Nitrate carrier induction and characterization in maize root plasma membrane using chlorate-36 as a radiotracer analog for nitrate
Lu, Qin
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Permalink
https://hdl.handle.net/2142/22116
Description
Title
Nitrate carrier induction and characterization in maize root plasma membrane using chlorate-36 as a radiotracer analog for nitrate
Author(s)
Lu, Qin
Issue Date
1992
Doctoral Committee Chair(s)
Briskin, Donald P.
Department of Study
Crop Sciences
Discipline
Crop Sciences
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Agriculture, Agronomy
Biology, Plant Physiology
Language
eng
Abstract
Previous studies with intact maize plants have shown an apparent induction of nitrate uptake capacity when plants are transferred to a nitrate containing nutrient solution. Whether this phenomenon reflects a change in nitrate carrier activity at the membrane level or an effect of nitrate metabolism has not been determined as yet due to the complexity of investigating nitrate transport with intact tissue. The use of a membrane vesicle approach has also been limited by the time associated with conventional membrane isolation methods. In this study, an improved plasma membrane isolation method was developed and made it possible to investigate plasma membrane nitrate carrier activity at the membrane level.
Induction studies were conducted with isolated plasma membrane vesicles and $\rm \sp{36}{\rm ClO}\sb3\sp-$ as a radiotracer analog for nitrate. When plasma membrane fractions were prepared from maize roots during the induction timecourse and $\Delta$pH-driven $\rm \sp{36}{\rm ClO}\sb3\sp-$ uptake (H$\sp+$ co-transport) was examined, radiotracer uptake for the isolated vesicles dramatically increased over the first 2 hours following nitrate treatment. When nitrate was removed from the nutrient solution, $\Delta$pH-driven $\rm \sp{36}{\rm ClO}\sb3\sp-$ uptake decreased by one-half within about 3 hours. NAD(P)H effects on $\rm \sp{36}{\rm ClO}\sb3\sp-$ uptake were also investigated using isolated plasma membrane vesicles. Root plasma membrane associated nitrate reductase represented only 0.45% of the total nitrate reductase activity of root tissue. The results suggest that plasma membrane associated nitrate reductase activities are either insignificant or not related to nitrate transport.
The specificity of PGO, vanadate (VO$\sb4\sp{-3}),$ and tungstate (WO$\sb4\sp{-2})$ inhibition was examined for the plasma membrane H$\sp+$-ATPase, nitrate carrier, nitrate reductase, and nitrate reductase transcription. The results indicate that these proteins display some similarities. The degree of inhibition was time, concentration, location, and specific inhibitor dependent. As such it cannot be argued that these chemicals can be used to specifically block the activity of these enzymes in intact tissue during transport studies.
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