Polygalacturonase-mediated dissolution and depolymerization of pectins in solutions mimicking the pH and mineral composition of tomato fruit apoplast

• Published in: Plant science (Limerick) Vol. 172; no. 6; pp. 1087 - 1094
• Main Authors: Almeida, Domingos P.F., Huber, Donald J.
• Format: Journal Article
• Language: English
• Published: Shannon Elsevier Ireland Ltd 01.06.2007; Elsevier Science
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; Calcium; Cell wall; cell walls; Economic plant physiology; enzyme activity; Fructification, ripening. Postharvest physiology; fruits (plant anatomy); Fundamental and applied biological sciences. Psychology; Growth and development; Lycopersicon esculentum; mineral content; pectinesterase; Pectinmethylesterase; pectins; plant biochemistry; Polygalacturonase; Polyuronides; Solanum lycopersicum var. lycopersicum; tomatoes; uronic acids; Pectinmethylesterase; Polyuronides; Polygalacturonase; Calcium; Cell wall; Lycopersicon esculentum; Fruit; Enzyme; Apoplast; Dicotyledones; Glycosidases; Angiospermae; Hydrolases; Spermatophyta; Solanaceae; O-Glycosidases
• ISSN: 0168-9452; 1873-2259
• DOI: 10.1016/j.plantsci.2007.03.008

The effects of polygalacturonase (PG) on pectin dissolution and depolymerization were examined in cell walls from mature-green tomato fruit incubated in a conventional (C) buffer (30 mM sodium acetate, 150 mM NaCl, pH 4.5) and in buffers mimicking the apoplastic solution of mature-green (MG) and ripe fruit (R). Pectin dissolution from cell walls was much higher in C-buffer than in MG- or R-buffers. Buffered phenol inactivated cell walls incubated in C-buffer released 4.9 μg mg −1 pectin, which increased to 86.4 μg mg −1 when PG was added. In the R-buffer, PG increased the pectin dissolution from inactive cell walls from 0.5 to 18.3 μg mg −1. However, when the assay was conducted in buffer mimicking mature-green fruits, added PG did not increase pectin dissolution. The release of uronic acids from active cell walls in C-buffer and R-buffer was consistently lower than that from inactive walls due to the activity of pectinmethylesterase. Gel filtration profiles of CDTA-soluble pectins extracted from cell walls previously incubated in C-buffer or R-buffer with PG reveal that the enzyme is capable of hydrolyzing insoluble, ionically bound, pectins. These data support the idea that pH and mineral composition of the fruit apoplast provide a means for biochemical regulation of cell wall metabolism.