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UBC Theses and Dissertations

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UBC Theses and Dissertations

The regulation of phosphate uptake by intact barley plants Lefebvre, Daniel Denis


The study of phosphate influx in roots of intact barley (Hordeum vulgare L. var. Bonanza) revealed the presence of two distinct regulatory processes for phosphate absorption. One of these processes, which was elicited in response to phosphate deprivation, in the form of enhanced phosphate uptake, became evident between 11 and 13 days after germination. At 16 days the uptake rates of these plants had reached a maximum value at 2.43μmol/g.f.wt./hour which compared to a value of 0.39μmol/g.f.wt./hour for phosphate sufficient plants. Simultaneously, differences between the respective treatments were also noted in growth rates and phosphate pools. A second regulatory process brought about a rapid reduction of phosphate influx upon the provision of orthophosphate to plants previously starved of phosphate during the phase of enhanced uptake. Within hours of supplying inorganic phosphate to these plants influx was reduced by greater than 50% and during this period influx values were linearly correlated with root orthophosphate concentrations. The time scale of this second response is suggestive of an allosteric inhibition of influx by internal orthophosphate levels. Both regulatory systems studied represented physiological adaptations which would better enable plants, under field conditions, to obtain a sufficient phosphate supply. Severe phosphorus deprivation eventually resulted in a morphological response such as the production of longer, narrower roots providing, the plants a greater surface area, presumably for greater phosphate absorption. At a later time, an increased formation of root-hairs resulted in even greater surface area modification.

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