Effect of combined nitrogen on the distribution pattern of photosynthetic assimilates in nodulated soybean plant as revealed by¹⁴c

Abstract

A general relationship was found between combined nitrogen nutrition and translocation pattern of "C assimilates in an experiment carried out in greenhouse with soybean plant grown in nitrogen-free water culture and supplied with 40 ppm N in the form of NOs-or NH. + for 1 week before exposure to "C02 at initial pod filling stage.The longest the cold chase time after "C02 exposure, the highest the percentage of total recovered .. c was translocated from the leaves to the different plant parts. Ammonium cecreased the capacity of leaves for exportation of labeled photosynthates. A relatively high percentage of total recovered "c was observed in the stems and pods of NOs--treated plants as compared to NH. + -treated plants, and the opposite was true with root system. In different plant parts except nodules, nitrate-treated plants had high specific radioactivities and ammonium-treated plants had low specific radioactivities compared with control. Among the different plant parts other than leaves, pods showed the highest specific radioactivity particularly with nitrate treatment. Specific radioactivity of nodules was lower than that for roots. Both nitrate and ammonium decreased the share of photosynthates distributed in nodules. Additional Index Words: nitrate, ammonium, dry matter, "C02 ,

Effect of Nitrate in the Rooting Medium on Carbohydrate Composition of Soybean Nodules

“…One of the main sources of support for the concept that nitrate inhibits the growth and activity of nodules by limiting the availability of carbohydrates comes from studies showing a reduction in the proportion of '4C in nodules from 14CO2 assimilated by shoots when plants are supplied with nitrate (10,14,18). These results may be explained without invoking a carbohydrate deprivation hypothesis if nitrate inhibits nodule growth and/or function by some mechanism unrelated to carbohydrate and lowers the demand for carbohydrate in nodules.…”

“…' The concept that the negative effect of nitrate on nodule development is mediated via a reduction in carbohydrate accumulation in nodules has recently been rediscovered (6,11,17,18). Most of the recent support for the conce?t has been derived from demonstrations that the proportion of' CO2 assimilated by shoots which is transported to nodules is reduced when plant roots are supplied with nitrate (10,14,18). Wong has shown recently that supplying sugars with nitrate to nodulated lentil roots nullifies the negative effect of nitrate on specific acetylene reduction activity of nodules (25).…”

Influence of ammonium: Nitrate ratios on the growth and nitrogen uptake of pearl millet

“…Chlorosis and necrosis of leaves, epinasty, and stem lesions are also manifestations of ammonium toxicity (13,14,15). Ammonium nutrition has also been found to decrease the capacity of leaves for exportation of photosynthates (17). Ammonium can be an effective, reversible uncoupler of photosynthetic phosphorylation (18).…”

Systemic and local effects of long-term application of nitrate on nodule growth and N2fixation in soybean (Glycine max[L.] Merr.)

“…The local and rapid nitrate inhibition on nodule growth and nitrogen fixation was attributed to the decrease in the photoassimilate flux into nodules, COlTesponding to the increase in photoassimilate utilization in roots (Latimore et al 1977;Rabie et al 1980;Kouchi et al 1986;Vessey et al 1988;Fujikake et al 2003). Also the decrease in nitrogen fixation activity may be related to the decrease in 02 permeability caused by nitrate accumulation in the nodule cortex (Becana et al 1989;Vessey and Waterer 1992;Mizukoshi et al 1995) or the decrease in sucrose utilization which reduced nodule respiration and energy supply (Gordon et al 2(02).…”