An investigation into nucleic acids of powdery mildew spores, and some effects of mildew infection on host plant nuclear material

Part I of the thesis is concerned with the nucleic acid content of spores of members of the genus Erysiphe whilst Parts Il and III deal with the phenomenon of altered host DNA susceptibility to perchloiic acid extraction resulting from infection. The results are considered generally in relation to the obligate life style of the parasite. Spore RNA was analysed both qualitatively and quantitatively and the RNA content was found to be 6.9 + 0.4 x 10711 g/spore. Using polyacrylamide gel electrophoresis the majority of this was found to, be ribosomal RNA with molecular weights typical of the fungi. The presence of DNA in E. graminis and E. cichcracearum spores was established qualitatively by a variety of methods based on detection of both thymine and deoxyribose and quantitative analysis for DNA by two methods gave good agreement, with values of approximately 1.9 ± 0.6 x.10 12.g/cell. The values reported. for RNA and DNA are high in comparison with other fungi but combine to give an RNA : DNA ratio of approximately 35 : 1 which is within the range encountered amongst the fungi..In Part, II a series of experiments is reported which was.s designed to explore the distribution of the phenomenon of increased DNA extractability induced in the host as a result of infection. The results showed that both mildew and virus infections of barley induced increased DNAextractability. Furthermore the phenomenon was also exhibited by uninfected senescent barley, but not by rust infected wheat. These results are discussed in an attempt to determine the significance of the distribution of the phenomenon of increased DNA extractability. The results reported. in Part III are of experiments designed to determine the changes at the nuclear level which are associated with altered DNA extractability during infection and senescence. Preliminary: experiments suggested that the chromatin proteins were involved and subsequently an extraction technique, for purified chromatin was devised. This allowed the quantitative and qualitative changes in histone and non-histone protein fractions as a result of infection and senescence to be followed. Although both protein fractions showed changes on infection and senescence, theoretical consideration suggested that the histone protein fraction was most likely to be responsible for the altered behaviour of DNA during perchloric acid extraction. However experimental evidence was not consistent with this view and indicated,that changes in non-histone chromatin proteins were more likely to be involved. The detailed results of this experimentation are considered in association with the Chemical basis of perchloric acid action on and with the broader topic of protein DNA interaction. Also the above results and the overall phenomenon of increased DNA extractability are considered in relation to the. concept of senescence induced alterations of the host. It is suggested that the phenomenon is associated with senescence rather than specifically with obligate parasitism and` also that many other of the so called specific effects of infection may in. fact bee results of enhanced senescence.potential of altered DNA extractability ad a' basic parameter of various situations is also considered, as is 'the possibility that the phe~ome~on is a specific effect, at host genome level, of infection by an obligate parasite.