PSEUDOMONAS SPP.-MEDIATED REGULATION OF TOTAL PHENOLIC AND ROSMARINIC ACID LEVELS IN SHOOT-BASED CLONAL LINES OF THYME (THYMUS VULGARIS L.)

Abstract

Plant phenolics are secondary plant products, sometimes synthesized as chemical defenses to microorganisms, and also serve as potential sources of food preservatives. In this study, we have investigated the extent of stimulation of total phenolics and rosmarinic acid (RA) levels in three in vitro shoot culture-based thyme clonal lines in response to a novel Pseudomonas spp. previously isolated from oregano tissue cultures. Clonal lines chosen for this study were the high phenolic line T-12 and the medium- and low-phenolic lines T-16G and M-3. Results indicate that different strains of Pseudomonas stimulated total phenolic levels and RA accumulation to varying degrees. Mucoid strain M4 elicited the highest levels of RA in clonal line T-12 on day 25. A moderate degree of RA stimulation in response to M4 was observed in clonal line M-3. Mucoid strain F elicited the highest total phenolic levels in T-12 on day 25. Nonmucoid strain NMA elicited stimulation of total phenolic compounds and RA to some degree only in clonal line T-16G. A 30 day time course analysis in line T-12 indicated that strains F and NMA elicited the highest phenolic levels. RA synthesis appeared to be stimulated in response to M4 at later stages of growth and reduced stimulation was apparent in response to F and NMA. The mechanical rigidity of T-12 shoots appeared to be highest in response to mucoid strain M4, indicating the possibility of increased lignin formation. This Pseudomonas-thyme clonal system provides a foundation to investigate the microbially-elicited stimulation of biosynthetic pathways leading to novel antimicrobials and antioxidants.