| The ZmPEPC,ZmPPDK and ZmNADP-ME,three key C4-specific photosynthesis genes of maize,hold great promise for helping increase the photo synthetic rate of C3 type plants.To investigate the effects of overexpression of C4-specific photosynthesis genes on photosynthetic rate and drought tolerance of C3 plants,we transformed Arabidopsis thaliana plants with maize phosphoenopyruvate carboxylase(ZmPEPC),pyruratedikinase(ZmPPDK),NADP-malic enzyme(ZmNADP-ME),ZmPEPC+ZmPPDK,and ZmPPDK+ZmNADP-ME genes,respectively,using agrobacterium mediated transformation.Wild type and transgenic Arabidopsis plants were firstly grown under well-water conditions and then stopped watering at flowering stage to start drought stress treatment.Samples of both wide type and transgenic Arabidopsis plants were collected 1 d before the stress started,5d and 10d after the stress treatment,and 5 d after re watering to analyze relative expression of transgenes,PEPC,NADP-ME and PPDK activities,net Photosynthetic rate(Pn)and water use efficiency(WUE).The main results as follows:1.We transformed wild-type Arabidopsis thaliana plants and ZmPPDK transgenic plants with ZmNADP-ME,using agrobacterium mediated transformation.PCR and western blot assay result indicate than ZmNADP-ME insert into the genome of wild-type Arabidopsis thaliana plants and ZmPPDK transgenic plants and NADP-ME protein can normally translate.2.Relative expression of objective gene in the Arabidopsis leaves increased compared with their non-stressed transgenic controls after 5 d of drought treatment,and decreased after 10 d of the drought treatment due to severe drought damage,but were recovered in various degrees 5 d after restoring watering.3.PEPC、NADP-ME、PPDK enzyme activities of wild-type plants were 2.41,0.13,1.62μmol/mg(pro)/h,respectively.PEPC enzyme activities of ZmPEPC and ZmPEPC+PPDK transgenic plants were 36%and 52%significantly higher than those in wild-type under normal water condition,respectively.NADP-ME enzyme activities of ZmNADP-ME and ZmPPDK+NADP-ME transgenic plants were 67%and 97%significantly higher than those in wild-type under normal water condition,respectively.PPDK enzyme activities of ZmPPDK,ZmPEPC+PPDK and ZmPPDK+NADP-ME transgenic plants were 40%,20%and 19%significantly higher than those in wild-type under normal water condition,respectively.The general tendency of PEPC、NADP-ME、PPDK enzyme activities in differern genotype transgenic plants,under different drought stress,were roughiy indentical compared with those in wild-type under normal water condition.All the measured parameters in the Arabidopsis leaves increased compared with their non-stressed transgenic controls after 5 d of drought treatment,and decreased after 10 d of the drought treatment due to severe drought damage,but were recovered in various degrees 5 d after restoring watering.ZmPEPC,ZmPPDK,ZmNADP-ME can significantly improve corresponding PEPC,PPDK,NADP-ME enzyme activities in transgenic plants.Overall ZmPEPC+ZmPPDK transgenic plants had the highest PEPC enzyme activities in these measured parameters under different drought stress conditions,and the ZmPEPC transgenic plants were the second.ZmPPDK+ZmNADP-ME transgenic plants had the highest NADP-ME enzyme activities in these measured parameters under different drought stress conditions,and the ZmNADP-ME transgenic plants were the second.ZmPPDK transgenic plants had the highest PPDK enzyme activities in these measured parameters under different drought stress conditions.4.Net Photosynthetic rate(Pn)in wild-type plants were 3.78μmolCO2·m-2·s-1 under normal water condition.Pn in ZmPEPC,ZmPPDK,ZmPEPC+PPDK transgenic plants were 19%,21%and 24%significantly higher than those in wild-type under normal water condition,respectively.The general tendency of Pn in differem genotype transgenic plants,under different drought stress,were roughiy indentical compared with those in wild-type under normal water condition.All the measured parameters in the Arabidopsis leaves increased compared with their non-stressed transgenic controls after 5 d of drought treatment,and decreased after 10 d of the drought treatment due to severe drought damage,but were recovered in various degrees 5 d after restoring watering.Overall ZmPEPC+ZmPPDK transgenic plants had the highest Pn in these measured parameters under different drought stress conditions,and the ZmPEPC transgenic plants were the second.5.Water use efficiency(WUE)in wild-type plants were 0.54g/kg under normal water condition.WUE in ZmPEPC,ZmNADP-ME,ZmPPDK,ZmPEPC+PPDK,ZmPPDK+NADP-ME transgenic plants were 39%,31%,39%,55%and 33%significantly higher than those in wild-type under normal water condition,respectively.The general tendency of wue in differem genotype transgenic plants,under different drought stress,were roughiy indentical compared with those in wild-type under normal water condition.All the measured parameters in the Arabidopsis leaves increased compared with their non-stressed transgenic controls after 5 d of drought treatment,and decreased after 10 d of the drought treatment due to severe drought damage,but were recovered in various degrees 5 d after restoring watering.Overall ZmPEPC+ZmPPDK transgenic plants had the highest Pn in these measured parameters under different drought stress conditions,and the ZmPEPC transgenic plants were the second.6.Under drought treatments,the SOD activities in transgenic plants changed a lot,compared with POD and CAT,the SOD activities were higher for transgenic plants,especially for ME and PCK transgenic Arabidopsis than for WT plants.Other transgenic plants showed not significant difference in protective enzyme activities compared with GLI,but the protective enzyme activities are higher than GLI.exogenous gene It shows the transgenic plants with C4-NADP-ME gene have a stronger active oxygen scavenging system. |
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