Studies on proliferation in sunflower tissues induced by escherichia coli
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
An investigation has been carried out on the effects of inoculating sunflower tissues with Escherichia coli following Philipson and Sheat’s (1963) report of the stimulatory action of this bacterium on sunflower hypocotyl tissue. No consistent results could be obtained when aseptically grown decapitated seedlings were inoculated with E.coli, so that in most experiments 1 mm-thick disks of sunflower hypocotyl were grown on a simple sucrose-inorganic salts medium which was modified on occasion with the addition of indole acetic acid. Disks cultured in this way were inoculated with bacteria and grown in the light or darkness at 250 C. _ After treatment observations were made of the gross morphology of the disks while fresh and dry weights were recorded. In addition a detailed histological study was carried outo The reactions to inoculation of older sunflower plants and of clonal pith tissue were also investigated. Hypocotyl disks inoculated with E. coli and grown in the light proliferated from the lower surface and formed numerous long roots while those in the dark were usually inhibited in comparison with uninfected disks. Inoculation of disks with the crown gall bacterium, Agrobacterium tumefaciens, induced proliferation mainly from the upper surface and a few short roots were formed. Although the addition of 0.01 ppm IAA to uninfected disks induced growth similar to that in E. coli- inoculated disks grown in the light on the simple medium, histological studies showed that the proliferating tissues were different in charactero The histological studies also showed distinct differences between the proliferation in E and AQ tumefaciens-infected disks. By increasing the time between wounding and inoculation with E. coli the growth response of the disks was shown to be closely connected with wounding. Since E. coli can produce IAA and vitamins under certain culture conditions, and other bacteria have been shown to produce cytokinins, it was suggested that the bacteria produce some sub stances of this nature. reacting with freshly-wounded tissue, which induce proliferation in light-grown disks or inhibition in disks grown in the dark.