인산공급이 대두근류의 인산형태와 bacteroid의 인산흡수에 미치는 영향

Effect of external-phosphorus supply on the phosphorus status of soybean nodules and the P-uptake system of isolated bacteroids

기주 식물에 대한 인산공급이 근류의 인산 형태와 bacteroid의 인산흡수에 미치는 영향을 살펴보고자 B. japonicum MN 110을 접종한 대두식물을 1.0, 0.25, 0.05 mM-P 조건에서 재배하였다. 1.0, 0.25, 0.05 mM-P 조건에서 재배한 대두식물의 근류 Pi 농도는 각각 4.1, 2.5, 2.0 mM이었으며 인산공급이 근류의 Pi, SOP, lOP의 분포에는 유의성 있는 영향을 미치지 못하였다. 0.25, 0.05 mM-P 조건에서 재배한 대두식물의 유엽 Pi 농도는 대조구(1.0 mM-P)의 각각 33%, 20%이었으며 노엽 Pi 농도는 대조구의 각각 16%, 7%였다. 잎에서는 인산 결핍이 전인산에 대한 Pi의 분포를 감소시켰으나 lOP의 분포는 증가시켰다. 근류내의 bacteroid의 수는 $0.87-1.30{\times}10^{11}\;/GFW\;nodule$이었으며, 인산흡수도는 15-16 pmoles /min/$10^8$ bacteroid로 기주식물의 인산공급에는 영향을 받지 않았다 이러한 결과는 인산결핍 대두식물의 근류내 Pi농도는 bacteroid의 생육과 번식에 충분하며 인산결핍에 의하여 기주식물의 생육이 저해될 때에도 bacteroid의 인산흡수는 억제상태에 있음을 나타낸다.

Soybean plants inoculated with Bradyrhizobium japonicum MN 110 were supplied with nutrient solutions containing 1.0, 0.25 and 0.5.nM-P to characterize the effect of externaI-P supply on the phosphorus status of nodules and on the P-uptake system of isolated bacteroids from nodules. After 48 days of growth, whole plant dry mass in the 0.25 and 0.05 mM-P treatments decreased significantly. The Pi concentrations in nodules were 4.1, 2.5 and 2.0 mM for 1.0, 0.25 and 0.05 mM-P treatments, respectively. The external-P supply did not significantly affect the distribution of phosphorus among inorganic phosphate(Pi), soluble organic-phosphorus(SOP) and insoluble organic-phosphorus(TOP) fractions in nodules. The Pi concentrations in young leaves of 0.25 and 0.05 mM-P plants were 33% and 20% , respectively, of those in young leaves of 1.0 mM-P plants and Pi concentrations in old leaves were only 16% and 7%, respectively, of those in old leaves of 1.0 mM-P plants. Phosphorus deficiency decreased the percentage of total leaf phosphorus in the Pi fraction and increased the percentage of total leaf phosphorus in the IOP fraction. The bacteroid number ranged from 0.87 to $1.30{\times}10^{11}$ Per GFW nodule regardless of external-P supply to the host Plants and Plant age, The P-uptake rates were the same (15-16 pmoles /min./$10^8$ bacteroids) for the bacteroids isolated from nodules of 1.0 mM-P and 0.05 mM-P plants. These results indicate that Pi concentrations in nodules of phosphorus-deficient plants are sufficient for proliferation of bacteroids and that the P-uptake system of bacteroids is in a repressed state even when host plant growth is severely restricted by phosphorus-deficiency stress.