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Kitren G. Weis and Barbara D. Webster

The drought-adapted, disease-resistant tepary bean (Phaseolus acutifolius A. Gray. var. acutifolius) is of great value as a potential gene donor of useful traits to the common bean (P. vulgaris L.). Analyses of flowering and fruiting patterns of tepary indicate that anthesis and abscission of reproductive structures within a raceme follow well-defined spatial and temporal patterns. Flowering occurs acropetally, and the probability of flowering decreases with distance from the most basal bud of the raceme. The probability of bud or pod abortion increases with distance from the basal bud, and the rate of abortion is highest in buds and pods proximal to the apex. Buds that never reach anthesis abort in the green-bud stage of development and aborting fruits cease development within the first 25% increase in pod length. In nonaborting fruits, the rate of seed abortion is 6%. A marked increase in abscission of all buds and fruits at all raceme nodes occurs before cessation of flowering.

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Christine Coker, Mike Ely, and Thomas Freeman

straight pod development. Harvest most often begins ≈70 d after planting and may continue for 25 to 30 d. Pods are 11 to 31 inches long and sometimes longer. The pods are used much like traditional pole beans ( Rubatzky and Yamaguchi, 1997 ; Van Horn and

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Wesley Gartner, Paul C. Bethke, Theodore J. Kisha, and James Nienhuis

commercialized as fresh or frozen snap beans. In a few cases, sugar contents in P. vulgaris fruit or fruit tissues have been sampled at multiple times of development. Reducing sugars, primarily fructose and glucose, in the snap bean cultivar Burpee’s Stringless

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Emilie Proulx, Yavuz Yagiz, M. Cecilia, N. Nunes, and Jean-Pierre Emond

The continuous development of improved snap bean cultivars throughout the years has provided germplasm with wide variety of colors, textures, shapes, and sizes to meet the growing conditions and taste preferences of consumers from many different

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Kiyozo Asada, Toshiharu Ohba, Shuichi Takahashi, and Ikunoshin Kato

Endo-xyloglucan transferase (EXGT, also called xyloglucan endotransglycosylase, or XET) is a cell wall enzyme catalyzing molecular grafting between xyloglucan molecules, which is essential for expansion and morphological change of plant cells. EXGT gene was first isolated by us from Azuki bean hypocotyl and sequenced and later isolated by several other groups from variety of plants including monocots. In tomato, three genes have been identified, i.e., LeEXGT, tXET-B1, and tXET-B2. LeEXGT mRNA accumulated transiently in early stage of development (immature green and mature green stage). It accumulated slightly also in breaker stage in which fruit color turns to pink. The peak of LeEXGT mRNA accumulation was ≈12 days after pollination. To elucidate a physiological role of EXGT, especially in fruit development, tomato plants were transformed to produce LeEXGT sense or antisense RNA constitutively using Ti plasmid-based transformation system, and we obtained several lines of plants with different levels of LeEXGT transcripts. In these transgenic tomatoes, fruit size was positively correlated with the level of LeEXGT transcripts monitored at its peak stage of expression. However, the refractive index of tomato fruit sap, which is closely correlated with the total solids contents and reflects the sugar status of the fruit, was negatively correlated with the level of LeEXGT transcripts. These results first represent the evidence that EXGT can control in vivo morphological and biochemical properties of plants by changing the level of its expression. This finding opens the possibility of improvement by transgenic approach of fruit plants, such as melon, watermelon, kiwifruit, and apple, in which sugar contents are important economic characters for evaluation.

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MiAe Cho, Brandon M. Hurr, Jiwon Jeong, Chaill Lim, and Donald J. Huber

Green or common beans ( Phaseolus vulgaris L.) are harvested at a physiologically immature stage of development. Growth is rapid at the time of harvest and beans exhibit comparatively high respiration rates, even when held at low temperatures

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Bruce D. Whitaker and Gene E. Lester

Increases in phospholipase D (PLD) and lipoxygenase (LOX) activities are thought to play a key role in senescence of mesocarp tissues in muskmelon fruit. We have cloned and characterized two full-length cDNAs, CmPLDα and CmLOX1, encoding PLDα and LOX proteins in honeydew melon (Cucumis melo L. Inodorus Group). Levels of expression of the corresponding genes were determined by semi-quantitative RT-PCR in developing and mature fruit mesocarp tissues (20–60 d after pollination; DAP), and in roots, leaves, and stems from 4-week-old and flowers from 6-week-old plants. The coding regions of CmPLDα1 and CmLOX1 cDNAs are, respectively, 2427 and 2634 nucleotides long, encoding proteins 808 and 877 amino acids in length. CmPLDα1 is most similar to PLDα genes in castor bean, cowpea, strawberry, and tomato (77% nucleotide identity), and is the first cucurbit PLD gene cloned. CmLOX1 has 94% nucleotide identity to a cucumber LOX gene expressed in roots and 80% identity to cucumber cotyledon lipid body LOX. Transcript of CmPLDα1 was much more abundant than that of CmLOX1, but relative levels of transcript in the various organs and tissues were similar for the two genes. Expression was highest in roots, flowers, and fruit mesocarp tissues. CmPLDα1 expression in fruit was high throughout development, although maximum levels occurred at 50 and 55 DAP, respectively, in middle and hypodermal mesocarp. CmLOX1 expression was generally higher in middle than in hypodermal mesocarp with maximum transcript levels at 55 and 50 DAP, respectively. Overall, the patterns of expression of CmPLDα1 and CmLOX1 are consistent with a model in which their encoded enzymes act in tandem to promote or accelerate senescence in fruit mesocarp tissues.

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Bruce D. Whitaker and Gene E. Lester

Increases in phospholipase D [PLD (EC 3.1.4.4)] and lipoxygenase [LOX (EC 1.13.11.12)] activities are thought to play a critical role in senescence of mesocarp tissues in netted and nonnetted muskmelon (Cucumis melo L.) fruits. We have cloned and characterized two full-length cDNAs, CmPLDα1 and CmLOX1, encoding PLDα and LOX proteins in honeydew melon (C. melo Inodorus Group cv. Honey Brew). Relative levels of expression of the corresponding genes were determined by semi-quantitative RT-PCR in developing and mature fruit mesocarp tissues [20-60 d after pollination (DAP)], as well as in roots, leaves, and stems from 4-week-old and flowers from 6- to 7-week-old plants. The coding regions of CmPLDα1 and CmLOX1 cDNAs are, respectively, 2427 and 2634 nucleotides long, encoding proteins 808 and 877 amino acids in length. CmPLDα1 is very similar to PLDα genes from castor bean (Ricinis communis L.), cowpea (Vigna unguiculata L.), strawberry (Fragaria ×ananassa Duch.) and tomato (Lycopersicon esculentum Mill.) (77% nucleotide identity), and is the first PLD gene cloned from a cucurbit species. CmLOX1 has 94% nucleotide identity to a cucumber (Cucumis sativus L.) LOX gene expressed in roots and 80% identity to cucumber cotyledon lipid body LOX. In general, transcript of CmPLDα1 was much more abundant than that of CmLOX1, but relative levels of transcript in the various organs and tissues were similar for the two genes. Expression was highest in roots, flowers, and fruit mesocarp tissues. CmPLDα1 expression in fruit was essentially constitutive throughout development, although maximum levels occurred at 50 and 55 DAP, respectively, in middle and hypodermal mesocarp. CmLOX1 expression was generally higher in middle than in hypodermal mesocarp with maximum transcript levels occurring at 55 and 50 DAP, respectively. Overall, the patterns of expression of CmPLDα1 and CmLOX1 are consistent with a model in which their encoded enzymes act in tandem to promote or accelerate senescence in fruit mesocarp tissues.

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Paul J.R. Cronje, Graham H. Barry, and Marius Huysamer

in Clementine and orange fruit during ripening J. Hort. Sci. 62 531 537 Todd, G.W. Bean, R.C. Propst, B. 1961 Photosynthesis and respiration in developing fruits. II. Comparative rates at various stages of development Plant Physiol. 36 69 73 Turrell

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Mari Marutani, Joseph Tuquero, Robert Schlub, and James McConnell

The effects of a vesicular–arbuscular mycorrhizal fungus, Glomus aggregatum inoculation were examined on growth of vegetable crops in pot culture and field experiments with Guam cobbly clay loam soil (clayey, gibbsitic, nonacid, isohyperthermic Lithic Ustorthents). In pot experiments, the growth response of yard-long beans (Vigna unguiculata subs. sesquipendalis), sweet corn (Zea mays), watermelon (Citrullus lanatus), cucumber (Cucumis sativus), okra (Abelmoschus esculentus), green onion (Allium fistulosum), eggplant (Solanum melongena), and papaya (Carica papaya) were significantly improved with mycorrhizal inoculation. A pot experiment was also conducted to evaluate effects of G. aggregatum inoculation on the growth of corn seedlings at four different water regimes. Seedlings inoculated with G. aggregatum significantly improved the plant growth and the mineral uptake at all levels of water treatments. In the first field trial, prior to seed sowing the media in seedling trays were either inoculated or not inoculated with G. aggregatum. Treated watermelon and eggplant seedlings were transplanted in field. It was found that inoculating seedlings did not improve the harvest yield of two fruit-bearing crops. The second field experiment was conducted to study G. aggregatum inoculation and different levels of inorganic fertilizer application on growth of corn. Mycorrhizal colonization had positive effects on corn development and uptake of some minerals such as Fe. Experiments in the study suggested potential uses of a mycorrhizal fungus in an alkaline soil in the tropics.