Annual Report 2006

such as proteins. However, there have been no
detailed studies about the defense activities of
mulberry trees against insect herbivory or the
involvement of mulberry latex in the plant
defense. In this study, we addressed these
subjects.
We found that mulberry leaves are highly
toxic to lepidopteran larvae other than the
silkworm, (such as the Eri silkworm,
and notorius pest species, the
cabbage moth larvae, ), due
to the ingredients of the latex. When Eri
silkworm and the cabbage moth larvae were
fed mulberry leaves, they bit in the leaves but
they didnt grow, and died at last (Fig. 1, upper
left photo, left part). The toxicity of mulberry
leaves was lost when latex was washed off (Fig.
1, upper left photo, right part). Also, latex-added
artificial diets showed toxicity and growth
inhibitory effects to the Eri silkworm (Fig. 2A).
Mulberry ( ) latex contained very
high concentrations of alkaloidal sugar-mimic
glycosidase inhibitors (sugar-mimic alkaloids)
reported to have anti-diabetic activities, such as
1,4-dideoxy-1,4-imino-D-arabinitol (D-AB1), 1-
deoxy nojirimycin (DNJ), and 1,4-dideoxy-1,4-
imino-D-ribitol (Fig 1, right). Their concentrations,
altogether, in latex reached 1.5-2.5% (8-18% to
dry weight) in several mulberry varieties
(Table 1), which were 100 times the concentrations
previously reported from whole mulberry
leaves. These sugar-mimicking alkaloids showed
toxicities to caterpillars (Fig. 2 B,C), but not to
the silkworm, (Fig. 2 D). Our results
suggest that mulberry latex and sugarmimicking
alkaloids in it play key roles in
defense of mulberry against insect herbivory,
and also suggest the existence of some adaptive
mechanisms in the silkworm, .
This study shows, for the first time in long
history of sericulture, the existence of strong
latex-borne defense mechanisms in mulberry,
and gives practical answer to mulberrysilkworm
interactions. This study, together
with our previous studies on latex-borne
defense mechanisms of papaya and fig trees
carried out by cysteine proteases in latex,
shows that medically applicable chemicals (i. e.
anti-diabetic sugar-mimic alkaloids) exist in
mulberry latex in surprisingly high
concentrations (18% of dried latex), and they
are easily purified from latex, and shows the
possibility of mulberry latex as a source of
interesting and applicable chemicals in medical
and agricultural field. Also, this study will
contribute to researches on pest resistance of
mulberry varieties.
Reference
1) Konno K., Ono H., Nakamura M., Tateishi K.,
Hirayama H., Tamura Y., Hattori M., Koyama
A., Kohno K. (2006) Mulberry latex rich in antidiabetic
sugar-mimic alkaloids forces dieting on
caterpillars. 103,
1337-1341.
Table 1 Concentrations of sugar-mimic alkaloids in mulberry latex
Concentrations in latex (%)
Species, populations, and cultivars D-AB1 DNJ 1,4-dideoxy-1,4-imino-D-ribitol
(or )
Wild, Ishigaki, Okinawa, Japan
Wild, Tsukuba, Honshu, Japan
Cultivar Yukishirazu
Cultivar Ichibei
Cultivar Shinichinose
Values indicate means SD ( = 4-5 for wild populations, = 2-3 for cultivars)