Effects of Nitrate and Ammonium Nitrogen Sources on the Seedling Growth and Root Phosphoenolpyruvate Carboxylase Activity of Different Crop Species

硝酸態與銨態氮源對作物幼苗生長與根部PEP Carboxylase活性之影響

劉大江(D. J. Liu) ； 王強生(C. S. Wang) ； 魏夢麗(M. L. Wei)

《中華農業研究》 36卷3期 (1987/09) Pp. 283-295

https://doi.org/10.29951/JARC.198709.0006

摘要

將水稻與玉米等七種作物培養於含有150ppm之硝酸態或銨態氮水耕液中，測定幼苗生長速率，又由於發現銨態氮可顯著提高作物根部PEP carboxylase活性，故以水稻爲材料，初步究明其特性，供爲深入探討氮源對以PEP爲中心之碳素代謝作用影響的依據。試驗結果顯示各種作物幼苗在含硝酸態氮之水耕液中的生長較爲良好，但水稻與小麥莖葉生長則以銨態氮處理爲佳，亦即作物間的反應具有差異。銨態氮可使各種作物幼苗葉片與根部PEP carboxylase活性升高，其幅度在葉片爲8~61%，在根部最高可達4.5倍以上。由本試驗方法萃取所得臺農67號水稻根部PEP carboxylase具有極高的穩定性，萃取後7小時之活性仍未降低；其最適pH值在使用Tris-HCl或Hepes-KOH緩衝液時，均爲8.0至8.5。對此一自水稻根部萃取之酵素的Kinetic特性試驗得知，針對PEP濃度之反應曲線在pH爲8.0係屬hyperbolic，在pH爲7.0係屬sigmoid，經計算pH爲8.0時之Km值爲0.16mM。初步判定此一酵素與C-3型植物葉片內PEP carboxylase之特性相同。由於PEP在作物含碳化合物之代謝作用方面極具重要生，而極低之銨態氮濃度(1-10ppm)即可提升根部PEP carboxylase酵素活性，故爲探討氮素作物性理活生影響之良好資料。

並列摘要

Seven crop species, including maize, sorghum, rice, wheat, barley, peanut and soybean, were grown hydroponically with either nitrate or ammonium N at a concentration of 150 ppm. Rates of seedling growth were determined to study the effect of N sources on the performances of carbon metabolism. As ammonium N could enhance the activity of PEP carboxylase in the roots of many crops, attempts had been made to clarify the characteristics of this enzyme in order to provide basis for further studies. Experimental results showed that crops grew better in nitrate N than in ammonium N medium. However, shoots of rice and wheat gained more fresh weight when treated with ammonium N which was different from the results on maize, sorghum and peanut, indicating difference in response to N sources among plant species. Amnionium N could enhance the activity of PEP carboxylase of various crops. The increase was 8-61% in the leaf blade and as high as 4.5 folds in the root. PEP carboxylase extracted from the roots of Tainung 67 rice with the methods employed in this experiment was extremely stable. No decrease in enzyme activity was observed up to 7 hrs after extraction. Optimal pH for rice root PEP carboxylase was between 8.0 and 8.5 with either Tris-HCl (100 mM) or Hepes-KOH(50 mM) buffer. Kinetic study showed that the response curves of velocity versus substrate (PEP) concentration was hyperbolic at pH 8.0 and sigmoid at pH 7.0. Reciprocal plots of the data was linear, indicatng Michaelis-Menten kinetics. Km value for PEP was calculated to be 0.16 mM at pH 8.0. Preliminary results suggested that the ammonium-N responsive root PEP carboxylase was similar to the same enzyme from leaf blades of C3 plants in many aspects. As PEP plays a very important role in carbon metabolism, and in view that ammonium-N at a very low concentration (e. g., 1 ppm) could enhance significantly the activity of root PEP carboxylase, the finding of this experiment could be utilized for further study on the interaction of N and carbon metabolism in plants.