光强对喜树幼苗叶片次生代谢产物喜树碱的影响

喜树碱是我国特有树种——喜树中所含的重要次生代谢产物 ,在人工控制条件下观察了光强对喜树幼苗叶片喜树碱含量的影响。喜树幼苗叶片的喜树碱含量随着遮荫程度的增加 (光照强度降低 )而增加 ,但严重遮荫的 (光强为全光照的 2 0 % )在处理后期 (75 d)喜树碱含量降低。叶片的喜树碱产量 (喜树碱含量与叶片生物量乘积 )在处理初期 (30 d)随光强减弱而缓慢地略有增加 ,处理后期 (45 d以后 )随光强的减弱而有明显增加 ,但光强低于全光照的 6 0 %以后喜树碱产量迅速下降。喜树碱的增加可能是喜树幼苗通过次生代谢过程对不良环境 (遮荫 )的一种适应性反应

Effects of light intensity on secondary metabolite camptothecin production in leaves of Camptotheca acuminata seedlings

Alkaloids represent one of the largest groups of natural products. In general, alkaloids serve as defense chemicals against herbivores and to a lesser degree against bacteria, fungi, and viruses or provide a means of interaction with other plants. Camptothecin (CPT) is a monoterpenoid indole alkaloid originally isolated from Camptotheca acuminata, a deciduous tree, and native to south China, that has gained great attention for its significant antitumor activities in experimental studies. CPT is present in all organs of C. acuminata, but the contents are usually very low. To enhance CPT yield in plants, some studies on the relationship between CPT production, accumulation and environmental conditions have been preformed. In the present work, under controlled conditions, we observed the effects of light intensity on CPT production in leaves of C. acuminata seedlings. Seedlings were grown from seeds in a greenhouse and transported to pots (diameter 15 cm, depth 15 cm). The ventilating windows had been opened to get a similar air temperature and humidity to outdoors in the greenhouse since July 8. On July 15, when the fourth real leaves came out, shading-controlled experiments were conducted with shade-cloth to achieve five different irradiances of 100%, 80%, 60%, 40%, and 20% of full sunlight, respectively. 5 Seedlings were harvested every 15 days from July 30 to October 2 and sampled 5 times. All leaves collected from each seedling were grouped for one sample and the 5 different seedlings harvested at the same time were looked as 5 repetitions. In full sunlight, leaf biomass gradually increased, and decreased at the end of season of October 2. When the light intensity reduced, the increase of leaf biomass slowed down, but when the irradiance lowered than 40% of full sunlight, leaf biomass tended to decrease after 45 days of treatment. In full sunlight, CPT content in leaves of C. acuminata seedlings increased during the whole seedling development, and more increment was observed at the end of the growing season, so did in 80% and 60% of full sunlight. When irradiance was 40% of full sunlight, there was little increment of CPT content between the last two samples. On the contrary, under irradiance of 20% of full sunlight, CPT content decreased after 75 days of treatment (Fig. 3 and Fig. 4). Treatment with shading promoted the accumulation of CPT in the leaves of C. acuminata seedlings, however long-term treatment (such as 75 d) with heave shading (irradiance lower to 40% of full sunlight or less) prevented alkaloids content from increasing. The product of CPT content and leaf biomass results in CPT yield in leaves of C. acuminata seedlings. In 100% and 80% of full sunlight, CPT yields increased during seedling development. In 60% of full sunlight, CPT yield increased in the first 60 days under treatment, but then decreased in the samples treated for 75 days. In 40% and 20% of full sunlight, CPT yield increased in the first 30 days of treatment, and decreased after 60 days of treatment (Fig. 5). Under shading treatment, light shading (irradiance of 60% of full sunlight or higher) boosted CPT yield, but with the heavier shading, CPT yield declined during the period of the treatment (Fig. 6). The enhancement of CPT accumulation in C. acuminata seedlings under shading treatment suggests a kind of defensive mechanism. Shading treatment could be selected as a method to enhance CPT content and yield in leaves of C. acuminata seedlings.