Abstract
Mitochondrial pyruvate dehydrogenase (mtPDH) is a key respiratory enzyme that links glycolysis and the tricarboxylic acid cycle, and it is negatively regulated by mtPDH kinase (mtPDHK). Arabidopsis lines carrying either a constitutive or seed-specific antisense construct for mtPDHK were used to test the hypothesis that alteration of mtPDH activity in a tissue- and dosage-dependent manner will enhance reproductive growth particularly at elevated CO2 (EC) through a combined enhancement of source and sink activities. Constitutive transgenic lines showed increased mtPDH activity in rosette leaves at ambient CO2 (AC) and EC, and in immature seeds at EC. Seed-specific transgenic lines showed enhanced mtPDH activity in immature seeds. A strong relationship existed between seed mtPDH activity and inflorescence initiation at AC, and at EC inflorescence stem growth, silique number and seed harvest index were strongly related to seed mtPDH activity. Leaf photosynthetic rates showed an increase in rosette leaves of transgenic lines at AC and EC that correlated with enhanced inflorescence initiation. Collectively, the data show that mtPDHK plays a key role in regulating sink and source activities in Arabidopsis particularly during the reproductive phase.
Highlights
The present study is the first to show an enhancement of mitochondrial pyruvate dehydrogenase (mtPDH) activity at elevated CO2 (EC) compared to ambient CO2 (AC) in both in source and sink tissues in Arabidopsis, providing direct enzymatic evidence for upregulation in the supply of carbon for mitochondrial metabolism via mtPDH in plants grown at EC (Dahal et al, 2014; Leonardos et al, 2014)
Robertson et al (1995) showed an increase in mtPDH protein levels in wheat at EC. If this holds true for Arabidopsis, the fact that mtPDH activity in WT at AC is not different from EC may be because of mtPDH kinase (mtPDHK) suppression
Elevated mtPDH activity in transgenic lines at EC shows that this repression in WT could be alleviated by antisense suppression of mtPDHK
Summary
Less than predicted enhancements in photosynthetic capacity and yield in plants under elevated CO2 (EC) have been attributed to insufficient sink capacity and end-product inhibition of photosynthesis (Clough et al, 1981; Arp, 1991; Stitt, 1991; Ainsworth et al, 2004; Long et al, 2004, 2005; Rogers et al, 2004; Sharkey et al, 2004; Ainsworth and Rogers, 2007; Leakey et al, 2009). When citrate synthase and the mitochondrial pyruvate dehydrogenase (mtPDH) enzyme complex activities were enhanced, significant positive results on growth were observed at AC, effects on seed production and harvest index were not reported (Zou et al, 1999; Koyama et al, 2000; Marillia et al, 2003). These data provide evidence that dark respiration plays an important role in anabolic processes in plants and in maintaining sink activity and source-sink balance
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