Hypoxic Induction of Anoxia Tolerance in Root Tips of Zea mays

Abstract

When root tips of fully aerobic, intact maize (Zea mays L.) seedlings are made anaerobic, viability normally is only 24 hours or less at 250C. We find that viability can be extended to at least 96 hours if seedlings are given a hypoxic pretreatment for 18 hours by sparging the solution with 4% 02 in nitrogen (v/v) before anoxia. Fully aerobic root tips (sparged with 40% 02) had very low alcohol dehydrogenase (ADH) activity (per gram root fresh weight), and the level remained low under anoxia. In hypoxically pretreated roots, however, high levels of ADH activity were induced, and activity rose further during the initial 24 hours of anoxia, and then remained high at about 20 times that of controls in 40% 02. ADH activity in roots in solution sparged with air (21% 02) was about three times that in 40% 02. Improved viability of hypoxically pretreated root tips was associated with maintenance of a high energy metabolism (ATP concentration, total adenylates, and adenylate energy charge). Roots that were not pretreated lost 94% of the total adenylates and ATP at 24 hours of anoxia. The relation between induced ADH activity, energy metabolism, and improved anoxia-tolerance in acclimated maize root tips is discussed.Many dryland plant species, including maize, sustain injury or even death when the soil becomes excessively wet through irrigation, poor drainage of the soil profile, or transient flooding (7,8). Flooding injury is initiated when the concentration of molecular oxygen in the rooting zone is too low to maintain aerobic respiration throughout the root tissue. Below this COP,2 energy metabolism in cells progressively declines (28) with inhibition of root growth, ion transport, and alterations in water and hormone relations (5,8).A critical feature for plant survival under these conditions may be the ability of root cells to maintain their energy status anaerobically. Some native wetland species and rice can survive extended periods of anoxia (2,12,14,15,17). Survival and a relatively high AEC are associated with sustained ethanolic fermentation which results in a net synthesis of ATP during glycolysis (15,17,23,24). Most dryland species do not display a comparable degree of anoxia tolerance.

Mitochondrial Respiration and Hemoglobin Gene Expression in Barley Aleurone Tissue

“…The energy charge of the starchy seeds after several hours of anoxia was greater than 0.6, whereas the lipidcontaining seeds maintained energy charges of less than 0.35. Maize roots, exposed to a period of hypoxia prior to experiencing anoxic conditions, remain viable for longer periods (Johnson et al, 1989). This has been attributed to the induction of Adk, providing ATP synthesis through anaerobic fermentation.…”

The Role of Sugars, Hexokinase, and Sucrose Synthase in the Determination of Hypoxically Induced Tolerance to Anoxia in Tomato Roots

“…Maize (Saglio et al, 1988;Johnson et al, 1989) and wheat (Waters et al, 1991) primary roots do not resist more than 8 to 10 h of anoxic shock. An early study by Webb and Armstrong (1981) with pea, pumpkin, and rice roots showed that apices survived only 6, 12, and 4 h of anoxia, respectively.…”

“…An early study by Webb and Armstrong (1981) with pea, pumpkin, and rice roots showed that apices survived only 6, 12, and 4 h of anoxia, respectively. In wheat and maize a hypoxic pretreatment has been reported to enhance survival, from 24 h for wheat (Waters et al, 1991) to more than 96 h for maize (Saglio et al, 1988;Johnson et al, 1989). Studies of the effects of hypoxic acclimation in maize root tips led to the conclusion that two main strategies are involved in improved toIerance to anoxia.…”

Elongation and Termination Reactions of Protein Synthesis on Maize Root Tip Polyribosomes Studied in a Homologous Cell-Free System

“…The biochemical and physiological responses of maize root tips to low oxygen tensions (hypoxia) have been studied in some detail (9,(24)(25)(26). We have used the homologous maize in vitro translation system to examine how changes in intracellular pH which occur during hypoxia may affect elongation and termination reactions, by replicating those conditions in vitro.…”