Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/9/1997
Publication Date: N/A
Interpretive Summary: Substantial economic loss occurs annually in the U.S. from flooding injury to corn plants. Knowledge about what happens in the plant during flooding could provide clues for developing plants that are more tolerant to flooding. In this study, corn survival during flooding was correlated with the root sugar level. An enzyme (sucrose synthase) which causes the breakdown of sucrose into the simple sugar components, glucose and fructose, was produced during flooding stress. The role of sucrose synthase in the flooding tolerant response was determined using corn single or double mutants which lack either one or both genes coding for that enzyme. These mutants grew as well as wild type plants under non-flooded conditions, indicating that the genes were not essential for normal metabolism. However, the mutants were much less tolerant to flooding than wild type plants. The flooding tolerance of these mutants was correlated with the number of genes and their levels of expression. The results indicated, for the first time, the critical role of sucrose synthase in the flooding tolerance of corn and will assist in the engineering and breeding of flood-tolerant corn cultivars.
Technical Abstract: Principally active in vitro in sucrose breakdown, SuSy has been shown to be important in phloem loading and in sucrose metabolism in sink tissues. The induction of the SuSy gene by low oxygen, low temperature and limiting carbohydrate supply suggests that it may also be important in carbohydrate metabolism under stress conditions. The isolation of a functionally normal lmaize subline mutant for the two SuSy genes shows that SuSy activity is dispensable during aerobic growth and further allows the possibility of investigating its importance during anaerobic stress. Tolerance to 48 h of submergence stress, assessed by the elongation potential of radicals, was directly correlated with the number of SuSy genes and the level of SuSy expression, as was hypoxically induced tolerance to 24 h of anoxic incubation. Furthermore, root death in double mutant seedlings during anoxic incubation could be attributed to the impaired utilization of sucrose, primarily due to the loss of both SuSy enzymes. Collectively, these data provide, for the first time, unequivocal evidence that SuSy plays a critical role in anoxic tolerance in maize.