Interactions and Effects on Cysteine Synthase Activity of Aminooxyacetate and Boc-Aminooxyacetate on the Bioherbicides <i>Colletotrichum truncatum</i>and <i>Alternaria cassia</i>and Their Weed Hosts

Aminooxyacetate (AOA) is a pyridoxal phosphate antagonist that inhibits various plant enzymes (including transaminases) which require pyridoxal phosphate as a cofactor and it exhibits phytotoxic and herbicidal properties. We examined AOA and its analog, N-t-butoxycarbonyl-AOA (Boc-AOA) for phytotoxicity, interactions with weed pathogens (bioherbicides), and effects on an important pyridoxal requiring enzyme, cysteine synthase (CS, E.C. 4.2.99.8). Studies were performed on two weeds, i.e., hemp sesbania [Sesbania exaltata (Raf.) Rybd. Ex A.W. Hill] and sicklepod (Senna obtusifolia), and two pathogens, (Colletotrichum truncatum and Alternaria cassiae), that are bioherbicidal agents against hemp sesbania and sicklepod, respectively. Pathogenicity tests, and assays for extractable, and in vitro CS activities were utilized. Phytotoxicity bioassays indicated that the bulky t-butoxycarbonyl moiety substitution on the AOA molecule did not substantially hinder expression of biological activity of Boc-AOA in these tests. Generally, spray application of the compounds to young dark-grown seedlings caused little growth effects, but root-feeding of the chemicals reduced growth (stem elongation) in both weeds. Hemp sesbania was generally more tolerant than sicklepod to these compounds. The only apparent positive interaction of the chemicals with these pathogens was the Boc-AOA: C. truncatum combination treatment on hemp sesbania. Both compounds reduced extractable CS in the seedlings by 30%, 72 h after treatment. CS activity was reduced by 15% in hemp sesbania treated with C. truncatum but increased 20% above control levels after infection of sicklepod by A. cassiae. This latter effect suggests that CS may be involved in sicklepod defense mechanisms against this pathogen.

Differences in the gene expressive quantities of carbonic anhydrase and cysteine synthase in the weathering of potassium-bearing minerals by Aspergillus niger

We investigated the differences in the gene expression of carbonic anhydrase （CA） and cysteine synthase （CysM） between two weathering conditions, with either soluble potassium or insoluble potassium. We cultured a strain of A. niger by adopting a variant Czapek medium （using NazHPO4 as a substitute for KzHPO4） in two groups, Group A （containing silicate minerals bearing potassium but without KC1） and Group B （with KCI） . We extracted the mRNAs of CA and CysM from these two groups and performed real-time quantitative polymerase chain reactions （RT-qPCR）. We constructed relative standard curves by using glyceraldehyde-3-phosphate dehydrogenase （GAPDH） as the reference to confirm a consistent amplification effi- ciency of the target genes （CA and CysM） and the reference gene and quantified the gene expression of the targets in a relative manner. Our results showed that CA and CysM in Group A were upregulated for 1.7 times and 11.7 times, respectively, com- pared with those in Group B. Furthermore, we also analyzed some metabolic pathways and functions of the A. niger-induced weathering of potassium-bearing minerals, which involved the synthesizing of these two enzymes. Thus our work provides materials for further study of the roles of A. niger in the metabolic regulation during the weathering process of potassi- um-beating minerals.