EXPRESSION AND LOCALIZATION OF PHOSPHOENOLPYRUVATE CARBOXYLASE IN DEVELOPING AND GERMINATING WHEAT GRAINS

Phosphoenolpyruvate carboxylase (PEPC) activity and corresponding mRNA levels were investigated in developing and germinating wheat (Triticu m aestivum) grains. During grain development PEPC activity increased t o reach a maximum 15 d postanthesis. Western-blot experiments detected two main PEPC polypeptides with apparent molecular masses of 108 and 103 kD. The most abundant 103-kD PEPC subunit remained almost constant throughout the process of grain development and in the scutellum and aleurone layer of germinating grains. The less-abundant 108-kD polypep tide progressively disappeared during the second half of grain develop ment and was newly synthesized in the scutellum and aleurone layer of germinating grains. PEPC mRNA was detected throughout the process of g rain development; however, in germinating grains PEPC mRNA accumulated transiently in the scutellum and aleurone layer, showing a sharp maxi mum 24 h after imbibition. Immunolocalization studies revealed the pre sence of the enzyme in tissues with a high metabolic activity, as well as in the vascular tissue of the crease area of developing grains. A clear increase in PEPC was observed in the scutellar epithelium of gra ins 24 h after imbibition. The data suggest that the transiently forme d PEPC mRNA in the scutellar epithelium encodes the 108-kD PEPC subuni t.