EFFECTS OF PROLINE AND PROLINE ANALOGS ON TOTAL PHENOLIC AND ROSMARINIC ACID LEVELS IN SHOOT CLONES OF THYME (THYMUS-VULGARIS L.)

Plant phenolic compounds such as rosmarinic acid exhibit antioxidant a nd antimicrobial activities and have potential as functional food ingr edients. Our model has proposed that a cellular redox cycle linking py roline-5-carboxylate and proline can stimulate the pentose phosphate, shikimate and phenylpropanoid pathways, and ultimately lead to an incr ease in phenolic synthesis, including rosmarinic acid (RA). In this st udy, the response of thyme shoot clones to proline and/or proline anal ogs was investigated through measurement of total phenolics, rosmarini c acid and proline levels, as well as glucose-6-phosphate dehydrogenas e (G6PDH) and phenylalanine ammonia-lyase (PAL) activities. A genetica lly uniform, high phenolic-containing thyme shoot-based clonal line T- 12 was used. Results indicate that supplementation of exogenous prolin e did not enhance total phenolic and rosmarinic acid content. Therefor e, exogenous proline may not have stimulated the proline-linked pentos e phosphate pathway. However, increases in proline, total phenolics an d rosmarinic acid synthesis were observed following supplementation wi th the proline analogs, hydroxyproline and azetidine-2-carboxylate. Th ese analogs through proline synthesis may have activated the pentose p hosphate pathway and therefore the phenylpropanoid pathway by linking steps involved in NADP/NADPH interconversions. As a result, increases in total phenolic and rosmarinic acid levels were observed. This mode of regulation via proline synthesis-linked to pentose phosphate pathwa y may be important for synthesis of RA and its overexpression in elite thyme clonal lines for food and medicinal applications.