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  • Author or Editor: Seong Mo Kang x
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Abstract

Glutamate synthase (L-glutamine:2-oxoglutarate aminotransferase, NADPH-oxidizing, E.C. 2.6.1.53) was isolated from bark tissue of the apple (Malus domestica Borkh. cv. Golden Delicious). The enzyme was partially purified by ammonium sulfate fractionation and diethylaminoethyl-cellulose chromatography. The enzyme was specific for L-glutamine and α-ketoglutarate as a nitrogen donor and acceptor, respectively. Both NADH and NADPH were found to be equally effective as reductants, although NADH appeared to be a physiological electron donor. The enzyme exhibited maximal activity at pH 8.0. Michaelis-Menten constants of the enzyme were 440, 50, 2.6, and 2.4 μΜ for L-glutamine, α-ketoglutarate, NADH and NADPH, respectively. L-Glutamate inhibited the enzyme activity competitively with respect to α-ketoglutarate, the estimated inhibition constant being 0.48 mm. The significance of this enzyme in the annual nitrogen recycling process in the apple is discussed.

Open Access

Heavy pruning to lower tree height of persimmon results in excessive production of water sprouts and reduced yield. This experiment was conducted on ‘Fuyu’ (Diospyros kaki) trees to assess if the time for terminal bud set of water sprouts affected flower bud formation. Some sprouts were not pruned to serve as fruiting branches for the next season. Thirty to 40 water sprouts were tagged in 2005 and 2006, the growth of which stopped from mid-June to late August. The later terminal buds set, the lower the percent dry weight in the apical 10 cm. The apical segments of sprouts that continued to grow to mid- to late August were characterized by low soluble sugars, starch, and inorganic elements such as nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) compared with those that set terminal buds earlier. The number of flower buds from the water sprouts that set terminal buds by early August the previous year bore more than 12 flower buds the next year, whereas those that grew to mid- to late August bore fewer than three. It was concluded that water sprouts could be used as fruiting branches for the next year as long as terminal buds set by early August, thereby alleviating yield reductions that come with heavy pruning.

Free access

The effects of fruit load and nitrogen (N) rate (0, 20, and 40 g N per tree) on fruit characteristics and the composition of nitrogenous compounds (e.g., amino acids and protein) and nonstructural carbohydrates in different plant tissues were determined in container-grown 5-year-old ‘Fuyu’ persimmon trees. Leaf-fruit (L/F) ratios were adjusted to either 20 (high) or 10 (low) by fruit thinning on 2 July. N was applied by fertigation as 1% (w/v) urea from 3 July to 20 Sept. The low L/F ratio decreased size and coloration of fruits, whereas increasing N rate resulted in fruits with low skin color and soluble solids but with high firmness. The high L/F ratio increased N concentrations only in 1- to 4-year-old wood and the trunk, whereas increasing N rate increased N concentrations of all tree tissues, especially of roots. The L/F ratio did not significantly affect the composition of nitrogenous compounds and carbohydrates in the tree tissues. As N rate increased, amino acid concentrations increased in all the tree parts, especially in aerial wood and roots where a three- to eightfold increase was observed between the 0- and 40-g N rates. Although not great, protein concentrations also increased with increasing N rate. Increasing N rate significantly reduced soluble sugars in fruit, trunk, and root and starch in leaf and root. The results indicated that an excessive supply of supplemental N could delay fruit maturation and reduce carbohydrate accumulations of ‘Fuyu’ trees regardless of the L/F ratios.

Free access

Abstract

The extractable protein in bark tissue of 1-year-old shoots of apple trees (Malus domestica Borkh. cv. Golden Delicious on Mailing (M) 26 rootstocks) declined dramatically during spring growth, while amino acids increased. Extensive degradation of protein was first visible at the silver-tip stage of growth. Prior to this period, some redistribution of nitrogenous compounds was indicated by the increase in amino acids while protein remained unchanged. Total extractable nitrogen declined during spring growth, indicating that it was mobilized to developing tissues. In vitro activity of an acid endoprotease increased rapidly upon regrowth, but its increase preceded the in vitro decline in proteins. The autolytic activity, however, did not change in the early growth stage, and protein had already declined 50% when this activity significantly increased. Electrophoretic separation of intact proteins indicated a substantial shift in relative mobility from higher to lower molecular weights as the season advanced. However, the majority of proteins showed little evidence of net breakdown during early spring growth. Two polypeptides of 38,000 and 56,000 daltons which were present up until mid-April were not detected in extracts of shoots collected in May. The 65% decline in total protein observed by May 10, however, could not be accounted for by the loss of these 2 peptides. It is thus concluded that the immediate requirement of nitrogen at the early stage of growth (up to silver-tip) is met by the transport of soluble nitrogen present in adjacent bark and that redistributed from the wood. The large requirement of nitrogen after silver-tip stage of growth is then met by massive breakdown of storage proteins.

Open Access

A possible relationship between leaf SPAD readings and nitrogen (N) concentrations was evaluated at different growing stages of ‘Fuyu’ persimmon trees under different N regimes in pots and in the field. When 5-year-old trees grown in pots received 0 to 40 g N over the growing season, leaf SPAD reading, N concentration, and specific leaf weight tended to increase with increasing N rate. The correlation between leaf SPAD reading and N concentration was statistically significant from late April to early November (R 2 = 0.72 to 0.97). It was noted that the slope of regression line decreased as the season progressed. Similar significant correlations were found from pot-grown 4- to 7-year-old trees grown under various nutrient regimes (R 2 = 0.67 to 0.96). Significant correlations were also confirmed with the leaves collected from 31 commercial orchards at different locations. The highest coefficient of determination was observed from the leaves collected at harvest time in both the pot and field experiments. Although the regression equations differed depending on the growing stage of trees, SPAD readings were found useful in estimating leaf N status at a specific time and in quickly judging the need for N application at that time. Seasonal changes of leaf SPAD readings from five well-managed orchards are presented as a reference guide for practical use.

Free access

To study ripening-related chilling injury in pepper (Capsicum annuum L.), chilling-tolerant ‘Buchon’ and chilling-sensitive ‘Nockgwang’ fruit were harvested at mature green (MG), breaker (BR), and red-ripe (RR) stages and stored at 1, 5, and 10 °C for 21 d. ‘Buchon’ did not show surface pitting (SP) regardless of ripeness stage and storage temperature, whereas ‘Nockgwang’ at MG and BR exhibited SP at 1 and 5 °C. After 14 days of storage at 1 °C, chilling-sensitive ‘Nockgwang’ did not show SP when fruit were at the RR stage. Compared with ‘Buchon’, ‘Nockgwang’ at MG and BR had more electrolyte leakage increase during storage at 1 and 5 °C. ‘Buchon’ at all ripeness stages showed significantly higher ethylene production during storage regardless of storage temperatures. Contents of β-carotene and lycopene increased in both cultivars as ripening progressed. The contents of β-carotene and lycopene were similar between the two cultivars regardless of storage temperatures and ripeness stages. Susceptibility of pepper fruit to chilling appeared to be related to superoxide dismutase (SOD) and catalase (CAT). Activities of SOD and CAT were much higher in ‘Buchon’ than ‘Nockgwang’, more apparently at MG and BR. The results suggest that chilling-tolerant ‘Buchon’ and fruit at RR could have been equipped with a more efficient antioxidizing system, even if it was not clear whether oxidative stress is a cause or an effect of the CI in pepper.

Free access

To study ripening-related chilling injury (CI) of bell pepper (Capsicum annuum L.), fruit at mature green, breaker, and red-ripe stages were stored at 1, 5, 7, and 10 °C for 4 weeks. Surface pitting was evaluated after storage at 1 °C for 2 weeks followed by a 2-day exposure to room temperature (20 °C). Exposing fruit to 1 °C enhanced water loss, respiration, ethylene production, and electrolyte leakage, but slowed color change. Weight loss, respiration, ethylene production, electrolyte leakage, and color change increased more in breaker than in mature green and red-ripe fruit. No pitting symptom was observed at temperatures of 5 to 10 °C. After storing peppers at 1 °C for 2 weeks, breaker stage fruit exhibited chilling symptoms of severe surface pitting with more sheet pitting and deeper peel depression. Mature green fruit showed only moderate pitting. However, red-ripe peppers showed no injury and cells showed a normal appearance after low-temperature storage (1 °C). These results show that bell peppers tended to be more susceptible to chilling temperature while at the breaker stage and that the increase in visible CI is correlated with increased water loss, respiration, ethylene production, electrolyte leakage, and color change during storage.

Free access