Open AccessEffects of Altered Carbohydrate Availability on Whole-Plant Assimilation of 15NO3−
Author(s) -
Thomas W. Rufty,
Charles T. MacKown,
Richard J. Volk
Publication year - 1989
Publication title -
plant physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.554
H-Index - 312
eISSN - 1532-2548
pISSN - 0032-0889
DOI - 10.1104/pp.89.2.457
Subject(s) - darkness , shoot , nicotiana tabacum , assimilation (phonology) , carbohydrate , respiration , botany , photosynthesis , chromosomal translocation , zoology , biology , chemistry , horticulture , biochemistry , linguistics , philosophy , gene
An experiment was conducted to investigate the relative changes in NO(3) (-) 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 (15)NO(3) (-) for 6 hour intervals during a normal 12 hour light period and a subsequent period of darkness lasting 42 hours. Uptake of (15)NO(3) (-) 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 (15)NO(3) (-) assimilation processes, which were distinctly different than those in (15)NO(3) (-) uptake. During the extended dark period, translocation of absorbed (15)N out of the root to the shoot varied rhythmically. The adjustments were independent of (15)NO(3) (-) 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 (15)NO(3) (-) always was limited more than uptake. The assimilation of (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 (15)NO(3) (-) reduction and synthesis of insoluble reduced-(15)N even when (15)NO(3) (-) uptake was severely restricted and minimal carbohydrate reserves remained in the tissue.