Characteristics of sucrose formation, and the influence of UV irradiation on the feeding by the silkworm, in leaves of the mulberry
1997
Yazawa, M. (National Inst. of Sericultural and Entomological Science, Tsukuba, Ibaraki (Japan))
The mode of formation of sucrose, which is not only a nutritional material but also a phagostimulant for larvae of Bombyx mori, was investigated by measuring the rates of photosynthesis and carbon dioxide fixation in mulberry leaves. Also examined was the influence of UV irradiation to mulberry leaves on the feeding by larvae, as an increase in total amounts of UV rays arriving the surface of the earth due to the destruction of ozone layer has recently led to a global issue. Using mesophyll cells isolated from mulberry leaves, the photosynthetic rate was determined by the oxygen electrode method, and the pathway of carbon dioxide fixation was analyzed by the incorporation of radioactive precursors. In comparison with Ichinose, a popular Japanese race of mulberry, Thailand races investigated were found to be peculiar in that their photosynthetic activities were lower and the photorespiration (glycolic acid cycle) activities were higher, although the synthetic rate of sucrose and its content were much higher than those of Ichinose. It is thus likely that the photorespiration pathway is more important to the sucrose formation in the Thailand races than in Ichinose. In addition, the temperatures during cultivation of mulberry trees was found to influence the relative contributions of photosynthesis and photorespiration to the sucrose formation
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