Differential effects of low-temperature inhibition on the propylene induced autocatalysis of ethylene production, respiration and ripening of 'Hayward' kiwifruit

Previous studies (Stavroulakis and Sfakiotakis, 1993) have shown an inhibition of propylene-induced ethylene production in kiwifruit below a critical temperature range of 11-14.8 degrees C. The aim of this research was to identify the biochemical basis of this inhibition in kiwifruit below 11-14.8 degrees C. 'Hayward' kiwifruit were treated with increasing propylene concentrations at 10 and 20 degrees C. Ethylene biosynthesis pathways and fruit ripening were investigated. Kiwifruit at 20 degrees C in air started autocatalysis of ethylene production and ripened after 19 d with a concomitant increase in respiration. Ethylene production and the respiration rise appeared earlier with increased propylene concentrations. Ripening proceeded immediately after propylene treatment, while ethylene autocatalysis needed a lag period of 24-72 h. The latter event was attributed to the delay found in the induction of 1-aminocyclopropane-1-carboxylate synthase (ACC synthase) activity and consequently to the delayed increase of l-aminocyclopropane l-carboxylic acid (ACC) content. In contrast propylene treatment induced 1-aminocyclopropane-1-carboxylate oxidase (ACC oxidase) activity with no lag period. Moreover, transcription of ACC synthase and ACC oxidase genes was active only in ethylene-producing kiwifruit at 20 degrees C. In contrast, treatment at 10 degrees C with propylene strongly inhibited ethylene production, which was attributed to the low activities of both ACC synthase and ACC oxidase as well as the low initial ACC level. Interestingly, fruit treated with propylene at 10 degrees C appeared to be able to transcribe the ACC oxidase but not the ACC synthase gene. However, propylene induced ripening of that fruit almost as rapidly as in the propylene-treated fruit at 20 degrees C. Respiration rate was increased together with propylene concentration. It is concluded that kiwifruit stored at 20 degrees C behaves as a typical climacteric fruit, while at 10 degrees C behaves like a non-climacteric fruit. We propose that the main reasons for the inhibition of the propylene induced (autocatalytic) ethylene production in kiwifruit at low temperature (less than or equal to 10 degrees C), are primarily the suppression of the propylene-induced ACC synthase gene expression and the possible post-transcriptional modification of ACC oxidase.

A possibility for non-invasive diagnosis of superficial scald in 'Rocha' pear based on chlorophyll a fluorescence, colorimetry, and the relation between alpha-farnesene and conjugated trienols

This study aimed to identify physiological markers in superficially scalded 'Rocha' pear (Pyrus communis L 'Rocha') that would relate to chlorophyll a fluorescence (CF), allowing a non-invasive diagnosis of the disorder. Conditions chosen before shelf life provided two fruit groups with different developing patterns and severity of superficial scald: T fruit fully developed the disorder in storage, while C fruit developed it progressively throughout shelf life. Principal component analysis (PCA) of all the measured variables, and simple linear correlations among several major parameters and scald index (SI)/shelf life showed that scald and ripening/aging were concurring processes, and that it was not possible to isolate a particular variable that could deliver a direct non-invasive diagnosis of the disorder. For both fruit groups the SI resulted from the balance between the reducing power (OD200) and the content of conjugated trienols (CTos) and alpha-farnesene (alpha-Farn) in the fruit peel. At OD200 > 150 there was a linear relationship between CTos and OD200, suggesting that the level of antioxidants was self-adjusted in order to compensate the CTos level. However, at OD200 < 150 this relationship disappeared. A consistent linear relationship between dos and alpha-Farn existed throughout shelf life in both fruit groups, contrarily to the early storage stage, when those compounds do not relate linearly. The CF variables F-0, F-v/F-m, and the colorimetric variables, L* and h degrees were used in multi-linear regressions with other physiological variables. The regressions were made on one of the fruit groups and validated through the other. Reliable regressions to alpha-Farn and CTos were obtained (R approximate to 0.6; rmsec approximate to rmsep). Our results suggest that a model based on CF and colorimetric parameters could be used to diagnose non-invasively both the contents and the relationship between alpha-Farn and CTos and hence the stage of scald development. (C) 2011 Elsevier By. All rights reserved.