Studies On Phosphorus Utilization Efficiency Of PhyA2Transgenic Maize

Phosphorus is one of the necessary macronutrients for crop growth and development. About50%~80%phosphorus in soil exists in the form of organic phosphorus, in which about50%is phyticacid. This form of phosphorus is difficult to be absorbed by plants. It is of great significance forimproving crop phosphorus nutrition and promoting the sustainable utilization of phosphorus resourceto increase the absorption of organic phosphorus. In order to improve phosphorus use efficiency ofcrops, microbial phytase genes were introduced into plants through transgenic technology. Thetransgenic plants expressed phytase genes efficiently in roots and exuded the heterologous phytase intothe rhizosphere. The previous research had shown that phyA2transgenic maize had a normal growth anddevelopment in controlled environment such as agar and hydroponic media using phytate as the solesource of phosphorus. However, whether transgenic maize could use soil organic phosphorus effectively,the mechanism of using soil organic phosphorus, and the effects of transgene on soil microbialcommunity had not been well understood. Therefore, the physiological, biochemical and microbialmechanisms of phosphorus utilization of phyA2transgenic maize were studied by hydroponic and soilpots experiments. The main results were as follows:(1) The preliminary field experiment showed that transgenic maize C63, C83-1-7and C84-1-14increased soil acid phosphatase activity and activated soil organic phosphorus, especially the labileorganic phosphorus. The plant growth of C63, C83-1-7and C84-1-14was higher than that of negativecontrols significantly. The straw biomass, grain yield and phosphorus accumulation were higher thanthose of negative controls significantly in mature period. Compared with the corresponding negativecontrol, the greatest difference was noted in C63.(2) A hydroponic experiment was carried out to investigate the mechanism of phosphorus efficientutilization of phyA2transgenic maize. It indicated that phytase activity of the root and root secretion oftransgenic maize C63was more than40times higher than that of the negative control in hydroponicmedia using phytate as the sole source of phosphorus. Organic phosphorus (phytate) was hydrolyzed tophosphate by phytase and used for plant growth. The root length, root surface area and root volume oftransgenic maize C63increased significantly.(3) A soil pots experiment was carried out to investigate the mechanism of phosphorus efficientutilization of phyA2Transgenic Maize. It indicated that the rhizosphere phosphatase activity of C63wassignificantly higher than negative control under supplying with phytate and without phosphate condition,which increased by5.17%and5.48%respectively. Compared with negative control, moderately labileorganic phosphorus reduced significantly by28.2%under no phosphate treatment, and it was alsoreduced by18.2%and16.2%respectively under supplying phosphate and phytate treatments, but thedifference was not significant. The phosphorus accumulation of C63was significantly higher thannegative control under supplying with phytate and without phosphate condition, which increased by140%and100%respectively. There was no significant difference in phosphorus accumulation betweentransgenic maize and negative control under supplying with phosphate treatment. The growth of the transgenic plants was significantly higher than negative control under supplying with phytate andwithout phosphate condition. There is no significant difference in growth between transgenic maize andnegative control under supplying with phosphate treatment. The influence of phyA2Transgenic Maizeon soil microorganisms was also investigated in soil pots experiment. It indicated that the phytaseexpression had very little impact on bacteria in short time, while it had some influence on fungi whichthe number of a certain fungi had a rising trend.The results demonstrated that the phyA2transgenic maize improved the ability to acquirephosphorus from organic source. The roots of phyA2transgenic maize produced phytase which wassecreted to soil and resulted in an increase of rhizosphere phosphatase activity when grown on phytateas the only source of phosphorous and phosphorous deficiency condition. Organic phosphorus washydrolyzed to phosphate by phytase and could be used as phosphorus resource for the root growth andthe plants growth. The phosphorus accumulation of the phyA2transgenic maize can be increasedsignificantly than control lines.