Chlorogenic Acid Facilitates Root Hair Formation in Lettuce Seedlings

Abstract

Root hairs, which arise from root epidermal cells, are tubular structures that increase the efficiency of water absorption and nutrient uptake. A low pH (pH 4) medium induced root hair formation in lettuce (Lactuca sativa L.) seedlings, and the decapitation of shoots inhibited root hair formation. The addition of shoot extract to the medium restored root hair formation in the decapitated lettuce seedlings. These results suggest that factors essential to the formation of root hairs may be present in the shoot. We purified one factor from the shoot that facilitates root hair formation. This factor was identified as chlorogenic acid (CGA), a common polyphenol in higher plants. The presence of exogenous CGA in the medium induced root hair formation in decapitated lettuce seedlings at pH 4.0 and in intact lettuce seedlings at pH 6.0. The optimum concentration of CGA for root hair formation was identified as 10(-5) M. Decapitation of the shoots reduced the CGA content in the roots to approximately one-third that in intact plants. Application of the CGA biosynthesis inhibitor L-alpha-aminooxy-beta-phenylpropionic acid (AOPP, 10(-6) M) to intact seedlings grown at pH 4.0 reduced both the CGA content of the roots and the total amount of root hairs. The addition of exogenous CGA restored root hair formation in intact seedlings treated with AOPP. These results suggest that CGA is essential for root hair formation in lettuce seedlings.

Light-induced root hair formation in lettuce (Lactuca sativa L. cv. Grand Rapids) roots at low pH is brought by chlorogenic acid synthesis and sugar

“…Hence, light was essential for root hair formation and probably for CGA synthesis in lettuce seedlings. Because CGA facilitates root hair formation at pH 4.0 in decapitated lettuce seedlings (Narukawa et al 2009), our results suggest that induction of root hair formation by light at pH 4.0 is most likely mediated through CGA synthesis. However, induction of CGA synthesis by light also occurred in lettuce seedlings grown at pH 6.0 when very few root hairs were formed ( Fig.…”

“…One possible reason for the inconsistency is the difference in seedling ages between the two experiments. The lettuce seedlings used in this paper were 24 h younger than the seedlings used in Narukawa et al (2009). However, the responses of root hair formation to exogenous CGA were similar between studies.…”

“…Quantification of endogenous CGA CGA was determined as previously described by Narukawa et al (2009).…”

“…We demonstrated previously that application of CGA restores root hair formation in decapitated seedlings grown under white light at pH 4.0. In this case, the seedlings had been pre-cultured for 24 h under white light before decapitation (Narukawa et al 2009). Our present findings appear inconsistent with this previous study.…”

“…Previously, we found that CGA is essential for root hair formation in lettuce seedlings (Narukawa et al 2009). CGA synthesis is initiated by light exposure in many species (Zucker 1963;Aerts and Baumann 1994;Percival and Baird 2000;Abbasi et al 2007).…”