Response Of MG Scavenging System In The Formation Of Heat Tolerance Induced By Interaction Of MG And Calcium Signaling In Maize Seedlings

Global warming has severely affected crop yields,and it is important to investigate the mechanism underlying the development of heat tolerance in crops for scientific and agricultural guidance.Previous studies had shown that methylglyoxal（MG）interacted with calcium signals to improve the heat tolerance of maize（Zea mays L.）seedlings,but its mechanism was still elusive.Therefore,in this experiment,we investigated the response of MG scavenging system in the interaction between MG and calcium signals to increase the heat tolerance of maize seedlings,also obtained the following results.To investigate the effect of MG and calcium signaling interaction on the heat resistance of seedlings,seedlings were treated with MG and calcium chloride（CaCl₂）as well as scavengers and inhibitors,and their heat resistance indexes were measured.The results showed that MG and CaCl₂ alone and in combination increased the survival rate（SR）and tissue viability of seedlings after high temperature compared to the control,and alleviated the increase in electrolyte leakage（EL）and malondialdehyde（MDA）content.In addition,the calcium chelator ethylene glycol-bis（α-aminoethyl ether）-N,N,N’,N-tetraacetic acid（EGTA）and the calcium channel blocker neomycin（NEC）in combination with MG significantly reduced the EL;the calcium membrane channel blocker lanthanum（Ⅲ）chloride（LaCl₃）and the calmodulin（CaM）antagonist trifluoperazine（TFP）treatment in combination with MG significantly reduced SR and tissue viability and increased EL,whereas EGTA and NEC treatment in combination with MG significantly reduced SR and increased EL and MDA content after high temperature compared to MG,LaCl₃ and TFP treatment in combination with MG significantly reduced SR and tissue viability and increased EL and MDA content,respectively.In addition,treatment with the MG scavenger aminoguanidine（AG）and N-acetyl-L-cysteine（NAC）in combination with CaCl₂significantly increased SR and tissue viability,decreased EL and MDA content after high temperature compared to the control.In contrast,the combination of NAC and CaCl₂ treatment significantly increased the EL compared to CaCl₂.These data suggest that the interaction of MG and calcium signaling induces the development of heat tolerance in seedlings.To further elucidate the interaction between MG and calcium,MG and Ca²⁺content in mesocotyl and root tip were determined.The results showed that before high temperature,MG and CaCl₂ alone and in combination treatment significantly increased Ca²⁺content in mesocotyl and root tip compared to the control,while the above mentioned Ca²⁺inhibitor and MG combination treatment obtained opposite results compared to MG,and MG scavenger and CaCl₂combination treatment obtained opposite results compared to CaCl₂.After high temperature stress,MG and CaCl₂treatment alone and in combination significantly reduced MG content and increased Ca²⁺content in mesocotyl and root tip compared to the control;the above mentioned Ca²⁺inhibitor in combination with MG gave opposite results compared to MG;and MG scavenger in combination with CaCl₂ gave opposite results compared to CaCl₂.These results further support the existence of an interaction between MG and calcium.To investigate the mechanism by which MG and calcium interacted to improve heat tolerance in maize seedlings,the activity of MG scavenging system was tested.Compared to the control,MG and CaCl₂ treatment alone and in combination significantly increased the activity of glyoxalase Ⅱ（GlyⅡ）,MG reductase（MGR）and glutathione peroxidase（GR）,GSH content,and GSH/GSSG ratio,and activated the expression of ZmGlyⅡafter high temperature.The combination of EGTA,LaCl₃,NEC and TFP with MG significantly reduced the activity and GSH content of GlyⅡand MGR,and decreased the expression of ZmGlyⅡ,Zmaldr1 and ZmGR1 after high temperature compared to MG.Treatment with AG and NAC in combination with CaCl₂,respectively,significantly reduced the activity of glyoxalaseⅢ（GlyⅢ）and GR and decreased the expression of ZmAKR1 and ZmGR1 after high temperature compared to CaCl₂.The above data further suggest that the MG scavenging system responds to MG and calcium interactions induced by the formation of heat tolerance in seedlings.In summary,MG and calcium signaling interaction exsited in the development of seedling heat tolerance,and the MG scavenging system played a regulatory role in the induction of heat tolerance in maize seedlings by MG and calcium interaction.