Mechanisms of glyphosate toxicity in velvetleaf (Abutilon theophrasti medikus)

Document Type

Article

Publication Date

9-1-2002

Publication Source

Pesticide Biochemistry and Physiology

Abstract

In velvetleaf source leaves, glyphosate caused gradual inhibition of photosynthesis that increased over several days and was nearly complete by five days. Gas exchange measurements revealed that a Dec.rease in stomatal conductance was a major factor in this reduction. Calvin cycle metabolite levels diminished along with photosynthesis rates but to a lesser extent than stomatal conductance, as indicated by the rise in water use efficiency and the lowering of internal leaf carbon dioxide. Though accumulation of shikimate confirmed that glyphosate was being taken up by the source leaves, this was insufficient to explain the lessened effect on photosynthesis. The protracted inhibition of photosynthesis allowed for greater translocation of glyphosate to sink tissues where it inflicted substantial damage. Consequently, sink tissue processes were more susceptible to disruption by glyphosate than were source leaf processes. The data also support the view that death of velvetleaf tissues was a result of restriction of water availability to the shoot induced by lethal disruption of root processes. The mechanism of prolonged plant death generated by sink tissue toxicity in velvetleaf contrasts with the mechanism observed in sugar beet, where death occurs rapidly due to the inhibition of source leaf processes.

Inclusive pages

27-39

ISBN/ISSN

0048-3575

Publisher

Elsevier

Volume

74

Peer Reviewed

yes

Issue

1

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