Intraspecific variation of Rhizoctonia solani AG 3 isolates recovered from potato fields in Central Iran and South Australia.

Pectic zymogram, RFLP and PCR analyses were used to characterize Rhizoctonia solani AG 3 isolates collected from diseased potatoes in South Australia. The pectic zymogram data were compared with those obtained for isolates collected from central Iran. Analyses of bands corresponding to pectin esterase and polygalacturonase revealed three zymogram subgroups (ZG) in AG 3. In addition to the previously reported ZG7 (here renamed ZG7-1), two new zymogram subgroups, ZG7-2 and ZG7-3, were identified. Of the 446 isolates tested, 50% of the South Australian and 46% of the Iranian isolates were ZG7-1. The majority of the isolates originating from stem and root cankers were ZG7-1, whereas most of the isolates designated ZG7-2 and ZG7-3 originated from tuber-borne sclerotia. Pathogenicity tests revealed that ZG7-1 generally produced fewer sclerotia and more severe cankers of underground parts of the potato plants than the other two ZGs. Two random DNA clones, one originating from an AG 3 isolate and the other from an AG 4 isolate, were used as probes for RFLP analyses of Australian isolates. The AG 3 probe, previously identified to be specific to this group, detected a high level of genetic diversity, with 11 genotypes identified amongst 50 isolates analysed. The low-copy AG 4 probe resolved three genotypes amongst 24 isolates. For 23 isolates analysed with both markers, the combined data distinguished a total of six genotypes and similarity analysis resolved the isolates into two main groups with 50% homology. PCR, using primers for the plant intron splice junction region (R1), also revealed variation. No obvious relationship among pectic zymogram groups, RFLP and PCR genotypes was observed.

Kinetics of ATP synthesis in pea cotyledon submitochondrial particles.

A kinetic study of oxidative phosphorylation by pea submitochondrial particles gave two K(m) values for ADP, one low, the other high. The high value probably reflected a damaged site or a population of leaky mitochondria. Only the high affinity site with a low K(m) for ADP was involved in ATP synthesis. alpha,beta-Methylene ADP was found to be a competitive inhibitor of ATP synthesis. The inorganic phosphate analog, thiophosphate, decreased the apparent K(m) of ADP while the rate of the reaction remained approximately the same. Adenyl imidodiphosphate, a specific inhibitor of ATP hydrolysis activity, had little effect on oxidative phosphorylation. A slight decrease in the K(m) of the high affinity binding site for ADP was noted. Aurovertin was found to be a potent inhibitor of oxidative phosphorylation in pea submitochondrial particles. The K(m) of the high affinity site was increased 10-fold. Also, the inhibition normally exerted by ADP on ATPase activity was severely reduced by aurovertin. In contrast, increasing the concentration of aurovertin only slightly affected the level of inhibition caused by adenyl imidodiphosphate on ATP hydrolysis.

Regulation of ribosomal RNA accumulation by auxin in artichoke tissue.

Artichoke (Helianthus tuberosus L.) tuber tissue cultured in the presence of the auxin 2,4-dichlorophenoxyacetic acid accumulates ribosomal RNA at a rate of 0.135 micrograms per hour per explant whereas there is little accumulation in nontreated tissue. The addition of auxin enhanced the transcription of the 2.5 x 10(6) precursor 3.5-fold and increased the rate of processing 1.8-fold. The major effect of auxin, however, was a vast increase in the rate of processing of the 1.39 x 10(6) precursor to the 1.3 x 10(6) mature ribosomal RNA. The incorporation of label into the 0.7 x 10(6) mature ribosomal RNA of treated tissue was in 10-fold excess over the control after a 30-minute pulse and remained so throughout the remainder of the labeling period. This level, however, was not reached for the complementary 1.3 mature RNA until 3 hours of continuous labeling, decreasing from a initial value of 40-fold excess. A complication in the processing of ribosomal RNA is the apparent increase in the stability of the 0.7 x 10(6) mature RNA with auxin treatment.

Purine metabolism and differential inhibition of spore germination in Phytophthora infestans.

An analysis of the effect of various purines and pyrimidines on the germination process in three different isolates of the late blight fungus, Phytophthora infestans, revealed increased rates of indirect germination in one isolate by adenine, hypoxanthine, and the riboside of dimethylaminopurine. This observation coupled with the capacity of sporangia of the race affected (1.2.3.4) for the uptake and interconversion of purines, as demonstrated by experiments with labelled purines under in vivo and in vitro conditions, pointed to hypoxanthine as a key intermediate in the purine metabolism directly associated with spore formation and development. This enhanced germination contrasted sharply with the almost complete arrest of indirect germination that occurred when sporangia were incubated with the purine analogue, benzimidazole, or with either of the respiratory inhibitors, sodium azide and 2,4-dinitrophenol. The pattern of differential inhibition exhibited by sporangia versus zoospores upon treatment with actinomycin D, 4-FLUOROURACIL, OR CYCLOHEXIMIDE INDICATED THat continued translation on preformed messenger RNA may be one essential requirement for the formation and release of zoospores, whereas their subsequent germination and development may depend upon renewed transcription as well.