Changes in the synthesis of rubisco in rice leaves in relation to senescence and N influx.
OBJECTIVE
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).


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.
Imai
Kazuhiro
K
Department of Applied Plant Science, School of Agricultural Sciences, Tohoku University, 1-1 Tsutsumidori-Amamiyamachi, Aoba-ku, Sendai 981-8555, Japan. j113241@yahoo.co.jp
Suzuki
Yuji
Y
Mae
Tadahiko
T
Makino
Amane
A
D001692:Biological Transport; D016922:Cellular Senescence / Q000235:genetics; D002734:Chlorophyll / Q000378:metabolism; D018744:DNA, Plant / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D012275:Oryza / Q000033:anatomy & histology / Q000235:genetics / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000378:metabolism; D018515:Plant Leaves / Q000033:anatomy & histology / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000096:biosynthesis* / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D018749:RNA, Plant / Q000378:metabolism; D012273:Ribulose-Bisphosphate Carboxylase / Q000096:biosynthesis*; D020524:Thylakoids / Q000378:metabolism
D018744:DNA, Plant; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D012333:RNA, Messenger; D018749:RNA, Plant; D002734:Chlorophyll; D012273:Ribulose-Bisphosphate Carboxylase; D009584:Nitrogen