Changes in the Xanthophyll Cycle and Fluorescence Quenching Indicate Light-Dependent Early Events in the Action of Paraquat and the Mechanism of Resistance to Paraquat in Erigeron canadensis(L.) Cronq

Abstract

Violaxanthin de-epoxidation, chlorophyll fluorescence quenching, and photosynthetic O 2 evolution in the presence of paraquat (Pq) were studied in intact attached leaves of Pq-susceptible, and Pq-resistant (PqR) biotypes of Erigeron canadensis under different light conditions. Initially, similar changes were induced in the two biotypes, but the effects relaxed only in the PqR plants, indicating a Pq elimination process. The penetration of Pq into the chloroplasts of PqR plants proved to be somewhat restricted and highly light-dependent, as revealed by both the light response curves of violaxanthin deepoxidation and fluorescence quenching and the short-term high-light pre-illumination experiments. An irregular downregulation of the non-photochemical fluorescence quenching processes was observed, reflected by lower steady-state zeaxanthin and non-photochemical fluorescence quenching levels as compared with the corresponding non-treated highlight controls. It is concluded that light is essential not only for the initiation of the mechanism of resistance to Pq, but also for the penetration of Pq into the chloroplasts in the PqR E. canadensis. Also, the Pq elimination process may cause a modification to the regulation of the non-radiative energy dissipation in PqR plants in the presence of Pq.

Directed Biosynthesis of Phytotoxic Alkaloids in the Cyanobacterium Nostoc 78–12A

“…The effect of nostocarboline might be comparable to the non-selective herbicide paraquat (methylviologen, 1,1'-dimethyl-4,4'-bipyridinium), which is a strong autooxidable electron acceptor in PS I; and its presence in light-exposed plants has several drastic consequences, like the production of superoxide. [24] Similarly, downregulation of photosynthesis in the light after nostocarboline treatment could lead to an enhanced production of light-driven reactive oxygen species which could be responsible for the formation of the necrotic lesions.…”

Eficiência quântica do fotossistema II de mudas de abacaxizeiro 'imperial' em resposta a associação com Piriformospora indica e herbicidas

“…Esses herbicidas podem afetar a formação de outros pigmentos, como xantofilas (VÁRADI et al, 2000) e carotenoides (KIM et al, 2004), causando interferência no fluxo de elétrons (WAKABAYASHI;BöGER, 2004). E outros, como sulfentrazone, podem modificar a síntese de intermediários utilizados no processo fotossintético, em virtude de a produção de clorofila ser inibida pelo bloqueio da rota (DUKE et al, 1991).…”

Efeitos de herbicidas na atividade fotossintética e no crescimento de abacaxi (Ananas comossus)

“…Dentre os herbicidas utilizados, podem-se destacar aqueles que interferem na biossíntese de clorofila, resultando em perda deste pigmento, e nos cloroplastos, alterando-os funcionalmente (Fayez, 2000). Esses compostos, além de interferirem na síntese de clorofila, também podem afetar a formação de outros pigmentos, como xantofilas (Váradi et al, 2000) e carotenóides (Kim et al, 2004), causando interferência no fluxo de elétrons (Wakabayashi & Böger, 2004) e redução na produção de ATP por inibição da atividade da ATP-sintase no processo de fotofosforilação (Wakabayashi & Böger, 1995).…”