Abstract: The ralationship between the developing chloroplast ultrastructure and glutamine synthetase (GS) activity of wheat (Triticum aestivum L. ) leaf has been studied by electron microscopy, DEAE-cellulose column chromatography and GS enzyme activity assay. The results showed that net photosynthesis rate and GS activity increased from basal meristerm to the tip of the leaf along with the development of chloroplasts. The investigation of the incorporation of a H-Uracil and 3 H-Leucine into isolated plastids and Northern blot indicated that the level of gene expression was the highest in basal section. The acumulation of GS-mRNA was most abundant in the developing chloroplast and GS activity was the highest in the developed chloroplast. Within 72 hours of illumination to etiolated seedlings, the quantity of GS mRNA and GS activity increased gradually to the same level of normal seedlings, these observations suggested that the light inducible regulation of GS gene expression is at least at a transcriptional level and the increase in GS on illumination is due largely to the de nove protein synthesis.

Key words: Glutamine synthetase, Gene expression, Chloroplast development, Light, Wheat