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- Author or Editor: J. Perez x
- Journal of the American Society for Horticultural Science x
Abstract
Optimum conditions for in vivo activity of nitrate reductase (NR) from grape leaves (Vitis vinifera L.) were pH 7.5, 100 mm NO3 substrate, and incubation at 40°C. Pretreatment with low concentrations of NO3 (0.05m) at room temperature did not increase activity substantially.
Induction of NR by NO3 substrate was investigated. Enzyme activity was maximum at the highest NO3 levels.
Intact-tissue assay detected NR in mature leaves of grapevines, walnut (Junglans regia L.), plum (Prunus domestica L.), pears (Pyrus communis L.), and sweet cherry (Prunus avium L.) grown under field conditions. In addition, a particulate NR was demonstrated in walnuts and grapevine leaves by in vitro assay.
Bolting causes significant economic losses in sweet onion (Allium cepa L.) production. Although temperature and photoperiod are considered to be the main factors that initiate bolting in onions, preliminary results suggested that low N fertilization rates increased bolting. The objective of our study was to determine the relationships of bolting, yield and bulb decay with N fertilization rates. The N fertilization rates applied ranged from the infraoptimal to the supraoptimal (from 102 to 302 kg·ha-1 N). Shoot and bulb N content increased with increasing N rates, but there were no differences in the respective shoot and bulb N contents among cultivars. Bolting incidence declined steadily with increasing N fertilization rates up to 197 kg·ha-1 N. Bolting incidence was among the highest in the cultivar Pegasus. The percent of decayed bulbs also increased at a steady rate with the rate of N applied. Total (14.7 t·ha-1) and marketable (0.8 t·ha-1) yields at the lowest N rate (102 kg·ha-1 N) were lower (P ≤ 0.01) than those at higher N rates. Rates of N ≥145 kg·ha-1 had no significant effect on either total (mean = 33.6 t·ha-1) or marketable (mean = 21.6 t·ha-1) yields. Losses in marketable yield were primarily a combination of bolting and bulb decay and were minimized at 162 kg·ha-1 N. Yield losses at low N rates were mostly due to bolting while yield losses at high N rates were mostly due to decay. Thus, excess applications of N fertilizer should be avoided since they have little effect on yields or bolting but they increase bulb decay.
Abstract
There was an accumulation of total free amino acids (calculated as the sum of the individual amino acids) in corollas from cut ‘Sonia’ roses (Rosa hybrida) stored at 2C (cold-stored flowers) but not in those kept at 20C (control flowers). In cold-stored flowers, senescence was retarded, as indicated by only a slight opening of the corolla and no subsequent petal abscission. Hence, there appeared to be no direct correlation between senescence of cut roses and accumulation of total amino acids in corollas; neither was there a relationship between individual or total free amino acids and protease activity in the corollas from either cold-stored or control flowers. Changes in the contents of all free amino acids, except alanine and lysine, were affected by cold storage. The effect on aspartic acid was statistically significant, but not spectacular. Cold storage delayed the decrease in contents of glutamic acid, asparagine, tyrosine, glycine, leucine, isoleucine and valine, and prevented accumulation of phenylalanine, proline, and histidine. We detected only one theoretically expected interconversion between two amino acids; i.e., glutamic acid to proline, that occurred in corollas from control flowers during the first 6 days of storage. We suggest that the patterns of changes in the contents of tyrosine, valine, isoleucine (or isoleucine plus leucine), and phenylalanine are not restricted to the cultivar Sonia.
Antioxidants, antioxidant capacity, and the expression of isoprenoid metabolism–related genes and two pigmentation-related transcription factors were studied in four native and four hybrid tomato (Solanum lycopersicum) genotypes with different-colored fruit. Red fruit genotypes were associated with greater lycopene, β-carotene, lipophilic antioxidant capacity, and greater chromoplast-specific lycopene β-cyclase (CYC-B) transcript levels. Orange fruit genotypes had greater concentrations of tocopherols and greater transcript levels of homogentisate phytyl transferase (VTE-2), 1-deoxy-D-xylulose phosphate synthase (DXS), and 4-hydroxyphenylpyruvate dioxygenase (HPPD). The yellow fruit genotype was greater in total polyphenol and hydrophilic antioxidant capacity with greater expression of geranylgeranyl reductase (GGDR), phytol kinase (VTE-5), phytoene synthase (PSY) 2, lycopene β-cyclase (LCY-B), SlNAC1, and SINAC4. Greater levels of individual antioxidants were associated with specific coloration of tomato fruit. Moreover, the negative correlations between the expression of PSY1 and VTE-5, and between lycopene and chlorophyll, suggest a balance between carotenoids, tocopherols, and chlorophylls. The results of this study support either the direct commercialization of tomatoes with different color fruit or use of their genotypes in breeding programs to increase antioxidant levels among existing cultivars.
The differences in growth and yield in the Junebearing strawberry (Fragaria ×ananassa Duch.) `Elsanta' and the everbearing `Bolero' and `Everest' were evaluated under field conditions. The seasonal patterns of radiation use efficiency and assimilate partitioning were also studied. Growth, development and yield showed considerable differences among cultivars. `Elsanta' showed the highest and `Bolero' and `Everest' the lowest values for almost all the vegetative parameters (leaf area, leaf dry weight, runner number). `Elsanta' produced large leaves and few crowns per plant in contrast to the everbearing cultivars which had more but smaller leaves and a larger number of crowns per plant. The production of flowers by `Elsanta' was concentrated in June with fruit production following in July. `Bolero' and `Everest' produced more than one flush of flowers during the season and fruited until October. As a result, yields of `Bolero' and `Everest' were greater than `Elsanta'. The higher yields of `Bolero' and `Everest' also reflected the greater number of crowns produced by these cultivars. The maximum intercepted and absorbed photosynthetically active radiation (PAR) occurred between July and August when the three cultivars showed the greatest increase in vegetative growth. Harvest index clearly differed among cultivars and this was related to the duration of cropping. The greatest harvest indexes were found for `Bolero' and `Everest'.
Mulch (black plastic, wheat straw, or bare ground) and irrigation (drip or overhead sprinkler) treatments were evaluated for their effect on center rot of onion (Allium cepa L.), caused by the bacterium Pantoea ananatis, over the course of two seasons. Irrigation type had no effect on center rot incidence or severity in either year. In contrast, center rot development was delayed by 7 to 14 days on onions grown in straw mulch or bare ground compared to those in black plastic. Straw mulch resulted in later harvest dates and was associated with reduced levels of center rot. In contrast, black plastic increased disease incidence and hastened the onset of the epidemic. The spatial distribution of disease incidence in both years indicated the presence of a primary disease gradient. At harvest, infected plants were segregated by treatment and by duration of infection [based on disease ratings taken from the time of first symptom expression (beginning at 110 to 120 days after transplanting and then every 5 to 10 days until harvest)]. Early-vs. late-infected plants had no significant effect on yield (bulb weight). However, symptom expression in terms of the number of days after planting was significantly correlated with a disease severity index. Amount of rot in bulbs from plants displaying their first symptoms only 1 to 2 days before harvest (late-season infection) was not significant from rot levels in control bulbs at harvest. However, at 4 weeks after harvest, onions from plants with late-season infections exhibited significantly more rot in storage compared to the control.