ABSTRACT
Soybean (Glycine max) alcohol dehydrogenase (ADH) cDNAs were amplified in vitro from total RNA by the polymerase chain reaction (PCR). The amplification strategy involved first strand cDNA synthesis from anaerobic cotyledon total RNA using an 18-thymidine primer. The second strand cDNA primer was a conserved sequence near the 5' end of known plant ADH transcripts. The PCR products were ligated into a plasmid vector and unique clones were isolated on the basis of size and restriction pattern. Sequence analysis revealed three distinct classes of soybean ADH cDNAs, all of which showed high homology to Adh genes from maize and peas. RNA blot hybridization analyses showed differential expression patterns for these genes. One gene, expressed constitutively in all seedling organs, was inducible by anaerobiosis, one gene was expressed only in anaerobic organs, and the third gene was expressed predominantly in anaerobic roots.
ABSTRACT
The postanoxic injury, also known as reperfusion injury, is associated with the returning of anoxic tissues to normal atmosphere. Using tetrazolium chloride staining, ATP content, and seedling growth rate as indicators, we found that postanoxic injuries in soybean (Glycine max) seedlings were more severe after 1 and 2 hours of anoxia than after longer anoxic durations (3 to 5 hours). Anaerobic incubation of root tips in the presence of 100 mm ascorbate, an antioxidant and free radical-scavenging compound, alleviated the postanoxic injury associated with the short durations of anoxia. Extracts from soybean seedling roots returned to air from 1 hour of anoxia had an elevated capacity to produce superoxide radicals over extracts from postanoxic roots stressed for 3 or 5 hours. Activity of superoxide dismutase in soybean roots returned to air from 1 and 2 hours of anoxia was 30 to 50% lower than activities in roots returned to air from 5 hours of anoxia. Superoxide dismutase-specific transcripts were also lower in postanoxic roots stressed for 1 hour than in roots stressed for longer anoxic durations. The evidence suggested that the postanoxic injury of soybean roots after a short anoxic stress was associated with an increased superoxide radicals production capacity coupled with a reduced superoxide dismutase activity. Periods of anoxia of at least 3 hours were necessary for soybean seedlings to develop the ability to cope with postanoxic stress.
ABSTRACT
Flooding is a frequently occurring environmental stress that can severely affect plant growth. This study shows that treatment of corn (Zea mays L.) seedlings with abscisic acid (ABA) increases their tolerance to anoxia 10-fold over untreated seedlings and twofold over seedlings treated with water. Corn seedlings stressed anoxically for 1 day showed only 8% survival when planted in vermiculite. Pretreatment of root tips with 100 micromolar ABA or water for 24 hours before the 1 day anoxic stress increased the anoxic survivability of seedlings to 87% and 47%, respectively. Cycloheximide (5 milligrams per liter), added together with ABA, reduced the seedling survival rate, indicating that the induction of anoxic tolerance in corn by ABA was partly a result of the synthesis of new proteins. ABA treatment induced a threefold increase in alcohol dehydrogenase enzyme activity in corn roots. However, after 24 h of anoxia, alcohol dehydrogenase enzyme activity between the ABA-pretreated and non-pretreated corn roots was not significantly different. The results indicated that ABA played an important role in inducing anoxic tolerance in corn and that the induced tolerance was probably mediated by an increase in alcohol dehydrogenase enzyme activity before the anoxic stress.