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

by Dittrich P., Mayer M. (1978)

Botanisches Institut der Universität, Menzinger Str. 67, D-8000 Miinchen 19, Federal Republic of Germany

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In Planta 139: 167–170 – https://doi.org/10.1007/BF00387143 –

https://link.springer.com/article/10.1007%2FBF00387143#citeas

The uptake of glucose and other carbohydrates into the guard cells of Commelina communisL. 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.

(14C) Carbon dioxide fixation by isolated leaf epidermes with stomata closed or open

 

 

by Raschke K., Dittrich P. (1977)

1. .Institut für Botanik und Mikrobiologie der Technischen Universität München, München 2, Federal Republic of Germany
2. Botanisches Institut der Universität München, München 19, Federal Republic of Germany

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in Planta 134: 69-75 – https://doi.org/10.1007/BF00390097 –

https://link.springer.com/article/10.1007/BF00390097#citeas

Abstract

Isolated epidermes of Tulipa gesneriana L. and Commelian communis L. were exposed to ¹⁴CO₂ in the light and in darkness, when stomata were either closed or open.

The labelling patterns did not differ: the main products of CO₂ fixation were malate and aspartate.

Small amounts of radioactivity appeared also in acids of the tricarboxylic-acid cycle and their transamination products. Since the capacity of epidermis to assimilate CO₂ is known to reside in the guard cells, we can state that guard cells continuously take up CO₂ if present, and are thus able to recognize the presence of CO₂ in their environment at all times.

Epidermal samples exposed to ¹⁴CO₂ in the light contained only small amounts of radioactive 3-phosphoglyceric acid (3-PGA) and sugar phosphates, or none at all. Epidermal samples from Commelina communis did not contain labelled 3-PGA if all adhering mesophyll cells had been removed before exposure to ¹⁴CO₂.

Homogenates of clean epidermal strips of Commelina communiswere able to convert exogenous ribulose diphosphate to 3-PGA at a low rate, but could not catalyze the conversion of exogenous ribulose-5-phosphate to ribulose diphosphate.

Guard cells of Commelina communis, and probably also those of Tulipa gesneriana, appear not to possess the reductive pentosephosphate pathway, despite the presence of chloroplasts. In such species, the guard cells will have to rely on import in order to maintain their carbon balance.

Earlier findings of photosynthetic reduction of CO₂ by epidermal tissues were probably obtained with samples that were contaminated with mesophyll cells.

Malate metabolism and stomatal functioning

 

 

Malate metabolism in isolated epidermis of Commelina communis L. in relation to stomatal functioning

by Dittrich P., Raschke K. (1977)

Botanisches Institut der Universität München, Menzinger Straße 67, D-8000, München 19, Federal Republic of Germany.

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in Planta 134: 76–82 – doi: 10.1007/BF00390098 –

Google Scholar –

https://www.ncbi.nlm.nih.gov/pubmed/24419583

Abstract

Epidermal strips with closed stomata were exposed to malic acid labelled with (14)C either uniformly or in 4-C only. During incubation with [U-(14)C]malate, radioactivity appeared in products of the tricarboxylic-acid cycle and in transamination products within 10 min, in sugars after 2 h. Hardly any radioactivity was found in sugars if [4-(14)C]malate had been offered. This difference in the degree of labelling of sugars indicates that gluconeogenesis can occur in epidermal tissue, involving the decarboxylation of malate. Epidermis incubated with labelled malate was hydrolyzed after extraction with aqueous ethanol. The hydrolysate contained glucose as the only radioactive product, indicating that starch had been formed from malate. Microautoradiograms were black above stomatal complexes, showing that the latter were sites of starch formation. In order to follow the fate of malate during stomatal closure, malate was labelled in guard cells by exposing epidermes with open stomata to (14)CO2 and then initiating stomatal closure. Of the radioactive fixation products of CO2 only malate was released into the water on which the epidermal samples floated; the epidermal strips retained some of the malate and all of its metabolites. In the case of rapid stomatal closure initiated by abscisic acid and completed within 5 min, 63% of the radioactivity was in the malate released, 22% in the malate retained, the remainder in aspartate, glutamate, and citrate. We conclude that during stomatal closing guard cells can dispose of malate by release, gluconeogenesis, and consumption in the tricarboxylic-acid cycle.

Malate and stomatal functioning

 

 

Malate metabolism in isolated epidermis of Commelina communis L. in relation to stomatal functioning

by Dittrich P., Raschke K. (1977)

in  Planta 134, 77–81. –

doi: 10.1007/BF00390098 – 

PubMed Abstract | CrossRef Full Text | Google Scholar

Based on available literature, 109 known metabolites in guard cells are represented as a network based on their structural and biochemical relationships. –
http://www.frontiersin.org/files/Articles/144863/fpls-06-00334-HTML/image_m/fpls-06-00334-g001.jpg

Abstract

Epidermal strips with closed stomata were exposed to malic acid labelled with ¹⁴C either uniformly or in 4-C only. During incubation with [U-¹⁴C]malate, radioactivity appeared in products of the tricarboxylic-acid cycle and in transamination products within 10 min, in sugars after 2 h. Hardly any radioactivity was found in sugars if [4-¹⁴C] malate had been offered.

This difference in the degree of labelling of sugars indicates that gluconeogenesis can occur in epidermal tissue, involving the decarboxylation of malate.

Epidermis incubated with labelled malate was hydrolyzed after extraction with aqueous ethanol. The hydrolysate contained glucose as the only radioactive product, indicating that starch had been formed from malate.

Microautoradiograms were black above stomatal complexes, showing that the latter were sites of starch formation. In order to follow the fate of malate during stomatal closure, malate was labelled in guard cells by exposing epidermes with open stomata to ¹⁴CO₂ and then initiating stomatal closure.

Of the radioactive fixation products of CO₂ only malate was released into the water on which the epidermal samples floated; the epidermal strips retained some of the malate and all of its metabolites.

In the case of rapid stomatal closure initiated by abscisic acid and completed within 5 min, 63% of the radioactivity was in the malate released, 22% in the malate retained, the remainder in aspartate, glutamate, and citrate.

We conclude that during stomatal closing guard cells can dispose of malate by release, gluconeogenesis, and consumption in the tricarboxylic-acid cycle.

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