AOBPreview originally published online on October 26, 2007
Annals of Botany 2008 101(1):135-144; doi:10.1093/aob/mcm270
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Changes in the Synthesis of Rubisco in Rice Leaves in Relation to Senescence and N Influx
Department of Applied Plant Science, School of Agricultural Sciences, Tohoku University, 1-1 Tsutsumidori-Amamiyamachi, Aoba-ku, Sendai 981-8555, Japan
* For correspondence. Present address: Weed Science Center, Utsunomiya University, 350 Mine, Utsunomiya, Tochigi 321, Japan. E-mail j113241{at}yahoo.co.jp
Received: 16 July 2007 Returned for revision: 17 August 2007 Accepted: 4 September 2007 Published electronically: 26 October 2007
Background and Aims: The amount of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4·1·1·39) synthesized in a leaf is closely correlated with N influx into the leaf throughout its lifetime. Rubisco synthesis and N influx are most active in the young leaf during expansion, but are very limited in the senescent leaf. However, it is not established whether Rubisco synthesis can be observed if N influx is increased, even in a very senescent leaf. This study first investigated changes in the relationships between rbcS and rbcL mRNA contents and Rubisco synthesis per unit of leaf mass with leaf senescence. Next, leaves were removed during late senescence, to examine whether Rubisco synthesis is re-stimulated in very senescent leaves by an increase in N influx.
Methods: Different N concentrations (1 and 4 mM) were supplied to Oryza sativa plants at the early (full expansion), middle and late stages (respectively 8 and 16 d after full expansion) of senescence of the eighth leaf. To enhance N influx into the eighth leaf 16 d after full expansion, all leaf blades on the main stem, except for the eighth leaf, and all tillers were removed and plants received 4 mM N (removal treatment).
Key Results: Rubisco synthesis, rbcS and rbcL mRNAs and the translational efficiencies of rbcS and rbcL mRNAs decreased with leaf senescence irrespective of N treatments. However, in the removal treatment at the late stage, they increased more strongly with an increase in N influx than in intact plants.
Conclusions: Although Rubisco synthesis and rbcS and rbcL mRNAs decrease with leaf senescence, leaves at the late stage of senescence have the potential actively to synthesize Rubisco with an increase in N influx.
Key words: Senescence, Rubisco, N influx, rbcS mRNA, rbcL mRNA, translational efficiency, rbcL DNA, Oryza sativa
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