Ethylene synthesis and photosynthetic responses in bean and maize plants exposed to auxins

Abstract

Auxins IAA (indole-3-acetic acid), 2,4-D (2,4-dichlorophenoxyacetic acid) and 2,4,5-T (2,4,5-trichlorophenoxyacetic acid) were applied on maize (Zea mays, monocot) and bean (Phaseolus vulgaris, dicot) plants, with the goal to understand the mechanisms that lead to different responses in relation to the metabolism of ethylene. Maize plants treated with auxins did not produce ethylene, whereas beans produced a lot of it after the treatment. After being sprayed with auxins, maize did not produced any 1-Aminocyclopropane-1-carboxylic acid (ACC), which was observed on beans. The maximum quantum yield of the photosystem II (F_v/F_m ratio) and the levels of photosynthetic pigments were not altered in maize plants treated with auxins. Bean plants showed significant decreases in both variables after the treatment with 2,4-D and 2,4,5-T, but not with IAA. The reduction of chlorophyll levels in bean plants treated with 2,4-D and 2,4,5-T was related to the observed chlorosis, since there was a more accentuated degradation of chlorophylls than carotenoids. Xantophylls also had a more accentuated degradation than alpha and beta carotene in bean plants treated with 2,4-D and 2,4,5-T. When aminoethoxyvinylglycine (AVG) and Co²⁺ were provided to bean plants together with auxins, there was no fall in the F_v/F_m ratio and in the pigment levels, except for the alpha carotene.