The ultrastructural impact of low ethylene biosynthesis (less than 0.5% of normal levels) was evaluated in transgenic (A11.1) tomatoes (Lycopersicon esculentumMill.) expressing an antisense 1-aminocyclopropane-1-carboxylic acid synthase (ACC-S) transgene by means of transmission and environmental scanning electron microscopy. In 48-day mature green fruit, no significant ultrastructural differences were found between transgenic and control tomatoes. In 78-day control fruit, which were overripe and showed deteriorated texture, many areas of the cytoplasm were devoid of structures, and micrographs showed cell collapse with folding and dissolution of the cell wall. On the other hand, in 90-day transgenic fruit, which were firm and not ripe, the cytoplasm showed a relatively high electron density. Plastids retained remnants of chloroplast thylakoids along with significant amounts of osmiophylic plastoglobuli, but lycopene was not detected. Conspicuous starch granules were observed in mature green transgenic tomatoes, but were not detected in 90-day chlorochromoplasts. Electron-dense regions reflecting the integrity of the middle lamella alternated with other partially degraded regions. This incipient dissolution of the middle lamella pectic polymers may be attributable to nonenzymatic deaggregation or to cell-wall hydrolases which could be ethylene independent or responsive to very low levels of ethylene. Besides, cells were attached along extended contact areas and appeared turgid. This feature may provide an explanation of firmness retention that does not solely involve cell walls. Disruption of the middle lamella and development of lycopene crystalloids were observed when exogenous ethylene (12 ppm) was applied.
Barrett D.M., Garcia E. and Wayne J.E. (1998). Textural modification of processing tomatoes. CRC Critical Reviews in Food Science and Nutrition38: 173–258.
2.
Ben-Arie R., Kislev N. and Frenkel C. (1979). Ultrastructural changes in the cell walls of ripening apple and pear fruit. Plant Physiology64: 197–202.
3.
Brummell D.A., Harpster M.H., Civello P.M., Palys J.M., Bennett A.B. and Dunsmuir P. (1999). Modification of expansin protein abundance in tomato fruit alters softening and cell wall polymer metabolism during ripening. The Plant Cell11: 2203–2216.
4.
Carey A.T., Holt K., Picard S., Wilde R., Tucker G.A., Bird C.R., Schuch W. and Seymour G.B. (1995). Tomato exo-(1.4)- •-D-galactanase. Isolation, changes during ripening in normal and mutant tomato fruit, and characterization of a related cDNA clone. Plant Physiology108: 1099–1107.
5.
Carpita N.C. and Gibeaut D.M. (1993). Structural models of primary cell walls in flowering plants: consistency of molecular structure with the physical properties of the walls during growth. The Plant Journal3: 1–30.
6.
Crookes P.R. and Grierson D. (1983). Ultrastructure of tomato fruit ripening and the role of polygalacturonase isoenzymes in cell wall degradation. Plant Physiology72: 1088–1093.
7.
D'Souza M.C., Singha S. and Ingle M. (1992). Lycopene concentration of tomato fruit can be estimated from chromaticity values. Hort Science27: 465–466.
8.
Fishman M.L., Gross K.C., Gillespie D.T. and Sondey S.M. (1989). Macromolecular components of tomato fruit pectin. Archives of Biochemistry and Biophysics274: 179–191.
9.
Fraschina A.A., Cascone O. and Sozzi G.O. (2000). Alpha-Larabinofuranosidase during growth and ripening of tomatoes expressing an antisense ACC synthase transgene. In: Abstracts of IV International Conference on Postharvest Science. Jerusalem, Israel. March 26–31, 2000.
10.
Fraser P.D., Truesdale M.R., Bird C.R., Schuch W. and Bramley P.M. (1994). Carotenoid biosynthesis during tomato fruit development. Evidence for tissue-specific gene expression. Plant Physiology105: 405–413.
11.
Hallett I.C., MacRae E.A. and Wegrzyn T.F. (1992). Changes in kiwifruit cell wall ultrastructure and cell packing during postharvest ripening. International Journal of Plant Science153: 49–60.
12.
Harris W.M. and Spurr A.R. (1969a). Chromoplasts of tomato fruits. I. Ultrastructure of low-pigment and high-beta mutants. Carotene analyses. American Journal of Botany56: 369–379.
13.
Harris W.M. and Spurr A.R. (1969b). Chromoplasts of tomato fruits. II. The red tomato. American Journal of Botany56: 380–389.
14.
Hendry G.A.F., Houghton J.D. and Brown S.B. (1987). The degradation of chlorophyll—A biological enigma. New Phytologist107: 255–302.
15.
Hobson G. and Grierson D. (1993). Tomato. In: Seymour G.B., Taylor J.E. and Tucker G.A. (eds), Biochemistry of Fruit Ripening. University Press, Cambridge: Chapman and Hall. pp. 405–442.
16.
Kobayashi H. (1991). Differentiation of amyloplasts and chromoplasts. In: Bogorad L. and Vasil I.K. (eds.), The Photosynthetic Apparatus. Molecular Biology and Operation. New York: Academic Press. pp. 395–415.
17.
Lichtenthaler H.K. (1987). Chlorophylls and carotenoids: pigments of photosynthetic biomembranes. Methods in Enzymology148: 350–382.
18.
Maclachlan G. and Brady C. (1994). Endo-1,4- •-glucanase, xyloglucanase and xyloglucan endo-transglycosylase activities versus potential substrates in ripening tomatoes. Plant Physiology105: 965–974.
19.
Mignani I., Greve C., Ben-Arie R., Stotz H.U., Li C., Shackel K.A. and Labavitch J.M. (1995). The effects of GA 3and divalent cations on aspects of pectin metabolism and tissue softening in ripening tomato pericarp. Physiologia Plantarum93: 108–115.
20.
Mohr W.P. (1979). Pigment bodies in fruits of crimson and high pigment lines of tomatoes. Annals of Botany44: 427–434.
21.
Oeller P.W., Min-Wong L., Taylor L., Pike D.A. and Theologis A. (1991). Reversible inhibition of tomato fruit senescence by antisense RNA. Science254: 437–439.
22.
Orfila C. and Knox J.P. (2000). Spatial regulation of pectic polysaccharides in relation to pit fields in cell walls of tomato fruit pericarp. Plant Physiology122: 775–781.
23.
Pesis E., Fuchs Y. and Zaubermann G. (1978). Cellulase activity and fruit softening in avocado. Plant Physiology61: 416–417.
24.
Platt-Aloia K.M., Thomson W.W. and Young R.E. (1980). Ultrastructural changes in the walls of ripening avocados: transmission, scanning and freeze fracture microscopy. Botanical Gazette141: 366–373.
25.
Platt-Aloia K.M. and Thomson W.W. (1981). Ultrastructure of the mesocarp of mature avocado fruit and changes associated with ripening. Annals of Botany48: 451–465.
26.
Pressey R. (1983). •-Galactosidases in ripening tomatoes. Plant Physiology71: 132–135.
27.
Rottmann W.H., Peter G.F., Oeller P.W., Keller J.A., Shen N.F., Nagy B.P., Taylor L.P., Campbell A.D. and Theologis A. (1991). 1-Aminocyclopropane-1-carboxylate synthase in tomato is encoded by a multigene family whose transcription is induced during fruit and flower senescence. Journal of Molecular Biology222: 937–961.
28.
Seymour G.B. and Gross K.C. (1996). Cell wall disassembly and fruit softening. Postharvest News and Information7: 45N–52N.
29.
Shackel K.A., Greve L.C., Labavitch J.M. and Ahmadi H. (1991). Cell turgor changes associated with ripening in tomato pericarp tissue. Plant Physiology97: 814–816.
30.
Sitrit Y. and Bennett A.B. (1998). Regulation of tomato fruit polygalacturonase mRNA accumulation by ethylene: a reexamination. Plant Physiology116: 1145–1150.
31.
Smith C.J.S., Watson C.F., Morris P.C., Bird C.R., Seymour G.B., Gray J.E., Arnold C., Tucker G.A., Schuch W., Harding S. and Grierson D. (1990). Inheritance and effect on ripening of antisense polygalacturonase genes in transgenic tomatoes. Plant Molecular Biology14: 369–379.
32.
Smith D.L., Starret D.A. and Gross K.C. (1998). A gene coding for tomato fruit •-galactosidase II is expressed during fruit ripening. Cloning, characterization, and expression pattern. Plant Physiology117: 417–423.
33.
Sozzi G.O. and Fraschina A.A. (1997). Evaluation of sensory attributes and biochemical parameters in transgenic tomato fruit with reduced polygalacturonase activity. Food Science and Technology International3: 93–102.
34.
Sozzi G.O., Camperi S.A., Cascone O. and Fraschina A.A. (1998). Galactosidases in tomato fruit ontogeny: decreased galactosidase activities in antisense ACC synthase fruit during ripening and reversal with exogenous ethylene. Australian Journal of Plant Physiology25: 237–244.
35.
Spurr A.R. (1969). A low-viscosity epoxy resin embedding medium for electron microscopy. Journal of Ultrastructural Research26: 31–43.
36.
Steele N.M., McCann M.C. and Roberts K. (1997). Pectin modification in cell walls of ripening tomatoes occurs in distinct domains. Plant Physiology114: 373–381.
37.
Su L., McKeon T., Grierson D., Cantwell M. and Yang S.F. (1984). Development of 1-aminocyclopropane-1-carboxylic acid synthase and polygalacturonase activities during the maturation and ripening of tomato fruit. Hort Science19: 576–578
38.
Trinchero G.D., Sozzi G.O., Cerri A.M., Vilella F. and Fraschina A.A. (1999). Ripening-related changes in ethylene production, respiration rate and cell-wall enzyme activity in goldenberry (Physalis peruvianaL.), a solanaceous species. Postharvest Biology and Technology16: 139–145.
39.
Tucker G.A. (1993). Introduction. In: Seymour G.B., Taylor J.E. and Tucker G.A. (eds.), Biochemistry of Fruit Ripening. University Press, Cambridge: Chapman and Hall. pp. 1–51.
40.
Yang S.F. and Hoffman N.E. (1984). Ethylene biosynthesis and its regulation in higher plants. Annual Review of Plant Physiology35: 155–189.
41.
Zarembinski T.I. and Theologis A. (1994). Ethylene biosynthesis and action: a case of conservation. Plant Molecular Biology26: 1579–1597.
