Nitrogen Forms Alter Triterpenoid Accumulation and Related Gene Expression in Cyclocarya paliurus (Batalin) Iljinsk. Seedlings

Abstract

Cyclocarya paliurus (Batalin) Iljinsk. is a multiple function tree species distributed in subtropical areas, and its leaves have been used in medicine and nutraceutical foods in China. However, little information on the effects of nitrogen (N) forms and ratios on growth and secondary metabolite accumulation is available for C. paliurus. The impact of five NO3−/NH4+ ratios on biomass production, triterpenoid accumulation and related gene expression in C. paliurus seedlings was evaluated at the middle N nutrition supply. Significant differences in seedling growth, triterpenoid accumulation and relative gene expression were observed among the different NO3−/NH4+ ratio treatments. The highest triterpenoid content was achieved in a sole NO3− or NH4+ nutrition, while the mixed N nutrition with equal ratio of NO3− to NH4+ produced the highest biomass production in the seedlings. However, the highest triterpenoid accumulation was achieved at the treatment with the ratio of NO3−/NH4+ = 2.33. Therefore, the mixed N nutrition of NO3− and NH4+ was beneficial to the triterpenoid accumulation per plant. The relative expression of seven genes that are involved in triterpenoid biosynthesis were all up-regulated under the sole NH4+ or NO3− nutrition conditions, and significantly positive correlations between triterpenoid content and relative gene expression of key enzymes were detected in the leaves. Our results indicated that NO3− is the N nutrition preferred by C. paliurus, but the mixture of NO3− and NH4+ at an appropriate ratio would improve the leaf triterpenoid yield per area.