The diseases of purple laver (red alga Porphyra) can be conveniently assorted into two types, one is the disease caused by parasitic microorganisms such as fungi or bacteria, the another is caused by physical, chemical or physiological damages. The pythium disease is well known as a typical example of the former, and for the latter shot hole and tumor are included. Besides these diseases, whose causes are comparatively well established, white blight and white rot have been recognized as popular ones characterized by the appearance of decolorized cell or cells especially in the marginal regions of the fronds. It is believed that these diseases develop on unhealthy fronds after being exposed to such unfavorable conditions as the deficiency of light quantities, low salinity of sea water and unsufficient daily exposure in the air. Several descriptions have been published on the environments and frond conditions when the symptoms of those diseases begin to be visible, however, little knowledge has yet been obtained about their causes and about the changes of chemical components in the cells during the development of the diseases.
The purpose of the present study is to elucidate the physiological changes in the cells when thalli were infected by white rot. The authors reported here the differences in the contents of extractive amino acids and nitrogen, extractive and total, between the infected and the healthy fronds. The results can be summarized as follows:
1) When infected with white rot, such extractive amino acids decreased conspicuously as aspartic acid, glutamic acid, alanine and taurine contained in purple laver grown at the culture field.
2) On the contrary, it was observed that the contents of glycine and citrulline stayed almost unchanged or rather increased.
3) Purple lavers were cultured at different salinities of sea water in concrete tanks for about a week. The low salinity induced both the decrease of dominant extractive amino acids and the increase of unhealthy cells.
4) Little differences were observed in the contents of the extractive amino acids among the samples cultured at varied periods of daily exposure in the air.
5) No close relations were detected between the degrees of disease and the contents of extractive basic amino acids such as lysine, histidine and arginine.
6) The contents of extractive and total nitrogen, and ammonia changed irrespectively to the degrees of disease of the fronds.