Pyrroloquinoline quinone (PQQ) is believed to be an important factor for mammalian growth and development and has, therefore, been declared a vitamin by some researchers. However, this issue remains controversial, and from a nutritional viewpoint, accurate determination of PQQ levels in a variety of foods is very important. Here, we describe a simple, highly sensitive, and highly selective method for quantitative analysis of PQQ. Liquid foods or aqueous extracts of solid foods were analyzed using high-performance liquid chromatography (HPLC) combined with electrospray-ionization (ESI) tandem mass spectrometry (MS/MS). (15)N-labeled PQQ was added to the samples as an internal standard. Quantitative analyses of PQQ were performed by multiple reaction monitoring (MRM) with LC/MS/MS. Free PQQ was detected in almost all food samples in the range 0.19-7.02 ng per g fresh weight (for solid foods) or per mL (liquid foods). This method will enable the rapid and simple determination of PQQ levels in many samples.

No abstract

No abstract

Changes in exudation rate and cytokinin activities in the exudates were measured in two varieties of rice (Oryza sativa L.), cv Nipponbare (a Japanese normal cultivar) and cv Akenohoshi (a highyielding cultivar). The exudation rates of Akenohoshi, the leaves of which remained green for a longer time, were higher than those of Nipponbare after the booting stage. Cytokinin activities in the exudates of Akenohoshi were higher than those of Nipponbare during the ripening period. Cytokinins in the exudates collected during the middle of the ripening stage were analyzed with mass spectrometry using deuterium-labeled standards. trans-Zeatin, trans-ribosylzeatin, and N'-isopentenyladenosine were detected as free cytokinins, and zeatin was detected in the hydrolysates of highly polar fractions ("conjugated zeatin") in the exudates of both cultivars. Conjugated zeatin was the predominant cytokinin in both cultivars. Therefore, we suggest that conjugated zeatin is an important form of cytokinin during the ripening stage. The level of each of the cytokinins in Akenohoshi was higher than that in Nipponbare. Also, we discuss the correlation between the leaf senescence and cytokinin content in root exudates.In a previous study to clarify the physiological and ecological characteristics of high-yielding rice varieties (11, 12), it was reported that the yield in Akenohoshi was about 1780 kg/ha higher than that in Nipponbare, a Japanese standard cultivar, and that Akenohoshi had a higher dry matter production capacity compared with Nipponbare. This was attributed to the maintenance of a higher net assimilation rate during the ripening period in the former. 1724 stage were 9.2 ,umol of CO2 m-2 s-' (44.6% of its maximum rate at the panicle formation stage) and 12.7 smol of CO2 m-2 S-1 (62.0%), respectively. In addition, the cause for these differences between the two cultivars was examined by measuring the active and passive water absorption abilities of the roots. The rate of exudation from the main stem and the resistance to water transport from the root surface to the leaves under intense transpiration were higher and lower in Akenohoshi than in Nipponbare, respectively. These differences between the two cultivars were especially large during the ripening stage. This fact suggests that physiological activity in the roots of Akenohoshi was higher than that in Nipponbare. It is known that a decline in the physiological activity of roots causes leaf senescence and death of the leaves at the lower positions (10), but the mechanism by which this occurs is not understood well.Cytokinins transported from the roots via the xylem are known to delay leaf senescence (6,16,18). In the exudate of rice plants, several cytokinins were identified (15). However, the constitution of cytokinins in the exudate, the level of these cytokinins, and their effects on leaf photosynthesis and senescence have been examined in only a few studies (20).In this report, we discuss the changes in the exudation rates and cytokinin activities in the exudat...