Inhibition Of Stomatal Opening Research Articles

Inhibition of inward K+ channels and stomatal response by abscisic acid: an intracellular locus of phytohormone action.

Abscisic acid (ABA), a plant hormone whose production is stimulated by water stress, reduces the apertures of stomatal pores in the leaf surface, thereby lessening transpirational water loss. It has been thought that inhibition of stomatal opening and promotion of stomatal closure by ABA are initiated by the binding of extracellular ABA to a receptor located in the guard-cell plasma membrane. However, in the present research, we employ three distinct experimental approaches to demonstrate that ABA can act from within guard cells to regulate stomatal apertures. (i) The extent to which ABA inhibits stomatal opening and promotes stomatal closure in Commelina communis L. is proportional to the extent of ABA uptake, as assayed with [3H]ABA. (ii) Direct microinjection of ABA into the cytoplasm of Commelina guard cells precipitates stomatal closure. (iii) Application of ABA to the cytosol of Vicia faba L. guard-cell protoplasts via patch-clamp techniques inhibits inward K+ currents, an effect sufficient to inhibit stomatal opening. These results demonstrate an intracellular locus of phytohormone action and imply that the search for hormone receptor proteins should be extended to include intracellular compartments.

Regulation of Stomatal Opening in Epidermal Strips of Commelina communis L. by Phytochrome

Pfr stimulates opening. The inhibition of stomatal opening by far red light depends upon their ability to open in red light. Pretreatment of epidermis strips, in which stomata open below 2 µm, with EGTA stimulates stomatal opening in red light and increases the inhibitory effect of far red light. Lanthanum affects stomatal opening similarly to far red light. TEA and quinidine prevent stomatal opening and closure (induced by the transfer of epidermal strips with open stomata to low KC1 concentration) in red light. These channel blockers fail to affect opening and closure in the presence of far red light. It is proposed that phytochrome affects cytosolic CA2+ concentration which in turn regulates the inward and outward K+ channels.

Inhibition of stomatal opening in sunflower leaves by carbon monoxide, and reversal of inhibition by light

When leaves of Helianthus annuus, whose stomates had been opened in the dark in the absence of CO2, were exposed to 25% carbon monoxide (CO), stomatal conductivity for water vapor decreased from about 0.4 to 0.2 cm·s(-1). The CO effect on stomatal aperture required a CO/O2 ratio of about 25. As this ratio was decreased the stomata opened, indicating that inhibitio of cytochrome-c oxidase by CO is competitive in respect to O2. Photosynthetically active red light was unable to reverse CO-induced stomatal closure even at high irradiances, when CO2 was absent. When it was present, stomatal opening was occasionally, but not consistently observed. Carbon monoxide did not inhibit photosynthetic carbon reduction in leaves of Helianthus.In contrast to red light, very weak blue light (405 nm) increased the stomatal aperture in the presence of CO. It also increased leaf ATP/ADP ratios which had been decreased in the presence of CO. The blue-light effect was not related to photosynthesis. Neither could it be explained by photodissociation of the cytochrome a 3-CO complex which has an absorption maximum at 430 nm. The data indicate that ATP derived from mitochondrial oxidative phosphorylation provides energy for stomatal opening in sunflower leaves in the dark as well as in the light. Indirect transfer of ATP from chloroplasts to the cytosol via the triose phosphate/phosphoglycerate exchange which is mediated by the phosphate translocator of the chloroplast envelope can support stomatal opening only if metabolite concentrations are high enough for efficient shuttle transfer of ATP. Blue light causes stomatal opening in the presence of CO by stimulating ATP synthesis.

SUGGESTED INVOLVEMENT OF CALCIUM AND CALMODULIN IN THE RESPONSES OF STOMATA TO ABSCISIC ACID

SummaryA requirement for calcium during the inhibition of stomatal opening by abscisic acid (ABA) was reported in a previous study, and evidence is now presented which gives further indications of the part played by calcium. Calcium‐channel blockers (lanthanum, verapamil and nifedipine) reduced the ability of stomata to respond to ABA. A calcium ionophore (A 23187) reduced stomatal opening, presumably because it mimicked the effect of ABA in increasing permeability of the plasma membrane to calcium. In the presence of three calmodulin antagonists, the inhibitory effect of ABA was much reduced. The synthetic auxin naphth‐l‐ylacetic acid (NAA) prevented stomatal opening, but this action did not appear to be dependent on calcium ions.It is suggested that the action of ABA on guard cells requires a free passage of calcium ions into the cytosol. They may act as second messengers, interacting with calmodulin to produce the overt cellular responses to ABA.Although the data presented apply only to stomata, these experiments may have provided insight into the basic mechanism by which ABA acts on cellular processes. It is suggested that some reported effects of Ca2+on the action of other plant growth substances could have resulted from complex interactions involving endogenous ABA.

ChemInform Abstract: A Comparison between Sodium and Potassium in the Inhibition of Stomatal Opening by Cyclic ′Crown′ Polyethers (Untersuchungen an Commelina communis; Kronenether: Benzo‐18‐crown‐6, Acetyl‐, Ethyl‐, ter.‐Butylbenzo‐18‐crown‐6, Benzo‐15‐crown‐5,tert.‐Butylbenzo‐15‐crown‐5, Dibenzo‐30‐crown‐10; Bildung von 2:1‐Komplexen mit Na).

ChemInform Abstract: A Comparison between Sodium and Potassium in the Inhibition of Stomatal Opening by Cyclic ′Crown′ Polyethers (Untersuchungen an Commelina communis; Kronenether: Benzo‐18‐crown‐6, Acetyl‐, Ethyl‐, ter.‐Butylbenzo‐18‐crown‐6, Benzo‐15‐crown‐5,tert.‐Butylbenzo‐15‐crown‐5, Dibenzo‐30‐crown‐10; Bildung von 2:1‐Komplexen mit Na).

Light and Stomatal Metabolism

The effect of sulfite and arsenite on stomatal opening and light modulation of enzymes was examined in isolated epidermal strips of Pisum sativum L. var Little Marvel leaves. Sulfite or arsenite at 10 micromolar rapidly inhibited the stomatal opening process in light. Light activation of phosphoenolpyruvate carboxylase and NADP-malate dehydrogenase was completely diminished when the epidermal strips were incubated for 2 hours in light with either sulfite or arsenite at 10 micromolar. The data obtained suggest that the inhibition of stomatal opening by sulfite or arsenite in light might result from the inhibition of light modulation of key enzymes in guard cells.

A comparison between sodium and potassium in the inhibition of stomatal opening by cyclic ‘crown’ polyethers

Cyclic ‘crown’ polyethers are found to inhibit stomatal opening in abaxial epidermal peels of Commelina communis when they are floated on bathing media containing 10 m M MES and 50 m M KCl or NaCl buffered to ph 6.1 and irradiated with light in CO 2-free air. Increasing potassium ion concentration in the medium overcomes this inhibition to stomatal opening by reducing the leakage of potassium out of the guard cells. Evidence is presented for 2:1 ligand to sodium complexes in the guard cell membrane when sodium is used in the bathing medium.

Inhibition of Stomatal Opening in Vicia Faba Epidermal Tissue by Vanadate and Abscisic Acid

Summary Stomatal opening in isolated Vicia faba epidermal peels was blocked by 1 mM sodium vanadate and by 10 −4 M abscisic acid (ABA). Light-induced hydrogen ion release and potassium accumulation were also inhibited by vanadate. Vanadate-treated guard cells could still respond to fusicoccin (FC) after removal of the inhibitor. ABA inhibited light-induced guard cell opening within 20 min of treatment. ABA also prevented guard cell potassium accumulation, but only partially inhibited hydrogen ion release (~50%) during the first 90 min of treatment. The possible modes of action of vanadate and ABA are discussed.

Inhibition of stomatal opening by cyclic ‘crown’ polyethers in commelina communis, and a correlation with lipophilicity and bonding

Epidermal peels of Commelina communis have been treated with three series of cyclic crown polyethers based respectively on substituted 15-crown-5, 18-crown-6 and 30-crown-10 ligands. The concentrations of the crown compounds required just to inhibit stomatal opening under the test conditions correlate well with their lipophilicities measured by partition, and also with bonding stoichiometries for potassium as observed in organic solvents and in isolated crystalline complexes.

Inhibition of Stomatal Opening by Analogues of Abscisic Acid

Twenty analogues of abscisic acid have been tested for their activity as inhibitors of stomatal opening in isolated epidermis of Commelina communis. A number of derivatives showed slight activity but only two treatments resulted in significant stomatal closure and this was accompanied by destruction of the guard cell membranes. Such damage is characteristic of the stomatal response to farnesol, another sesquiterpenoid also thought to be involved in control of water loss. The implication of these results in the study of antitranspirants is considered.

Inhibition of stomatal opening during uptake of carbohydrates by guard cells in isolated epidermal tissues

The uptake of glucose and other carbohydrates into the guard cells of Commelina communis L. was found to inhibit the opening of the stomata. The concentration of glucose necessary to achieve about 50% inhibition was of the same order of magnitude as the potassium concentration required for opening; the uptake systems for potassium and glucose appear to be competitive and to exhibit the same degree of affinity. It is suggested that the uptake of glucose occurs via a proton cotransport, which, depolarizing the membrane potential, slows down the electrogenic import of potassium ions. The process of stomatal closure, in contrast, appears not to be affected by carbohydrate uptake. In guard cells of Tulipa gesneriana L. and Vicia faba L., which do not possess subsidiary cells, import of glucose or other carbohydrates did not interfere with the regulation of stomatal movements.

The Role of Farnesol as a Regulator of Stomatal Opening inSorghum

Fine, very dilute aqueous emulsions of all-trans farnesol applied to intact leaves of Sorghum bicolor caused appreciable inhibition of stomatal opening which persisted for 2 d, after which time the stomata regained their capacity to open. The inhibitory effect of farnesol was not overcome by flushing the leaves with CO2-free air, indicating that it was not the result of an accumulation of CO2. This conclusion was supported by measurements of CO2 compensation, which increased only slightly after farnesol treatment. All-trans farnesol has previously been reported to be formed in water-stressed plants of Sorghum. The data presented here suggest that it could be acting as an endogenous antitranspirant, in a comparable role to that already established for abscisic acid in several species. It would appear, however, to have a less prolonged inhibitory effect than abscisic acid, and it could be responsible for the rapid responses of Sorghum stomata to water stress and their quick recovery after the plant has regained turgor, a characteristic which distinguishes Sorghum from many other genera so far investigated

Chemical control of stomatal movements

Artificially induced partial closure of stomata can improve the efficiency with which plants use available water; in other words, there is a fall in the transpiration: photosynthesis ratio. The careful use of some metabolic inhibitors can achieve the required inhibition of stomatal opening, but properly controlled application under field conditions is difficult and metabolic inhibition of photosynthesis in the mesophyll can occur. In the search for a more specific inhibitor of the activities of stomatal guard cells, most attention has been focused on abscisic acid, a hormone which appears to function as an endogenous regulator of stomatal opening. External application of abscisic acid achieves a useful reduction in the transpiration: photosynthesis ratio. Studies are being made of the effects of chemical analogues of abscisic acid in the search for more active compounds. Another naturally occurring substance which induces stomata to close, all- trans -farnesol, has been found in water-stressed sorghum plants. Sorghum is better able to tolerate water shortage than most crops, and further studies of its physiological mechanisms should lead to a better understanding of how we can provide protection for more susceptible crops.

Characterisation of abscisic acid inhibition of stomatal opening in isolated epidermal strips

Abscisic acid (ABA) inhibited the light-induced opening of stomata in isolated epidermal strips of Commelina benghalensis. It did not alter stomatal closure in the dark. The ABA-induced inhibition in light was released under conditions conducive for cyclic photophosphorylation and remarkably reversed by ATP in the presence of pyruvate. Cyclic photophosphorylation rates of isolated guard cell chloroplasts were significantly reduced by ABA. It is proposed that the direct effect of ABA on stomatal opening was mediated in two ways: (1) by inhibition of cyclic photophosphorylation activities of guard cell chloroplasts and (2) by blocking organic acid formation in guard cells.

Studies of the Mechanism by which Daminozide (B9) Inhibits Stomatal Opening

the mechanism by which the synthetic growth retardant dammozide (?59) inhibits stomatal opening has been investigated, and its action compared with that of the naturally occurring growth hormone, abscisic acid. The inhibition of stomatal opening by low concentrations of daminozide in normal air is largely reversed in C02-free air, suggesting that the main effect is due to an increase in internal CO2 concentration. This is supported by observations of a raised level of CO2 compensation in treated leaves. The C02-independent light reaction of stomata does, however, also appear to be inhibited by daminozide. Higher concentrations cause damage to cells of the epidermis, and such effects could also be found in normal practical use of the growth retardant. The mechanism of action of daminozide on stomata has little in common with that of abscisic acid, which does not operate by increasing the internal CO2 concentration and does not induce cellular damage. Daminozide cannot be recommended for practical use as an antitrans pirant because of its mechanism of action, which is likely to cause a decrease in the efficiency of water use.