The effect of ammonium and nitrate on carbondioxide compensation point and enzymes associated with carbondioxide exchange in wheat

Abstract

The carbondioxide compensation point (Γ), dry matter production, and the activities of nitrate reductase (NR), glycolate oxidase (GO), ribulose 1,5-bisphosphate carboxylase (RuBPC) and phosphoenolpyruvate carboxylase (PEPC) were measured in wheat, grown on media, containing nitrate or ammonium. Significantly higher Γ and lower dry matter was observed in plants supplied with ammonium-nitrogen (NH4-N), as compared to those supplied with nitrate-nitrogen (NO3-N). The activities of NR and PEPC were higher in plants grown on NO3-N than to those grown on NH4-N. There were no significant differences in the activities of GO and RuBPC irrespective of whether NO3-N or NH4-N was supplied. None of the enzymes was found to be associated directly with the Γ.PEPC activity accounted the measured differences in the Γ and biomass production between NH4-N and NO3-N supplied plants. The relationship between PEPC and the Γ is discussed.

In vivo phosphoenolpyruvate carboxylase activity is controlled by CO2 and O2 mole fractions and represents a major flux at high photorespiration rates

“…That is, it probably leads to a misestimation of the compensation point. In fact, a relationship has been found between PEPC activity in leaf extracts and observed CO 2 compensation point in wheat (Sharma & Sirohi, ). By contrast, P varies with CO 2 mole fraction (present work) and thus participates in the variation of apparent assimilation and, as such, should not compromise R d estimation (provided R d remains constant regardless of CO 2 mole fraction, an assumption that might be incorrect; Tcherkez et al ., ).…”

“…However, the result probably depends on physiological conditions such as nitrogen metabolism, and not only O 2 /CO 2 . Typically, nitrate availability affects leaf PEPC activity (Sharma & Sirohi, ). In addition, PEP can be used by secondary metabolism.…”

Genotypic variations in activities of phosphoenolpyruvate carboxylase and correlations with leaf photosynthetic characteristics and crop productivity of cassava grown in low-land seasonally-dry tropics

“…Moreover, activities of PEPC, CO 2 compensation concentration (Γ), and dry matter production of the C 3 wheat (Triticum aestivum L.) cv. Sonalika, were found to be affected by the form of nitrogen fertiliser (Sharma and Sirohi 1988). Compared to NH 4 -N grown plants, NO 3 -N grown plants had statistically significant higher PEPC activities, lower Γ, and higher dry matter (DM) production.…”

Whole Leaf Carbon Exchange Characteristics of Phosphate Deficient Soybeans (Glycine max L.)

“…The CO2 compensation point can increase with environmental conditions such as low N (14), N source (25), high leaf temperature (3), high 02 concentration, seasonal variation, and leaf age (3). Whereas the increase in the CO2 compensation point was about 1.5 Pa for N-stressed barley (14), we observed an increase of 5.0 Pa for Pi-stressed soybean leaves, yet Pi-stressed spinach showed no shift in the compensation point (6).…”