Monitoring leaf senescence in rocket leaf under temperature stress using physiological and biochemical parameters

Reduction in photosynthetic activity, increase of respiration and cell membrane degradation are senescence physiological processes that greatly induce quality losses in leafy vegetables. These effects are enhanced by the occurrence of abiotic stresses such as variations of storage temperature. In order to study the senescence progress at low and high metabolic state, rocket leaves (Diplotaxis tenuifolia L.) were collected and stored at 4°C and 20°C for 14 and 4 days respectively. Chlorophyll a fluorescence was measured to evaluate the senescence by monitoring the leaf health status. The maximum quantum efficiency of PSII (Fv/Fm) declined progressively at both storage temperatures. The performance index, as overall evaluation of leaf functionality, was 2.6 soon after harvest and declined faster at higher temperature. The dissipation energy expressed for reaction center (DIo/RC) or per cross section (DIo/CS) increased progressively with storage time. Means of lipid peroxidation and sugars content determination were evaluated. Reduction in sugars level and increase in lipid peroxidation were observed early at 20°C and lately at 4°C. We investigate also the influence of storage temperature and time on head space Volatile Organic Compounds composition. We were able to identify the major volatile compounds associated with rocket aroma and show significant changes in the overall VOC profile during storage. We were also able to separate the VOC profiles from the different temperatures indicating that VOCs may be useful markers as indicators of the effects of these parameters on quality. Our results showed that the storage temperature has a direct effect on the quality and shelf life of rocket by influencing the occurrence of senescence associated processes. Moreover, photosynthetic indexes can be considered as good non-destructive markers of senescence during storage.