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Degradation of chlorophyll in spinach (Spinacia olearacea L. cv. Hybrid 612) appeared to be regulated through the peroxidase-hydrogen peroxide pathway, which opens the porphyrin ring, thus resulting in a colorless compound. This conclusion was arrived at from the analysis of chlorophylls (Chls) and their metabolizes by HPLC and of enzyme activities catalyzing the degradative reactions. Chls decreased at 25C but not at 1C. The chlorophyll oxidase pathway was not active, as noted by the lack of accumulation of a reaction product named Chl a-1. Lipid peroxidation increased with storage, but the products of the reaction. did not degrade chlorophyll, as noted by the lack of increase in Chl a-1. Chlorophyllase activity increased, but chlorophyllide, the expected product of the reaction, changed minimally during senescence. Ethylene at 10 ppm did not alter the pathway that degraded chlorophyll in spinach.

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22 UV-B irradiation was applied to broccoli florets to investigate its effect on 23 chlorophyll degradation and chlorophyll-degrading enzyme activities in stored broccoli. 24Broccoli florets were irradiated with UV-B doses at 4.4, 8.8 and 13.1 kJ m -2 and then 25 kept at 15 ºC in darkness. We found that a UV-B dose of at least 8.8 kJ m -2 efficiently 26 delayed the decrease of the hue angle value and the contents of chlorophylls a and b. 27Chlorophyllide a and 13 2 -hydroxychlorohyll a gradually decreased with senescence. 28Pheophorbide a and pyropheophorbide a levels were significantly higher in broccoli 29 without UV-B treatment. Chlorophyllase and chlorophyll-degrading peroxidase activities 30 with UV-B treatment were suppressed, as well as the activity of Mg-dechelatase. Mg-31 dechelating substance activity was also suppressed with this treatment. We concluded 32 that UV-B treatment effectively suppressed chlorophyll degradation in broccoli florets 33 during storage, suggesting that the effect could be due to the suppression of chlorophyll-34 degrading enzyme activities.

Environmental stress conditions such as drought, heat, salinity, or pathogen infection can have a devastating impact on plant growth and yield, resulting in a mandate for stress-tolerant crop varieties. Crossbreeding tropical and cultivated onion species provided a hybrid F1 generation possessing genetic and metabolic parental properties that aided abiotic stress tolerance. The targeted metabolite profiling using liquid chromatography-tandem mass spectrometry (LC-MS/MS) integrated with transcriptional analysis of their relevant genes, provide insight into the metabolic and genomic architecture between onion double haploid (A. cepa L., DHC), shallot double haploid (A. cepa L. Aggregatum group, DHA), and F1 hybrid. Of a complete set of 113 targeted metabolites, 49 metabolites were found to be statistically different within genotypes; 11 metabolites were characteristic for DHC, 10 for DHA, 14 for F1, and 14 metabolites were mutual among the three genotypes. Several key genes and metabolites introgressed in abiotic stress response have been up-regulated in DHA and F1 genotypes as compared to DHC. Principal component analysis (PCA) and Volcano plot analysis revealed that metabolic traits and their relevant genes (i.e., amino acid, carbohydrate, flavonoid, and phospholipid biosynthesis) were strongly linked with DHA and F1, reflecting the adaptability of DHA and F1 toward abiotic stress as compared to DHC.

Pigments were monitored in parsley leaves stored in air, air + 10 ppm GH.,, or 10% O2 + 10% CO2 controlled atmosphere (CA). Chlorophylls a and b, as determined with HPLC, decreased sharply in leaves held in air or air + 10 ppm GH4. The decrease was less in leaves held in 10% O2 and 10% CO2 CA. The oxidized product of chlorophyll a, lo-hydroxychlorophyll a, did not accumulate and chlorophyllide accumulated minimally. Xanthophylls decreased but new pigments, suspected to be esterified xanthophylls, formed with yellowing of leaves. Neither the pathway of Chl degradation or xanthophyll products were altered by GH, or CA.

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