| Popis: |
Light can become highly polarised when reflected from leaves. Polarisation-sensitive visual systems are very commonly found in insects, meaning it is possible that the polarisation of light reflected from plants may influence the behaviour of insects. This might result in the evolution of adaptive viral symptom~ which alter the polarisation properties of infected plants, in order to influence the attractiveness of infected plants to insect vectors and thereby enhance viral transmission. The primary aim of this project was to investigate whether plant viruses affect the polarisation of light reflected from leaves, and whether such effects may be different between insect vectored and non-insect vectored viruses. Given that surface features are a key determinant of polarised reflectance, the effects of viral infection on the expression of genes involved in the synthesis of leaf waxes and hairs was also analysed. It was found that two aphid vectored viruses, Potato virus Y and Cucumber mosaic virus, caused significant reductions in the degree of polarisation of light reflected from Nicotiana tabacum leaves, whereas Tobacco mosaic virus and Pepino mosaic virus, both non-insect vectored viruses, did not induce this effect. The aphid vectored viruses also induced more pronounced upregulation of leaf surface structure gene expression than the non-vectored viruses, in N. tabacum and Arabidopsis thaliana. Polarisation reflection was also analysed using a range of A. thaliana mutants deficient in the formation of leaf waxes or hairs, to establish whether these mutant phenotypes have any significant impacts on polarisation reflection. It was found that mutations in wax synthesis and leaf hair formation genes can significantly alter polarisation reflection from leaves. The impacts of viral infection on leaf wax structure and hair numbers were also analysed in wild type A. thaliana plants, although no significant differences between healthy and infected leaves were found in these experiments. Finally, a preliminary study was carried out to investigate the possible influence of polarisation signals on the behaviour of asexual wingless morphs of the green peach aphid, Myzus persicae, an efficient vector of many plant viruses. A series of choice tests were performed; however, these preliminary investigations did not reveal any differences in the attractiveness of wingless M. persicae to stimuli with differing polarisation properties. |
