Carbohydrate Supply and N₂ Fixation in Soybean

Abstract

ABSTRACIWhen arrival of shoot supplied carbohydrate to the nodulated root system of soybean was interrupted by stem girdling, stem chilling, or leaf removal nodule carbohydrate pools were utilized, and a marked decline in the rates of CO2 and H2 evolution was (11,12,16,28) and are therefore unlikely to play a role in the support of nodule respiration. However, nodule starch and sugar levels decline under conditions of carbohydrate limitation (15,22,25)

Partitioning of 14C‐labelled photosynthate to developing nodules and roots of soybean (Glycine max)

“…Second, regulation of maturation of nodule meristems into functional nodules might involve short distance and systemic interactions (CaetanoAnolles et al 1991 ;Francisco & Akao, 1993), as well as physiological controls imposed by the availability of carbon (Kosslak & Bohlool, 1984) and nitrogen (Atkins et al, 1989) for nodule development. The dependence of N^ fixation on the supply of carbohydrate from photosynthesis has been clearly demonstrated (Walsh, Vessey & Layzel, 1987). Singleton & van Kessel (1987) showed that, in the absence of mineral N, C flow to roots and nodules was affected by the export of fixed N from nodules.…”

Glycolytic Flux Is Adjusted to Nitrogenase Activity in Nodules of Detopped and Argon-Treated Alfalfa Plants1

“…Walsh et al (1987) showed that the decline in nitrogenase activity caused by stemgirdling coincided with a decline in the total soluble-sugar content of nodules. Vessey et al (1988) found that the decline in nitrogenase activity caused by NO 3 Ϫ treatment coincided with a decrease in the size of the nodule starch pool and in the partitioning of the 14 C-labeled photosynthate to nodules.…”

“…There has been considerable interest in the possible involvement of nodule carbohydrates, particularly Suc, in the regulation of nitrogenase activity and nodule O 2 permeability (Walsh et al, 1987;Vessey et al, 1988;Weisbach et al, 1996;Gordon et al, 1997). Walsh et al (1987) showed that the decline in nitrogenase activity caused by stemgirdling coincided with a decline in the total soluble-sugar content of nodules.…”

“…Nitrogenase is O 2 labile, but the root nodule provides an environment that protects it from excess O 2 . Nitrogenase activity in legume root nodules is rapidly inhibited by treatments that affect plant C and N metabolism, such as exposure of the roots to C 2 H 2 , replacement of N 2 in the rhizosphere with Ar, NO 3 Ϫ fertilization, defoliation, detopping, phloem girdling, and drought (Minchin et al, 1983Sheehy et al, 1983;Witty et al, 1984Witty et al, , 1986Carroll et al, 1987;Durand et al, 1987;Hartwig et al, 1987Hartwig et al, , 1990Hartwig et al, , 1994Hunt et al, 1987;Walsh et al, 1987;Schuller et al, 1988;Vessey et al, 1988;Guérin et al, 1990;King and Layzell, 1991;Denison et al, 1992;Diaz del Castillo et al, 1992Heim et al, 1993;Drevon and Hartwig, 1997). In most cases the decline in nitrogenase activity can be overcome by increasing the O 2 concentration in the rhizosphere.…”

“…Previous studies have shown that the decline in nitrogenase activity due to phloem girdling, NO 3 Ϫ fertilization, and defoliation is associated with depletion of nodule Suc and starch pools (Walsh et al, 1987;Vessey et al, 1988;Weisbach et al, 1996), but it is still controversial whether the decline in nodule Suc and starch pools is the cause of the decline in nitrogenase activity or whether it reflects the decreased carbohydrate-sink strength of the nodules once nitrogenase activity has already declined. Part of the reason for this ambiguity is the fact that nodule Suc and starch pools are relatively large.…”