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A study of the possible protection afforded by copper, ferrous and ferric ions against the actions of 2,4-dichlorophenoxy acetic acid Jowett, Philip Anthony

Abstract

The possibility that iron and copper can ameliorate the effects of 2,4-dichlorophenoxy acetic acid (2,4-D) on the morphology and yield of plants has been investigated by Wort (64). A study of the literature indicates that although there is considerable variation among plant species and also parts of the same plant, 2,4-D concentrations below 50 p.p.m. promote or have no effect on respiration, while higher concentrations are generally inhibitory. Photosynthesis is generally inhibited. An experiment was planned and executed to determine whether iron and copper protect against the effects of 2,4-D on photosynthesis and respiration, and on fresh, dry and ash weights. Each treatment was replicated six times. Potato (Solanum tuberosum L.) plants were grown to the age required for treatment (4-7 weeks) in a hydroponic system. Treatment was applied either in the form of 'Attaclay' dust including growth substance and/or metal, or as aqueous spray in which the metal was applied two hours before the growth substance. At given intervals after treatment, photosynthesis and respiration in the leaflets were determined by the diethanolamine buffer method (60) on the Warburg apparatus. After the leaflets had been removed for the final determination of photosynthesis and respiration, the plants were harvested and their fresh, dry and ash weights were determined. A comparison was made of photosynthetic values based on both area and fresh weight. The results were analysed for statistical significance by the analysis of variance and Duncan's new multiple range test. Coefficients of variability (C.V.%) were calculated for the various measurements. In most cases the coefficients were shown to decrease by half during the course of the experiment. Results showed that 2,4-D was more inhibitory to gas exchange than its copper salt and also caused greater deformation of the plants. Further results indicated that application of iron with 2,4-D inhibited the effects measured for 2,4-D. Gas exchange values for the 2,4-D treated plants were frequently significantly different from those of plants treated two hours earlier with an iron spray. The iron spray when followed by 2,4-D application caused a significant height increase. This suggested that the effective concentration of 2,4-D had been lowered by the iron. These observations are discussed in the light of recent publications on the role of metal chelation in auxin action.

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