Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/2/1996
Publication Date: N/A
Interpretive Summary: The absorption of mineral nutrients by plants is important for crop plant productivity and nutritional quality. Potassium (K) is the mineral nutrient that is maintained in plant cells at the highest concentrations. It is essential for plant growth and development, yet its transport is still poorly understood. This paper reviews the recent breakthroughs in the cloning of genes encoding plant K+ transporters in the leaf and root. At this time, there are gaps in our understanding of how these transporters function to provide this essential element to the plant. The recent molecular research has demonstrated that there are a number of different types of K transporters in plants, and some of these only function in certain cell types or plant organs. Also, the different transporters are regulated in different ways. The significance of these findings is that we are beginning to realize that plant K transport, which is often used as a model system for studying mineral transport in plants, is much more comple than previously thought. Only through research that integrates molecular approaches with research focusing on the whole plant will we gain a more complete understanding of how plants acquire and utilize this essential mineral nutrient.
Technical Abstract: The kinetics and characteristics of malate degradation were studied in four acid soils ranging in both pH(4.30 to 5.00) and vegetation type. The breakdown of malate was rapid in all soils with a half life of approximately 1.7 h, Km of 1.7 mM and Vmax of 70 nmol g-1 soil h-1. No relationship was observed between malate decomposition rate and pH. Co- metabolism studies with other C and N substrates (glucose, glycine, glutamate, citrate and succinate) indicated that the microorganisms were not N limited and competitive inhibition of malate breakdown was only observed in the presence of succinate. Studies with isolated mixed bacterial cultures indicated that the bacterial malate uptake was mediated by an energy dependent, dicarboxylate transporter which can be inhibited by succinate and is independent of pH between pH 5.0 and 7.0. The Km and Vmax parameters ranged from 279-955 yM and 0.1-17 ymol mg-1 protein h-1 for the mixed bacterial cultures depending on the bacteria's previous C source. Th results indicate that in acid topsoils where microbial populations are high, the microbes may provide a considerable sink for organic acids. If organic acids are being released by roots in response to an environmental stress (e.g. Al toxicity, P deficiency) it can be expected that the efficiency of these root mediated metal resistance mechanisms will be markedly reduced by rapid microbial degradation.