Fluxes of Reserve-Derived and Currently Assimilated Carbon and
Nitrogen in Perennial Ryegrass Recovering from Defoliation. The
Regrowing Tiller and Its Component Functionally Distinct
Zones1
Hans Schnyder* and
Ries de Visser
Chair of Grassland Science, Technische Universität
München, D-85350 Freising-Weihenstephan, Germany (H.S.); Research Institute of Agrobiology and Soil Fertility (AB-DLO),
P.O. Box 14 NL-6700 AA Wageningen, The Netherlands (R.d.V.); and Institut für Pflanzenbau, Universität Bonn, Katzenburgweg
5, D-53115 Bonn, Germany (H.S.)
The quantitative significance of
reserves and current assimilates in regrowing tillers of severely
defoliated plants of perennial ryegrass (Lolium perenne
L.) was assessed by a new approach, comprising C/12C and 15N/14N
steady-state labeling and separation of sink and source zones. The
functionally distinct zones showed large differences in the kinetics of
currently assimilated C and N. These are interpreted in terms of
"substrate" and "tissue" flux among zones and C and N turnover
within zones. Tillers refoliated rapidly, although C and N supply was
initially decreased. Rapid refoliation was associated with (a)
transient depletion of water-soluble carbohydrates and dilution of
structural biomass in the immature zone of expanding leaves, (b) rapid
transition to current assimilation-derived growth, and (c) rapid
reestablishment of a balanced C:N ratio in growth substrate. This
balance (C:N, approximately 8.9 [w/w] in new biomass) indicated
coregulation of growth by C and N supply and resulted from
complementary fluxes of reserve- and current assimilation-derived C and
N. Reserves were the dominant N source until approximately 3 d
after defoliation. Amino-C constituted approximately 60% of the net
influx of reserve C during the first 2 d. Carbohydrate reserves
were an insignificant source of C for tiller growth after d 1. We
discuss the physiological mechanisms contributing to defoliation tolerance.
1
This work was supported by the Commission of the
European Communities, Directorate General VI for Agriculture, Divison
for the Coordination of Agricultural Research, Brussels, Belgium (grant no. GT920078 to R.d.V.), and the Deutsche Forschungsgemeinschaft (grant
no. SFB 607).
*
Corresponding author; e-mail
schnyder{at}romeo.grass.agrar.tu-muenchen.de; fax 49-8161-713243.
Plant Physiol. (1999) 119: 1423-1436
Copyright Clearance Center: 0032-0889/99/119//14
© 1999 American Society of Plant Physiologists
