THE CALCIUM-BINDING PROTEIN CALRETICULIN IN POLLEN OF LIRIODENDRON-TULIPIFERA L

We have analysed the distribution of the endoplasmic reticulum (ER) an d the occurrence of the high capacity, low affinity Ca2+ binding prote in calreticulin in mature pollen of Liriodendron tulipifera L. Two pro tein bands of 56 and 54 kDa were highlighted by antibodies against spi nach calreticulin and the ER retention signal HDEL. The same proteins stained blue with Stains All on SDS-PAGE, bound Ca-45 in overlays and showed a highly acidic isoelectric point. N-terminus sequencing confir med their identity as calreticulin isoforms, only one of which was fou nd to be glycosylated. The role of the ER and of its resident protein calreticulin in Ca2+ signalling during pollen germination is discussed . (C) 1998 Elsevier Science Ireland Ltd.