Coordinated nitrogen and carbon remobilization for nitrate assimilation in leaf, sheath and root and associated cytokinin signals during early regrowth of Lolium perenne.
The efficiency of N assimilation in response to defoliation is a critical component of plant regrowth and forage production. The aim of this research was to test the effect of the internal C/N balance on NO3- assimilation and to estimate the associated cytokinin signals following defoliation of perennial ryegrass ( Lolium perenne L. 'Grasslands Nui') plants.



Plants, manipulated to have contrasting internal N content and contrasting availability of water soluble carbohydrates (WSCs), were obtained by exposure to either continuous light or short days (8:16 h light-dark), and watered with modified N-free Hoagland medium containing either high (5 m m ) or low (50 μ m ) NO3- as sole N source. Half of the plants were defoliated and the root, sheath and leaf tissue were harvested at 8, 24 and 168 h after cutting. The spatiotemporal changes in WSCs, synthesis of amino acids and associated cytokinin content were recorded after cutting.



Leaf regrowth following defoliation involved changes in the low- and high-molecular weight WSCs. The extent of the changes and the partitioning of the WSC following defoliation were dependant on the initial WSC levels and the C and N availability. Cytokinin levels varied in the sheath and root as early as 8 h following defoliation and preceded an overall increase in amino acids at 24 h. Subsequently, negative feedback brought the amino acid response back towards pre-defoliation levels within 168 h after cutting, a response that was under control of the C/N ratio.



WSC remobilization in the leaf is coordinated with N availability to the root, potentially via a systemic cytokinin signal, leading to efficient N assimilation in the leaf and the sheath tissues and to early leaf regrowth following defoliation.
School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand.
Jessica
J
Roche
School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand.
Matthew H
MH
Turnbull
School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand.
Qianqian
Q
Guo
Laboratory of Growth Regulators, Centre of the Region Haná for Biotechnological and Agricultural Research, Institute of Experimental Botany CAS & Faculty of Science of Palacký University, Šlechtitelu 27, 783 71 Olomouc, Czech Republic.
Ondrej
O
Novák
Swedish Metabolomics Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences KBC, Umeå University, Linnéus väg, SE-90182 Umeå, Sweden.
Jana
J
Späth
School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand.
Steven P
SP
Gieseg
School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand.
Paula E
PE
Jameson
School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand.
Jonathan
J
Love
D002244:Carbon / Q000378:metabolism*; D003583:Cytokinins / Q000378:metabolism*; D008129:Lolium / Q000254:growth & development / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D018515:Plant Leaves / Q000254:growth & development* / Q000378:metabolism; D018517:Plant Roots / Q000254:growth & development / Q000378:metabolism
D003583:Cytokinins; D002244:Carbon; D009584:Nitrogen
Lolium perenne; Nitrogen; assimilation; cytokinin; defoliation; nitrate; regrowth; water-soluble carbohydrates