Lignin and gum deposition in wounded 'Oroval' clementines as affected by chilling and peel water content

Induction of lignin synthesis and gum deposition by wounding in the albedo and flavedo of 'Oroval' clementines exposed to low temperature has been studied. Wounded and non-wounded fruit were kept for 24 h at 20°C (initial separate experiment), six and 18 days at 2.5°C (cold storage), and 18 days at 2.5°C plus two additional days at 20°C (shelf-life). At 2.5°C, fruit were kept under two different conditions: saturated humidity or at 85-90% relative humidity (RH). During the separate initial control and shelf-life periods RH was 60%. The greatest weight loss (WL) was found in wounded fruit stored at 85-90% RH. Chilling injury (CI) was enhanced by wounding in all treatments. The most severe water loss occurred in flavedo of wounded fruit kept at 85-90% RH but, not surprisingly, at saturated humidity, no difference was found. Albedo water content was lower than that of flavedo and decreased again after shelf-life. Cell wall residue (CWR) progressively increased during cold storage in both albedo and flavedo of wounded fruit kept at 85-90% RH. Lignin-thioglycolic compounds increased in flavedo and albedo of wounded fruit kept at 20°C during the 24-h period of the separate initial control. Under cold storage, however, these compounds did not increase together with CI development and fruit senescence. Wounding, CI and senescence considerably increased the deposition of ethanol-extractable phloroglucinol/HCl- (pg/HCl) positive compounds in flavedo, indicating (specific test) that wound gum deposition was more likely related than lignin biosynthesis to healing process and to pitting development under chilling conditions. © 1996 Elsevier Science B.V. All rights reserved.