Calcium Influx into Corn Roots as a Result of Cold Shock

Abstract

Corn roots or washed corn root tissue exposed to cold shock absorb 20 to 24% more "Ca2" into a nonexchangeable phase than control roots.Addition to fusicoccin largely prevents this additional calcium influx. The results are discussed in relation to injury-induced changes in nmebrane permeability of root ceOl membranes.Corn roots respond to a variety of injuries (cutting, rubbing, cold shock, or osmotic shock) by rapid blockage of electrogenic H+ efflux pumping, with resultant decline in cell potential and (8'Rb)K' influx (3, 4, 10, 11). With washing (or 'adaptive aging,' Ref. 16), there is a gradual recovery of these physiological attributes; rapid recovery is produced by fusicoccin. Injury also initiates a rapid net K+ efflux from the tissue, which after 45 to 60 min reverses to a net influx (9, 13). Initial leakage of K+ from wounded or shocked plant tissues is a commonly observed phenomenon (15, 16).There are thus two initial responses to the reception and transmission of an injury signal in corn roots; an endogenous control mechanism is activated to shut down the H+-pumping ATPase, and there is an apparent increase in membrane permeability. These phenomena may be related, but there is no firm evidence on this point.A question can be raised about the reality of the increase in membrane permeability. Under the low-salt conditions of experimentation, the K+ is held in the root cells against an electrochemical gradient, presumably by direct or indirect linkage to the H+ pump (5). Depolarization attendant upon injury-induced inhibition of the H+ pump would increase the potential for K+ efflux and reduce the active influx. Hence, net K+ efflux could be realized without change in the physical conductance of the cell membranes to cations. One way of checking this point is to see if a cation which shows a very large electrochemical gradient for influx, such as Ca 2 (12,14), responds by passive influx subsequent to injury. If it does, there is better reason to speak of injury-induced changes in permeability.We report here an investigation of Ca2+ influx in corn roots due to cold shock. Cold shock is very effective in blocking net H+ efflux (3) and avoids the physical stress associated with cutting, rubbing, and osmotic shrinkage. The experiments show that cold shock increases Ca2+ influx.

Peroxidase Release Induced by Ozone in Sedum album Leaves

“…Plants were exposed to ozone in a 50 x 50 x 50-cm vinyl chamber placed in a controlled environment chamber in order to maintain light, temperature, and RH at the same levels as in the growth chamber. Air was drawn through a charcoal filter, supplemented with the desired ozone concentration before entering the exposure chamber, at a rate of 8 (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30) leaves/g) were harvested 24 h after ozone exposure always at the middle of the light period to prevent variability in data arising from the possible photoperiodic rhythms. After washing with distilled H20, leaves (1 g) were peeled and epidermes were washed with 100 mM KCI and homogenized in a glass homogenizer with 0.5 ml ice-cold 40 mM MOPS-KOH, 100 mm KC1 (pH 6.5) buffer.…”

Loss of Recovery Capacity of Plasmalemma K+ Influx after Cutting in Chlorsulfuron Pretreated Maize Roots

“…Cutting causes a rapid increase in membrane permeability followed by an increase in free cytosol Ca2" (15), and a rapid inhibition of H+ extrusion and K+ uptake probably through ATPase inactivation (6,16). The inhibition of active transport is gradually relieved by washing.…”

Reactions of Corn Root Tissue to Calcium

“…As mentioned above, we have found no evidence for Ca2+ influx as a causal agent, unlike the case with cold shock (26). Blocked cation influx may be involved; there is no initial effect of Ca2+ on Cl-influx (Fig.…”

“…The increased K+ uptake at the low K+ concentrations used here is against the electrochemical gradient, and is postulated to be carrier-linked with the H+-ATPase (6). The inhibitory effect of FC on Ca2+ influx has been observed previously (22,26), and is suggested to arise from hyperpolarization causing closure of voltage-gated ion channels (28).…”

“…Calcium entry into plant cells is passive down a large electrochemical gradient; efflux is active and driven by Ca2+-ATPase or H+/Ca2+ antiport (17). Microsomal membranes from corn roots exhibit both types of efflux transport (27), and root segments show passive Ca2+ influx which is greater under shock conditions which increase ion permeability (26).…”