Transport Interactions between Paraquat and Polyamines in Roots of Intact Maize Seedlings

Abstract

Interactions between absorption of paraquat and the polyamines putrescine, cadaverine, and spermine in roots of intact maize (Zea mays L. cv 3377 Pioneer) seedlings were examined. Concentrationdependent kinetics for paraquat and putrescine influx were similar and both kinetic curves could be resolved into a linear and a saturable component. The linear component was previously shown to represent cell wall/membrane binding. The saturable components for paraquat and putrescine uptake, which represent influx across the plasmalemma, had Km values of 98 and 120 micromolar, respectively, and Vmax values of 445 and 456 nanomoles per gram fresh weight per hour, respectively. Lineweaver-Burk transformation of the saturable component of paraquat influx in the presence of varying concentrations of putrescine indicated that the diamine competitively inhibited the saturable component of paraquat uptake. Reciprocal experiments similarly demonstrated that paraquat competitively inhibited the saturable component of putrescine uptake. Competitive inhibition of both paraquat and putrescine influx could also be demonstrated with the diamine cadaverine, which has a charge distribution similar to that of paraquat and putrescine. In contrast, the larger, tetravalent polyamine spermine appeared to noncompetitively inhibit the influx of paraquat and putrescine. These results strongly suggest that paraquat enters maize root cells via a carrier system that normally functions in the transport of diamines with a charge distribution similar to that of paraquat.Paraquat is a widely used postmergence contact herbicide that acts by accepting electrons from PSI of chloroplast membranes (3). To reach its site of action following foliar application, paraquat must be capable of crossing the plasmalemma (as well as the chloroplast envelope). In aqueous solution, however, paraquat exists as a divalent cation and is therefore unlikely to passively diffuse across the lipid bilayer of plant cell membranes. Until recently (11), however, little evidence has been reported for a paraquat transport mechanism in plant cell membranes.With the exception of 2,4-D (6, 18), herbicides have seldom been reported to require a carrier-mediated transport system for uptake across the plasmalemma. Recent evidence from our laboratories suggested that paraquat is taken up by maize (Zea mays L. cv 3377 Pioneer) root epidermal and cortical cells via a protein-mediated system. This is based primarily on concentration-dependent kinetic studies of paraquat absorption. In these studies, we demonstrated that paraquat influx across the plasmalemma is via a saturable system with a Km of 90 tiM and a Vmax of 458 nmol g-1 fresh weight h-1 (11).Paraquat uptake in animal tissues has also been reported to be mediated by a saturable system with a Km of 40 to 80 AM (17,21) and Vmax of 300 to 600 nmol g-' fresh weight h-1 (15,17). In contrast with our data from maize roots, influx into animal cells was reported to be sensitive to respiratory inhibitors such as cyanide and rotenone ...

Natural variation in a polyamine transporter determines paraquat tolerance in Arabidopsis

“…Moreover, we demonstrated that natural variation in RMV1 defines PQ uptake in A. thaliana. These data support the hypothesis that PQ enters plant cells via a transport system that inherently functions in the transport of PAs, which have structural similarities to PQ (17). Our data imply that other transporters in addition to RMV1 may participate in PA uptake in Arabidopsis, suggesting the existence of diverse transport systems, which might serve to increase the repertoire of PAs that plants can absorb from the environment.…”

“…Kinetic analysis further indicated that RMV1 is capable of mediating PQ transport against a concentration gradient (Fig. 3F) (17). Moreover, the PQ uptake in the OX-C transgenic plants showed pH dependency (Fig.…”

“…S1), functions as an oxidative stress inducer and is one of the most widely used herbicides, despite the fact that its ingestion can cause death by multiorgan failure (14,15). Data showing that PA and PQ (PA/PQ) displayed similar uptake characteristics in animal and plant systems suggested that PQ uptake is mediated by PA transporters (16,17), although little is known about the molecular components responsible for the influx of PA/PQ. Here, we identified an Arabidopsis L-type amino acid transporter (LAT) family transporter named RMV1 (resistant to methyl viologen 1) responsible for the uptake of PA and PQ by analyzing the natural variation of PQ tolerance in Arabidopsis accessions.…”

Constitutively Elevated Levels of Putrescine and Putrescine-Generating Enzymes Correlated with Oxidant Stress Resistance in Conyza bonariensis and Wheat

“…Putrescine is also a precursor of y-aminobutyrate (Flores, 1990), which may function as a signal molecule after stress in plants (Snedden et al, 1995(Snedden et al, ,1996. Putrescine may be involved in inhibiting paraquat uptake or the transport system, as found by Hart et al (1992) in an isolated root system. Because only putrescine levels were greatly enhanced, we only added putrescine exogenously to mimic this phenomenon.…”

Paraquat: An Oxidative Stress Inducer

“…In animal tissues it has been shown that paraquat transport occurs by carriers that also function as carriers of other molecules such as polyamines (Rannels et al, 1989, Jóri et al, 2007. Hart et al (1992aHart et al ( 1992b demonstrated that paraquat movement across plasma membrane root epidermal and cortical maize cells has a concentration-dependent kinetic and that the herbicide binds to cell wall, and its transport is facilitated by a carrier that normally functions in the movement of molecules that has a similar chemical structure or similar charge distribution such us diamines like putrescine and cadaverine. Using maize protoplast showed that paraquat uptake has similar concentration-kinetic to that observed in intact cells and the accumulation inside cells increase in a timedependent manner and is saturated after 10 min, although 50% of uptake occurs during the first 10 s. The saturable K m for paraquat uptake in maize cells and protoplasts was determined at 90 µM and 132 µM respectively, similarly the K m in rat lung was 70 µM www.intechopen.com Herbicides -Properties, Synthesis and Control of Weeds 136 suggesting in both animal and vegetal tissues a carrier-mediated process (Rannels et al, 1985).…”