Wingler A, Brownhill E, Pourtau N. Mechanisms of the light-dependent induction of cell death in tobacco plants with delayed senescence.
JOURNAL OF EXPERIMENTAL BOTANY 2005;
56:2897-905. [PMID:
16157651 DOI:
10.1093/jxb/eri284]
[Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
The relationship between leaf senescence and cell death was investigated using tobacco with delayed senescence due to auto-regulated production of cytokinin (SAG12-IPT). Although leaf senescence ultimately results in cell death, the results show that senescence and cell death can be uncoupled: in nutrient-deficient, but not in fertilized SAG12-IPT plants, necrotic lesions were detected in old, but otherwise green leaves. By contrast, wild-type leaves of the same age were yellow, but not necrotic. Chlorophyll fluorescence analysis revealed an over-reduction of the electron transport chain in old SAG12-IPT leaves, in combination with characteristic spatial patterns of minimum fluorescence (F0) quantum efficiency of open photosystem II centres (F(v)/F(m)) and non-photochemical quenching (NPQ), as determined by fluorescence imaging. The same patterns of F0, F(v)/F(m), and NPQ were induced by incubation of leaf discs from nutrient-deficient SAG12-IPT plants under illumination, but not in the dark, indicating that light-dependent reactions were responsible for the cell death. RT-PCR analysis showed that the pathogenesis-related (PR) genes PR-1b and PR-Q were strongly induced in old SAG12-IPT tobacco leaves with necrotic lesions. In addition, the ethylene-synthesis gene ACO was induced before lesions became visible in SAG12-IPT. It is proposed that over-reduction of the electron transport chain in combination with decreased electron consumption due to nutrient-deficiency led to oxidative stress, which, mediated by ethylene formation, can induce PR gene expression and hypersensitive cell death. Probably as a consequence of inefficient nutrient mobilization, flower development was prematurely aborted and reproduction thereby impaired in nutrient-deficient SAG12-IPT plants.
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