L. Bogoslavsky et Pm. Neumann, RAPID REGULATION BY ACID PH OF CELL-WALL ADJUSTMENT AND LEAF GROWTH IN MAIZE PLANTS RESPONDING TO REVERSAL OF WATER-STRESS, Plant physiology (Bethesda), 118(2), 1998, pp. 701-709
The role of acid secretion in regulating short-term changes in growth
rate and wall extensibility was investigated in emerging first leaves
of intact, water-stressed maize (Zea mays L.) seedlings. A novel appro
ach was used to measure leaf responses to injection of water or soluti
ons containing potential regulators of growth. Both leaf elongation an
d wall extensibility, as measured with a whole-plant creep extensiomet
er, increased dramatically within minutes of injecting water, 0.5 mM p
hosphate, or strong (50 mM) buffer solutions with pH less than or equa
l to 5.0 into the cell-elongation zone of water-stressed leaves. In co
ntrast, injecting buffer solutions at pH greater than or equal to 5.5
inhibited these fast responses. Solutions containing 0.5 mM orthovanad
ate or erythrosin B to inhibit wall acidification by plasma membrane H
+-ATPases were also inhibitory. Thus, cell wall extensibility and leaf
growth in water-stressed plants remained inhibited, despite the incre
ased availability of (injected) water when accompanying increases in a
cid-induced wall loosening were prevented. However, growth was stimula
ted when pH 4.5 buffers were included with the vanadate injections. Th
ese findings suggest that increasing the availability of water to expa
nding cells in water-stressed leaves signals rapid increases in outwar
d proton pumping by plasma membrane H+-ATPases. Resultant increases in
cell wall extensibility participate in the regulation of water uptake
, cell expansion, and leaf growth.