao, 1991, HortSci. 26:733). To further examine proteins that potentially may be associated with endodormancy, floral buds, spurs, and/or shoots were collected during winter from `Anna' apple, various blueberry cultivars, `MidSouth' grape, `20th Century' pear, `Hawthorne' peach, and `Santa Rosa' plum. Soluble proteins were extracted and analyzed by one-dimensional SDS-PAGE. A major protein of ∼62 kD was present in plum, and lesser amounts of one or two similar proteins were found in blueberry, but not in apple or grape. The 62 kD peach protein originally found in buds was also present, in lesser proportions, in peach shoot xylem and phloem tissues, but not in petioles or seeds. Apple exhibited a major protein band at ca. 31 kD that may be a storage protein. The similarities and disparities in protein profiles between fruit crops, as well as changes that occur during winter, will be discussed with respect to dormancy, cold hardiness, and storage compounds.

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R.M. Madakadze, J.E. Krochko, and T. Senaratna

Storage proteins in zygotic and somatic embryos of `Scarlet Orbit Improved', zonal geranium (Pelargonium hortorum L.H. Bail.) were identified and characterized using gel electrophoresis. The major seed storage proteins in zygotic embryos were an 11S globulin and two low molecular weight (LMW1-2) proteins. The 11S globulin consisted of four distinct subunits (53-74 ku), with each subunit being composed of an acidic polypeptide (A1-A4; 28-44 ku) linked via disulphide bonds to a basic polypeptide (B1-B4; 20-25 ku) and was named pelargin. The LMW (15.5 and 12,5 ku) albumins were not linked with disulphide bonds. Mature somatic embryos contained 80% of the proteins in zygotic embryos. Although protein profiles were more distinct in mature somatic embryos compared to nonmature, none of the zygotic embryo storage protein was present in the somatic embryos, indicating lack of complete maturity of somatic embryos. This study identified zygotic embryo proteins and demonstrated that maturation of somatic embryos improves protein content and types of proteins.

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Keith T. Birkhold and Rebecca L. Darnell

The relative contribution of storage and currently assimilated N to reproductive and vegetative growth of `Bonita' and `Climax' rabbiteye blueberry (Vaccinium ashei Reade) was estimated immediately before and during the fruit development period. Total and storage N decreased in roots and shoots of both cultivars during dormancy and early fruit development. The principle N storage form appeared to be protein, as indicated by a significant decline in total shoot and root protein during this same period. Storage N from roots and shoots in both cultivars was remobilized to flowers and/or fruit and new vegetative growth. At anthesis, 90% of the total N present in reproductive organs was estimated to come from storage N. By fruit maturity, ≈ 50% of the accumulated N was derived from storage pools. Storage N contributed 90% of the total N in developing vegetative growth of `Bonita' at leaf budbreak, which is concomitant with floral budbreak for this cultivar. Developing vegetative growth of `Climax' at leaf budbreak, which occurs ≈ 4 weeks after floral budbreak, derived ≈ 65% of its total N from storage and 35% from currently assimilated N. By fruit maturity, contribution of storage N to new vegetative growth had decreased to ≈ 20% in both cultivars, indicating that currently assimilated N became the principal N supply as vegetative growth became more established. Differences in timing of floral and vegetative budbreak between the two cultivars did not appear to affect allocation of either storage or currently assimilated N to new vegetative or reproductive growth.

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I.L. Goldman and W.F. Tracy

Changes in endosperm type used for commercial sweet corn (Zea mays L.) production may affect corn protein levels. The two most widely used endosperm types are sugary-1 (su1) and shrunken-2 (sh2). To determine the effects of endosperm type on protein concentration, we calculated kernel N concentrations of dry mature kernels of seven inbreds near-isogenic for su1 and sh2 and of four samples of commercially canned su1 and sh2 sweet corn. Nitrogen values were converted to protein values using a standard conversion factor for maize. For the dry kernels and the canned samples, significant differences were detected between endosperm types for kernel protein concentration when measured on a weight basis. Averaged overall inbreds, the sh2 dry kernels had 30% more protein than su1 kernels. On a weight basis, the sh2 canned samples averaged 22% more protein than the su1 samples. When compared on a kernel basis, protein concentration of the two endosperm types did not differ. Thus, sh2 sweet corn marketed as a frozen or canned product may be identified as a higher protein product when the serving size is based on weight or calories.

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Kathryn C. Taylor, Danielle R. Ellis, and Luciano V. Paiva

Zinc in xylem and phloem of the citrus rootstock, rough lemon [Citrus jambhiri (L.)] was associated with a Zn-binding protein, designated citrus vascular Zn-binding protein (CVZBP). The apparent molecular mass of the CVZBP was 19.5 kDa after nondenaturing size exclusion chromatography and 21.8 kDa after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Ion exchange chromatography demonstrated that CVZBP was anionic, requiring 0.43 n NaCl for elution from quaternary aminoethyl Sepharose. Antiserum to the protein cross-reacted more with total protein extracts from leaf midveins than with total protein from the rest of the leaf lamina, further suggesting a vascular location of the Zn-binding protein. Quantitative analysis indicated that ≈2 to 3 mol of Zn were associated with 1 mol of native protein. Binding studies with the partially purified CVZBP demonstrated a capacity to bind several divalent cations: Cd, Ni, Pb, and Zn. Reaction with Ellman's reagent suggested that the protein has significant sulfhydryl group content that may be involved in metal binding. N-terminal sequencing demonstrates identity with papaya latex trypsin inhibitor, sporamin, or other Kunitz soybean proteinase inhibitors.

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L. V. Gusta

Plants acclimate to abiotic stresses, e.g. heat, freezing drought and salinity, in response to environmental cues such as temperature, daylength and water. Plants can respond within minutes to the cue e.g. heat tolerance or within hours or days, e.g. drought and freezing tolerance. Heat shock proteins are measurable within 20 to 30 minutes of a heat stress and the plants aclimate almost immediately. In contrast, proteins related to freezing tolerance are measurable within hours but days are required before a measurable increase in freezing tolerance can be detected. In almost all stresses it appears that the environmental cue effects the water status of the plant which in turn affects the level of endogenous abscisic acid (ABA). ABA has been implicated to ameliorate the stress by inducing genes to produce stress proteins. There is a certain degree of commodity between stresses in ragards to stress proteins, however each stress has their own unique set of stress proteins. For example heat shock proteins did not confer stress tolerance. Proteins involved in water and osmotic stress tolerance share a high degree of commonality. I” all stresses a unique class of proteins are synthesized which are classified as heat or boiling stable (do not coagulate at 100°). These proteins are suggested to be involved in the stress response. Many of these heat stable proteins are induced by ABA alone or in combination with jasmonic acid (JA). Analogs of ABA which are either slowly converted to ABA or are degraded slowly or taken up at a faster rate than ABA have been tested for the efficacy in inducing the stress responses. Analogs have also been identified which inhibit the ABA induced response. How these analogs may have practical significance will be discussed.

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Begoña Del Cura, María I. Escribano, Jose P. Zamorano, and Carmen Merodio

The peel of `Fino de Jete' cherimoya (Annona cherimola Mill.) stored at 20 °C in air and in an atmosphere with high levels of CO2 was analyzed for changes in protein levels, color, chlorophyll content, and firmness. The accumulation of immunoreactive proteins was studied using Rubisco and polygalacturonase antibodies. During storage in air, cherimoya peel tissues exhibited a decrease in chlorophyll content and an immunodetected drop in the abundance of the large subunit of ribulose 1,5-biphosphate carboxylase (LSR). An immunodetected rise in polygalacturonase (PG)-related protein was quantified. High CO2 levels delayed the softening of cherimoya fruit, retarded the maximum accumulation of PG-related protein, and maintained LSR levels, greenness, and chlorophyll content of peel tissues.

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Robert Bevacqua, Eugene Mielke, Timothy Facteau, Ruth Lavon, and Paul Chen

An assay for pyruvate kinase (PK) was tested as a diagnostic tool for cork spot, a major physiological disorder in pear Pyrus communis L. cv. d'Anjou) fruit. PK activity and Ca and protein concentrations were measured in peel of normal and affected fruit during selected months in 2 years. Protein concentration was more closely associated with cork spot than PK activity or Ca concentration. These preliminary results suggested the PK assay was a poor diagnostic tool for cork spot.