Nitrate reductase expression in maize leaves (Zea mays) during dark-light transitions. Complex effects of protein phosphatase inhibitors on enzyme activity, protein synthesis and transcript levels

Margaret G. Redinbaugh, Steven C. Huber, Joan L. Huber, Keith W. Hendrix, Wilbur H. Campbell

Research output: Contribution to journalArticle

Abstract

The effects of cytoplasmic protein synthesis and protein phosphatase activity on NADH:nitrate reductase (NR) activity, protein and transcript were examined in maize (Zea mays L.) seedling leaves. A rapid increase in NR activity, measured in the presence of 5 mM Mg2+, was found upon exposure of excised leaves of light. Inhibitors of protein phosphatase activity (okadaic acid [OKA] and microcystin [MC]-LR) completely prevented the increase in NR activity. The cytoplasmic protein synthesis inhibitor, cycloheximide (CHX), did not affect Mg2+ inhibition of NR activity during the dark-to-light transition. V(max) NR activity, measured in the presence of P, and EDTA, remained constant or increased slightly in maize leaves during the first 2 h of the light period. OKA, MC-LR or CHX treatment caused a 40 to 50% reduction in V(max) NR activity during this time. Incorporation of 35S-Met into NR protein was reduced more than 90% by CHX and 80% by OKA. The inhibition of NR protein synthesis by CHX and OKA correlated with a 50 to 60% decrease in 35S-Met incorporation into total soluble protein over the treatment period. The increase in NR mRNA levels early in the light period was prevented by OKA and MC-LR, but not by CHX, OKA had a similar effect on sucrose phosphate synthase mRNA levels, but did not effect Catalase1 or Catalase3 mRNA accumulation. The data suggest that light-induced decreases in Mg2+ inhibition of NR activity and transcript levels are independent of new protein synthesis. The effects of OKA and MC-LR indicate that protein phosphatase activities could be involved, directly or indirectly, in the regulation of NR activity, protein synthesis and transcript accumulation.

Original languageEnglish (US)
Pages (from-to)67-76
Number of pages10
JournalPhysiologia Plantarum
Volume98
Issue number1
DOIs
StatePublished - Sep 1 1996

Keywords

  • Corn
  • Zea mays
  • enzyme activation
  • gene expression
  • maize
  • microcystin-LR
  • nitrate reductase
  • okadaic acid
  • protein phosphatase

ASJC Scopus subject areas

  • Physiology
  • Genetics
  • Plant Science
  • Cell Biology

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