%D 2001 %0 ARTICLE %T Heat-stress induced synthesis of chloroplast protein synthesis elongation factor ( EF-Tu ) in a heat-tolerant maize line . %J Planta %V 212 ( 3 ) %P 359-66 %A Bhadula SK %A Elthon TE %A Habben JE %A Helentjaris TG %A Jiao S %A Ristic Z %M pub11289600 %X A heat-tolerant maize ( Zea mays L ) line , ZPBL 1304 , synthesizes a unique set of five heat-shock polypeptides of 45 kDa . Previous studies suggested that these polypeptides might play a role in the development of thermotolerance in maize ( Ristic et al , 1996 , J Plant Physiol . 149 : 424-432 ; Ristic et al , 1998 , J Plant Physiol . 153 : 497-505 ) . In the present study , we isolated these polypeptides , sequenced them , and investigated their subcellular distribution and origin . Of the five polypeptides of 45 kDa , three polypeptides , including the two most abundant ones , yielded amino acid sequences similar to the chloroplast and bacterial protein synthesis elongation factor ( EF-Tu ) . This was further confirmed using an antibody raised against maize EF-Tu , which showed a very strong reaction with the 45-kDa heatshock protein ( s ) . Studies on subcellular distribution and origin revealed that the 45-kDa polypeptides were localized to the chloroplasts , and were likely of nuclear origin . A full-length maize EF-Tu cDNA ( Zmeftu1 ) , previously isolated from the B73 line of maize , was used as a probe for northern blot analysis of RNA extracted from the ZPBL 1304 maize line ( the nucleotide and deduced amino acid sequences of Zmeftu1 are 88% identical to the rice EF-Tu sequence ) . Northern blots showed a 1 . 85-fold increase in steady-state levels of EF-Tu mRNA during heat stress . An increase in EF-Tu transcript levels during heat stress was accompanied by increased levels of the EF-Tu protein . Isolated chloroplasts from heat-stressed plants also had higher levels of EF-Tu as compared to control chloroplasts . The maize EF-Tu polypeptides showed > 80% sequence similarity with the bacterial EF-Tu , which has recently been shown to function as a molecular chaperone and to play a role in the protection of other proteins from thermal denaturation ( Caldas et al , 1998 , J Biol . Chem . 273 : 11478-11482 ) . It is hypothesized that chloroplast EF-Tu of the ZPBL 1304 maize line plays an important role in the development of thermotolerance .