Effect of environmental conditions on seed germination and seedling growth in Cuscuta campestris

The dodder, Cuscuta, is an obligate parasitic plant that cannot survive without a host plant and causes major damage to crop yields. To know its growth characteristics before parasitism, we examined the effect of various environmental conditions on seed germination and seedling growth in Cuscuta campestris. As for the effect of light on germination, far-red light was rather preferable to red light and the reversible response of the seeds to red and far-red light was confirmed, implicating a phytochrome-mediated signaling opposite to that in many seed plants. Among amino acids, aspartic acid and alanine had a promotive effect and histidine had an inhibitory effect on germination. We further found that, in addition to gibberellic acid, methyl jasmonate was stimulatory to germination and shoot elongation. While 2,4-D extended the viability of trichomes around the root cap, kinetin induced the formation of scale leaves on the shoot and calli at the base of the shoot and the root tip. RT-PCR experiments confirmed that expression of a putative RbcS gene for photosynthesis showed no response to light but that of a Phytochrome A homolog was increased in the dark. Our results indicate that some of the molecular mechanisms to respond to light and hormone signals are uniquely modified in dodder seedlings, providing a clue for understanding the survival strategy of parasitic plants.