Regulation of sulfate metabolism in C4 plants: A whole plant perspective

Plants usually acquire sulfur, which is an essential macronutrient for the proper taste, smell and color of crop products, as sulfate. The availability of sulfate is, however, often suboptimal and hence sulfur availability limits crop yield and quality across the world. To improve sulfur fertilizer levels, a detailed understanding of the regulation of sulfate uptake and reduction is crucial. It is particularly important to appreciate this regulation in plants that employ C4 photosynthesis, since C4 crops may be increasingly cultivated. Research has, however, been focused on plants that employ C3 photosynthesis. Findings cannot simply be generalized from C3 to C4 plants, for these plants differ considerably in their physiology. Thus, my dissertation addresses the regulation of sulfate uptake and reduction in C4 plants.
I first emphasize the need for plant sulfur research by showing that sulfate deprivation is associated with the production of aberrant floral displays. Subsequently, I analyze the regulation of sulfate uptake and reduction at the whole plant level by exposing plants to atmospheric hydrogen sulfide (H2S). I observed that plants differ considerably in their response to gaseous H2S, though C3 and C4 plants did not respond distinctively to atmospheric H2S. Therefore, I conclude that the whole plant regulation of sulfate uptake and reduction profoundly differs among plants, but that C3 and C4 photosynthesis are not associated with markedly different types of this regulation. To understand the variation in whole plant sulfate metabolism, I recommend to conduct physiological experiments (instead of molecular biological experiments). I argue that regulatory mechanisms at the molecular level have no direct significance in determining the whole plant regulation of sulfate uptake and reduction.