| Virido-albina mutant in diploid wheat induced by X-rays
Taro FUJII National Institute of Genetics, Misima, Japan Chlorophyll mutants, besides often occurring spontaneously, are induced frequently by ionizing radiations. Most bf them are Mendelian recessives. Matsumura and Fujii (1955) found several chlorophyll mutants such as albina, chlorina, virido-albina, basi-viridis and striata etc. by X-irradiation of Einkorn wheat (Triticum monacoccum flavescens). Virido-albina mutant appeared in the X2-generation from seeds treated with 8,100gamma dose at 180 KVP. About 3/4 of the base of each leaf of this mutant were white, while the rest was light green. The characteristics of this mutant appeared already at the seedling stage and it was completely lethal in the field during the low temperature period. When this mutant was placed in the phytotron (20C) and exposed to fluorescent light (about 4,000 lux), the leaves became gradually green starting from the veins, and about 15 days late it resembled the basi-viridis mutant with a light green leaf base. It required further 30 days of treatment to recover a chlorophyll content similar to that of the normals. Similar results were obtained with the basi-viridis mutant with regard to increasing of chlorophyll content in the phytotron. On the other hand, albina, chlorina and striata did not increase their chlorophyll content under the same treatment. The chlorophyll content in the normals and several chlorophyll mutants are shown in table 1 by optical density (T= -log I/I0) of 10 times dilution of fresh leaves. Eventually, virido-albina mutants was heading in the phytotron, while being lethal in the field. Time of heading and ripening was delayed about 15 days, and plant height, number of tillers and fertility were significantly reduced in comparison with the normaIs. Seeds of the recovered virido-albina showed a relatively high germination rate of about 80%. Of course, the seedlings were virido-albina. When the recovered virido-albina was returned to the field, the successive leaves showed virido-albina character and the mutants died out in winter. Oxygen consumption or respiration rate was measured by Warburg respirometer. This rate in the virido-albina mutant was about half of that of the normals, and the rate of the recovered virido-albina was rather higher than that of the normals. But the activity of cytochrome oxidase in the mutants, grown in the field and in the phytotron, was similar to that of the normals. Fujii (1955) reported already a similar tendency toward a decrease of the chlorophyll content and activity of cytochrome oxidase in the chlorina mutant. From these results, it has been assumed that a recovery of the chlorophyll content without a normal activity of cytochrome oxidase would be not possible. |