Root signals and stomatal closure in relation to photosynthesis, chlorophyll a fluorescence and adventitious rooting of flooded tomato plants.
OBJECTIVE
An investigation was carried out to determine whether stomatal closure in flooded tomato plants (Solanum lycopersicum) results from decreased leaf water potentials (psi(L)), decreased photosynthetic capacity and attendant increases in internal CO(2) (C(i)) 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 C(i) and related parameters.


RESULTS
Flooding starting in the morning closed the stomata and increased psi(L) after a short-lived depression of psi(L). The pattern of closure remained unchanged when psi(;L) depression was avoided by starting flooding at the end rather than at the start of the photoperiod. Raising external CO(2) concentrations by 100 micromol mol(-1) also closed stomata rapidly. Five chlorophyll fluorescence parameters [F(q)'/F(m)', F(q)'/F(v)', F(v)'/F(m)', non-photochemical quenching (NPQ) and F(v)/F(m)] were affected by flooding within 12-36 h and changes were linked to decreased C(i). Closing stomata by applying abscisic acid or increasing external CO(2) 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 psi(L) or to increased C(i) resulting from impaired PSII photochemistry. Instead, stomatal closure depressed C(i) 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.
Else
Mark A
MA
East Malling Research, East Malling, Kent ME19 6BJ, UK.
Janowiak
Franciszek
F
Atkinson
Christopher J
CJ
Jackson
Michael B
MB
D000040:Abscisic Acid / Q000494:pharmacology; D002245:Carbon Dioxide / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism*; D003583:Cytokinins / Q000494:pharmacology; D055868:Floods; D005453:Fluorescence; D005875:Gibberellins / Q000494:pharmacology; D018551:Solanum lycopersicum / Q000187:drug effects / Q000502:physiology*; D010788:Photosynthesis / Q000187:drug effects / Q000502:physiology*; D045332:Photosystem II Protein Complex / Q000378:metabolism; D018515:Plant Leaves / Q000187:drug effects / Q000502:physiology; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism*; D054046:Plant Stomata / Q000187:drug effects / Q000502:physiology*; D018526:Plant Transpiration / Q000187:drug effects; D015398:Signal Transduction; D012987:Soil; D014867:Water / Q000502:physiology
D003583:Cytokinins; D005875:Gibberellins; D045332:Photosystem II Protein Complex; D012987:Soil; D014867:Water; D002734:Chlorophyll; D002245:Carbon Dioxide; D000040:Abscisic Acid; C007842:gibberellic acid