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Increased cytokinin levels in transgenic P SAG12 – IPT tobacco plants have large direct and indirect effects on leaf senescence, photosynthesis and N partitioning
Author(s) -
Jordi W.,
Schapendonk A.,
Davelaar E.,
Stoopen G. M.,
Pot C. S.,
De Visser R.,
Rhijn J. A. Van,
Gan S.,
Amasino R. M.
Publication year - 2000
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1046/j.1365-3040.2000.00544.x
Subject(s) - rubisco , cytokinin , senescence , nicotiana tabacum , photosynthesis , biology , shoot , botany , solanaceae , plant physiology , horticulture , auxin , biochemistry , gene , microbiology and biotechnology
We studied the impact of delayed leaf senescence on the functioning of plants growing under conditions of nitrogen remobilization. Interactions between cytokinin metabolism, Rubisco and protein levels, photosynthesis and plant nitrogen partitioning were studied in transgenic tobacco ( Nicotiana tabacum L.) plants showing delayed leaf senescence through a novel type of enhanced cytokinin syn‐thesis, i.e. targeted to senescing leaves and negatively auto‐regulated (P SAG12 – IPT ), thus preventing developmental abnormalities. Plants were grown with growth‐limiting nitrogen supply. Compared to the wild‐type, endogenous levels of free zeatin (Z)‐ and Z riboside (ZR)‐type cytokinins were increased up to 15‐fold (total ZR up to 100‐fold) in senescing leaves, and twofold in younger leaves of P SAG12 – IPT . In these plants, the senescence‐associated declines in N, protein and Rubisco levels and photosynthesis rates were delayed. Senescing leaves accumulated more ( 15 N‐labelled) N than younger leaves, associated with reduced shoot N accumulation (–60%) and a partially inverted canopy N profile in P SAG12 – IPT plants. While root N accumulation was not affected, N translocation to non‐senescing leaves was progressively reduced. We discuss potential consequences of these modified sink–source relations, associated with delayed leaf senescence, for plant productivity and the efficiency of utilization of light and minerals.