Key message Analysis of carotenoid-accumulating roots revealed that oxidative carotenoid degradation yields glyoxal and methylglyoxal. Our data suggest that these compounds are detoxified via the glyoxalase system and re-enter primary metabolic pathways. Abstract Carotenoid levels in plant tissues depend on the relative rates of synthesis and degradation. We recently identified redox enzymes previously known to be involved in the detoxification of fatty acid-derived reactive carbonyl species which were able to convert apocarotenoids into corresponding alcohols and carboxylic acids. However, their subsequent metabolization pathways remain unresolved. Interestingly, we found that carotenoid-accumulating roots have increased levels of glutathione, suggesting apocarotenoid glutathionylation to occur. In vitro and in planta investigations did not, however, support the occurrence of non-enzymatic or enzymatic glutathionylation of β-apocarotenoids. An alternative breakdown pathway is the continued oxidative degradation of primary apocarotenoids or their derivatives into the shortest possible oxidation products, namely glyoxal and methylglyoxal, which also accumulated in carotenoid-accumulating roots. In fact, combined transcriptome and metabolome analysis suggest that the high levels of glutathione are most probably required for detoxifying apocarotenoid-derived glyoxal and methylglyoxal via the glyoxalase pathway, yielding glycolate and d-lactate, respectively. Further transcriptome analysis suggested subsequent reactions involving activities associated with photorespiration and the peroxisome-specific glycolate/glyoxylate transporter. Finally, detoxified primary apocarotenoid degradation products might be converted into pyruvate which is possibly re-used for the synthesis of carotenoid biosynthesis precursors. Our findings allow to envision carbon recycling during carotenoid biosynthesis, degradation and re-synthesis which consumes energy, but partially maintains initially fixed carbon via re-introducing reactive carotenoid degradation products into primary metabolic pathways.

In this work, a vulcanized blend of natural rubber (NR) and styrene butadiene rubber (SBR) (i.e. at weight ratio of 50 : 50) as a model for tire rubber was devulcanized using probe sonicationP.

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Few studies have evaluated the effects of various levels of heavy metals on medicinal plants. The impact of gradually increased soil levels of copper (Cu) and cadmium (Cd) on the medicinal plant native to Southwest Asia and North Africa, Prosopis farcta, irrigated with metal-enriched water was determined. The exposure of plants to Cd or Cu decreased plant growth and increased Cd and Cu concentration in their shoots and roots. External Cd or Cu in the soil increased the uptake of both elements. Regression analysis showed that the weight of both shoots and roots decreased linearly with the increase of Cu and Cd contents in roots and shoots. Results showed that Cd was more toxic than Cu. The water content of shoots and roots decreased linearly with increased heavy metal levels. P. farcta could take up Cu and Cd in both Cu- and Cd-contaminated soils, however, it was more capable for transporting Cd from roots to shoots rather than Cu. P. farcta is a natural accumulator for Cu and Cd under gradually increased levels of these metals in the soil.