J. J. Pienaar

Effect of trifluoroacetate, a persistent degradation product of fluorinated hydrocarbons, on Phaseolus vulgaris and Zea mays.

The aim of this study was to quantify the effect of the pollutant, trifluoroacetate (TFA), on growth and photosynthesis of Phaseolus vulgaris (C(3)) and Zea mays (C(4)) in order to elucidate the physiological and biochemical basis of its inhibitory action. In whole plant studies, photosynthetic gas exchange, fast phase fluorescence kinetics and Rubisco activity were measured in parallel over a 14-day period in plants cultivated in a water culture system with NaTFA added at concentrations ranging from 0.625 to 160mgl(-1). Although initial stimulation of some photosynthetic parameters was observed at low TFA concentrations early on in the experiment, marked inhibition occurred at higher concentrations. In general Z. mays was affected more severely than P. vulgaris showing a large TFA-induced decrease in both apparent carboxylation efficiency (ACE) and in vitro Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase; EC 4.1.1.39) activity. Analysis of photosynthetic gas exchange revealed that besides constraints on mesophyll processes such as Rubisco activity, stomatal limitation also increased with increasing TFA concentration, especially in P. vulgaris. In depth analysis of the fast phase fluorescence transients pointed at TFA-induced uncoupling of the oxygen evolving complex (OEC) and inhibition of electron transport beyond Q(a) including possible constraints on the reduction of end electron acceptors of photosystem I.

Effect of Trifluoroacetate, a Persistent Degradation Product of Fluorinated Hydrocarbons, on C3 and C4 Crop Plants

TFA is a pollutant generated in the atmosphere by the degradation of hydrofluorocarbons (HFCs), as well as other anthropogenic sources such as teflon-cookware. The aim of this study was to quantify the physiological and biochemical basis of the inhibition of photosynthesis imposed by trifluoroacetate (TFA) in Phaseolus vulgaris and Zea mays, crop plants representing C3 and C4 photosynthesis respectively. Photosynthetic gas exchange and fast phase fluorescence kinetics were measured in parallel over a 12-day period in plants cultivated in a hydroponic system under strictly controlled conditions. Although initial stimulation of some photosynthetic parameters was observed at low TFA concentrations, marked inhibition occurred at higher concentrations. The inhibitory effect was reflected by chlorophyll a fluorescence and photosynthetic gas exchange derived parameters. Analysis of photosynthetic gas exchange revealed that besides constraints on mesophyll processes such as Rubisco activity and RuBP regeneration capaCity, stomatal limitation also increased with increasing TFA concentration, especially in P. vulgaris. Although the mechanism of inhibition was similar in both species, the C4 plants were affected more severely. In depth analysis of the fast phase fluorescence transients pointed at TFA-induced uncoupling of the oxygen evolving complex (OEC) and inhibition of electron transport beyond QA including constraints on ferredoxin- NADP+ oxidoreductase (FNR)-function.

Estimating the concentration of nucleation mode aerosol particles over South Africa using satellite remote sensing measurements

In this work satellite based observations were used to estimate the concentration of nucleation mode aerosols over South Africa. The nucleation mode aerosols can not be detected directly with satellite instruments since they are much smaller than the optically active aerosols, hence the concentrations were estimated using proxies introduced by Kulmala et al. (2011). Results showed enhanced values of both primary and regional scale nucleation proxies over the Mpumalanga Highveld industrial area, whereas over the Johannesburg-Pretoria megacity only the primary nucleation proxy showed elevated values. To estimate how well satellite based proxies work, the relation between satellite and in situ based quantities was studied in more detail. The correlation between aerosol optical depth (AOD) and condensation sink (CS) was 0.2-0.3 depending on the location. Boundary layer height affected the correlation somewhat, but there are other factors, such as the effect of dust on AOD, that are more likely to have a stron...