Emissions, biogenesis and metabolic utilization of chloromethane by tubers of the potato (Solanum tuberosum)

CH3Cl emissions by freshly harvested tubers of 61 potato cultivars ranged from less than 4 to 650 ng g(-1) f. wt d(-1). In experiments with Anna, the cultivar displaying the highest release rate, maximum emission of CH3Cl occurred at 20 degrees C but the rate diminished after 48 h, a decrease due in part to inhibition of CH,CI release by the accumulation of CH3Cl in the headspace. In 1995 and 1996, CH3Cl emission by tubers was first detectable 6 wk before the normal harvest date. If tubers were stored at 20 degrees C immediately following harvest, release attained a maximum of 350 ng g(-1) f. wt d(-1) about 4 d after harvest, falling to less than 4 ng g(-1) f. wt d(-1) within 3 wk of harvest. On storage at 6 degrees C post-harvest, maximum release of CH3Cl (c. 600 ng g(-1)) was delayed until 5 wk after harvest and release fell below 4 ng g(-1) f. wt d(-1) after 200 d. Release of CH3Cl was not significantly affected by cutting or bruising tuber tissue, and CH3Cl biosynthesis occurred in both core and superficial tissues of the tuber. The S-methyl group of either L- or D-methionine acted as a precursor of CH3Cl in sliced tubers, but the methylating system was specific for Cl-. An isotope dilution technique using (CH3Cl)-H-2 demonstrated that the amount of CH3Cl metabolized by the intact tuber was approximately 36% of the net release. However, investigations with (CH3Cl)-C-14 showed that only a small proportion (7%) of the CH3Cl metabolized was fixed in involatile form in the tuber. In both skin and core tissues, fixed C-14 was located primarily (80%) in the fraction soluble in phosphate buffer, but the specific activity of skin tissue was about twice that of core tissue. Autoradiography demonstrated that C-14 fixation in the tuber was greatest within the lenticels, possibly indicating a microflora adapted to use the locally high concentrations of CH3Cl. Significant C-14 fixation was also associated with the periderm but was not attributable to labelling of the O-methyl groups of the phenolic components of suberin. Within the core of the tuber, C-14 fixation was located primarily in the phloem, pith and medullary rays.