| Abstract: | Cell wall metabolism was studied in strawberry receptacles (Fragariaananassa, Duchesne) of known age in relation to petal fall (PF).Polysaccharide and protein composition, incorporation of 14C]glucoseand 14C]proline by excised tissue, and the fate of 14CO2 fixedby young, attached fruits were followed in relation to celldivision, cell expansion, fine structure, and ethylene synthesis. Cell division continued for about 7 d after PF although vacuolationof cells was already beginning at PF and the subsequent cellexpansion was logarithmic. There was an associated logarithmicincrease in sugar content per cell and a decreasing rate ofethylene production per unit fresh weight. During cell expansion radioactivity from 14C]glucose was incorporatedinto fractions identified as starch and soluble polyuronideand into glucose and galactose residues in the cell wall. Radioactivityfrom 14C]proline was also incorporated into the cell wall,but only 10 per cent of this activity was found in hydroxyproline.Correspondingly wall protein contained a low proportion of hydroxyprolineresidues. The proportion of radioactivity from 14CO2 fixed byfruitlets remained constant in most sugar residues in the cellwall. The proportion of radioactivity in galactose fell, indicatingturnover of these residues. Between 21 and 28 d after PF receptacles became red and softenedbut there was no change in the rate of ethylene production.Cell expansion continued for at least 28 d. Tubular proliferationof the tonoplast and hydration of middle lamella and wall matrixmaterial had begun 7–14 d after PF but became extremeduring ripening. Associated with the hydration of the wall,over 70 per cent of the polyuronide in the wall became freelysoluble, and arabinose and galactose residues lost from thewall appeared in soluble fractions. There was no increase intotal polysaccharide during ripening and incorporation of 14C]glucoseinto polysaccharides ceased, although protein increased andincorporation of 14C]proline into wall protein continued. |
