Effects of 2,4‐D, Iron, and Chelate Supplements on Dark CO 2 Fixation in Cell‐Free Homogenates of Field Beans 1

1 ^HE cellular metabolism of plants shows varied re•*sponses to 2,4-dichlorophenoxyacetic acid (2,4-D). Though best known as a herbicide for selective control of broadleaf weeds, 2,4-D under appropriate conditions may stimulate the vegetative and reproductive development of plants (12, 18). The mechanism of these effects is not known, but investigations have shown that plants pretreated with 2,4-D showed increased activity in several respiratory enzyme systems (2, 15). Added in vitro to mitochondrial preparations, 2,4-D has had no promotive effect but rather brought about a general inhibition of respiratory enzymes (15). Fang et al. found that both glucose uptake and respiratory CO2 evolved from glucose as initial substrate were increased in bean stem tissues pretreated with 2,4-D (4). They proposed that 2,4-D thus influences growth by affecting glucose utilization, which furnished both energy and substrates for synthesis of cellular constituents. The present study showed that several of the enzymes concerned in the dark fixation of CO2 in bean leaves also exhibit increased activity when leaves were pretreated with stimulatory levels of 2,4-D. It has been established that dark CO2 fixation results in the production of both sugars (3, 14) and large pools of organic acids in many plants (3, 7, 9). Thus, an increase in fixation of CO2 resulting from treatment with 2,4-D could be important in providing both sugars and organic acids, resulting in increased metabolic activity and growth. This study was undertaken to determine the effects of a range of low (sublethal) to high (near herbicidal) concentrations of 2,4-D as they influence dark CO, fixation in field beans. Since FeSO4 has been shown to reverse the effects of near herbicidal 2,4-D concentrations (11, 12, 18) this investigation also considers the response of 2,4-D concentrations in combination with FeSO4, FeEDDHA, and EDDHA.