ATP-dependent regulation of nuclear Ca2+ levels in plant cells

Localised alterations in cytoplasmic Ca2+ levels are an integral part of th e response of eukaryotic cells to a plethora of external stimuli. Due to th e large size of nuclear pores, it has generally been assumed that intranucl ear Ca2+ levels reflect the prevailing cytoplasmic Ca2+ levels, Using nucle i prepared from carrot (Daucus carota L.) cells, we now show that Ca2+ can be transported across nuclear membranes in an ATP-dependent manner and that over 95% of Ca2+ is accumulated into a pool releasable by the Ca2+ ionopho re A.23187. ATP-dependent nuclear Ca uptake did not occur in the presence o f ADP or ADP gamma S and was abolished by orthovanadate, Confocal microscop y of nuclei loaded with dextran-linked Indo-1 showed that the initial ATP-i nduced rise in [Ca2+] occurs in the nuclear periphery. The occurrence of AT P-dependent Ca2+ uptake in plant nuclei suggests that alterations of intran uclear Ca2+ levels may occur independently of cytoplasmic [Ca2+] changes. ( C) 2000 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.