Beneficial effect of rare earth elements on the growth of Dryopteris erythrosora

Abstract

The amount of rare earth elements in a fern, Dryopteris erythrosora, were determined by Instrumental Neutron Activation Analysis (INAA). In particular, the effect of La on the growth of Dryopteris erythrosora was examined in detail. Small sporophytes, about 2 cm high above the ground, were chosen. The Murashige-Skoog (MS) basal medium was used. The culture medium was dissolved in ultra-purified water and the pH was adjusted to 5.7 with 0.5 N NaOH or 0.5 N HCl. A La-containing medium was prepared by adding 10 mM LaCl3 to the MS basal medium before the pH adjustment. Ca- and Na-containing media were prepared in the same way. A 12-hr light/12-hr dark photoperiod was maintained, at a light intensity of 10,000 lux and 25 +/- 2 C. After 2 months of cultivation, the growth rate was measured. Compared with the addition of Ca and Na and the use of MS basal medium, the effect of La on the growth was significant. In addition, the ratio between the concentrations of rare earth metals in plant and soil was also measured. No correlation was detected between the concentrations of Ca and La measured for each fern, which suggested different responses of the fern to rare earth elements and Ca. The concentration ratio of lighter rare earth elements sometimes exceeded 1, which was larger than that of Ca.

シダの一種であるDryopteris erythrosora中の希土類元素の含有量を機器中性子放射化分析(INAA)を使って測定した。とくにDryopteris erythrosoraの成長に対するLaの効果について調べた。地上2cmに伸びた小さな胞子体を選び、Murashige-Skoog(MS)基本培地を使用し、培養培地は超純水に0.5-NのNaOHまたは0.5-NのHClでpHを5.7に調整した。10ミリモルのLaCl3をMS基本培地にpH調整の前に添加してLa含有の培地を調製した。Ca含有培地、Na含有培地も同様にして調製した。光の照度10,000ルックス、気温25±2度Cで12時間毎に明滅する周期で2ヶ月培養したのち、成長速度を測定した。Ca添加、Na添加およびMS基本培地などと比較して、La添加は成長に及ぼす効果が著しかった。また、土壌での濃度に対する植物での濃度の比を測定した。それぞれのシダで測定したCaとLaの濃度の間には、相関がなく、希土類元素とCaに対するシダの応答が異なることを示した。軽希土類元素の濃度比は1を越えることがあり、Caの濃度比より大きかった。