Characterization of Arabidopsis enhanced disease susceptibility mutants that are affected in systemically induced resistance

The evolutionarily recent transfer of the gene for cytochrome c oxidase subunit 2 (cox2) from the mitochondrion to the nucleus in legumes is shown to have involved novel gene-activation steps. The acquired mitochondrial targeting presequence is bordered by two introns. Characterization of the import of soybean Cox2 indicates that the presequence is cleaved in a three-step process which is independent of assembly. The final processing step takes place only in the mitochondria of legume species, and not in several non-legume plants. The unusually long presequence of 136 amino acids consists of three regions: the first 20 amino acids are required for mitochondrial targeting and can be replaced by another presequence; the central portion of the presequence is required for efficient import of the Cox2 protein into mitochondria; and the last 12 amino acids, derived from the mitochondrially encoded protein, are required for correct maturation of the imported protein. The acquisition of a unique presequence, and the capacity for legume mitochondria to remove this presequence post-import, are considered to be essential adaptations for targeting of Cox2 to the mitochondrion and therefore activation of the transferred gene in the nucleus.     

Tracking plant preference for higher‐quality mycorrhizal symbionts under varying CO2 conditions over multiple generations

The symbiosis between plants and root‐colonizing arbuscular mycorrhizal (AM) fungi is one of the most ecologically important examples of interspecific cooperation in the world. AM fungi provide benefits to plants; in return plants allocate carbon resources to fungi, preferentially allocating more resources to higher‐quality fungi. However, preferential allocations from plants to symbionts may vary with environmental context, particularly when resource availability affects the relative value of symbiotic services. We ask how differences in atmospheric CO₂‐levels influence root colonization dynamics between AMF species that differ in their quality as symbiotic partners. We find that with increasing CO₂‐conditions and over multiple plant generations, the more beneficial fungal species is able to achieve a relatively higher abundance. This suggests that increasing atmospheric carbon supply enables plants to more effectively allocate carbon to higher‐quality mutualists, and over time helps reduce lower‐quality AM abundance. Our results illustrate how environmental context may affect the extent to which organisms structure interactions with their mutualistic partners and have potential implications for mutualism stability and persistence under global change.     

Oestrous behaviour of Dutch Friesian heifers under subtropical conditions in Tunesia

The oestrous behaviour of Dutch Friesian heifers in the subtropical climate of Tunisia is studied. The variables pro- and met-oestrus, oestrus duration, ovulation time and oestrus cycle length are analysed, as well as the influence of season, age and group on these variables. Oestrous behaviour was clearly influenced by the subtropical conditions, adaptation to the high temperatures and low relative humidity is observed.     

Potential use of ovum pick-up for embryo production and breeding in cattle

The efficacy of transvaginal ultrasound-guided puncturing of ovarian follicles for collecting immature oocytes in cattle was studied. Three experiments were conducted to examine the effects of puncturing on follicle recruitment and on the number of oocytes collected. Puncture sessions were executed twice weekly at regular intervals of 3 and 4 d respectively. The oocytes were matured, fertilized and allowed to develop in vitro and the number of transferable embryos was recorded. The health of the cows was checked daily. In Experiment 1, dairy cows (n=10) were punctured over a period of 5 mo, and the collected oocytes were fertilized with the semen of 1 bull. In Experiment 2, oocytes were collected from one 12 year old high pedigree dairy cow and an one month pregnant cow were punctured. The oocytes of the old cow were fertilized with semen of 8 different bulls. In Experiment 3, beef cows (n=6) were punctured over a 2 mo period and the semen of 2 different bulls of the same breed was used to fertilize the oocytes from 3 of these cows. In Experiment 1, 14.5 +/- 0.4 (mean +/- SEM) follicles were punctured per session, and 8.0 +/- 0.3 (mean +/- SEM) oocytes were recovered. A mean of 16% of the oocytes developed into transferable embryos with a pregnancy rate of 40%. The results did not differ between the months of the experiments, indicating that the transvaginal puncturing method can be used successfully over a 5 mo period. No detrimental effects were observed after clinical and post mortem examinations, nor did breed, age or reproductive status appear to affect the results. However, large differences were observed between individual cows and between cow/bull combinations.     

Evaluation of transvaginal ultrasound-guided follicle puncture to collect oocytes and follicular fluids at consecutive times relative to the preovulatory LH surge in eCG/PG-treated cows

Holstein-Friesian cows (n=56) were synchronized with Syncro-Mate B, and those cows (n=47) developing a normal progesterone pattern were further treated im with 3,000 I.U. eCG at Day 10 and 22.5 mg PGF2alpha 48 h later. Blood samples were collected every hour from 30 until 49 h after PG administration. Cows (n=17, 36.2%) with fewer than 8 follicles larger than 8 mm in diameter at 28 to 30 h after PG treatment and animals without an LH peak (n=7, 23%) were excluded from the study. Transvaginal ultrasound-guided puncture of the follicles was carried out two times per cow, at 30 h after PG injection (4 to 5 follicles) and again at 1 to 5 (n=6), 12 (n=8) or 22 h (n=9) after the LH peak. No differences in the concentrations of progesterone and LH were observed among the 3 groups. An average of 18 follicles per cow was punctured (total of 415 punctures, n=23); 116 cumulus-oocyte-complexes and 370 follicular fluid samples were obtained producing average recovery rates of 28.0% and 89.2%. The number of cumulus-oocyte-complexes varied between puncture times; shortly before ovulation, at 22 h after the LH peak, the recovery rate was significantly 5 times higher than immediately after the LH peak. Overall, in 75 punctures the cumulus-oocyte-complex was accompanied by a pure follicular fluid sample (3.3 per cow). In conclusion, the transvaginal ultrasound-guided puncture of preovulatory-size follicles can be used to collect follicular fluids to study changes in the microenvironment of maturing oocytes upon superovulation. However, further research is required in order to obtain an equivalent number of accompying cumulus-oocyte-complexes.     

Expression of the Phytophthora infestans ipiB and ipi0 genes in planta and in vitro

The ipiB and ipiO genes of the potato late blight fungus Phytophthora infestans (Mont.) de Bary were isolated from a genomic library in a screen for genes induced in planta. Expression of these genes was studied during pathogenesis on various host tissues and different host plants, some of which show specific resistance against P. infestans infection. During pathogenesis on leaves and tubers of the fully susceptible potato cultivar (cv.) Ajax and on leaves of the fully susceptible tomato cv. Moneymaker, the P. infestans ipiB and ipiO genes show a transient expression pattern with highest mRNA levels in the early stages of infection. During the interaction with leaves of the partially resistant potato cv. Pimpernel, the expression is also transient but accumulation and disappearance of the mRNAs is delayed. Also in P. infestans inoculated onto a race-specific resistant potato cultivar and onto the nonhost Solanum nigrum, ipiB and ipiO mRNA is detectable during the initial stages of infection. Apparently, the expression of the ipiB and the ipiO genes is activated in compatible, incompatible and nonhost interactions. In encysted zoospores, ipiB and ipiO mRNA accumulation was not detectable, but during cyst germination and appressorium formation on an artificial surface the genes are highly expressed. Expression studies in mycelium grown in vitro revealed that during nutrient starvation the expression of the ipiB and ipiO genes is induced. For ipiO gene expression, carbon deprivation appeared to be sufficient. The ipiO gene promoters contain a sequence motif that functions as a glucose repression element in yeast and this motif might be involved in the regulation of ipiO gene expression.     

Gibberellin-EDDHA interaction in flowering and gibbosity of Lemna gibba G3

The effect of gibberellic acid (GA₃), in the presence of EDDHA,on the flowering and gibbosity of Lemna gibba G3 was studied.At 10 ppm and at higher concentrations of GA₃ the EDDHA-effect,i.e. profuse flowering and conspicuously gibbous fronds, wascompletely nullified. (Received July 15, 1974; )     

Salinity and dissolved substances in the Vaal River at Balkfontein,South Africa

Seasonal variation and interrelationships between environmental variables and salinity in the Vaal River at Balkfontein were investigated between 1985 and 1989. The salinity levels were high (min. 108, max. 1032, average 512 mg 1^-1), and indications are that salinisation of the river water is continuing at a rate of 15 mg 1^t-1 a^-1. The concentration of major ions (mg 1^-1 or meq 1^-1) in the river water occurred in the proportions of cations, i.e. Ca²⁺ Na⁺ > Mg²⁺ > K⁺ and of anions, i.e. SO₄ ^2- > HCO₃ ^- > Cl^-. The high S0₄ concentration (average 212 mg 1^-1) indicated SO₄ pollution at Balkfontein. High Ca concentrations (average 59 mg 1^-1) evidently interfered with the solubility of phosphate (PO₄) which could play an important role in the availability of PO₄ to phytoplankton in the system. Measured electrical conductivity (EC) values can be used to estimate salinity (S, in mg 1^-1) in the Vaal River, i.e. e. S = 7.13 * EC - 27.8 (from regression analysis) or S = 6.72 * EC (from TDS:EC ratio). Salinity in the river tends to be higher during the dry season, i.e. winter months. All the dissolved ions (except Si) showed decreased concentrations with increased run-off. The main importance of the high salinity in the Vaal River is evidently its influence on turbidity and the possible clarification of the water-column, which results in a deeper euphotic zone and thus more favourable conditions for photosynthesis followed by a biomass build-up of phytoplankton.