Morphological and plant hormonal changes during parasitization by <i>Cuscuta japonica</i> on <i>Momordica charantia</i>

<div><p>The holostemparasitic plant <i>Cuscuta</i> parasitizes various plants and sucks nutrients from the host stem. We used <i>Cuscuta japonica</i> as the parasite and <i>Momordica charantia</i> as the host plant, and described their interaction. The parasitized <i>Momordica</i> stems started swelling as a hypertrophic response within 3 days after parasitization. Concurrently, the <i>Cuscuta</i> stem grew rapidly and developed bigger scale leaves than usual. Parasitized <i>Momordica</i> stems reduced photosynthetic activity. Histological observation revealed no programmed cell death but an increased number of vascular bundles in the <i>Momordica</i> stem, especially near the <i>Cuscuta</i> hyphae. The defensive response of <i>Momordica</i> mainly involved the SA pathway. Drastic increase of tZ- and DZ-type cytokinins in <i>Momordica</i> stems would play an important role for hypertrophy. <i>Cuscuta</i> had higher cZ endogenously and our results imply that each subtype of CK might play different roles during parasitization process. Comprehensive plant hormone analysis provides new insights into plant interaction studies.</p>