Estimation of Carbon and Nitrogen Allocation during Stalk Elongation by ¹³C and ¹⁵N Tracing in Zea mays L.

Abstract

Zea mays L. (cv Dea) plants grown to the stage of stalk elongation, were allowed to assimilate 13C02 and 15N-nitrates from 45 to 53 days after sowing. Isotopic abundances in labeled nutrients were slightly enriched compared to natural abundances. The new C in plant was acropetally distributed and the new N was preferentially accumulated in the sheath and stalk in the medium region. C input was 25-fold higher than N input. The new C in total plant C was 20%, whereas it was 10% for N. The stalk acted as a major sink because it accumulated, respectively, 27.5 and 47.5% of the C and N inputs. The new C in soluble carbohydrates was 76% in growing organs (upper stalk) and only 39% in source leaves, whereas it was 43% and 13% in starch, respectively. New N in nitrates+amino-acids spanned in the range from 20% (leaf) to 50% (stalk). New C and N in soluble proteins were, respectively, 13.4 and 3.8% in leaves, 8.8 and 9.6% in stalk, and 8.7 and 14.3% in roots. In the middle stalk and leaves, the proteins and carbohydrates represent an equivalent C and N source for remobilization.Plant growth and seed production of grain crops are the result of the photosynthetic ability of source leaves and the integrated processes of allocation, accumulation and utilization of assimilated carbon at the whole plant level (14). Efficient translocation of photoassimilates to sink organs is one of the key factors in increasing production (14, 27). C and N metabolism are closely linked, so both should be considered when attempting to determine factors that limit efficient translocation. Recently, attention has been paid to relationships between C and N metabolism in the productivity of maize (1,26,28). However, only a few data are available on 13C and '5N redistribution in the Graminae (18), and little information is available for maize (8). Our interest was focused on C and N allocation in the stalk. This organ acts first as a sink during elongation and then as a source when ears develop (1, 23). We used here a CO2 assimilation system designed for long-time incorporation of C at a constant '3C

C and N Mobilization from Stalk and Leaves during Kernel Filling by 13C and 15N Tracing in Zea mays L.

“…Proteins would represent such dynamic storage metabolite, due to their turnover. In contrast, in our experiment, starch is a small storage compound and had a low turnover (4). This could be explained by the morphology of starch granules made of concentric layers (2).…”

“…Maize plants (Zea mays L., cv Dea) were grown in a greenhouse for 45 d. Control plants were maintained in the greenhouse while 15 other plants were put in a climatic chamber to assimilate '3C02 (1.2889 13C atom %) at 450 ppm in a controlled atmosphere and '5N-nitrates (1.9643 '5N atom %) in the nutrient solution (4), for an 8-d exposure. After the labeling, 3 plants were harvested and the 12 remaining plants continued their development in the greenhouse under previous conditions.…”

“…After the labeling, 3 plants were harvested and the 12 remaining plants continued their development in the greenhouse under previous conditions. The whole experimental procedure is detailed further in a previous paper (4). The use of stable isotope labeling at the natural abundance range and its use for estimation ofthe long-term partitioning was described previously (8,9).…”

Respiratory Carbon Metabolism following Illumination in Intact French Bean Leaves Using 13C/12C Isotope Labeling

“…Refixation of CO 2 produced in the light by photorespiration is probably not a problem in the above studies, although it can obscure the results when studying fluxes in a given pathway, i.e. the photorespiratory pathway, where knowledge of the specific radioactivity of the carbon feeding the pathway must be accurately known (Biehler and Fock, 1996).In darkened leaves, the measurements of 14 C labeling in respired CO 2 are scarce: Birecka et al (1969) found that the radioactivity of the respired CO 2 from the main shoot increased in wheat plants deprived of the ear, indicating that carbon losses in the last period of wheat development are due to more intensive respiration; Bort et al (1996), feeding ears and flag leaves of durum wheat (Triticum durum) with 14 C-labeled Suc and trapping the 14 CO 2 released by respiration, concluded that the apparent refixation of respiratory CO 2 in the ears was double that measured in the flag leaves; Goren et al (2000) showed that the radioactivity in the respired CO 2 was lower than 2% in citrus juice cells fed with [ (2002) showed that the total rate of respiration (as the sum of decarboxylation of stores and primary photosynthates) was not affected by light in cereals.Labeling techniques using 13 CO 2 have been used to study plant accumulation of assimilates and its relationship with seed storage mobilization (Cliquet et al, 1990a(Cliquet et al, , 1990bMaillard et al, 1994) or to examine the refixation of respiratory CO 2 in wheat ear (Gebbing and Schnyder, 2001, although CO 2 respired was not measured directly). At the whole-plant scale, Avice et al (1996) used the 13 C labeling in alfalfa (Medicago sativa) to show that the main 13 CO 2 loss involved root respiration.…”

“…Labeling techniques using 13 CO 2 have been used to study plant accumulation of assimilates and its relationship with seed storage mobilization (Cliquet et al, 1990a(Cliquet et al, , 1990bMaillard et al, 1994) or to examine the refixation of respiratory CO 2 in wheat ear (Gebbing and Schnyder, 2001, although CO 2 respired was not measured directly). At the whole-plant scale, Avice et al (1996) used the 13 C labeling in alfalfa (Medicago sativa) to show that the main 13 CO 2 loss involved root respiration.…”