Novel psbA1 Gene from a Naturally Occurring Atrazine-Resistant Cyanobacterial Isolate

A naturally occurring atrazine-resistant cyanobacterial isolate, strain SG2, was isolated from an atrazine-containing wastewater treatment system at the Syngenta atrazine production facility in St. Gabriel, La. Strain SG2 was resistant to 1,000 μg of atrazine per ml but showed relatively low resistance to diuron [3-(3,4-dichlorophenyl)-1,1-dimethyl urea]. Analyses of 16S ribosomal DNA indicated that strain SG2 falls into the Synechocystis/Pleurocapsa/Microcystis group. Photosynthetically driven oxygen evolution in strain SG2 was only slightly inhibited (about 10%) by 2,000 μg of atrazine per ml, whereas in the control strain Synechocystis 6803, oxygen evolution was inhibited 90% by 1,000 μg of atrazine per ml. No atrazine accretion, mineralization, or metabolites were detected when strain SG2 was grown with [(14)C]atrazine. Strain SG2 contained three copies of the psbA gene, which encodes the D(1) protein of the photosystem II reaction center. Nucleotide sequence analyses indicated that the psbA2 and psbA3 genes encoded predicted proteins with the same amino acid sequence. However, the psbA1 gene product contained five extra amino acids, which were not found in PsbA proteins from five other cyanobacteria. Moreover, the PsbA1 protein from strain SG2 had an additional 13 amino acid changes compared to the PsbA2/PsbA3 proteins and contained 10 amino acid alterations compared to conserved residues found in other cyanobacteria. Reverse transcriptase PCR analysis indicated that the psbA1 gene and the psbA2/psbA3 gene(s) were expressed in photosynthetically grown cells in the presence of atrazine. These results suggest that strong selection pressure conferred by the continual input of atrazine has contributed to the evolution of a herbicide-resistant, yet photosynthetically efficient, psbA gene in a cyanobacterium

Fertility and fertilization issues in rubber plantations: new insights from recent research works

Communication orale + résuméFertilization is a key cultural practice for any crops. However, few research works about the management of fertilization in rubber plantations have been published compared to other crops. Indeed, the relationship between fertilization and latex yield is still a matter of debate. On the other hand, concern about soil fertility of rubber plantations has raised with the extension of plantations in marginal areas and the long-term cultivation of rubber trees on the same lands in traditional areas. Therefore, there is a need to update and complete the knowledge on the management of fertilization and soil fertility in rubber plantations with regards to both the productivity of the plantations and the sustainability of rubber based agro-ecosystems. In this communication, we present a review of the scientific literature on this topic as well as some results from studies recently conducted in Thailand. These works provide a more comprehensive understanding of the effect of fertilization on the latex yield and functioning of a mature rubber plantation. They also highlight the importance of the management of soil fertility during the immature phase of the rubber plantations. As a conclusion, we discuss the alternative strategies to sustainably manage the fertility of rubber plantations