| dc.description.abstract | Inorganic phosphate (Pi) is an essential nutrient that plants must acquire from soil via
their roots and then distribute to all other organs, cells, and subcellular organelles to sustain
growth and development. However, Pi limits worldwide crop productivity due to its low
bioavailability. Because Pi mined for fertilizers is a finite and nonrenewable resource, a
comprehensive understanding of how plants acquire, store, recycle, and distribute this nutrient is
urgently needed to develop crops that maintain high yields with minimal Pi input. In this work, I
used genetically encoded Forster Resonance Energy Transfer (FRET)-based biosensors and
confocal microscopy to measure Pi concentrations in Arabidopsis thaliana roots with high spatial
and temporal resolution. I found distinct spatial patterns for Pi uptake, recycling, and vacuolar
sequestration. These processes were distinguished through the novel use of cyanide and mutant
comparisons. Cyanide blocked Pi assimilation into ATP to reveal a rapid increase in cytosolic Pi
concentration due to metabolic recycling. Additional gains in cytosolic Pi levels were detected
upon addition of exogenous Pi and I attributed these to uptake. Similar experiments conducted
with a vacuolar Pi transport mutant, pht5;1, (defect in vacuolar uptake) suggested that less Pi
sequestration occurs in cells of the transition zone than in cells of the flanking developmental
zones. Thus, I demonstrated that developmental control of vacuolar Pi sequestration is a major
determinant of the steady-state Pi distribution pattern in root cytosol. Additionally, I measured
relative ATP levels and dynamics in different root developmental zones, which confirmed a
correlation between cytosolic Pi and ATP levels. I also analyzed cytosolic Pi dynamics in root
hairs, which revealed that Pi gradients exist in root hairs with highest Pi levels at the tip. I showed that this gradient is established through high Pi uptake and low vacuolar sequestration at
the hair tip. | en |
