CALCIUM‐REGULATED NUCLEAR ENZYMES: POTENTIAL MEDIATORS OF PHYTOCHROME‐INDUCED CHANGES IN NUCLEAR METABOLISM?

Abstract

Calcium ions have been proposed to serve as important regulatory elements in stimulus‐response coupling for phytochrome responses. An important test of this hypothesis will be to identify specific targets of calcium action that are required for some growth or development process induced by the photoactivated form of phytochrome (Pfr). Initial studies have revealed that there are at least two enzymes in pea nuclei that are stimulated by Pfr in a Ca2+‐dependent fashion, a calmodulinregulated nucleoside triphosphatase and a calmodulin‐independent but Ca2+‐dependent protein kinase. The nucleoside triphosphatase appears to be associated with the nuclear envelope, while the protein kinase co‐purifies with a nuclear fraction highly enriched for chromatin. This short review summarizes the latest findings on these enzymes and relates them to what is known about Pfr‐regulated nuclear metabolism. Copyright © 1992, Wiley Blackwell. All rights reserved