Kinetics and relative significance of remobilized and current C and N incorporation in leaf and root growth zones of Lolium perenne after defoliation: assessment by 13C and 15N steady-state labelling

Autor: H. Vianden, R. De Visser, Hans Schnyder
Rok vydání: 1997
Předmět:
Zdroj: Plant, Cell & Environment 20 (1997)
Plant, Cell & Environment, 20, 37-46
ISSN: 1365-3040
0140-7791
DOI: 10.1046/j.1365-3040.1997.d01-9.x
Popis: The contribution of pre-defoliation reserves and current assimilates to leaf and root growth was examined in Lolium perenne L. during regrowth after defoliation. Differential steady-state labelling with 13 C (CO 2 with δ 13 C = -0.0281 and -0.0088) and 15 N (NO 3 - with 1.0 and 0.368 atom percentage, i.e. δ 15 N = 1.742 and 0.0052, respectively) was applied for 2 weeks after defoliation. Rapidly growing tissues were isolated, i.e. the basal elongation and maturation zones of the most rapidly expanding leaves and young root tips, with a biomass turnover rate > 1 d -1 . C and N weights of the elongation zone showed a transient decline. The dry matter and C concentration in fresh biomass of leaf growth zones transiently decreased by up to 25% 2 d after defoliation, while the N concentration remained constant. This 'dilution' of growth zone C indicates a decreased net influx of carbohydrates relative to growth-related influx of water and N in expanding cells, immediately after defoliation. Recovery of the total C and N weights of the leaf elongation zone coincided with net incorporation of currently absorbed C and N, as shown by the kinetics of δ 13 C and atom percentage 15 N in the growth zones after defoliation. C isotope discrimination (Δ 13 C) in leaf growth zones was about 23‰, 1-2‰ higher than the Δ in root tips. Δ 15 N in the leaf and root growth zones was 10 ± 3‰. The leaf elongation zones (at 0-0.03 m from the tiller base) and the distant root tips (about 0.2 m from the base) exhibited similar kinetics of current C and N incorporation. The amount of pre-defoliation C and N in the growth zones, expressed as a fraction of total C and N, decreased from 1.0 to 0.5 at 3 (C) and 5 (N) d after defoliation, and to 0.1 at 5 (C) and 14 (N) d after defoliation. Thus, the dependence of growth zones on current assimilate supply was significant, and stronger for C than for N. The important roles of current assimilates (as compared to pre-defoliation reserves) and 'dilution' of dry matter in regrowth after defoliation are discussed in relation to the method of labelling and the functional and morphological heterogeneity of shoot tissues.
Databáze: OpenAIRE
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