Since cysteine synthase was inhibited in vivo and in vitro by AOA and Boc-AOA, and because there was no major difference in phytotoxicity of the two compounds in these young plants, apparently the N-t -butoxycarbonyl group does not alter the activity of the AOA molecule. An exception however, was the greater growth reduction caused by Boc-AOA plusA. cassiae compared to the AOA plus A. cassiae treatment. Furthermore, these chemicals had no apparent interactions with C. truncatum and A. cassiae efficacy on their respective weed hosts.The increase in extractable cysteine synthase activity in sicklepod following infection by A. cassiae, may be related to defense mechanisms of this weed against this pathogen.There may be some inherent differences in the overall action of AOA and Boc-AOA, but it is not possible to tell from these results and the scope of this study. It is also not known if Boc-AOA is converted to AOA by enzyme hydrolysis of the substituted amide bond by these plants and their respective pathogens.A herbicidal analog of AOA, benzadox, is thought to be metabolized in planta to form AOA .
Also interesting is the naturally occurring compound irpexil, a herbicidal compound produced by the basidiomyceteIrpex pachyodon.This compound has structural features analogous to AOA and the herbicide benzadox.Benzadox is an inhibitor of alanineaminotransferase,but the mechanism of action of irpexil, is unknown.Benzadox has been shown to be metabolized in plants to produce AOA . Similar compounds such as aryl-substituted α-aminooxy carboxylic acids are also phytotoxic and act as auxin transport inhibitors. AOA has been tested as a synergist with C. coccodes a bioherbicide of velvet leaf. However, AOA was found to be inhibitory to the growth of this fungus on PDA in Petri dishes, when applied together with the fungus, or if applied via vacuum infiltration on velvetleaf leaves and furthermore, no synergy was observed in those studies.Although the interactions that we found during these experiments resulted in no major synergistic effects, novel information was generated on the important enzyme CS and on AOA interactions with two bioherbicides that have received major attention as weed control agents.The incorporation of plant materials to soils, with the objective of maintaining or improving fertility for the subsequent crop, is known as green manuring.
The inclusion of a legume fallow within a sugarcane cropping cycle is practiced to reduce populations of detrimental soil organisms,providing nitrogen through biological fixation for weed suppression . Interest in the use of green manure’s biomass has revived because of their role in improving soil quality and their beneficial N and non-N rotation effects . Because of its nitrogen fixation potential, legumes represent an alternative for supplying nutrients, substituting or complementing mineral fertilization in cropping systems involving green manuring. This practice causes changes in soil physical, chemical and biological characteristics, bringing benefits to the subsequent crop both in small- scale cropping systems and in larger commercial areas such as those grown with sugarcane. The area cropped with sugar canein Brazil shows rapid expansion, with most of the increase for ethanol production. The area cultivated with sugar- cane is now 9.6 Mha, with an increase of 5 Mha from 2000 and over 8.6 Mha of fresh sugarcane harvested per year. Sugarcane crops in Brazil are replanted every five to ten years. In southeastern Brazil, the interval between the last sugarcane harvest and the new plantings occurs during the spring-summer season, under high temperature and heavy rainfall. According to the Köppen climate classification, Piracicaba, SP, Brazil has Cwa climate, i.e., humid sub- tropical, with dry winter and an average temperature in the coldest month below 18°C and the hottest month, exceeding 22°C. Green manure fertilization of the soil with legumes has been recommended before a sugarcane field is re- planted.
This practice does not imply on losing the crop- ping season, does not interfere with sugarcane germination, and provides increases in sugarcane and sugar yield, at least during two consecutive cuts.Additionally, it protects the soil against erosion, prevents weed spreading and reduces nematode populations. Legumes usually accumulate large quantities of N and K, the nutrients which are taken up in the highest amounts by the sugarcane plants. The use of the 15N isotope provides precise information about the dynamics of the nitrogen in the soil-plant system. Residue incorporation studies of legumes using 15N label indicate that 10% to 34% of the legume N can be recovered in the subsequent rye or wheat crop, 42% in rice, 24% recovery from Velvet bean by corn crop, around 15% of N recovery from sunn hemp by corn plants in no-till system, 30% by maize , and 5% of N recovery from sunn hemp by sugarcane , and ranged from 19% to 21% when the recovery was observed from sunn hemp by two sugarcane harvest . The authors suggested that legume residue decomposition provided long-term supply of N for the subsequent crops, by not supplying the nutrient as an immediate source.