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Root signals and stomatal closure in relation to photosynthesis, chlorophyll a fluorescence and adventitious rooting of flooded tomato plants

Mark A. Else, Franciszek Janowiak, Christopher J. Atkinson and Michael B. Jackson
Annals of Botany
Vol. 103, No. 2, SPECIAL ISSUE: Flooding Stress (January 2009), pp. 313-323
Published by: Oxford University Press
Stable URL: http://www.jstor.org/stable/43575964
Page Count: 11
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Root signals and stomatal closure in relation to photosynthesis, chlorophyll a fluorescence and adventitious rooting of flooded tomato plants
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Abstract

• 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 (ψ), 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 Hooding starting in the morning closed the stornata and increased ψL after a short-lived depression of ψL. The pattern of closure remained unchanged when ψL 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 stornata 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 stornata 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 Stornata of flooded plants did not close in response to short-lived decreases in ψL 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 stornata during flooding. The possibility that this involves inhibition of cytokinin or gibberellin export was not well supported.

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