Effects of altered carbohydrate availability on whole-plant assimilation of sup 15 NO sub 3 sup minus 1
- North Carolina State Univ., Raleigh (USA)
- Univ. of Kentucky, Lexington (USA)
An experiment was conducted to investigate the relative changes in NO{sub 3}{sup {minus}} assimilatory processes which occurred in response to decreasing carbohydrate availability. Young tobacco plants (Nicotiana tabacum (L.), cv NC 2326) growing in solution culture were exposed to 1.0 millimolar {sup 15}NO{sub 3}{sup {minus}} for 6 hour intervals during a normal 12 hour light period and a subsequent period of darkness lasting 42 hours. Uptake of {sup 15}NO{sub 3}{sup {minus}} decreased to 71 to 83% of the uptake rate in the light during the initial 18 hours of darkness; uptake then decreased sharply over the next 12 hours of darkness to 11 to 17% of the light rate, coincident with depletion of tissue carbohydrate reserves and a marked decline in root respiration. Changes also occurred in endogenous {sup 15}NO{sub 3}{sup {minus}} assimilation processes, which were distinctly different than those in {sup 15}NO{sub 3}{sup {minus}} uptake. During the extended dark period, translocation of absorbed {sup 15}N out of the root to the shoot varied rhythmically. The adjustments were independent of {sup 15}NO{sub 3}{sup {minus}} uptake rate and carbohydrate status, but were reciprocally related to rhythmic adjustments in stomatal resistance and, presumably, water movement through the root system. Whole plant reduction of {sup 15}NO{sub 3}{sup {minus}} always was limited more than uptake. The assimilation of {sup 15}N into insoluble reduced-N in roots remained a constant proportion of uptake throughout, while assimilation in the shoot declined markedly in the first 18 hours of darkness before stabilizing at a low level. The plants clearly retained a capacity for {sup 15}NO{sub 3}{sup {minus}} reduction and synthesis of insoluble reduced-{sup 15}N even when {sup 15}NO{sub 3}{sup {minus}} uptake was severely restricted and minimal carbohydrate reserves remained in the tissue.
- OSTI ID:
- 7190378
- Journal Information:
- Plant Physiology; (USA), Vol. 89:2; ISSN 0032-0889
- Country of Publication:
- United States
- Language:
- English
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CARBOHYDRATES
BIOLOGICAL EFFECTS
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METABOLISM
BIOLOGICAL PATHWAYS
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TOBACCO
TRACER TECHNIQUES
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ISOTOPE APPLICATIONS
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NITROGEN COMPOUNDS
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551001* - Physiological Systems- Tracer Techniques