氮肥用量對青脆枝新梢枝葉養分及喜樹鹼含量周年變化的影響

Abstract

喜樹鹼 (camptothecin) 是21世紀最受矚目的抗癌藥物之一，青脆枝是被國際公認含喜樹鹼成分最高的植物。由於全世界的需要量增加造成自然資源短缺、環境及種源破壞且不同區域之青脆枝喜樹鹼含量不同，應可歸因於遺傳特性與環境因子之差異，人工栽培的方式愈形重要。喜樹鹼為含氮的二次代謝物，因此，與氮的營養之關係如何，仍不清楚。雖然根中喜樹鹼為各器官中最高者，但整株採收不合經濟效應。一般利用採摘青脆枝的莖、葉以萃取喜樹鹼。本研究之目的在探討不同量及不同來源的氮肥對青脆枝新梢枝葉養分及喜樹鹼濃度周年變化的影響。本研究採盆栽試驗地點位於農場溫室，共六種處理 (N1、N2、N3 、N4、O1、O2)，其中N1為每兩個月施氮0.5 g/pot，N2為1.0 g/pot，N3為1.5 g/pot，N4為2.0 g/pot，O1施氮0.5 g/pot，O2則為1.0 g/pot。N1-N4處理施尿素，O1與O2處理施有機肥料。每處理六重複，逢機完全區集排列。磷與鉀每三個月施用一次，其施用量均為0.5 g P/pot及0.5 g K/pot。從2007年4月4日至2007年12月4日，每兩個月由每盆每株採兩支枝條，剪取二十公分長度。2008年2月4日全株採收時並採集盆栽土樣。分析青脆枝收成後之土壤基本性質、有機質肥料及植物體樣品。結果顯示，不同量氮肥處理對二十公分長新生長枝條之乾重、總氮、硝酸態氮、磷、鉀、鈣與鎂之濃度均無顯著差異之影響。各處理青脆枝新梢枝葉進入秋冬季時的乾重下降，應是溫度與日照降低，影響光合作用、水與養分的吸收及乾物生產。處理一年後之全株乾重，則隨氮肥施用量增加而增加。青脆枝新梢之葉與莖中總氮、磷、鉀與鈣濃度以四月採收者顯著較高，六月與八月者最低，可歸因於五至八月時溫度與日照較高，植物體生長旺盛，乾物生長量較大所造成之稀釋效應；至十月以後則又因日照與溫度下降，植體之生長量下降，因此，其濃度上升；鎂之變化則不同，至十與十二月時之濃度最低。第二年二月全株採收後全株之乾重、氮與鎂的吸收量隨氮肥施用量增加而增加，磷、鉀與鈣的吸收量，則不因處理而有顯著差異。不同量有機肥料處理亦有相同之趨勢。各個處理新梢莖與葉之硝酸態氮濃度均低。所有處理的可溶性還原態氮佔總氮濃度高比例，為植物體中氮的主要成分。青脆枝全株均含喜樹鹼，不同器官中喜樹鹼濃度依次為根＞幼莖＞老莖＞葉。青脆枝整株喜樹鹼濃度540-933 mg/kg。不同量氮肥處理對新梢莖與葉之喜樹鹼濃度無一致性之影響。不同時間之莖與葉喜樹鹼濃度，則以六月及八月之葉部喜樹鹼濃度顯著高於他月份者，顯示夏天有利於喜樹鹼在葉片之累積。除六月老枝條之莖以外，各時期莖中喜樹鹼濃度皆高於葉中者，顯示喜樹鹼有在莖中累積之傾向。由處理一年後之不同部位喜樹鹼濃度可知，新莖與根中之濃度隨氮肥用量增加而有增加之趨勢，但N4處理例外，老莖與葉中的濃度則不受氮肥用量所影響。氮肥的施用可增進作物的品質及產量，乾物質產量增加，喜樹鹼的產量也隨之增加。環境因子對喜樹鹼影響十分複雜，不同營養、氣候與都會影響喜樹鹼含量。

Camptothecin (CPT) is regarded as one of the most promising anti-cancer drugs of the twenty-first century. Among several plant species known to contain the compound, by far the highest concentration has been reported from Nothapodytes nimmoniana (Icacinaceae). Owing to the growing demand for CPT, the species has been declared as endangered. There is significant variation in CPT content in N. nimmoniana among the plants growing in different regions. It is likely that the differences in the levels of CPT in N. nimmoniana are a function of both the genetic and environmental conditions of the population. Cultivation of N. nimmoniana becomes important to harvest CPT. CPT is a secondary metabolite which contains nitrogen (N). The concentration of CPT in N. nimmoniana in relation to N nutrition is not clear. The highest concentration of CPT in N. nimmoniana occurs in roots. Harvest the whole N. nimmoniana to get CPT is not economic. In practice, the new shoots of N. nimmoniana are harvested and extracted for CPT. The objective of this study was to investigate the effect of different kinds and rates of N fertilizers on the growth and physiological-nutrition of new shoot of N. nimmoniana and the camptothecin concentration around a year. The experiment was conducted in the pot culture in the greenhouse. There were six treatments, which were: 1. chemical N fertilizer of rate I (0.5 g N/pot/2 mon, N1); 2. chemical N fertilizer of rate II (1.0 g N/pot/2 mon, N2); 3. chemical N fertilizer of rate III (1.5 g N/pot/2 mon, N3); 4. chemical N fertilizer of rate IV (2.0 g N/pot/2 mon, N4); 5. Organic fertilizer of rate I (0.5 g N/pot/2 mon, O1); 6. Organic fertilizer of rate II (1.0 g N/pot/2 mon, O2). All treatments were replicated six times and arranged in a randomized complete block design. Phosphorous (P) and potassium (K) were applied every three months with the rates of 0.5 g P/pot and 0.5 g K/pot, respectively. Two new shoots with 20-cm in length were harvested every two months for each plant. The whole plants were harvested after treating for one year. The soil were also sampled after harvesting of the plants. The soil chemical properties, plant nutrient composition, and CPT concentration in each organs were analyzed. The results indicated that dry weight of 20-cm long new shoots the N, NO3-N, P, K, calcium (Ca), magnesium (Mg) concentrations were not affected by the rates of N applied. The dry weight of new shoots decreased during the fall and the winter. The N, P, K, and Ca concentrations in new shoots were also affected by the climatic condition. The higher concentration of the elements of the shoots growing in the fall and the winter and lower in summer. The growth of the whole plant and the amount of uptake of N and Mg after treating for one year increased as increased the rates of N applied. There were no significant difference as in the amount of uptake of P, K and Ca. The same effect was observed in organic fertilizer treatments. The NO3-N concentrations in different plant parts were low. However, the soluble N concentrations in different plant parts were high and were the most abundant composition of N. All plant organs contain CPT and the concentrations of CPT in different organs decrease in the following order: root ＞ new stem ＞ old stem ＞ leaves. The concentrations of CPT in the whole plants were 540-933 mg/kg. Different rates of N fertilizer has litter effect on the CPT concentration of the plants. However, there were significant differences in CPT concentrations of the new shoots sampled in different times. Higher concentrations of CPT in leaves were observed in the samples harvested in June and August, which meant that CPT accumulated in leaves in summer. The stems contain higher concentration of CPT than the leaves. Higher concentrations of CPT in new stems and roots were observed with the increase in N application rates except for the N4 treatment after treating for one year. The CPT concentrations in old stems and leaves were not affected by the rates of N applied after treating for one year. Higher N application rate results in the higher yield and the amount of CPT. The effect of environmental factor on the yield of CPT was complex. The concentration of CPT affected by the nutrition and climatic condition.