Abstract
Two studies were carried out to determine if the relatively constant length of seasons (LOS) for ‘Delicious’ apples (Malus domestica Borkh.) was controlled by the number of light-dark cycles (days). Potted, bearing trees received 19-hour light-dark (19 L-D) cycles and 24-hour light-dark (24 L-D) cycles in growth chambers during July and August. At the end of treatment period, 19 L-D trees received 15 more light-dark cycles than 24 L-D trees. In the second study, orchard trees were illuminated with 2200–4400 lux for 75 min beginning at midnight during July and August. Measurements of skin chlorophyll, flesh firmness, titratable acidity, total soluble solids content, and ethylene evolution of harvested fruits as well as internal C2H4 concentrations in attached fruit indicated that maturation and ripening of ‘Delicious’ apples were not affected by these treatments.
Abstract
There is continual change in the acidity of tomato fruits during development and maturation. The concn increases during development and reaches a maximum near incipient color, then decreases until well beyond maturity. The inheritance of citrate and malate concn in ‘Tondo Liscio’ (TL) and PI 263713 (PI) is controlled by a single gene for each compound. The dominant alleles, which were linked in the coupling phase in PI, condition a high concn of citrate and a low concn of malate. Recombination was about 18%. Study of divergent tomato accessions indicated that there are factors which condition higher and lower concn of citrate than the range delimited by TL and PI. There appears to be more than one malate factor controlling higher concn, but many tomato accessions are similar to the dominant low parent (PI). Current evidence indicates that there is no practical reason to breed for a specific citrate/malate ratio.
Abstract
cis, trans-Abscisic acid (ABA) was identified by combined gas chromatography-mass spectrometry (GC-MS) in a partially purified methanol extract of mature seeds of peach (Prunus persica (L.) Batsch). No germination of intact seeds occurred during seed maturation. Germination of excised embryos increased with maturity, but ABA content of embryonic axes and other seed parts was not related to germination potential. Drying and storage of seeds increased both free and bound ABA in the embryonic axes, but did not significantly affect ABA content of other seed portions. Free and bound ABA decreased on imbibition except for free ABA in the seed coat and bound ABA in the embryonic axis, Levels of free and bound ABA paralleled one another, suggesting that although the former may be converted to the latter, bound ABA is not a major source of free ABA.
An invertase gene was isolated and its mRNA activity and protein levels were determined during papaya (Carica papaya L.) fruit development. A complete invertase cDNA (AF420223) and a partial sucrose synthase cDNA (AF420224) were isolated from papaya fruit cDNA libraries. The invertase cDNA encoded a predicted polypeptide of 582 residues (MW 65,537 Da), and was 68% and 45% identical with carrot apoplastic and vacuolar invertases, respectively. Key amino acids indicative of an apoplastic invertase were conserved. A full-length gene corresponding to the putative apoplastic invertase cDNA was isolated and was organized into seven exons and six introns. Exon 2 (9 bp long) encoded part of a highly conserved region (NDPNG/A). Invertase mRNA and activity levels increased during fruit maturation and sugar accumulation just before ripening. In contrast, sucrose synthase mRNA levels were high during early fruit growth and low during the fruit sugar accumulation stage. A 73-kDa cell wall extractable protein that cross-reacted with carrot apoplastic invertase antisera substantially increased during papaya fruit maturation and declined in full ripe fruit. The increase in invertase protein levels occurred 2 to 4 weeks before maturity and was markedly higher than the overall increase in enzyme activity at this stage. Subsequently, the increase in enzyme activity was higher than the increase in protein levels between 2 weeks before maturity and fully ripe. The results suggested that mRNA level and invertase activity were related to maturity. The data suggested that the invertase was apoplastic, and that post-translational control of enzyme activity occurred, in which a significant accumulation of invertase occurred before the peak of enzymes activity.
Quantitative and qualitative changes in net production of volatile compounds by apples occurs during fruit development with a major transition to ester production occurring as fruit ripening begins. Ester production during fruit ripening is an ethylene-mediated response; however, differences in maturation patterns among apple cultivars led us to examine the relationship between ester production and onset of the ethylene climacteric in several commercial apple cultivars. Emission of volatile esters as a function of apple fruit development was evaluated for `Royal Gala', `Bisbee Delicious', `Granny Smith', and `Fuji' apple fruit during two harvest seasons. Apples were harvested weekly and analyses of harvest maturity were performed the day after harvest. Non-ethylene volatiles were collected from intact fruit using dynamic headspace sampling onto Tenax traps. Fruit from each harvest was stored at 1°C in air for 5 months (3 months for `Royal Gala') plus 7 days ripening at 20°C, then apples were evaluated for the development of disorders. The transition to ester production occurred after internal ethylene exceeded 0.1 μL for `Royal Gala', `Bisbee Delicious', and `Fuji'. Ester emission by `Granny Smith' apples remained low throughout the harvest period. Increased ester emission occurred after the optimum harvest date (as determined by the starch index and internal ethylene concentration) for controlled-atmosphere storage of `Bisbee Delicious' and prior to optimum maturity for `Royal Gala' and `Fuji'. A relationship between the potential for development of superficial scald and ester production at harvest was evident only for `Bisbee Delicious' apples.
Abstract
Internal ethylene of attached fruit of ‘Starkspur Golden Delicious’ apple as influenced by 6 rootstocks: Seedling, Mailing (M1) 1, Mailing Merton 106 (MM 106), M 7, OAR 1, M 26, at 2 levels each of soil-applied K and N were measured during maturation for 2 years (1980 and 1981). Ethylene evolution of detached fruit as a result of these treatments also was measured after 2.5 months of storage at 0°C in 1981. Internal ethylene in the attached fruit was less than 0.1 μl·liter-1 in late September and early October and began to rise between 9 Oct. and 15 Oct. Internal ethylene increased in all treatments, almost at the same time in 1980. In 1981, ethylene in the fruit on OAR 1 began to increase 9 days later than in the other rootstocks. However, levels of ethylene in the fruit were relatively low on OAR 1 and high on M 26 as compared to those on other rootstocks in late October 1980 and 1981 and during poststorage 1981 samplings. Ethylene levels in fruit from other rootstocks were similar. Because of these variable effects of rootstocks, and the effects of a low field temperature in reducing internal ethylene levels, field sampling of internal ethylene levels was an unreliable indicator of the proper harvest time, as measured by other maturity indices. No consistent influence of K or N applications was found in the internal ethylene of the attached fruit; however, high N applications increased ethylene evolution after storage.
Abstract
Total acidity was increased and pH reduced in ‘Cardinal’, ‘Tokay’, and ‘Pinot noir’ berries under a phototemperature of 15°C as compared to 35°C. Nyctotemp of 10, 15, and 20°C also increased acidity and reduced pH of fruits compared to those ripened at nyctotemp of 25 or 30°C, provided phototemp was not greater than 25°C. At 35°C phototemp, acidity of fruits ripened at 10°C nyctotemp was greater than that in fruits ripened at 30°C nyctotemp. Acidity and pH were usually not significantly different, however, between grapes matured at 15 and at 25°C nyctotemp. The level of malate in grape berries was inversely related to temp. Degree Brix of ‘Tokay’ fruits ripened at 35°C phototemp was less than that of fruits ripened at 15°C. However, nyctotemp had relatively little effect on concn of sugars in ‘Tokay’ and ‘Cabernet Sauvignon’ berries. Temperature during maturation had no significant effect on berry wt or on the level of arginine. The amount of proline in grapes depended on cultivar, fruit maturity, and temp during the ripening period.
Ethylene synthesis and sensitivity, and their relation to germination at supraoptimal temperatures, were investigated in lettuce (Lactuca sativa L.) seeds matured at 30/20 °C [12-h day/night, high temperature matured (HTM)] or 20/10 °C [12-h day/night, low temperature matured (LTM)]. HTM seeds of both thermosensitive `Dark Green Boston' (DGB) and thermotolerant `Everglades' (EVE) had greater germination at a supraoptimal temperature (36 °C), in both light or dark, than LTM seeds of DGB and EVE. HTM seeds of DGB and EVE produced more ethylene during germination than LTM seeds, regardless of imbibition conditions. The ethylene action inhibitor, silver thiosulfate, led to reduced germination in both cultivars. The ethylene precursor, 1-aminocyclopropane-1-carboxylic acid at 10 mm increased germination of both cultivars at supraoptimal temperatures, whereas germination of HTM seeds was greater than that of LTM seeds. No differences in ethylene perception were detected between HTM and LTM germinating seeds using a triple response bioassay. This study demonstrated that at least one method through which seed maturation temperature influences lettuce germination is by affecting ethylene production.
Abstract
Abscission layer formation during fruit maturation of sour cherry, Prunus cerasus L., occurred between the fruit and the pedicel. No abscission layer was formed between the pedicel and the spur. The abscission layer was first evident 12-15 days before fruit maturity. This layer was composed of 5-8 rows of cells in the transition zone between the fruit and pedicel and was first identified by its low affinity for haematoxylin. Cell separation occurred without rupturing of cell walls. Later cell wall collapse was apparent. Cells immediately distal and proximal to the line of separation were thin walled and prone to separate easily. No abscission layer was formed through the vascular bundles and no cell division was noted during layer formation. Abscission layer formation was observed in detached sour cherry fruit which was histologically similar to that observed in vivo. There was a close relationship between abscission layer formation and force required to separate the fruit from its pedicel. No abscission layer was observed, in the transition zone between the fruit and pedicel in the sweet cherry, Prunus avium L.
Thermotolerance in lettuce seed at high temperature was investigated using primed and nonprimed seed or seeds matured at 20/10°C and 30/20°C. During seed germination at 36°C, the structural changes of the seed coverings in front of the radicle tip were observed in an anatomical study. In all seeds during imbibition, regardless of seed maturation temperature or priming, a crack appeared on one side of the cap tissue and the endosperm separated from the integument in front of the radicle tip. Additional changes took place during imbibition: the protein bodies in the vacuoles enlarged and were gradually depleted, large empty vacuoles formed, the cytoplasm condensed, the endosperm shrank, the endosperm cell wall dissolved and ruptured, then the radicle elongated toward this ruptured area. The findings suggested that the papery endosperm layer presented mechanical resistance to lettuce seed germination and the weakening of this layer was a prerequisite to radicle protrusion at high temperature. Seeds of `Dark Green Boston', `Everglades', and PI 251245 matured at 30/20°C had greater thermotolerance than those matured at 20/10°C. Results of the anatomical study indicated that the endosperm cell walls in front of the radicle of seeds matured at 30/20°C were more easily disrupted and ruptured during early imbibition than seeds matured at 20/10°C, suggesting that these seeds could germinate quickly at supra-optimal temperatures. From anatomical studies conducted to identify and characterize thermotolerance in lettuce seed germination, it was observed that genotype thermotolerance had the ability to reduce physical resistance of the endosperm by weakening the cell wall and by depleting stored reserves.