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Hideaki Yamaguchi, Yoshinori Kanayama, Junichi Soejima, and Shohei Yamaki

Seasonal changes in the amounts of the NAD-dependent sorbitol dehydrogenase (NAD-SDH) (enzyme code, 1.1.1.14) protein in developing apple (Malus pumila Mill var. domestica Schneid) fruit were determined by immunoblotting analysis. The amounts of the enzyme protein were very low in young fruit and rose as fruit matured. The weak correlation between enzyme protein and NAD-SDH activity and also the changes in NAD-SDH specific activity suggested that there could be posttranslational modification to the pre-existing enzyme or isoenzyme(s) of NAD-SDH. The changes in the amounts of NAD-SDH protein did not show the same pattern as those in relative growth rate, which is used to express sink activity, especially in young fruit. The role of NAD-SDH on sink activity in apple fruit, therefore, could not be explained simply by the amount and activity of the enzyme. In young fruit, it seems that enzymes other than NAD-SDH would be more directly related with fruit growth.

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Heeock Boo, Honggi Kim, and Hyunhwa Lee

temperature. They have been found to aid plant growth with diverse climatic conditions ( Albregts and Chandler, 1992 ; Brown et al., 1992 ; Porter and Etzell, 1982 ). Fruit growth requires an increase in sink activity, which is provided by activating

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Douglas D. Archbold

Over 4 years, using estimates of fruit dry weight derived from diameter measurements in situ, cultivar variation in apple fruit relative growth rate (RGR) in the period following June drop was evident. These differences diminished as the season progressed however. Using estimates of dry weight per cell, fruit cell absolute growth rate increased over time and RGR showed no clear pattern in contrast to the RGR of whole fruit. There were no cultivar differences in carbohydrate allocation among the soluble, starch, and remaining ethanol-insoluble, non-hydrolyzable pools irrespective of cultivar RGR. The storage carbohydrate pool comprised an increasing fraction of the total dry weight over time with the starch pool comprising 10 to 25% of the storage carbohydrate, varying with season and cultivar. Neither fruit competition within a cluster nor post-June drop thinning altered fruit RGR or carbohydrate allocation patterns when compared to fruit thinned post-bloom.

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Douglas D. Archbold

Absolute and relative fruit growth rates (AGR and RGR) of apple (Malus domestics Borkh.) were calculated from the fruit dry weights of several cultivars harvested periodically following June drop during 1988-90. AGRs were constant or varied slightly, and RGRs generally declined as the season progressed. Generally, both AGR and RGR values were higher for relatively large fruit of several cultivars with similar days to maturity, e.g., `McIntosh' vs. `Jonathan' and for summervs. fall-ripening cultivars, e.g., `Stayman' vs. others. An exception was observed in 1990, when `Golden Delicious' exhibited a higher AGR but lower RGR than `Rome Beauty', yet ripened 1 month earlier. `Golden Delicious' AGR and RGR values were lower for both fruit of a pair on a spur than the values for a single fruit on a spur, and the dominant fruit of the pair exhibited higher growth rates than the inferior fruit. Rates of sorbitol accumulation (SAR) by cortex disks incubated in 14C-labeled sorbitol solutions in vitro declined as the season progressed. Within a cultivar, SARS were not related to fruit size, nor were differences found between cortex disks from competing fruit on a spur, although SARS were higher for both competing fruit on a spur as compared to that of a single fruit per spur. Due to a positive correlation between RGR and SAR values, the SAR of cortex cells may be regulated in such a manner as to be a physiological constraint on fruit sink strength and growth rate.

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E.W. PAVEL and T.M. DEJONG

The fruit growth of three peach (Prunus persica (L.) Batsch cvs. `Spring Lady', `Flamecrest', `Cal Red') and two apple cultivars (Malus domestica Borkh. cvs. `Cox Orange', `Golden Delicious') was measured weekly during the 1988 growing period. Seasonal patterns of fruit relative growth rate calculated on a dry weight basis were very similar for both species. Changes in nonstructural carbohydrate composition of peach mesocarp and apple pericarp were correlated with the two physiological phases of sink-activity of the relative growth rates Changes in sucrose concentrations seemed to coincide with increasing dry matter accumulation for both species, even though fructose was a dominant sugar in apples.

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W.G. Yang and D.M. Glenn

The osmotic potential and development of apple and peach floral and vegetative buds and tissue were determined pre- and post-bloom. Apple and peach floral and vegetative buds were removed pre-bloom and the osmotic potential and bud development measured pre- and post-bloom. The osmotic potential of vegetative and floral buds was related to the phenology of bud development. Developing buds had a lower (more negative) osmotic potential than dormant buds. Removal of peach floral buds lowered osmotic potential and increased vegetative bud development and early leaf growth rate. Removal of peach vegetative buds, however, reduced fruit bud development, fruit growth, and embryo survival. Osmotic potential was an index of sink activity during the pre- and post-bloom stages of development.

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Theodore M. DeJong

The growth and development patterns of fruit have been studied for many years and it has become traditional to think of peaches as having a double sigmoid pattern with three main stages fruit growth. This concept is primarily based on analyses of fruit absolute growth rates An alternative approach is to express growth on a relative growth rate (RGR) basis which is simply the weight increase perg of fruit weight per day. This analysis applied to dry-weight peach fruit growth results in a two-phase curve that is known mathematically as a Gompertz function. During the first growth phase the RGR decreases logarithmically and during the second phase the RGR remains relatively stable. Expressing fruit growth on a RGR basis is advantageous for fruit growth carbon budget modelling because RGR is directly related to respiration rates and for physiological studies because most analyses for physiologically active substances are expressed on a weight basis. There is obviously not only one “right” way to express fruit growth but it may be instructive to use the RGR approach particularly when studying factors that may be associated with “sink” activity.

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Thomas E. Marler and Haluk M. Discekici

`Known You 1' papaya seedlings were grown in split-root containers and fertilizer was applied to one (1/2) or two (2/2) halves of the root system to determine the influence on transport of assimilates from canopy to roots and transport of nitrogen from fertilized roots to non-fertilized roots and canopy. Following 6 weeks of growth, the plants were bare-rooted and the root system halves and canopy were dried to constant mass at 70°C. Tissue was then analyzed for total nitrogen content. Fertilization increased root mass more than 250% and total plant mass 300% compared with control plants, which received no fertilization during the 6 weeks. Total root or plant mass did not differ between the 1/2 and 2/2 plants. Roots were evenly distributed between the two halves for 2/2 plants, but the fertilized half in the 1/2 plants accounted for 60% of the total root mass. Nitrogen content of roots and canopy were increased by fertilization. Nitrogen content of the non-fertilized roots of 1/2 plants was not different from that of the fertilized roots. These results indicate that fertilizing a portion of the papaya root system increased the sink activity of that portion and that the absorbed nitrogen from that portion is efficiently transported throughout the plant.

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H. Yakushiji, K. Morinaga, and Y. Koshita

The effects of 2,3,5-triiodobenzoic acid (TIBA) and naphthaleneacetic acid (NAA) on berry maturation and photoassimilates partitioning were investigated. Five-year-old potted `Kyoho' grape grown under a non-heating glasshouse were used. TIBA (200 mg/L) and NAA (200 mg/L) were applied to clusters at the beginning of veraison (45 days after full bloom). TIBA application increased not only soluble solids concentration in the juice but also anthocyanin content of peel, compared with those of control. On the other hand, the application of NAA reduced berry growth and delayed the berry maturation with harder flesh, lower soluble solids, higher acidity and poor coloration. In order to examine the effect of both plant growth regulators on photoassimilates partitioning in plant tissues, the whole plants were fed with 13CO2 at 10 days and 20 days after application of TIBA and NAA. The 13C distribution of pericarp and peel in NAA application was found on the lowest among the treatments. However, there were no significant differences in the 13C distribution and 13C absorption rate of pericarps between TIBA and control. These results indicate that NAA weakened the sink activity in grape berries, resulted in smaller berry size and the delay of maturation, whereas the berry ripening induced by TIBA application could not be explained by the distribution of photoassimilates in grape berries.

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E.W. Pavel and T.M. DeJong

Dry weights of whole fruit and of different fruit tissues, such as the mesocarp (with exocarp) and the endocarp (with seed), were accumulated on early (`Spring Lady'), midseason (`Flamecrest'), and late-maturing (`Cal Red') peach [Prunus persica (L.) Batsch] cultivars during the 1988 growing season. Seasonal relative growth rate (RGR) patterns of whole fruit showed two distinct phases for `Flamecrest' and `Cal Red'; however, `Spring Lady' did not exhibit two distinct RGR phases. The shift from phase I to phase II of the whole fruit RGR curve was related to an intersection of mesocarp and endocarp RGR curves, indicating a change of physiological sink activities in those fruit tissues in the later-maturing cultivars, but not in the early cultivar. Nonstructural carbohydrate compositional changes in concentration or content were similar in the three peach cultivars. Sucrose accounted for most of the seasonal increase in mesocarp nonstructural carbohydrate concentration. A sudden rise of sucrose was associated with the phase shift of the fruit RGR curves of the midseason and late-maturing cultivars, but not of the early maturing cultivar; however, in the early maturing cultivar, mesocarp compositional carbohydrate changes and, particularly, the sucrose increase, indicate that the physiological processes normally associated with the two phases exist in very early maturing fruit but are not associated distinctly with two separate RGR phases.