Inhibitory Action of Glufosinate on Photosynthesis

Abstract

eine B otanik d er Jo h an n es G u ten b erg -U n iv ersität, D -W -6500 M ainz, B undesrepublik D eutschland Z. N aturforsch. 48c, 3 6 9 -3 7 3 (1993); received D ecem ber 2, 1992 G lufosinate, P hosphinothricin, P h o to resp iratio n , Photosynthesis, R ibulose-l,5-bisphosphate C arboxylase G lufosinate (phosphinothricin) irreversibly blocks the glutam ine synthetase which subse quently gives rise to an accum ulation o f am m onium and to a strong decrease in som e am ino acids, especially glutam ine an d glutam ate.U nder atm ospheric conditions (400 ppm C O ,, 21% 0 2) glufosinate causes a rapid inhibition o f photosynthesis, to o . H ow ever, u n d er n o n -p h o to re sp irato ry conditions (1000 ppm C 0 2, 2% 0 2) only a slight inhibition o f p h otosynthesis occurs w ith glufosinate. Since under b oth c o n d i tions an accum ulation o f am m o n iu m occurs, it is concluded th a t inhibition o f photosynthesis is n o t induced by the higher co n cen tratio n s o f am m onium . The results rath er suggest th a t the absence o f am ino do n o rs in the glycolate p ath w ay leads to a break-dow n o f the tran sa m in a tion reaction o f glyoxylate to glycine. This causes an inhibition o f p h o to resp iratio n and as a fu rth er consequence the in hibition o f p h otosynthesis. T here are tw o hypotheses fo r explaining this phenom enon. O ne o f them supposes th a t th e blockade in the glycolate pathw ay produces a lack o f C alvin cycle interm ediates which subsequently is the cause o f the inhibition o f p h o to synthesis. T he o th er one suggests a direct in h ib itio n o f the rib u lo se-l,5 -b isp h o sp h ate carb o x y lase by the accum ulation o f glyoxylate and P-glycolate.A fter treatm ent with different in term ediates o f the C alvin cycle and p h o to resp iratio n to gether w ith glufosinate no decrease in the in h ib itio n o f photosynthesis could be m easured. This suggests th a t the inh ib itio n o f p h o to sy n th esis is n o t induced by a depletion o f in te r m ediates o f the Calvin cycle.Tests on the effect o f glyoxylate an d P-glycolate on ribulosebisphosphate carboxylase activi ty show ed th a t in crude leaves extracts the enzym e activity can only be inhibited by high c o n centrations o f these substances. H ow ever, in in tac t spinach ch loroplasts the enzyme activity can be blocked by using m uch low er c o n cen tratio n s o f glyoxylate. TThis m ay indicate th a t the ribulosebisphosphate carboxylase activase is affected by this m etabolite and th a t this m ay be the reason for an inhibition o f p h o tosynthesis a fter treatm en t w ith glufosinate.

RNA-Seq transcriptome analysis of Amaranthus palmeri with differential tolerance to glufosinate herbicide

“…Ammonia accumulation is directly related to glufosinate toxicity. Inhibition of glutamine synthetase and ammonia accumulation triggers a cascade of reactions, including inhibition of ribulose-1,5-bisphosphate carboxylase/oxygenase (RUBISCO) enzyme [ 74 ] and photosystem electron flow [ 75 ], affecting photosynthesis [ 30 , 76 ] leading to plant death. Ammonia reduces pH gradient across the membrane, which uncouples photophosphorylation [ 75 ].…”

Herbicide safety relative to common targets in plants and mammals

“…Glyoxylate is an inhibitor of ribulose‐1,5‐bisphosphate carboxylase, a key enzyme in carbon fixation in photosynthesis. Inhibition of carbon fixation reduces the pools of ADP and other compounds that are normally reduced by PSI, leading to the dissipation of light energy absorbed by photosynthetic pigments by destructive photo‐oxidation of membranes in the light 31. In mammals the primary toxicological response to GS inhibitors is changes in neurological behavior, indicating that the CNS is the primary target site 32.…”

Glufosinate tolerance in hybrid corn varieties based on decreasing ammonia accumulation†

“…Necrotic water‐soaked spots appear within 3–5 days after application (DAA), followed by necrosis in 1–2 weeks and ultimately, plant death (William 1994). Glufosinate is an inhibitor of glutamine synthetase (GS; EC 6.3.1.2, Wild & Wendler 1993) and this results in glutamine impoverishment (Wild & Wendler 1990). This inhibitory process prevents ammonium ions being incorporated into amino acids, resulting in the accumulation of ammonium ions to toxic levels within the plant cells and leading to membrane breakdown and cell death (Sankula et al .…”