Anther-specific production of antimicrobial tuliposide B in tulips

Abstract

Strong antimicrobial activity was observed in water extracts of tulip anthers. Purification by column chromatography and structural analysis by various methods, such as liquid chromatography-mass spectrometry (LC-MS), 1H-, and 13C- nuclear magnetic resonance (NMR) revealed that the active compound was 6-tuliposide B (6-O-((S) 4′, 5′-dihydroxy-2′-methylenebutyryl)-D-glucopyranose). The antimicrobial susceptibility test revealed that it showed a strong growth inhibition against Gram-positive, Gram-negative bacteria and certain fungicide tolerant strains except for a yeast. Among the 22 cultivars (Tulipa gesneriana L.) and 15 Tulipa species, antimicrobial activities of the anthers from cultivars were stronger than those of the wild species. These production abilities of 6-tuliposide B in anthers were not related to pollen fertility. During anther development, the production of 6-tuliposide B was confined for a short period of approximately 7 to 12 days before flowering. Hence, it appeared that the 6-tuliposide B in anthers was produced in a tissue- and stage-specific manner with higher 6-tuliposide B accumulation than that observed in other tissues that produce both 6-tuliposides A and B. These results suggest that a novel defense strategy evolved in tulips to protect pollens from bacterial pollution in the reproductive process by producing an anther-specific 6-tuliposide B.