Analysis of CaCl2 postharvest treatment on strawberry cell wall metabolism and defense responses of the fruit.

LANGER, SILVIA E; MARINA, M.; CIVELLO, P.M.; MARTÍNEZ, G.A.; VILLARREAL, N.M.

Wageningen

Congreso; VII International Conference Postharvest Unlimited & XII International Symposium on Postharvest Quality of Ornamental Plants; 2023

International Society for Horticultural Science (ISHS)

Thesoftening of fleshy fruits is largely due to changes in the structure andcomposition of the primary cell wall, which is a dynamic structure capable ofadapting to various biotic and abiotic stimuli. Pectic polymers in strawberry (Fragariax ananassa, Duch.), can reach up to 60% and they are the main components ofthe middle lamella. Calcium immersion treatments have been shown to beeffective in extending the quality and shelf life of strawberries duringstorage. However, the molecular and biochemical mechanisms underlying theeffects of calcium on the cell wall of these fruits were not clear until recently.In this study, we investigated the influence of CaCl2 treatment onthe expression patterns and activities of enzymes highly linked to themetabolism of the strawberry cell wall. Furthermore, we aimed to characterizethe impact of the treatments on the defensive responses of the fruit. Ripestrawberries (80-90% of red surface coloration) of cv. Aroma were treated witha 10 g L-1 CaCl2 solution at 25°C for 30 min, whileanother group was submerged in distilled water at the same temperature andduration (control). Fruits were separated immediately after treatment (initialtime) and after storage for 8 days at 4 °C + 2 days at 4 °C (final time). Weanalyzed the firmness and pectic polymer content of the cell wall, as well asthe activities of pectin methyl esterase (PME) and polygalacturonase (PG)enzymes. We also measured the relative expression of key genes involved in thedegradation (FaPG1, FaPLA, FaPLB, and FaPLC) andstabilization (FaPME1) of pectins by Real-Time PCR. Our results showedthat the calcium treatment inhibited PG hydrolyzing activity while increasingthe PME pectin stabilizing activity, corresponding to a lower degree ofesterification found in treated fruits compared to controls. The expression ofthe FaPME1 gene increased, whereas the expressions of FaPG1, FaPLB,and FaPLC decreased at the initial time. Fruits treated with calciumafter storage had higher firmness and a higher content of pectins bound byionic interactions, indicating that Ca2+ ions preserved thestructure of pectins through positive regulation of FaPME1 and PMEactivity and negative regulation of genes involved in the disassembly of thestrawberry cell wall. The results related to the fruit defense revealed thatthe CaCl2 treatment had a positive effect on the total activities ofPPO, POD, chitinase, and β-1,3-glucanase enzymes, and also increased theexpression of genes responsible for encoding pathogen-related proteins (FaChi2-2,FaChi3, and FaβG2,3). Moreover, the treated fruit showed aninhibition of in vivo growth of Botrytis cinerea, indicating theeffectiveness of the CaCl2 treatment in activating fruit defenseresponses.