No abstract

In the space experiment 'Spores in artificial meteorites' (SPORES), spores of the fungus Trichoderma longibrachiatum were exposed to low-Earth orbit for nearly 2 years on board the EXPOSE-R facility outside of the International Space Station. The environmental conditions tested in space were: space vacuum at 10 −7 -10 −4 Pa or argon atmosphere at 10 5 Pa as inert gas atmosphere, solar extraterrestrial ultraviolet (UV) radiation at λ > 110 nm or λ > 200 nm with fluences up to 5.8 × 10 8 J m −2 , cosmic radiation of a total dose range from 225 to 320 mGy, and temperature fluctuations from −25 to +50°C, applied isolated or in combination. Comparable control experiments were performed on ground. After retrieval, viability of spores was analysed by two methods: (i) ethidium bromide staining and (ii) test of germination capability. About 30% of the spores in vacuum survived the space travel, if shielded against insolation. However, in most cases no significant decrease was observed for spores exposed in addition to the full spectrum of solar UV irradiation. As the spores were exposed in clusters, the outer layers of spores may have shielded the inner part. The results give some information about the likelihood of lithopanspermia, the natural transfer of micro-organisms between planets. In addition to the parameters of outer space, sojourn time in space seems to be one of the limiting parameters.

Prohexadione-Ca is currently developed as an inhibitor of excessive vegetative growth in apple. In addition to the control of shoot growth, distinct effects on the incidence of fireblight are observed that are not due to any bactericidal effect of the compound. Further, the compound often causes a delay of senescence. It is known that prohexadione-Ca acts as a structural mimic of 2-oxoglutarate thereby inhibiting dioxygenases, which catalyze distinct steps in gibberellin (GA) biosynthesis. As a result, levels of growth-active GAs are lowered and, hence, longitudinal shoot growth is reduced. Prohexadione-Ca also induces changes in flavonoid metabolism, which may also be related to the inhibition of dioxygenases involved in this pathway. Preliminary evidence is available that this effect is related to a lowered susceptibility of apple tissue towards infection with fireblight. ACC oxidase, another dioxygenase, which catalyzes the conversion of aminocyclopropane-carboxylic acid into ethylene, is also affected by prohexadione-Ca and related compounds. Lowered levels of ethylene may account for a delay of senescence.

No abstract

No abstract