Oxidation of ethylene by cotyledon extracts from Vicia faba L. : Cofactor requirements and kinetics

Analysis of ethylene oxide in ice creams manufactured with contaminated carob bean gum (E410)

Residues of ethylene oxide (EO), a banned fumigant in the EU, were found at amounts above the maximum residue limit (MRL) in carob (locust) bean gum (additive E410). The pesticide entered the food chain via stabiliser blends that are used as minor ingredients in the manufacture of ice cream. Consequently, all products that contained the non-compliant ingredient were withdrawn or recalled in several countries across the EU, in most cases irrespective of whether the pesticide residue was detectable or not in the final product. This is the first report of a reliable method to determine EO and its metabolite/marker compound 2-chloroethanol (2-CE), either together or independently in ice cream, with a limit of quantification at 0.01 mg EO/kg and recovery in the range of 87-104% across the levels investigated (0.01, 0.02 and 0.06 mg EO/kg). The method applies QuEChERS extraction and isotope dilution gas chromatography coupled with tandem mass spectrometry (GC-MS/MS). High resolution mass spectrometry (HRMS) confirmed the specificity of low mass ions. Data on the stability of EO and 2-CE under thermal conditions revealed that 2-CE is relatively stable in an ice cream matrix (ca. 80% recovery of spiked material). Importantly, this study also demonstrates that not EO, but 2-CE is the predominant analyte detected in the contaminated samples, which is new information of significance in terms of the overall risk assessment of EO in foodstuffs.

Distinctive diel growth cycles in leaves and cladodes of CAM plants: differences from C3 plants and putative interactions with substrate availability, turgor and cytoplasmic pH

Distinct diel rhythms of leaf and cladode expansion growth were obtained in crassulacean acid metabolism (CAM) plants under water-limited conditions, with maxima at mid-day during phase III of CO₂ assimilation. This pattern coincided with the availability of CO₂ for photosynthesis and growth during the decarboxylation of malic acid, with maximum cell turgor due to the nocturnally accumulated malic acid, and with the period of low cytoplasmic pH associated with malic acid movement from vacuole to cytosol. Maximum growth rates were generally only 20% of those in C₃ plants and were reached at a different time of the day compared with C₃ plants. The results suggest that malic acid, as a source of carbohydrates, and a determinant of turgor and cytoplasmic pH, plays a major role in the control of diel growth dynamics in CAM plants under desert conditions. The observed plasticity in phasing of growth rhythms under situations of differing water availability suggests that a complex network of factors controls the diel growth patterns in CAM plants and needs to be investigated further.

Ethylene metabolism in Pisum sativum L

The possible role of C2H4 metabolism in mediating the responses of plants to C2H4 is re-examined. It is demonstrated that (i) the effects of inhibitors upon C2H4 action do not correspond with their effects on metabolism, (ii) elicitors of C2H4 effects do not have appropriate effects on C2H4 metabolism, (iii) inhibitors of C2H4 metabolism do not affect the response of plants to C2H4. It is concluded that metabolism of C2H4 is not linked to the mode of action of the growth regulator.