Morales Quintana, Luis

Abstract: Fruit development and ripening are controlled by multiple plant hormones; for strawberries, recent evidence supports the role of abscisic acid (ABA) as a promoter of fruit ripening. Fruit softening during ripening is mainly a consequence of the solubilization and depolymerization of cell wall components mediated by the action of a complex set of enzymes and proteins. In the present work, we performed a comparative study (ABA-treatment vs. control) of the changes in the physiological properties of the cell wall-associated polysaccharide contents of strawberry fruit (Fragaria x ananassa ‘Camarosa’) via analysis of thermogravimetry (TG) combined with analysis of mRNA abundance, enzymatic activity and physiological characteristics. ‘Camarosa’ did not show a decline in the fruit firmness at 48 h post-treatment; however, we observed changes in cell wall stability based on the TG and differential thermogravimetric (DTG) analysis curves, which demonstrated the degradation of the cell wall polymers after ABA hormone treatment for 48 h, principally for hemicellulose polymers. Additionally, DTG analysis showed that dried samples derived from the treatment of the fruit with the ABA biosynthesis inhibitor fluridone maintained the same thermal stability as the control samples. Finally, the existence of a relationship between thermal stability, transcriptional analysis and enzymatic activity after hormone treatment was demonstrated, which provides the basis for a model for understanding the changes in the cell wall polymers of F. x ananassa mediated by the ABA hormone during fruit ripening. Graphic abstract: [Figure not available: see fulltext.]

Fragaria chiloensis (Chilean strawberry) fruit has been described as a fruit with excellent organoleptic properties, highlighting its flavor and aroma. However, the fruit has a high softening rate. Fruit softening during the ripening process is a consequence of the solubilization and depolymerization of cell wall components. In the present work, we performed a comparative study of the changes in the physiological properties of the cell wall-associated polysaccharide contents of Chilean strawberry fruit via thermogravimetric analysis (TGA) combined with analyses of mRNA abundance, enzymatic activity, and physiological characteristics. The results showed that the thermal stability was lower in the ripe stage sample than in the other two samples, while the first derivative of the thermogram (DTG) curve described four maximum peaks of degradation, between 175 and 375 °C. The percentage cumulative depolymerization (PCD) was higher in the ripe samples, and the PCD value of 325° C, where 51.65% of the carbohydrate polymers present in the cell wall have been depolymerized, was highlighted. Finally, the existence of a relationship between the percentage of the cell wall polymer degradation and the solid soluble concentration (SSC)/firmness ratio, provides the basis for a model for understanding the changes in cell wall polymers during fruit development. Graphic abstract: [Figure not available: see fulltext.]