Differential Accumulation of Manganese-Superoxide Dismutase Transcripts in Maize in Response to Abscisic Acid and High Osmoticum

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Abstract
The plant growth regulator abscisic acid (ABA) has multiple physiological effects during embryogenesis and seed formation. Although a number of genes induced by ABA have been characterized, the functions of the encoded proteins remain, for the most part, obscure. In this paper we demonstrate that members of the manganese-superoxide dismutase (MnSod) gene family encoding antioxidant isozymes of known function during development and oxidative stress respond differentially to ABA and high osmoticum in developing maize (Zea mays L.) embryos. Expression of the maize Sod3.1 does not respond to ABA or high osmoticum, whereas the steady-state levels of the maize Sod3.2, Sod3.3, and Sod3.4 transcripts are induced by ABA. Total SOD-3 protein and enzymatic activity, however, remain constant. Additionally, we examined the requirement for ABA in the accumulation of MnSod transcripts in response to high osmoticum in wild-type and mutant embryos of an ABA-deficient line (M1A4; vp5). RNA blot analyses show that multiple Sod3 transcripts are also found in line M1A4, and ABA increases the accumulation of the Sod3.2, Sod3.3, and Sod3.4 transcripts in both wild-type and vp5 mutant embryos. Interestingly, although accumulation of the Sod3.3 and Sod3.4 transcripts in the vp5 mutant embryo was induced by ABA, it was not induced by high osmoticum. Both superoxide dismutase and ABA have been implicated in plant tolerance to environmental stress; results from this study demonstrate a connection between the action of ABA and oxidative stress during embryo maturation in maize.

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