Three standard assays for pyruvate gave equivalent measurements of relative pungency for two leek cultivars ( 'Tadorna' and 'Ramona'). Background pyruvate levels varied depending on the assay used, ranging from 0.4 (lactate dehydrogenase) to 1.5 (high-performance liquid chromatography, HPLC) micromol g(-1) fresh weight (FW) on average. The relative pungencies of the two leek cultivars were also compared to total concentrations of the S-alk(en)yl-L-cysteine sulfoxides (RCSOs). The average ratio of EPy to total RCSOs was 10.9, indicating that standard pungency assays underestimate the levels of RCSOs in the tissue. A detailed analysis of 'Tadorna' leaves showed that total RCSO concentrations decreased acropetally. Profiles were composed of (-/+)-methyl-, (-/+)-ethyl-, (+)-propyl-, and (+)-1-propenyl-L-cysteine sulfoxide (MCSO, ECSO, PCSO, and 1-PeCSO, respectively). (+)-PCSO was the most prominent in green (2.4 mg g (-1) FW), yellow (5.5 mg g (-1) FW), and white (3.8 mg g (-1) FW) tissues. The prop(en)yl-L-cysteine sulfoxide derivatives were dominant in tissues that had photosynthetic capacity. The (+)-MCSO levels were high in the bulb (3.6 mg g (-1) FW). Interestingly, detectable levels of (-/+)-ECSO were measured in the leaves ( approximately 0.5 mg g (-1) FW). RCSO profiles of the different tissue regions were similar, but more (+)-PCSO and (+)-1-PeCSO were detected in the bulb. In general, mature upper leaf tissues had lower levels of total RCSOs. Overall, mild extraction methods and a low-temperature HPLC protocol (preferably with long retention times) achieved adequate compound separation and resolution of the diastereomers.

The effects of temperature on leaf photosynthesis and transpiration were investigated for two leek (Allium porrum L.) cultivars that showed differing pseudostem pungencies, when grown in a controlled greenhouse environment. Basal sections of 20 week old cv. Tadorna were shown to be nearly four times as pungent as those of cv. Ramona. Greenhouse climate data indicated 37% of weekly average temperatures were above 25°C, approaching the temperature at which leek growth is inhibited. Due to the environmental influence of temperature on tissue pungency, leaf gas exchange was measured at 20°C and 27°C to see if the gas exchange characteristics of the cultivars differed as well. The net carbon exchange rate (NCER) and leaf transpiration of cv. Ramona remained relatively steady over the photoperiod at both 20°C and 27°C, but were reduced by the increased temperature. In comparison, NCER and leaf transpiration of cv. Tadorna were greatly reduced by elevated temperature during the morning and early afternoon periods. Gas exchange of mature and immature leaf tissue was also measured. Immature leaves of cv. Tadorna had lower NCER and displayed a significant decline in photosynthesis and transpiration during the photoperiod. Despite having reduced productivity under the greenhouse conditions, Tadorna displayed higher tissue pungency upon maturity.

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