Adenine nucleotide content of corn roots as affected by injury and subsequent washing.

The adenine nucleotide content of the 2-centimeter segments excised from tray-grown corn (Zea mays L., WF9 x Mo17) roots declines for the first hour after excision. Concomitant with the loss of adenine nucleotides is a decline in respiration and a leakage of K(+). With continued washing, these parameters partially or completely recover and increased phosphate influx develops. Increasing the wound effect by cutting 0.5-centimeter segments gives a more rapid and pronounced degradation of adenine nucleotides and slower recovery. Conversely, the mild injury caused by submerging intact roots induces less degradation and produces greater net adenine nucleotide synthesis during recovery; adding auxin to the washing medium produces a similar result. With all treatments, there is stabilization of energy charge at about 0.85.Brief submersion or rubbing of intact roots, as well as recutting washed and recovered root segments, will initiate the transient loss of adenine nucleotides but will not induce increased phosphate influx.It is suggested that the loss in adenine nucleotides may reflect homeostasis in energy charge via catabolism arising from membrane permeability changes.

Effect of ATPase inhibitors on cell potential and k influx in corn roots.

Experiments were performed to determine the effect of plasmalemma ATPase inhibitors on cell potentials (Psi) and K(+) ((86)Rb) influx of corn root tissue over a wide range of K(+) activity. N,N'Dicyclohexylcarbodiimide (DCCD), oligomycin, and diethylstilbestrol (DES) pretreatment greatly reduced active K(+) influx and depolarized Psi at low, but not at high, K(+) activity (K degrees ). More comprehensive studies with DCCD and anoxia showed nearly complete inhibition of the active component of K(+) influx over a wide range of K degrees , with no effect on the apparent permeability constant. DCCD had no effect on the electrogenic component of the cell potential (Psi(p)) above 0.2 millimolar K degrees . Net proton efflux was rapidly reduced 80 to 90% by DCCD. Since tissue ATP content and respiration were only slightly affected by the DCCD-pretreatment, the inhibitions of active K(+) influx and Psi(p) at low K degrees can be attributed to inhibition of the plasmalemma ATPase.It is concluded that by DCCD treatment, the energy-linked electrogenic system at high K degrees is separated from the energy-linked K(+) influx system at low K degrees . The results are analyzed in terms of electrical analogue models of the membrane. The presence of two, algebraically additive electrogenic components is indicated; one is better modeled as a current source (system I) and one as a voltage source (system II). No K(+) stimulation of system II is required to produce the observed K degrees dependence of Psi(p).

Comparison of the responses of corn root tissue to fusicoccin and washing.

A comparison has been made of the effects of fusicoccin with those of washing on segments of corn (Zea mays L.) root tissue. Both fusicoccin and washing caused increases in K(+)((86)Rb) influx, net H(+) efflux, and electrogenic cell membrane potential, but with no effect on respiration rate. The similarity was most evident with fresh tissue during the initial phases of washing, prior to the developmental changes which augment the anion and general solute transport rates of the tissue. After the development of enhanced transport capacity the proportional response to fusicoccin was much diminished. It is suggested that the fusicoccin-like response to washing may be a manifestation of recovery from injury.