PHOSPHORYLATION OF AN ENVELOPE-ASSOCIATED HSP70 HOMOLOG IN AMYLOPLASTS ISOLATED FROM CULTURED-CELLS OF SYCAMORE (ACER-PSEUDOPLATANUS L.)

The presence of Hsp70 and Hsp60 molecular chaperones in amyloplasts is olated from cultured sycamore cells was analyzed by immunoblotting. Hs p70 homologs were located in both amyloplast envelope and stromal frac tions, but no Hsp60 homologs were detected in any of the different sub organellar fractions. Incubation of whole amyloplasts or their envelop e fraction with Mg2+ gamma-P-32-ATP resulted in a rapid phosphorylatio n of the envelope-associated Hsp70 homolog, which constitutes a major target of phosphorylation in these plastids.