不同濃度的鉀、鐵、錳及不同硝銨比對水耕雷公根產量及centelloside濃度之影響

Abstract

雷公根中最具有指標性的有效成分為三萜類化合物，包括羥基積雪草酸苷、積雪草酸苷、羥基積雪草酸與積雪草酸，這些成分具有消炎、治癒傷口、促進膠原蛋白增生及神經保護等功效，也可做為治療癲癇及麻風的藥物。由於雷公根單位產量較低、水分含量高，如何增加其產量及有效成分濃度是雷公根栽培之重要課題。除組織培養及代謝工程外，經由栽培處理也是其一。本研究探討不同濃度的鉀、鐵、錳及不同硝銨比對水耕雷公根產量及centelloside濃度之影響。試驗於臺灣大學農場溫室進行，設計採完全隨機區集排列設計，調整二分之一強度的Hoagland養液進行處理分為對照組 (N5A1) 及以相同的總氮濃度將硝銨比調整NO3--N: NH4+-N = 1: 5 (代號為N1A5)；於對照組養液配方增加鉀之濃度為5和7.5 mM (代號為K-2和K-3)，增加錳之濃度為45 μM (代號為Mn-5)，增加鐵之濃度為200 μM (代號為Fe-5)，共六種處理，每處理四重複，每種處理皆與對照組比較。雷公根共栽培135天，採收三次，分別於處理後第35、85天採收地上部兩次；第三次於第135天採收全株並採集水耕液樣品。植體洗淨後分為地上部與根部，測定總氮、硝酸態氮、磷、鉀、鈣、鎂、鐵、錳、銅、鋅及centelloside濃度。水耕液過濾後分析可溶性有機碳、總游離胺基酸態氮及總微生物菌數。結果顯示除了Fe-5處理會使乾物重顯著降低，其它處理組統計上皆無顯著差異。N1A5處理後植體中硝酸態氮濃度顯著低於對照組；K-2和K-3處理後不影響植體中鉀的濃度及吸收量；Mn-5處理後顯著增加植體中錳的濃度及吸收量，但並未產生毒害。Fe-5處理後雖使植株中鐵濃度增加，而吸收量卻顯著降低。水耕液中的可溶性有機碳與總游離胺基酸態氮大致皆隨栽培時間而降低，而Mn-5及Fe-5處理組之可溶性有機碳於30天顯著下降後又在45天顯著上升。綜觀而言，K-3處理可顯著提高植體內羥基積雪草酸苷濃度，而N1A5與K-2則可顯著提高羥基積雪草酸與積雪草酸濃度。

The active constituents of Centella asiatica are pentacyclic triterpenes, centelloside comprising of madecassoside, asiaticoside, medacassic acid and asiatica acid, which has anti-inflammatory, wound healing, stimulation of type I collagen and neuroprotection. Centelloside can also be used as a drug to treat epilepsy and leprosy. C. asiatica is a herbaceous annual plant, having creeping stolons with a low biomass yield. Therefore, high biomass yield and high concentration of centelloside are very important in order to use this plant. In addition to tissue culture and metabolic engineering, cultivation of C. asiatica is the most popular practice to harvest centelloside. The objective of this study was to investiagate the effects of different concentrations of potassium (K), iron (Fe), manganese (Mn) nutrients and nitrate nitrogen (N) to ammonium N ratio on the biomass and centelloside concentrations of C. asiatica under hydroponic culture. The experiment was conducted in the green house of National Taiwan University. All treatments were arranged in a randomized comlete design. One half strength of modified Hoagland’s solution with nitrate N to ammonium N ratio of 5 : 1 was used as control (N5A1). The other treatments included : 1. solution with nitrate N to ammonium N ratio of 1 : 5 (N1A5), and 2. solution with K concentrations of 5, 7.5 mM (K-2 and K-3), and 3. Mn concentration of 45 μM (Mn-5), and 4. Fe concentration of 200 μM (Fe-5). All treatments were conducted with four replications. During the growth period, the plants were harvested three times, 35 days, 85 days and 135 days after planting (DAP). Only the shoots were sampled at 35 and 85 DAP and the whole plant was harvested at 135 DAP. The nutrient solutions were sampled at 85 and 135 DAP. The plants of the third harvesting were separated into shoot and root. The concentrations of total N, nitrate-N, ammonium-N, phosphorus (P), K, calcium (Ca), magnesium (Mg), Fe, Mn, copper (Cu), zinc (Zn), madecassoside, asiaticoside, medacassic acid and asiatic acid were analyzed. The soluble carbon, total free amino acids and total colony counts of nutrient solution were analyzed. The results showed that the dry matter yield was the greatest in N5A1 treatment and the least in Fe-5 treatment. The nitrate N concentration in C. asiatica of N1A5 was significantly lower than the control. There was no difference in the concentrations and amount of K among different K treatments. Mn concentration in plant of Mn-5 treatment was significantly higher than the Mn-1 treatment. Higher Fe concentration in nutrient solution resulted in the higher concentration of Fe in the plant, however, the uptake of Fe decreased with the higher Fe concentration treatment. The soluble carbon and total free amino acids in different hydroponic solutions decreased with the cultivation time. However, this was not true in Mn-5 and Fe-5 treatments. The concentration of madecassoside in plant was significantly higher in K-3 treatment, while the concentrations of madecassic acid and asiatic acid were significantly higher in N1A5 and K-2 treatments as compared with the other treatments.