Much research has been conducted on the changes in gene expression of the model plant Arabidopsis to low-oxygen stress. Flooding results in a low oxygen environment in the root zone. However, there is ample evidence that tolerance to soil flooding is more than tolerance to low oxygen alone. In this study, we investigated the physiological response and differential expression of root-related transcription factors (TFs) associated with the tolerance of soybean plants to soil flooding. Differential responses of PI408105A and S99-2281 plants to ten days of soil flooding were evaluated at physiological, morphological and anatomical levels. Gene expression underlying the tolerance response was investigated using qRT-PCR of root-related TFs, known anaerobic genes, and housekeeping genes. Biomass of flood-sensitive S99-2281 roots remained unchanged during the entire 10 days of flooding. Flood-tolerant PI408105A plants exhibited recovery of root growth after 3 days of flooding. Flooding induced the development of aerenchyma and adventitious roots more rapidly in the flood-tolerant than the flood-sensitive genotype. Roots of tolerant plants also contained more ATP than roots of sensitive plants at the 7th and 10th days of flooding. Quantitative transcript analysis identified 132 genes differentially expressed between the two genotypes at one or more time points of flooding. Expression of genes related to the ethylene biosynthesis pathway and formation of adventitious roots was induced earlier and to higher levels in roots of the flood-tolerant genotype. Three potential flood-tolerance TFs which were differentially expressed between the two genotypes during the entire 10-day flooding duration were identified. This study confirmed the expression of anaerobic genes in response to soil flooding. Additionally, the differential expression of TFs associated with soil flooding tolerance was not qualitative but quantitative and temporal. Functional analyses of these genes will be necessary to reveal their potential to enhance flooding tolerance of soybean cultivars.

A substantial increase in the number of soybean [Glycine max (L.) Merr.J cultivars has occurred in recent years. Many of these are derived from a narrow genetic base, which makes traditional cultivar identification increasingly difficult. As a result, new techniques that detect minor biochemical differences need to be evaluated for their ability to differentiate among cultivars. This study examines the applicability of reversed phase high performance liquid chromatography (RP‐HPLC) for soybean cultivar identification. Salt soluble proteins of 14 cultivars were extracted from unimbibed seeds, eluted from a reversed phase C4 column with increasing concentrations of acetonitrile, and monitored at 280 nm. Seeds were obtained for study from three differing growing locations in Ohio. While no qualitative differences of elution profiles were detected within cultivars and locations, comparisons of quantitative RP‐HPLC seed protein profiles permitted separation of genetically diverse genotypes. Retention time ratios for selected peaks were not significantly different among cultivars, but peak area percentage showed that quantitative differences were useful criteria for distinguishing closely related lines. This study documents that RP‐HPLC analysis of soybean seed proteins can distinguish divergent soybean genotypes and suggests that peak area percentage of RP‐HPLC profiles is a superior method of cultivar analysis.

Early planted corn (Zea maysL.) is frequently subjected to flooding stress, especially in poorly drained soils. This study characterizes the role of pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH) enzymes in the flooding susceptibility of corn seeds; PDC and ADH activities were assayed in a flood‐tolerant (A632) and a flood‐susceptible (Mo17) inbred during flooding at 10 and 25 °C. Each inbred consisted of two seed lots possessing different germination levels (95 and 75% germination). Flooding induced an increase in the activity of both enzymes. However, the increase was greater and sustained longer for ADH than PDC. The maximum level of ADH activity achieved was similar in both inbreds, but was greater in the high‐quality than in the low‐quality seeds. Since the highquality seeds survived flooding longer than the lowquality seeds, no correlation between flooding susceptibility and maximum ADH activity was observed. The two inbreds also exhibited similar ADH isoenzyme patterns. These data indicate that flooding susceptibility is not associated with PDC or ADH activities in corn seeds.