AOBPreview originally published online on November 10, 2008
Annals of Botany 2009 103(2):313-323; doi:10.1093/aob/mcn208
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Root signals and stomatal closure in relation to photosynthesis, chlorophyll a fluorescence and adventitious rooting of flooded tomato plants
1 East Malling Research, East Malling, Kent ME19 6BJ, UK
2 Institute of Plant Physiology, Polish Academy of Sciences, Niezapominajek 21, 30-239 Krakow, Poland
3 School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK
* For correspondence. E-mail mike.jackson{at}bristol.ac.uk
Received: 3 July 2008 Returned for revision: 14 July 2008 Accepted: 28 August 2008 Published electronically: 10 November 2008
Background and Aims: An investigation was carried out to determine whether stomatal closure in flooded tomato plants (Solanum lycopersicum) results from decreased leaf water potentials (
L), decreased photosynthetic capacity and attendant increases in internal CO2 (Ci) or from losses of root function such as cytokinin and gibberellin export.
Methods: Pot-grown plants were flooded when 1 month old. Leaf conductance was measured by diffusion porometry, the efficiency of photosystem II (PSII) was estimated by fluorimetry, and infrared gas analysis was used to determine Ci and related parameters.
Key Results: Flooding starting in the morning closed the stomata and increased L after a short-lived depression of L. The pattern of closure remained unchanged when `L depression was avoided by starting flooding at the end rather than at the start of the photoperiod. Raising external CO2 concentrations by 100 µmol mol–1 also closed stomata rapidly. Five chlorophyll fluorescence parameters [Fq'/Fm', Fq'/Fv', Fv'/Fm', non-photochemical quenching (NPQ) and Fv/Fm] were affected by flooding within 12–36 h and changes were linked to decreased Ci. Closing stomata by applying abscisic acid or increasing external CO2 substantially reproduced the effects of flooding on chlorophyll fluorescence. The presence of well-aerated adventitious roots partially inhibited stomatal closure of flooded plants. Allowing adventitious roots to form on plants flooded for >3 d promoted some stomatal re-opening. This effect of adventitious roots was not reproduced by foliar applications of benzyl adenine and gibberellic acid.
Conclusions: Stomata of flooded plants did not close in response to short-lived decreases in L or to increased Ci resulting from impaired PSII photochemistry. Instead, stomatal closure depressed Ci and this in turn largely explained subsequent changes in chlorophyll fluorescence parameters. Stomatal opening was promoted by the presence of well-aerated adventitious roots, implying that loss of function of root signalling contributes to closing of stomata during flooding. The possibility that this involves inhibition of cytokinin or gibberellin export was not well supported.
Key words: Root to shoot communication, flooding stress, stomatal closure, photosynthesis, chlorophyll fluorescence, gas exchange, adventitious roots, plant hormones, abscisic acid, cytokinins, gibberellic acid
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