Spatial Distribution of Cell Division Rate Can Be Deduced from that of p34cdc2 Kinase Activity in Maize Leaves Grown at Contrasting Temperatures and Soil Water Conditions

We have investigated the spatial distributions of cell division rate, p34(cdc2) kinase activity, and amount of p34(cdc2a) in maize (Zea mays) leaves grown at contrasting temperatures and soil water conditions. An original method for calculating cell division rate in all leaf tissues is proposed. In all studied conditions, cell division rate was stable and maximum in the first 2 cm beyond the leaf insertion point, declined afterward, and reached zero at 7 cm from the insertion point. The spatial distribution of p34(cdc2) kinase activity, expressed on a per cell basis, followed the same pattern. In contrast, the amount of p34(cdc2a) was maximum in the first centimeter of the leaf, declined afterward, but remained at 20% of maximum in more distal zones with a near-zero cell division rate. A mild water deficit caused a reduction in cell division rate and p34(cdc2) kinase activity by approximately 45% in all leaf zones, but did not affect the amount of p34(cdc2a). Growth temperature affected to the same extent cell division rate and p34(cdc2) kinase activity, but only if p34(cdc2) kinase activity was assayed at growth temperature, and not if a standard temperature was used in all assays. A common linear relationship between cell division rate and p34(cdc2) kinase activity applied to all causes of changes in cell division rate, i.e. cell aging, water deficit, or changes in temperature. It is shown that temperature has two distinct and additive effects on p34(cdc2) kinase activity; first, an effect on the rate of the reaction, and second, an effect on the amount of p34(cdc2a).