Effect of hormic dose of UV radiation (UV-C) on the delayed ripening of tomato pericarp disc: Biochemical and physiological basis

Effect of UV-C treatment on the ripening behavior of tomato pericarp discs was investigated. Pericarp discs were treated with UV dose of 1.4 KJ.m -2, and were stored at 15°C for up to 20 days. Ripening of pericarp discs was monitored by color development, pigments, tissue texture, respiration rate and ethylene production throughout the storage period. UV treatment induced significant delays in color development, chlorophyll degradation and lycopene production compared with the control. However, the treated discs developed a bronzing or brownish-red coloration, which developed slowly and became evident towards the end of the storage period. The climacteric ethylene peak was delayed by two days but the overall ethylene production during storage was greater in the treated discs compared with the control. The respiratory climacteric peaks were observed concomitantly for both the treated and untreated tomato discs, but the overall respiratory rate was higher in the treated discs. UV treatment did not affect significantly the textural changes, although a small effect on tissue preservation was observed. The results indicate that UV irradiation of tomato pericarp discs alters ripening behavior of tomato pericarp discs, especially those associated with chloroplast to chromoplast transition, whereas tissue softening appears to be less affected.; To study the effect of hormic dose of UV-C (1.4 KJ m-2) on the chloroplast activity and ultra-structure in tomato pericarp disc chlorophyll fluorescence and Transmission Electron Microscopy techniques were used to determine the function and structure of chloroplasts of the irradiated tissue during storage. UV-irradiation retarded the decline of the chlorophyll-a fluorescence ratios Fv/Fm and DeltaF/Fm', the two parameters related to the maximum and operational quantum yield of photosystem II electron transport, respectively. UV light also affected the ultra-structural evolution of chloroplasts. The treated tissue maintained higher chlorophyll content than the control until the end of the storage period. In addition the transition of chloroplast to chromoplast was delayed in the treated tissue. The organelles in the treated tissue were mixed structures of chloro/chromoplast, consisting of stroma thylakoids and plastoglobuli at the end of the storage period. Thus the maintenance of chloroplast structure and chlorophyll content contributes to the delay in the color change from green to red in the UV-treated discs. (Abstract shortened by UMI.)...