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

Abstract Dodder ( Cuscuta ) is an obligate parasitic plant that cannot survive without a host and causes significant damage to crop yields. To understand its growth characteristics before parasitism, we examined the effects of environmental conditions on seed germination and seedling growth in Cuscuta campestris Yunck. Among various factors, we focused on the effects of light, pH, temperature, sugars, salts, hormones, amino acids and polyamines on seeds sown on agar plates. Regarding the effect of light on germination, far-red light was preferable rather than red light and the reversible response of seeds to red and far-red light was confirmed, implicating a phytochrome-mediated signaling pathway opposite to that in many seed plants. Among the amino acids, aspartic acid and alanine had a promotive effect, while histidine had an inhibitory effect on germination. We further found that, in addition to gibberellic acid, methyl jasmonate stimulated both 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 undifferentiated cell clusters at the base of the shoot and root tip. Real-time reverse transcriptase PCR (RT-PCR) experiments confirmed that the expression of a putative RbcS gene for photosynthesis showed no response to light, whereas that of a Phytochrome A homolog increased in the dark. Our results indicate that some of the molecular mechanisms involved in responding to light and hormone signals are uniquely modified in dodder seedlings, providing clues for understanding the survival strategy of parasitic plants.