The relationship between 1-deoxynojirimycin (DNJ) content and alpha-glucosidase inhibitory activity in mulberry (Morus) leaves is discussed. Mulberry leaves were collected from the Center for Bioresource Field Science, Kyoto Institute of Technology, Kyoto, Japan on 19 May, 9 July, and 9 August, 2003. Mulberry leaves were extracted with 75% ethanol. The inhibitory activity for rat intestinal crude enzyme was measured using maltose. The content of DNJ in the extracts was measured using HPLC. The mean DNJ content in the 0.04-0.06% range was high in collected samples. The inhibitory activities in July and August were higher (P < 0.01) than in May, and the activity in July was higher (P < 0.01) than in August. A strong correlation (r = 0.901, r (2) = 0.811, n = 15) existed between DNJ content and alpha-glucosidase inhibition in leaves of Morus bombycis harvested in July. Similarly, correlation coefficients of the other mulberry varieties in July were higher than they were in May or August. The inhibitory activity and the DNJ content of Morus latifolia in August were lower than for any other mulberry variety. These results show that the high inhibitory cultivars harvested in July, except for M. latifolia, are more suited to products that contain high DNJ contents.

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The seasonal and polyploidal changes of ␣-glucosidase (rat-intestinal) inhibitory activity in mulberry leaves were compared in 12 mulberry varieties. Enashi, Fusoumaru, No. 325 and Kenmochi which are classified as 3 major varieties in Japan were harvested in May or August as the field samples. Shimaguwa and the 3 different wild types such as Kuromiguwa, Nagamiguwa, Midoriguwa were harvested in May as the greenhouse samples. Some varieties harvested in the field or greenhouse indicated a difference in ␣-glucosidase. In the field Enashi was strong, while Kenmochi was rather weak. The seasonal changes of inhibition between May and August were differed among the varieties. The 3x variety in the field or greenhouse showed the strong inhibition within the same variety. Keywords: ␣-glucosidase, inhibitor, mulberry, Morus, polyploidy, variety Mulberry leaves (Morus alba L.) have been used as a traditional medicine with anti-inflammatory and anti-hyperglycemic action . The mulberry leaf component such as 1-deoxynojirimycin (DNJ;Yoshikuni, 1988;Asano et al., 1994), 2-arylbenzofuran derivatives (Basnet et al., 1993) and polyhydroxylated alkaloids (Asano et al., 2001) inhibit the activity of ␣-glucosidase of the small intestine, and also prevent sudden hydrolysis of disaccharides, absorption of glucose into the blood vessel, and resultant increase of blood glucose level. DNJ showed stronger inhibitory activity towards rat intestinal maltase and yeast ␣-glucosidase compared with DNJ-trehalamine-fused and -linked compounds (Shiozaki et al., 1998). The extract derived from mulberry leaves potentiated the pilocarpine-induced salivary flow which was correlated with antihyperglycemic effects . Fagomine from mulberry leaves increased the plasma insulin level in STZ-diabetic mice, and this insulin release by fagomine might partly contribute to the antihyperglycemic action (Nojima et al., 1998;Taniguchi et al., 1998). The maximum reduction in blood glucose of leaf extract was ob-served among fruit, trunk bark and root bark (Hosseinzadeh & Sadeghi, 1999).On the other hand, there are many reports concerning artificially polyploidy from the point of view of cytology (Seki & Oshigane, 1953, 1957, 1959Tojyo, 1954Tojyo, , 1963Tojyo, , 1966Das & Krishnaswami, 1964;Das et al., 1970) as mulberry breeding is extremely valuable for the sericulture. It is well accepted that major characteristics of 3, 4x polyploidy are indicated a large leaf, high saccharide content, high yield and high feed efficiency on silkworm among the different polyploidy. We observed that the changes of ␣-glucosidase inhibitory activity in leaves were occurred among mulberry polyploidy. Activity for lowering blood-glucose levels of autumn-rearing silkworm was higher than that of spring-rearing silkworm (Ryu et al., 1997). The changes in ␣-glucosidase inhibitory activity in leaves can be observed in some mulberry varieties, there is no reports concerning of seasonal or varietal changes on the ␣-glucosidase inhibition in leaves of any mulberry variety.In this study the ...