Morphology and anatomy of mature embryos and seedlings in parasitic angiospermCuscuta japonica

Abstract

Morphological and anatomical features of mature embryos and seedlings were observed at different growth stages in the parasitic angiospermCuscuta japonica Choisy. The spirally coiled embryos from scarified seeds had no cotyledons but possessed blunt radicles. Seeds germinated at 30°C in the dark. Although most embryo cells incubated for 16 h did not have starch grains, the shoot cells of three-day-old seedlings possessed numerous starch grains. After these seedlings were transferred to a lightened growth chamber, all the shoot apical regions of seedlings grown for 6,8, and 10 days became greenish and hooked. Most of the shoot cells, including the green apical parts, contained abundant starch grains. The hooks opened only when one seedling made contact with another seedling. This suggested that the green and hooked shoot apical regions played an important role in searching for and twining about their host plants. In some two-day-old seedlings, the massive roots were circular or semi-circular. This enabled the shoot axes to stand erect on some substratum. It would assist the shoots in making contact with the host plant. In eight-day-old seedlings, the green apical regions also were hooked and the roots were considerably degraded.