ALDOLASES IN BARLEY (HORDEUM-VULGARE L) - PROPERTIES AND REPRESSION OF THE PLASTID ENZYME IN THE PLASTOME MUTANT ALBOSTRIANS

The plastidic and cytosolic aldolases were purified from green leaves of barley (Hordeum vulgare L. cv. Salome) to almost homogeneity on DEA E-Fractogel, P-Cellulose and Fractogel AX 300 (HPCL). The two homotetr americ aldolases have molecular masses of the subunits of 36 and 38 kD a, respectively, and Km(FBP) values of 10 mu M and 2 mu M, respectivel y. Both enzymes were extremely unstable. Loss of activity could partly be prevented by the addition of the protease inhibitors leupeptin or PMSF. In white leaf tissue of the plastome mutant <<albostrians>> of b arley the activity of the plastidic isoenzyme is strongly reduced whil e the activity of the cytosolic isoenzyme was little affected. Western and Northern blot analyses indicated a strong reduction in protein co ntent and in mRNA level of the plastidic but not of the cytosolic aldo lase. The protein content and mRNA level of the cytosolic aldolase wer e similar in white and green leaf tissue. The results support the hypo thesis that a plastidic signal causes the repression of the nuclear-en coded plastidic aldolase on a transcriptional level but does not affec t the expression of the cytosolic aldolase.