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 al bedo and flavedo of 'Oroval' clementines exposed to low temperature ha s been studied. Wounded and non-wounded fruit were kept for 24 h at 20 degrees C (initial separate experiment), six and 18 days at 2.5 degre es C (cold storage), and 18 days at 2.5 degrees C plus two additional days at 20 degrees C (shelf-life). At 2.5 degrees C, fruit were kept u nder two different conditions: saturated humidity or at 85-90% relativ e humidity (RH). During the separate initial control and shelf-life pe riods RH was 60%. The greatest weight loss (WL) was found in wounded f ruit stored at 85-90% RH. Chilling injury (CI) was enhanced by woundin g in all treatments. The most severe water loss occurred in flavedo of wounded fruit kept at 85-90% RH but, not surprisingly, at saturated h umidity, no difference was found. Albedo water content was lower than that of flavedo and decreased again after shelf-life. Cell wall residu e (CWR) progressively increased during cold storage in both albedo and flavedo of wounded fruit kept at 85-90% RH. Lignin-thioglycolic compo unds increased in flavedo and albedo of wounded fruit kept at 20 degre es C during the 24-h period of the separate initial control. Under col d storage, however, these compounds did not increase together with CI development and fruit senescence. Wounding, CI and senescence consider ably increased the deposition of ethanol-extractable phloroglucinol/HC l- (pg/HCl) positive compounds in flavedo, indicating (specific test) that wound gum deposition was more likely related than lignin biosynth esis to healing process and to pitting development under chilling cond itions.