Abstract
1. From rice plants, one of the growth-stimulating factors for X. oryzae was isolated and it was identified as cystine. The apparent concentration of cystine in rice plants was usually enough to support the growth of the bacterium, yet the concentration of cystine and other sulfur containing amino acids in leaf vessel was uncertain. The biographic properties of the growth-stimulating factors in leaf or root of rice plants seemed to be similar between the resistant and susceptible varieties.
2. Regarding the nutritional requirements of X. oryzae, it seems evident that the bacterium lacks the ability of utilizing inorganic sulfur sources including sulfate, sulfite, thiosulfate and sulfide with or without serine and that the bacterium requires for its growth each one of the sulfur containing amino acids including cysteine, cystine, homocysteine or methionine.
3. In the minimum basal medium, a linear relationship between the growth rate and the concentration of L-cystine added in the medium was observed when logarithmic scale was taken for both axes.
4. The presence of the inhibitory substances which counteract against the growth-stimulating factors in rice plants was recognized. The presence suggested possible mechanism which made the host either resistant or susceptible, yet the host specificity of the bacterium remained unsolved.
