Bromoacetic acid inhibits pyruvate orthophosphate dikinase and reduces photosynthetic activity in maize

Pyruvate orthophosphate dikinase (PPDK) catalyzes the conversion of pyruvate to phosphoenolpyruvate, and its activity is essential to maintain photosynthetic CO2 assimilation in C4 plants. Thus, it has been described as a promising target for the development of selective herbicides for C4 weeds. We evaluated whether bromoacetic acid, a known PPDK inhibitor of Clostridium symbiosum, can also inhibit the PPDK of a C4 plant, maize, in in vitro experiments. We also evaluated the effects of foliar application of 0.5–10 mM bromoacetic acid on the leaf pyruvate content and gas exchange of maize plants. Bromoacetic acid reduced maize PPDK activity in vitro in a dose-dependent manner; the degree of inhibition ranged from 13.6 to 73.6% with 0.5–10 mM bromoacetic acid. The foliar application of bromoacetic acid increased the leaf pyruvate content, suggesting that this compound may also inhibit PPDK activity in vivo. As a consequence, impairments to the gas exchange parameters of maize plants were noted, with a marked reduction in the photosynthetic rate and an increase in the intercellular CO2 concentration. Despite the abrupt decrease in stomatal conductance and transpiration, the plants showed large dehydration and reduction of leaf fresh weight after 48 h of application to bromoacetic acid. Our data allow us to affirm that bromoacetic acid has a potent herbicidal effect on a C4 plant, maize; the most likely mechanism of action is the inhibition of PPDK.