The relationship between fruit maturation and accumulation of hydrogen peroxide (H2 O2), lipid peroxidation, ethylene (C2 H4) production, antioxidant activity (hydrophilic, lipophilic and total) and the antioxidant enzyme ascorbate peroxidase (APX, EC 184.108.40.206) in fruit pericarp tissue of `Chandler' (Fragaria × ananassa Duch.) strawberry were measured. `Chandler' fruit pericarp maturation and ripening were accompanied by a decline in H2 O2 content early in fruit development followed by a rapid accumulation. An increase in membrane lipid peroxidation (thiobarbituric acid reactive substances, TBARS) coincided with accumulation of H2 O2, which preceded a rise in C2 H4 production. In general, antioxidant activity declined as fruit matured and ripened. APX enzyme activity increased by 2-fold and peaked at the pink stage of development and then gradually declined with ripening. H2 O2 may serve as a signal molecule to initiate the cascade of oxidative processes during maturation and ripening. APX enzyme activity during maturation and ripening was not substantial and thus, may not have a role in alleviating accumulation of H2 O2 and subsequent events related to oxidative senescence in fruit pericarp. To our knowledge, this is the first study to present fractionated antioxidant activities (HAA, LAA and TAA) from strawberry pericarp as assessed by the ABTS∼+ radical cation assay. A fundamental understanding of the mechanisms involved in the senescent related-oxidative changes during strawberry fruit ontogeny in relation to quality and nutrition is discussed.
Floyd M. Woods*, William A. Dozier Jr., Robert C. Ebel, David G. Himelrick, Cecilia Mosjidis, Raymond H. Thomas, Bryan S. Wilkins, and James A. Pitts
Chao Gao, Rui Yang, and Deyi Yuan
Camellia oleifera is an important woody edible oil plant in southern China. In this study, the developmental differences in ovules at different positions in the ovary of C. oleifera were observed. The developmental type and characteristics of aborted ovules, ratios of normal and aborted ovules, and their developmental differences after flowering were examined. Ovules near the stylar end and in the middle exhibit normal development and are able to form embryo sacs; lower ovules near the pedicel end are usually aborted. The proportion of abortion of four examined cultivars ranges from 10.2% to 33.3%. Aborted ovules can be divided into four categories: 1) nascent egg apparatus lacking distinguishable cells; 2) completely absent egg apparatus structure consisting of flocculent tissue; 3) lack of tissue, comprising only integument cells; and 4) the inner integument not constituting a micropyle channel, with incomplete egg apparatus development and generating abnormal ovules. At 120 days after pollination (DAP), significant distinguishable size differences were found between fertile and aborted ovules; aborted ovules ceased growth at 180 DAP. On fruit maturation, aborted seeds were still attached to the placenta.
Huicong Wang and Lailiang Cheng
Apple maturity is often assessed by starch hydrolysis index, skin color, soluble solids, flesh firmness, and the rate of ethylene evolution. In red-fruited apple cultivars, the intensity and extent of coloration is an important consideration in determining the time of fruit harvest. Negative relationships have been found between tree nitrogen (N) status and fruit skin pigmentation, but how N affects flesh starch breakdown has not been examined in detail. The objective of this study was to determine how N supply affects flesh starch breakdown relative to skin color development. Seven-year-old ‘Gala’/M.26 trees were provided with four levels of N (8.8, 26.4, 52.7, and 105.4 g N per tree) in a modified Hoagland's solution. The effects of N supply on yield, fruit quality, and fruit maturation were evaluated. At harvest, fruit in the lowest N treatment was significantly smaller and had lower soluble solids but higher starch concentration, better color, and higher firmness than those grown at higher N supplies. Increasing N supply decreased both anthocyanin synthesis and chlorophyll degradation in fruit skin. Flesh starch concentration was higher at higher N supply at 38 days before harvest but was lower at higher N supply at harvest. Starch degradation was completed earlier during cold storage with increasing N supply. These results indicate that increasing N supply delays skin red color development but accelerates flesh starch degradation in ‘Gala’ apples. These differential effects of N supply should be taken into account when assessing fruit maturity for optimizing harvest time.
Haim Nerson, Ron Cohen, Menahem Edelstein, and Yosef Burger
The effects of paclobutrazol (cultar, PP333) on yield and fruit quality of muskmelon (Cucumis melo L. var. reticulatus Naud. cv. Galia) were examined in a series of field experiments, in the spring at Newe Ya’ar (northern Israel) and in autumn at Biq’at HaYarden (lower Jordan Valley, eastern Israel). In the spring experiments, paclobutrazol applied at 2 and 4 mg·liter−1 as a drench to the media-mix of muskmelon transplants increased total fruit yield 15% to 20% at various plant populations and in combination with ethephon and/or chlorflurenol, but tended to decrease the early yield. Yield increase was due to an increase in fruit weight rather than number. Paclobutrazol, in general, tended to improve marketable yield, yield concentration, and netting index. In the autumn experiment, paclobutrazol was applied at 250 mg·liter−1 as a spray from flowering through fruit maturation and compared with benzyladenine (BA), and N, P, and K fertilization. Paclobutrazol reduced early leaf-yellowing symptoms, but was not as effective as BA. Paclobutrazol in the autumn experiment did not affect yield or yield components, but soluble solids content was significantly increased and keeping-quality was unaffected. Chemical names used: β-[(4-chlorophenyl)methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-l ethanol (paclobutrazol); (2-chloroethyl)phosphonic acid (ethephon); (methyl-2-chloro-9-hydroxyfluorene-(9)-carboxylate) (chlorflurenol); benzyladenine (BA).
Avinoam Golomb and Eliezer E. Goldschmidt
Two alternate-bearing ‘Wilking’ mandarin (Citrus reticulata Blanco) trees, an “on” and an “off” tree, were uprooted and dissected into 11 organ types during the time of fruit maturation (February). Total or water-soluble N, P, K, Ca, and Mg (nitrate for soluble N) content were determined for each organ. Calcium was separated further into water-soluble, exchangeable, insoluble, and oxalate fractions. Leaves and twigs of on trees had reduced N, P, and particularly K levels. Organs of on trees, including minor roots and fruit, contained increased nitrate levels. Leaves, twigs, and minor roots of on trees accumulated Ca, mainly as Ca oxalate. The amounts of N, P, and K present in the fruit represented 32.2%, 43.7%, and 57.8%, respectively, of the total for an on tree. Fruit were very low in Ca, containing only 6% of the tree total. A 15-month follow-up of seasonal fluctuations in minerals of on and off ‘Wilking’ trees showed that the mineral composition of leaves and twigs was rapidly changed by the presence or absence of fruit. Defruiting in July prevented mineral depletion and permitted reasonable flower-bud differentiation on subsequent year. Leaf disks of on trees had low initial nitrate–reductase activity but responded weakly to nitrate induction. Leaves of overloaded on trees appear to suffer from a metabolic disorder involving relatively high nitrate levels, Ca accumulation, and loss of the nitrate–reductase induction response.
Anita Nina Miller, Beth Allyn Krizek, and Christopher S. Walsh
The rate of ethylene evolution of peach fruit (Prunus persica L. Batsch) and ACC content of peach pericarp/mesocarp and seeds was determined during development. Ethylene measurements of whole fruit began 18 days after anthesis (DAA), and ACC quantification was started 32 DAA. ACC levels and ethylene evolution followed similar patterns during stages I and II of fruit growth. At 39 DAA, there was an increase in ethylene evolution and extractable ACC concentration of both pericarp and seeds; however, variability was high at this time. Ethylene evolved by nondeveloping fruit of the “second wave” and “June drop” increased after senescence of the ovule was observed. By 49 DAA, ethylene production and ACC concentration reached a minimum that lasted until a 10-fold increase in ethylene evolution was detected in late stage III. This 10-fold increase in ethylene occurred in four different peach cultivars sampled at “firm-ripe” stage. Seeds excised at 67 DAA, which were incubated for 6 hr in ambient O2 conditions, evolved 400 nl·g−1·hr−1 ethylene and ACC concentration averaged 54 nmol·g−1 fresh weight. It is suggested that in split-pit fruits, ethylene generated by the seeds may accelerate fruit maturation and ripening. Chemical name used: 1-aminocyclopropane-1-carboxylic acid (ACC).
T. J. Facteau
Foliar applications of gibberellic acid (GA3) to mature ‘Lambert’ sweet cherry trees (Prunus avium L.) about 21 days before harvest increased fruit weight (fresh and dry), soluble solids (SS), alcohol-insoluble substances (AIS) (both concentration and per fruit), ash weight, and fruit firmness at harvest. Application of GA3 did not affect concentrations of ethylene diamine-tetraacetic acid (EDTA) or pectinase-soluble pectins and fruit Ca. GA3-treated fruit had lower concentrations of water-soluble pectins and reduced surface pitting. Fruits sampled at 3–7 day intervals (starting about 21 days before harvest) from control and GA3-treated trees showed that as an average response over a 29-day sampling period GA3 increased fruit weight, firmness, AIS concentration, AIS per fruit, pectinase-soluble pectins, and decreased water-soluble pectins. Neither total, residual, or soluble fruit Ca were affected by treatment with GA3. Fruit Ca levels remained constant, on a per fruit basis, during the last 3 weeks of fruit maturation but Ca concentration, expressed as fresh or dry weight, decreased as a result of increased fresh and dry weight. Higher Ca levels were not associated with firmer fruit (comparing GA3 and nontreated fruit), but were correlated positively with firmness in nontreated fruit.
G. Nir, I. Klein, S. Lavee, G. Spieler, and U. Barak
The effect of evaporative cooling on budbreak and yield of Vitis vinifera L. (‘Perlette’ and ‘Thompson Seedless’) vines grown in the southern Jordan Valley in Israel was investigated. Overhead microsprinklers were operated from 0600 to 1800 hr daily during the autumn and winter months, either alone or in combination with cyanamide sprays after pruning. Evaporative cooling decreased the temperature of buds exposed to direct sunlight from 30° to 16°C and that of shaded buds from 25° to 13°. Evaporative cooling induced an early uniform budbreak. However, when evaporative cooling was combined with cyanamide spray, its effect was evident only during the initial phase of bud emergence. In 1985 cyanamide spray and evaporative cooling alone increased yield of ‘Perlette’ by 6% and 6% to 24%, respectively, and by 17% to 46% when both treatments were combined. In 1986 prolonged evaporative cooling increased the yield of ‘Perlette’ by 25% but, in combination with cyanamide, by only 11.6% over the unwetted cyanamide-treated control. In both years, evaporative cooling with or without cyanamide advanced fruit maturation.
Sylvia M. Blankenship and C.R. Unrath
Internal ethylene levels, fruit firmness, soluble solids content, and starch–iodine reaction in ‘Delicious’ and ‘Golden Delicious’ apples (Malus domestica Borkh.) were measured weekly for 6 to 8 weeks during fruit maturation for 3 years. Internal ethylene level did not consistently correlate with minimum maturity as judged by agricultural inspection or optimum maturity as judged by a taste panel in either cultivar. Internal ethylene levels ranged from 0 to 26 μl·liter−1 in ‘Delicious’ and 0 to 41 μl·liter−1 in ‘Golden Delicious’ on taste panel harvest dates. Decreases in fruit firmness and increases in starch conversion and soluble solids content were observed prior to any increase in internal ethylene in both ‘Delicious’ and ‘Golden Delicious’. Thus, internal ethylene concentration is not a reliable index of maturity for harvest determination for immediate sale on the fresh market. The combination of fruit firmness decrease, soluble solids increase, and conversion of starch seem to be more closely tied to perception of maturity by both the agricultural inspectors and taste panel.
Shohei Yamaki and Kazuko Ishikawa
Activities and roles of 4 sorbitol enzymes, sorbitol-6-P dehydrogenase, NAD+-dependent sorbitol dehydrogenase, NADP+-dependent sorbitol dehydrogenase and sorbitol oxidase, and acid invertase in apple (Malus domestica Borkh. ‘Jonnagold’) leaves and fruit were studied. Almost all of the soluble carbohydrates in leaves are present as sorbitol throughout the season. Sorbitol-6-P dehydrogenase had the highest activity among the enzymes, being high in young leaves and decreasing with age; whereas NAD+- and NADP+-dependent sorbitol dehydrogenases and sorbitol oxidase activities were barely detectable. Sorbitol was translocated from leaves to fruits where it was readily metabolized to other sugars, so the sorbitol concentration did not increase. NAD+-dependent sorbitol dehydrogenase that converts sorbitol to fructose had the highest activity of the 4 enzymes in developing fruits. Its activity rose in June, decreased in midseason, and increased again with fruit maturation. The fluctuation in enzyme activity corresponded to changes in fructose concentration. Sorbitol oxidase activity, which was about one-fifth that of NAD+-dependent sorbitol dehydrogenase, increased proportionately as fruits enlarged. Acid invertase activity was distinctly higher than sorbitol enzyme activities in both leaves and fruit, but its roles in sugar translocation and metabolism were not clearly established. The levels of sorbitol in stems and peduncles remained relatively constant during the season indicating that little metabolism occurred in the phloem during transit.