บทคัดย่องานวิจัย

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Evidence for cell wall synthesis during tomato (Lycopersicon esculentum mill.) fruit softening

Mitcham, Elizabeth Jeanne

Thesis (Ph. D.), University of Maryland at College Park, 1990. 192 p.

1990

บทคัดย่อ

EVIDENCE FOR CELL WALL SYNTHESIS DURING TOMATO (LYCOPERSICON ESCULENTUM MILL.) FRUIT SOFTENING.

Texture is the primary determinant of postharvest quality and resistance to decay of fruits and vegetables.  The major source of textural changes which occur during ripening is cell wall modification.  An emphasis on cell wall hydrolytic enzymes, such as polygalacturonase, has failed to explain the softening process.  Cell wall synthesis may have a plausible role in fruit softening.

 To study cell wall synthesis, a ((14)C(U)) sucrose pedicel injection technique was developed which uniformly radiolabeled the cell walls of the outer pericarp of tomato fruit in vivo.  Cell wall synthesis in normal-ripening 'Rutgers' fruit continued throughout development and ripening to the red stage and exhibited a transient increase in synthesis at the breaker stage.  Cell wall synthesis in the ripening mutant rin decreased to relatively low levels early in development (35 days post-anthesis) and remained low.  Cell wall synthesis in the ripening mutant nor occurred at a low level throughout development (20 to 75 days post-anthesis).  No increase in cell wall synthesis occurred in mature rin or nor fruit, which indicated that the burst in cell wall synthesis that occurred in 'Rutgers' fruit was ripening-related.

 Qualitative shifts in synthesis of 'Rutgers' pericarp tissue cell walls were indicated by a decrease in the specific activity of galactosyl residues in covalently-bound pectin (CBP) from the immature green to the mature green stage, indicating a specific decrease in the synthesis of galactose-containing CBP polymers.  Additionally, an increase in the specific activity of glucosyl and rhamnosyl residues in CBP occurred at the MG2 stage of development.  A qualitative shift in the types of cell wall polymers synthesized at the MG2 stage may provide biologically active wall fragments capable of stimulating fruit ripening.

 Synthesis of UDP- ((14)C(U)) -D-galacturonic acid by radish root (Raphanus sativus L.) and mung bean epicotyl (Phaseolus aureus Roxb.) enzyme particulate fractions was characterized and optimized.  HPLC technique was developed for separation and purification of UDP- ((14)C(U)) -D-galacturonic acid from other reaction products.  UDP- ((14)C(U)) -D-galacturonic acid can be used to assay galacturonan synthase during tomato fruit development and ripening.