Journal of Experimental Botany, Vol. 53, No. 367, pp. 287-296,
February 1, 2002
© 2002 Oxford University Press
Original Papers |
Is the ABA concentration in the sap collected by pressurizing leaves relevant for analysing drought effects on stomata? Evidence from ABA-fed leaves of transgenic plants with modified capacities to synthesize ABA
Laboratoire d'Ecophysiologie des Plantes sous Stress Environnementaux (LEPSE), UMR INRA-ENSAM, 2 place Viala, 34060 Montpellier Cedex 1, France
Most studies on the role of ABA in the stomatal response of the whole plant to drought rely on a good estimate of ABA concentration in xylem sap. In this report, varying volumes of sap (Vsap) were collected by pressurizing leaves cut from several lines of N. plumbaginifolia with modified capacities to synthesize ABA. Leaves were fed with solutions of known ABA concentration ([ABA]solution from 0–500 µmol m-3) for 2–3 h before sap collection. ABA concentration in extruded sap ([ABA]sap) was compared with [ABA]solution. In low-volume extracts (less than 0.35 mm3 cm-2 leaf area) collected from leaves of well-watered plants, [ABA]sap was close to [ABA]solution. For all lines, [ABA]sap decreased with increasing Vsap. The same dilution effect was observed for leaves pressurized just after sampling on droughted plants, suggesting, as for detached leaves fed with ABA, that [ABA]sap in low-volume extracts approximated well with the concentration of ABA entering leaves still attached on droughted plants. However, ABA-fed leaves sampled from droughted plants yielded higher [ABA]sap than ABA-fed leaves sampled from well-watered plants. [ABA]sap was also increased, although very slightly, when leaves were preincubated in highly enriched ABA solution. This indicates that some leaf ABA contributed to the ABA concentration returned in the extruded sap. Consistently, [ABA]sap in medium-volume extracts (0.35–0.65 mm3 cm-2 leaf area) was lower for leaves sampled on under-producing lines than on the wild type. Despite these distortions between [ABA]solution and [ABA]sap in medium-volume extracts, stomatal conductance of ABA-fed leaves closely correlated with [ABA]sap with a similar relationship in all cases, whilst relationships with [ABA]solution were more scattered.
Key words: Abscisic acid, drought, Nicotiana plumbaginifolia, stomatal conductance, xylem sap.
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