Luretta D. Spiess

Comparative Response of Pylaisiella selwynii to Agrobacterium and Rhizobium Species

Thirty-five strains of Agrobacterium and five strains of Rhizobium were tested for their ability to induce developmental changes in the moss Pylaisiella selwynii. The avirulent A. radiobacter (seven strains) and nontumorigenic strains of A. tumefaciens (four strains) had relatively little effect on moss development. Virulent strains of A. tumefaciens (17 strains), A. rubi (two strains), and A. rhizogenes (five strains) significantly altered development of the moss. Bud formation was induced by most strains, and these developed into normal gametophores, abnormal gametophores, or callus masses, depending on the strain of Agrobacterium. Agrobacterium rhizogenes and three strains of A. tumefaciens induced formation of numerous rhizoid-like filaments and only occasional gametophores. All five species of Rhizobium tested induced bud formation and normal gametophore development. The most effective of these strains, R. leguminosarum C56, required contact between moss and bacterium, similar to that required by A. tumefaciens. This strain also competed with virulent A. tumefaciens for attachment sites on the moss filaments, suggesting Agrobacterium and Rhizobium adhere to the moss via similar bacterial wall components. The rhizoid-inducing substance produced by A. rhizogenes strain TR7 readily passed through filters separating bacterium and moss in a parabiotic chamber, indicating it is released into the medium by the bacterium. The correlation between higher plant infectivity and the ability to induce developmental changes in P. selwynii suggests this system may offer unique possibilities for the study of Agrobacterium and Rhizobium infectivity.

Photocontrol of Germination of Spores of the Fern Polypodium aureum

Although Polypodium aureum produces spores throughout the year when grown indoors, these spores show a seasonal germination response which may be due to phytochrome levels induced in spores as they form. The maximum germination obtained with 5 days of R during October-January was 24%, but it increased to 79% during January-April. Germination induced by R is reversed by FR; longer periods of FR were no more effective in inhibiting germination than 1 day of FR. Kinetin, GA, IAA or cAMP did not induce germination in darkness, but kinetin and GA together with 1 day of R increased germination over that induced by 1 day of R alone. Cyclic AMP had a slight stimulatory effect with R, and IAA inhibited germination. Kinetin, GA, and cAMP were effective in preventing FR reversal of R-induced germination. Blue light alone did not induce germination. Germination was reduced if blue light followed 1 day of R, but blue light had no effect if 3 or 5 days of R had been given. Blue light followed by 1, 3, or 5 days of R increased the germination effect of R alone.

Bacteria Isolated from Moss and Their Effect on Moss Development

Bacteria from four species of mosses from different geographical locations were isolated either on media selective for agrobacteria or on nutrient broth. Many isolates induced developmental changes in Pylaisiella selwynii protonemal filaments comparable to those obtained with agrobacteria. No bacteria induced crown gall or hairy root symptoms on beans, tomato, or Kalanchoe, although a few promoted callus growth on potato tuber and also promoted callus and roots on carrot disks, similar to Agrobacterium rhizogenes. Many isolates bind to specific Agrobacterium attachment sites in wounds; five of seven tested isolates competed with virulent Agrobacterium tumefaciens for these sites on bean leaves. No isolate could unequivocally be assigned to the genus Agrobacterium by several physiological and biochemical tests used to classify Agrobacterium. These results demonstrate that bacteria adhering to moss in nature may affect protonemal growth and gametophore initiation and thus may be an important ecological factor in regulating normal life cycle events at this stage of moss development.

Specificity of Moss Response to Moss-Associated Bacteria: Some Influences of Moss Species, Habitat, and Locale

Bacteria adhering to three unrelated species of wild moss growing in similar or different habitats were isolated on a nonselective medium and tested for their effect on protonemal growth and development of four species of moss. Of the six groups of bacterial isolates from separate moss samples (283 isolates), 48%-68% promoted the development of their host moss; relatively few were inhibitory. Two species of moss belonging to separate families, Pylaisiella selwynii and Heterophyllium haldaneanum, collected from the same oak log, responded similarly to the bacterial isolates; the bacteria isolated from each had no distinguishable effects on the different mosses. Atrichum undulatum collected on the ground within a few meters of the other mosses responded differently to these bacteria, and bacteria from this species differed from the others in the proportion that were active on other mosses. Pylaisiella selwynii from Illinois and Wisconsin, ca. 170 miles apart, did not differ in their response to these bacteria, nor did the two samples of A. undulatum from the same two sites. Also, there were no significant differences between the groups of bacteria obtained from the same species of moss from the two different locales. More limited results with bacteria from P. selwynii collected in Minnesota, where a much greater change in latitude was involved, showed they were significantly different from bacteria collected from this moss growing in Wisconsin when tested on the latter moss. This group of bacteria was significantly more effective, however, on P. selwynii from Wisconsin than on Funaria hygrometrica. These data indicate that habitat as well as the species of moss and possibly major changes in locale may influence the kinds of bacteria found adhering to the same moss in nature, as estimated by their ability to alter growth and development of the different mosses.

Moss Growth and Development is Facilitated by Natural Bacterial Flora

Optimal conditions for growth, development or reproduction in many organisms often depend on association with a second unrelated organism in either a parasitic, mutualistic or protocooperative relationship. Several examples of such natural relationships between plants and a second organism which allows them to adapt and survive in a particular environment have been described. The lichen results from a symbiotic association in which the algal cells supply photosynthates to the fungus and the fungus absorbs moisture and shields the algae from intense light, allowing both to exist together in an otherwise unfavorable environment (Ahmadjian 1967). Rhizobia aid legume growth through symbiotic nitrogen fixation (Nester, Kosuge 1981). Spirillum lipoferum (Smith et al. 1976) and Azospirillum brasilene (Kapulnik et al. 1981) function in a similar manner in association with grasses. Pseudomonas interacts with plant roots, inducing a mechanism for choline sulfate uptake (Nissen, 1973).

Role of the Moss Cell Wall in Gametophore Formation Induced by Agrobacterium tumefaciens

The induction of buds and gametophores on the moss Pylaisiella selwynii by Agrobacterium tumefaciens was inhibited by cell walls (CW) isolated from dicots (potato, tomato, bean) but not by those from monocots (asparagus, onion). Pectin and polygalacturonate were also inhibitory; the latter was more effective. CW from Pylaisiella protonema also inhibited gametophore induction by A. tumefaciens; CW from Pylaisiella gametophores were less inhibitory; and CW from Polytrichum commune protonema or gametophores showed little inhibitory activity. Unlike Pylaisiella, P. commune does not show increased bud formation when incubated with Agrobacterium. After Polytrichum protonema or gametophore CW are treated with pectinesterase, they inhibit the Pylaisiella response to Agrobacterium. Pylaisiella gametophore CW also become more inhibitory when treated with pectinesterase. Pectinesterase treatment of intact Polytrichum protonema makes them sensitive to Agrobacterium, as shown by increased bud and gametophore formation. We suggest that the absence of suitable Agrobacterium adherence sites on Polytrichum CW and the generation of such sites by pectinesterase action account for these results.