Effect of nitrogen nutrition on the stability of orchid-syimbiont association

在盘龙参与其菌根共生体的共生培养中，对氮源的适宜性进行了比较。白蛋白是远远优于无机氮的上级氮源。在24种氨基酸中，精氨酸是唯一适合于该氮水平的氨基酸，其它氨基酸的适宜性和利用率都不高，但程度不同。谷蛋白中氮的阈值水平远低于粉状谷物，如燕麦或小麦。研究了茎尖布朗宁和原球茎死亡与原球茎或真菌菌丝中氮含量之间的关系。原球茎对面筋蛋白水平的反应因真菌而异：一种真菌的原球茎鲜重随面筋蛋白水平的增加而显著下降，而另一种真菌的原球茎鲜重在此氮水平下受影响不大。在原球茎鲜重下降的情况下，菌体中的氮浓度降低，原球茎中的氮浓度升高，菌体中的氮浓度降低，而在健康的原球茎中，原球茎中的侵染区占原球茎的下半部分，因此共生关系得以维持，茎和根的伸长迅速进行。在发病的情况下，感染面积迅速增加，最终几乎占据整个原球茎，导致原球茎死亡。这些观察结果表明，这种疾病是从共生到寄生的变化的结果。

In the symbiotic culture of Spiranthes sinensis with its mycorrhizal symbionts, the suitability of nitrogen sources was compared. Alubumin was far superior nitrogen source to inorganic nitrogen. Among 24 amino acids tested, however, arginine was only suitable one at this nitrogen level, and all the others were less suitable or harnful although they varies in their degree. The threshold levels of nitrogen over which detrimental effects appear were far lower at gluten than at powdered sereal grains, e.g. oats or wheats.The relation between the occurrence of the disorder such as browning of shoot tips and death of protocorms ans nitrogen content in protocorms or in fungal mycelia was investigated. The response of protocorms to gluten levels varied according to fungi : the fresh weight of protocorms with a fungus decreased remarkably with an increase of gluten level, whereas that with another fungus was not much affected at this nitrogen level. Of those decreased in the fresh weight of protocorms, suffered severer disorder, and the nitrogen concentration of the them was increased in protocorms and decreased in fungal body.In the case of healthy protocorms, the infected area in a protocorm balanced occupying less than a lower half of a protocorm section, thus symbiosis was sustained and elongation of shoot and root rapidly proceeded. In the case of those suffered disorder, infected area increased rapidly and ultimately occupied almost whole protocorm resulting in the death of the protocorm. These observation suggested that this disorder was the result of change from symbiosis to parasitism.