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Diurnal Fluctuations of Nitrate Uptake and In Vivo Nitrate Reductase Activity in Pima and Acala Cotton
Author(s) -
Aslam M.,
Travis R.L.,
Rains D.W.
Publication year - 2001
Publication title -
crop science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.76
H-Index - 147
eISSN - 1435-0653
pISSN - 0011-183X
DOI - 10.2135/cropsci2001.412372x
Subject(s) - nitrate reductase , darkness , biology , nitrate , diurnal cycle , zoology , botany , fiber crop , horticulture , gossypium hirsutum , ecology , climatology , geology
This study was conducted to determine whether diurnal fluctuations of nitrate reductase activity in two cotton species, Pima ( Gossypium barbadense L.) and Acala ( Gossypium hirsutum L.), are regulated by NO − 3 uptake or leaf NO − 3 concentration. The two species differ greatly in their N use efficiency. The seedlings were grown for 25 d in nutrient solutions containing 0.05, 0.10 or 1.0 m M NO − 3 under a 14‐h light/10‐h dark cycle at 30°C/20°C. Uptake rates were measured by following NO − 3 depletion from the uptake solutions at 20°C or 30°C. Nitrate reductase activity (NRA) in fully expanded first true leaves was determined by an anaerobic method in vivo. Upon illumination uptake rates for both species, measured at 30°C, increased until they plateaued in about 5 h and were maintained at that level for the remainder of the light period and the following dark cycle. When measured at 20°C in the dark, however, the uptake rates decreased 25 to 30% for the first 3 h and then remained constant. Leaf NRA increased rapidly during the first hour of illumination, reached a plateau and then decreased after 4 to 6 h of illumination. The decline was more rapid when NRA was assayed in the absence of NO − 3 In darkness, NRA levels were low and did not fluctuate. Upon illumination, leaf NO − 3 concentration also increased for about 7 h and then decreased gradually. The results indicate that (i) the diurnal rhythm of NO − 3 uptake is modulated by temperature rather than by light/dark transitions, and (ii) while the increase in NRA upon illumination may be regulated by NO − 3 flux from roots to shoots, the decrease in NRA under prolonged illumination is independent of that flux.