Movements of Abaxial and Adaxial Stomata

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Summary The responses of abaxial and adaxial stomata to indole‐3‐acetic acid (IAA) were examined on isolated epidermis of Commelina communis. IAA was remarkably effective in producing wide adaxial apertures accompanied by a massive increase in the stomatal K+ content, and, therefore, eliminating the normal disparity in both the opening and K+ accumulation between abaxial and adaxial stomatal cells; it also reversed the suppressive effect of abscisic acid. IAA may affect the transport of K+ either directly or indirectly through its control of the proton pump. If the IAA‐induced adaxial opening and K+ accumulation is a result of a stimulation of proton extrusion, then, under normal conditions, the proton pump should operate at a lower capacity in adaxial than in abaxial guard cells. Alternatively, the lack of stomatal sensitivity to IAA in the presence of Na+ ions suggests a possibility that it might have a direct effect on the K+ transport. In either case, as reported here, an external supply of IAA would enhance K+ accumulation in adaxial guard cells. The inherent disparity in opening and accompanied K+ accumulation between abaxial and adaxial stomatal cells is postulated to be a result of differences in endogenous auxin level between the two epidermes and/or of differential adaxial and abaxial sensitivity to auxin. Thus, the results indicate a hormonal basis for the differential adaxial and abaxial opening.

Section: Discussionsupporting

confidence: 44%

Section: Resultsmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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DIFFERENTIAL ABAXIAL AND ADAXIAL STOMATAL RESPONSES TO INDOLE‐3‐ACETIC ACID INCOMMELINA COMMUNISL.

Pemadasa

1982

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“…Even so, the two surfaces of a leaf often react differently to environmental changes (Turner, 1970;Aston, 1978;Nagarajah, 1978;Pemadasa, 1979). In L. perenne, which has similar leaf morphology to F. arundinacea, the apparently higher humidity adjacent to the stomata on the deeply ridged adaxial surface seems to buffer adaxial stomata somewhat against the effects of the surrounding air (Wilson, 1975).…”

Section: Humiditymentioning

confidence: 99%

EFFECT OF AMBIENT HUMIDITY AND LEAF DISPOSITION ON LEAF DIFFUSIVE CONDUCTANCE OF FESTUCA ARUNDINACEA CV. S170

Silcock

Wilson

1982

SUMMARYThe effects of changes in humidity on leaf diffusive conductance of Festuca arundinacea cv. SI 70 during a sequence of changes in leaf orientation were studied in a controlled environment cabinet. Reducing the vapour pressure deficit from 0-95 to 0-32 kPa at 25 °C (increasing relative humidity from 70 to 90 %) increased total leaf conductance by 73 %. Leaf orientation markedly influenced the conductance of individual leaf surfaces, the uppermost nearly always having the greater conductance.Total leaf conductance was greater when the ridged adaxial surface was uppermost and, overall, the adaxial surface was more sensitive than the abaxial to humidity and orientation changes. Mean leaf conductance was significantly greater 8 h after the lights were switched on than after 1 and 4 h. Leaves which naturally displayed the adaxial surface upwards had a higher leaf conductance than those in which the abaxial surface was normally uppermost for most of their length.

“…This suggested that, in addition to its inhibition of blue light reception, PAA also has other effects on guard cell functioning. The experiments described here examine this possibility, and the results show contrasting responses of adaxial and abaxial stomata to variations of PAA concentration, and, therefore, reveal further complications in the unknown mechanism of differential abaxial and adaxial stomatal behaviour (Turner, 1970(Turner, , 1979Pemadasa, 1979aPemadasa, , 1981. …”

mentioning

confidence: 87%

Effects of Phenylacetic Acid on Abaxial and Adaxial Stomatal Movements and Its Interaction With Abscisic Acid

Pemadasa

1982

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SUMMARY The effects of varying concentrations of phenylacetic acid (PAA), alone and in combination with abscisic acid (ABA), on abaxial and adaxial stomatal movements were examined on isolated epidermis of Commelina communis. Increasing PAA concentration progressively suppressed abaxial opening, while up to 5 mol m−3 PAA produced remarkably wide adaxial apertures but higher concentrations caused closure; the stomatal K.+ changed accordingly. PAA, like the K+ ionophore benzo‐18‐crown‐6, showed strong antagonistic interactions with ABA. The results are interpreted by postulating that PAA, like benzo‐18‐crown‐6, increases the membrane permeability to K+. The normal abaxial permeability allows a net K+ gain required for opening, but the PAA‐induced increase in permeability causes a net K+ loss leading to closure, because the efflux down a concentration gradient outweighs the influx coupled with proton extrusion. In contrast, the normal K+ content is much less in adaxial than in abaxial guard cells, clear evidence of an inherent restriction to K+ fluxes; this is attributed to restricted membrane permeability to K+, which PAA is postulated to alleviate progressively with increasing concentration. Thus, an increase in permeability up to a critical limit favours a net K+ gain and promotes opening, but any further increase leads to a net K+ loss and causes closure, as in abaxial guard cells. This interpretation is substantiated by both the progressive reduction of PAA‐induced closure with increasing KC1 in the medium and the close similarity of the effects of PAA and benzo‐18‐crown‐6, alone and in antagonism with ABA, on abaxial and adaxial stomata.