Oxidative burst in Chenopodium rubrum suspension cells:

Lowering of the osmotic value of the medium has been reported previously to induce an oxidative burst in plant cells. This has been explained by a sequence of events, including solute influx, cellular swelling and the activation of stretch-regulated channels, triggering the production of reactive oxygen species. Moreover, it is known that the plant growth hormone auxin induces protoplast swelling. Together, these findings prompted the hypothesis that plant cells can respond to auxin-treatment with an oxidative burst. We tested this hypothesis using suspension cultured cells from Chenopodium rubrum L. and 2,7-dichlorodihydrofluorescein as the indicator for reactive oxygen species. An auxin-induced oxidative burst was found similar to an osmotically induced burst. Osmotic treatment consisted of a shift from 110 mOsm to 40 mOsm. The naturally occurring halogenated auxin 4-chloroindole-3-acetic acid was the most active compound tested, giving maximum rates of indicator oxidation corresponding to the formation of 4 x 10^?15 mol H₂O₂ cell^?1 min^?1. Auxin analogous (10 μ M ) exhibited the following order of effectiveness: 4-chloride indoleacetic acid (100%), indoleacetic acid (80%), 2,4-dichlorophenoxyacetic acid (75%), 2-naphthylacetic acid (52%) and 1-naphthylacetic acid (47%). Benzoic acid (23%) was used as a control. Fusicoccin (35%) showed only slight stimulation in conjunction with complex kinetics. The detection of oxidative burst responses to 10 n M indoleacetic acid revealed a high sensitivity of the assay for auxin. Cell-free medium from aged batch cultures and light were also found to stimulate the production of reactive oxygen species. These data indicate that reactive oxygen species can transduce and integrate developmental and environmental signals and thus play a general role in plant growth regulation.