|
Nucleic acid synthesis and adaptation in wheat
H. K. JAIN and P. K. DAS Division of Genetics, Indian Agricultural Research Institute, New Delhi, India Intervarietal differences in adaptability, generally tested through multilocation yield trials, are known to exist in wheat as in other crops. The present study was planned to determine some of the possible cytological and metabolic characteristics of wheat varieties, which have been found to differ significantly in their adaptability, through such tests. One of the characters for which these varieties have been tested is the turnover of DNA and RNA in their root tip cells at three different temperatures. Six Indian commercial varieties of wheat-C 303, C 306, NP 824, NP 823, NP 825 and NP 798 formed the experimental material. Of these C 306 is known to be highly adapted, while NP 823 and 825 show very poor adaptability. The other varieties show an average type of adaptability. The autoradiographic techniques was employed to study the synthesis of DNA and RNA in the root tip cells of the six varieties at temperatures of 20C, 30C and 38C. The seeds were germinated at these different temperatures and the root tips, when about 1 cm long, were fed with tritium labelled thymidine in one case, and thymdine in. the other. The thymidine (2C/ml, specific activity 3C/m Mol.) incorporation was allowed for a period of 10 hours while uridine (5C/ml, specific activity 2.24C/m Mol.) was fed for a period of 4 hours. A quantitative study of incorporation of thymidine was made by counting the silver grains formed over chromosomes of nearly 30 metaphase cells in each of a number of root tips. In the case of RNA synthesis, 29 interphase cells showing well spread silver grains were scored in five or more root tips of each variety. These observations on grain count are presented in Figures 1 and 2. It has been found that, in general, the DNA synthesis in the cells of a variety varies greatly with temperature. An important finding is that the variety C 306, known for its high adaptability, is relatively constant in its DNA synthesis at different temperatures. It will also be seen that all the six varieties show variation in RNA synthesis with change in temperature. C 306 and C 303 show the largest variation in RNA synthesis, in contrast to the poorly adapted varieties like NP 897. The above observations would suggest that constancy in DNA and plasticity in RNA synthesis under different environmental conditions may be important attributes of a well adapted genotype. That stability in the synthesis of DNA, the genetic material, should contribute to adaptability is understandable. It is possible that the capacity to vary the synthesis of RNA, the material closely associated with gene action, in response to changing environmental conditions also confers an adaptive advantage. (Received February 4, 1970) |