Effect of water stress and diclofop-methyl on photosynthesis, carotenoid and abscisic acid content of leaves of Avena byzantina and Avena fatua

A.K. Cowan, S.L. Turner, C.E.J. Botha
1995 South African Journal of Botany  
The effect of combined water stress and diclofop-melhyl treatment on photosynthesis and carotenoid and abscisic acid (ABA) content of leaves of A. byzantina and A. tatua was investigated. Sublethal doses of diclofop-methyl caused a tranSient decline in net assimilation rate and a decrease in p-carotene and zeaxanth in in leaves of both species. The decline in carotenoid levels occurred concomitant with a substantial but transient increase in ABA. A similar but less dramatic trend was observed
more » ... r water-stressed plants. Aecovery of photosynthesis in seedlings exposed simultaneously to diclofop-methyl and water stress, was associated with an increase in p-carotene and zeaxanthin co ntent and a return to basal ABA levels in le aves of A byzantina. By comparison, substantial accumulation of zeaxanthin was obse rved in leaves of A (alua following combined water stress and herbicide treatment, apparently at the expense of ABA. Similar findings were made regarding levels of zeaxanthin when diclofop-methyl was applied to already waterstressed plants of A. byzantina and A. (atua. It is proposed that herbicide-and/or water-stress-induced alterations in acetyl-coenzyme A carboxylase activity coupled with reduced demand for fatty acid synthesis, facilitate channelling of photosynthetically fixed carbon into isoprenoids and that alterations in the capacity lor terpenoid synthesis forms part of the mechanism by wh ich drought stress antagonizes the activity of aryloxyphenoxypropionic acid herbicides. Die invoed van gekombineerde waterstremming en diklofopmetiel-behandeling op die karoteno'ied-en ABA-konsentrasie van blare van A byzantina en A (alua is ondersoek. Subletale dosisse van dikloropmetiel het tot 'n Iydelike verI aging in die netto assimilasietempo en tot 'n verI aging in p-karoteen en zeaxantien in blare van albei spesies gelei. Die afname in karotenol'edvlakke het plaasgevind saam met 'n sterk maar tydelike verhoging in ABA. 'n Soortgelyke maar minder opvallende neiging is waargeneem in plante wal aan walerslremming onderhewig was . In saailinge van A byzantina wat aan be ide diklofopmetiel en waterstremm ing blootgestel is, het die herstel in fotosintese plaasgevind saam met 'n ve rhoging in p-karoteen en zeaxantienvJakke en 'n herstel van die ABA na die basale v/ak. In die geval van A. (atua wat aan diklo-fopmetieJ en walerstremming blootgestel is, is 'n aans ie nlike verhoging in zeaxanUen waargeneem, skynbaar ten koste van ABA. Soortgelyke waarnemings is gemaak met betrekking tot zeaxantienvlakke nadal diklofopmeliel toegedien is aan reeds watergestremde plante van A byzantina en A. (atua. Daar word voorgestel dal herbisied -enlof waterstremming-ge' indu seerde veranderings aan ACCase-aktiwiteit, gekoppel aan 'n verlaagde aanvraag vir vetsuursintese, tot die omskakeling van folos intese•gefikseerde koolstof na isopreno'iede lei. Wysigings in die vermoe om isopreno'iede Ie vorm , kan 'n deel uitmaak van die meganis me waarvolgens droogtestremming die aktiwiteit van AOPP herbisiede be'invloed.
doi:10.1016/s0254-6299(15)30464-6 fatcat:bpg5ao5qnnbxjfhcaqbifbjmsu