Responses Of Nitrogen And Camptothecin Metabolism In Camptotheca Acuminata Seedlings To Different Nitrogen Nutrition

Camptotheca acuminata, a tree species native to China, has gained great attention for its secondary metabolites camptothecin (CPT) which has remarkable anticancer and antiretrovirus activities. The change of nitrogen and CPT metabolism during the development of the seedlings supplied with different nitrogen concentrations and forms were studied by sand culture, and its responses to environmental nitrogen were analyzed. The nitrogen nutrition conditions to increase the CPT concentration in seedlings young leaves were also summarized and discussed. The results may provide some basic information for the research of the relationship between secondary metabolism in C. acuminata and its environment, and they also have some guidance significance in the practice of C. acuminata cultivation in order to gain high CPT concentration. The main results are as follows.1. Increase nitrogen supply significantly increased biomass of C. acuminata seedlings, 16 mmol.L^-1 may be the optimal nitrogen concentration for the seedlings growth. When the seedlings were supplied with deficient nitrogen, the growth of roots was preferential to absorb more nitrogen nutrition. Increase nitrogen supply significantly increased nitrogen concentration in the seedlings, and leaf nitrogen concentration was highest and had the most change extent with the increase of nitrogen supply, which suggest increase nitrogen supply may enhance the seedlings to absorb more nitrogen nutrition and preferentially partition to the leaves. Increase NO3-N ratio in nutrition solution was of advantage to the seedlings growth, the biomass was highest when NH₄⁺-N/NO₃^--N ratio was 25/75, and decreased when NO₃^--N was the sole nitrogen source, and significantly reduced when the seedlings were supplied only with NH₄⁺-N. Similarly, the seedlings absorbed more nitrogen nutrition and accumulated the most nutrition when NH₄⁺-N/NO₃^--N ratio was 25/75.2. Pigments, soluble protein, nitrate reductase (NR) and glutamine synthetase (GS) activities in leaves significantly increased with the increase of nitrogen supply (enzyme activity in roots was far lower than that in leaves), but excessive nitrogen supply (32 mmol . L^-1) didn't result in more soluble protein in the seedlings. NR and GS activities in leaves were relatively higher during early and middle stage of treatment, while relatively declined during late stage of treatment. Increase NO₃^--N ratio in nutrition solution may significantly induced leaf NR activity, the highest GS activity presented when NH₄⁺-N/NO₃^--N ratio was 50/50, while the optimal nitrogen conditions (NH₄⁺-N/NO₃^--N ratio was 25/75) was the most advantageous for pigments and soluble protein accumulation.3. CPT concentration in seedlings young leaves obviously declined with the increase of nitrogen supply, and it was the highest (6.72‰) when nitrogen supply was 4 mmol . L^-1, equal to 1.1 times of that when nitrogen supply was 16 mmol . L^-1. Proper deficient nitrogen stress can significantly increase the CPT concentration in seedlings young leaves. When NH₄⁺-N/NO₃^-1-N ratio was 25/75, CPT accumulation in young leaves displayed the best advantagesand increased in the early 30 days of treatment and then declined. A short-term treatment that NH4+-N/NO3-N ratio was 25/75 may gain high CPT concentration in young leaves.4. Tryptophan synthase (TSB) activity was the highest in young leaves and decreased sequentially in the stem bark, the mature leaves and the roots, which paralleled to CPT concentration. Tryptophan decarboxylase (TDC) activity was the highest in the stem bark, then in the young leaves, and the lowest in the mature leaves and the roots, which didn't parallel to CPT concentration. TSB activity increased and then declined to constant level with the time course. There was no significant difference between different nitrogen concentration treatments at late stage of treatment. TDC activity in stem barks decreased continuously along with treatment days increasing, and presented obvious increase with decrease nitrogen supply, and it was the highest when nitrogen supply was 4 mmol ? L"1. There was some parallelism between TDC activity in stem barks and CPT concentration in young leaves. TDC activity in the stem bark was the highest when NH/-N/NCV-N ratio was 25/75, and the change of TDC activity paralleled to CPT concentration in young leaves.To sum up, 16 mmol ? L"1 may be the optimal nitrogen concentration for the growth of C. acuminata seedlings, whease CPT concentration in young leaves was the highest when nitrogen supply was 4 mmol ? L"1. The optimal nitrogen conditions (NH4+-N/NO3-N ratio was 25/75) for seedlings growth was also the best advantageous for CPT accumulation. Therefore, it is an efficient method to increase CPT concentration in young leaves that proper short-term nitrogen deficient stress was conducted after a period of vigorous growth.