DNA quantiWcation is an important, frequently used technique, and inaccuracies can result in failures with ligation, restriction, polymerase chain reaction (PCR),1 ampli-Wed fragment length polymorphism (AFLP), Southern blotting, and other techniques. DNA is most commonly quantiWed using absorbance at 260nm, but because of the existence of many impurities, this can be an imprecise measurement and DNA levels can be more than 10 times overestimated in some cases [1]. QuantiWcation by agarose gel electrophoresis with a known amount of standard DNA [1,2] can provide more accurate data, but the procedures are complicated, the data often still are not accurate enough, and the technique is impractical for routine or high-throughput DNA quantiWcation [3]. Fluorescence spectroscopy using various DNA intercalating dyes is the most widely accepted technique for accurate DNA quanti-Wcation [4]. However, if the analysis is to be carried out with a Xuorescence spectrophotometer, a relatively large assay volume (e.g., 2ml) is required [5], and this is impractical for small DNA samples and expensive dyes. Fluorescence can also be measured with a smaller volume of DNA sample using other instruments such as Xuorescent microplate readers [6], microplate Xuorometers [7,8], and transilluminator-microplate-CCD camera systems [9], but the instruments might not be readily available in most molecular biology laboratories.

Fruits of 23 loquat (Eriobotrya japonica Lindl.) cultivars, of which 11 were white-fleshed and 12 red-fleshed, were analyzed for color, carotenoid content, and vitamin A values. Color differences between two loquat groups were observed in the peel as well as in the flesh. β-Carotene and lutein were the major carotenoids in the peel, which accounted for about 60% of the total colored carotenoids in both red- and white-fleshed cultivars. β-Cryptoxanthin and, in some red-fleshed cultivars, β-carotene were the most abundant carotenoids in the flesh, and in total, they accounted for over half of the colored carotenoids. Neoxanthin, violaxanthin, luteoxanthin, 9-cis-violaxanthin, phytoene, phytofluene, andβ-carotene were also identified, while zeaxanthin, R-carotene, and lycopene were undetectable. Xanthophylls were highly esterified. On average, 1.3- and 10.8-fold higher levels of colored carotenoids were observed in the peel and flesh tissue of red-fleshed cultivars, respectively. The percentage of -carotene among colored carotenoids was higher in both the peel and the flesh of red-fleshed cultivars. Correlations between the levels of total colored carotenoids and the color indices were analyzed. The a* and the ratio of a*/b* were positively correlated with the total content of colored carotenoids, while L*, b*, and H°correlated negatively. Vitamin A values, as retinol equivalents (RE), of loquat flesh were 0.49 and 8.77µg/g DW (8.46 and 136.41µg/100g FW) on average for whiteand red-fleshed cultivars, respectively. The RE values for the red-fleshed fruits were higher than fruits such as mango, red watermelon, papaya, and orange as reported in the literature, suggesting that loquat is an excellent source of provitamin A.

Loquat (Eriobotrya japonica Lindl.) fruit are non-climacteric and have a short postharvest life. During postharvest ripening over 8d at 20℃, fruit firmness increased and showed a positive correlation with accumulation of lignin in the flesh. Among the enzymes associated with lignin synthesis, phenylalanine ammonia lyase (PAL) activity increased rapidly during the first 3d after harvest and then declined in the fruit flesh, while cinnamyl alcohol dehydrogenase (CAD) and peroxidase (POD) activities showed a persistent rise over the whole 8d. Accumulation of lignin in flesh tissue was also positively correlated to activities of CAD, guaiacol-POD (G-POD) and syringaldazine-POD (S-POD). Cellulose content in flesh tissue decreased and showed a significant negative correlation with lignin content. Where fruit ripening was enhanced by ethylene treatment, or retarded by low temperature or use of 1-methylcyclopropene (1-MCP), the inhibitor of ethylene reception, firmness, lignification and the enzyme activities were consistently enhanced or retarded accordingly. Our results suggest that increase in firmness of loquat fruit during ripening is a consequence of tissue lignification, a process associated with increases in PAL, CAD and POD activities, and might involve a coordinated regulation of lignin biosynthesis and cellulose hydrolysis.

Chilling injury occurs in loquat (Eriobotrya japonica Lindl. cv. Luoyangqing) fruit when they are stored at temperatures lower than 5℃. In attempts to reduce this chilling injury, the effect of low temperature conditioning (LTC) was examined. Loquat fruit were conditioned at 5℃ for 6 days before 0℃ storage for up to 54 days. Control fruit stored at 0℃ exhibited severe symptoms of lignification and tissue browning, and a decrease in percentage juice. LTC treatment significantly reduced these chilling injury symptoms, and doubled storage life. In terms of acceptability (tissue browning, internal browning (IB) index <0.4; fruit decay, <10%; flesh firmness, <6.0 N; percentage juice, >60%), fruit could only be stored for 40 days at 0℃ with a 3 days shelf life at 20℃, while LTC fruit could be stored for 60 days at 0℃ with a similar shelf life. Similarly, LTC fruit could be stored for 40 days with a 5 days shelf life at 20℃, while fruit could be only stored for 20 days at 0℃with a 5 days shelf life. Our results confirm that LTC can effectively alleviate postharvest chilling injury of loquat fruit and may provide longer storage life with acceptable external and internal quality.