Effect of Water Stress on Cell Division and Cdc2-Like Cell Cycle Kinase Activity in Wheat Leaves1

Abstract

In wheat (Triticum aestivum) seedlings subjected to a mild water stress (water potential of ؊0.3 MPa), the leaf-elongation rate was reduced by one-half and the mitotic activity of mesophyll cells was reduced to 42% of well-watered controls within 1 d. There was also a reduction in the length of the zone of mesophyll cell division to within 4 mm from the base compared with 8 mm in control leaves. However, the period of division continued longer in the stressed than in the control leaves, and the final cell number in the stressed leaves reached 85% of controls. Cyclindependent protein kinase enzymes that are required in vivo for DNA replication and mitosis were recovered from the meristematic zone of leaves by affinity for p13 suc1 . Water stress caused a reduction in H1 histone kinase activity to one-half of the control level, although amounts of the enzyme were unaffected. Reduced activity was correlated with an increased proportion of the 34-kD Cdc2-like kinase (an enzyme sharing with the Cdc2 protein of other eukaryotes the same size, antigenic sites, affinity for p13 suc1 , and H1 histone kinase catalytic activity) deactivated by tyrosine phosphorylation. Deactivation to 50% occurred within 3 h of stress imposition in cells at the base of the meristematic zone and was therefore too fast to be explained by a reduction in the rate at which cells reached mitosis because of slowing of growth; rather, stress must have acted more immediately on the enzyme. The operation of controls slowing the exit from the G1 and G2 phases is discussed. We suggest that a water-stress signal acts on Cdc2 kinase by increasing phosphorylation of tyrosine, causing a shift to the inhibited form and slowing cell production.A decrease in soil water potential due to drought or salinity decreases the rate of leaf expansion, whereas root expansion is much less affected (Munns and Sharp, 1993). If the root water potential decreases suddenly, the response of leaf expansion is so rapid and large (Cramer and Bowman, 1991) that it must be due to a change in the rate of expansion of existing cells, rather than to a change in the rate of production of new cells. However, when plants have grown for some time in soils of low water potential, smaller leaves with fewer cells are formed (Clough and Milthorpe, 1975;Randall and Sinclair, 1988;Lecoeur et al., 1995). These observations suggest that reduced cell formation during water stress may limit final leaf size.Little is known about the effects of water stress on rates of cell division or on mitotic activity in leaves. Roots have received more attention. In roots there was a rapid decrease in mitotic activity after imposition of water stress (Yee and Rost, 1982;Robertson et al., 1990b; Bitonti et al., 1991; Bracale et al., 1997), and a similar response was found for soybean hypocotyls (Edelman and Loy, 1987). These sudden decreases in mitotic activity suggest, but do not prove, that water stress caused a sudden decrease in the rate at which new cells were being produced. To our knowledge, the only ...

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Differential Effect of Jasmonic Acid and Abscisic Acid on Cell Cycle Progression in Tobacco BY-2 Cells

“…It is frequently observed that stress signals not only induce plant resistance but also affect growth rate and cell division. For example, in wheat (Triticum aestivum) seedlings subjected to a mild water stress, leaf elongation is reduced in correlation with a rapid decrease of mitotic activity in mesophyll cells of the first leaf (Schuppler et al, 1998). Similar effects were found in water-stressed roots of maize (Zea mays; Sacks et al, 1997) and sunflower (Helianthus annuus; Robertson et al, 1990), where an involvement of abscisic acid (ABA) in the inhibition of the cell cycle was suggested.…”

Modelling leaf expansion in a fluctuating environment: are changes in specific leaf area a consequence of changes in expansion rate?

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