Malate metabolism, stomatal closure and PEPCK

 

 

Expression and manipulation of phosphoenolpyruvate carboxykinase 1 identifies a role for malate metabolism in stomatal closure.

by Penfield S.Clements S.Bailey K. J.Gilday A. D.Leegood R. C.Gray J. E.Graham I. A. (2012)

Steven Penfield, Sarah Clements, Karen J. Bailey, Alison D. Gilday, Richard C. Leegood, Julie E. Gray, Ian A. Graham(Department of Biology, Centre for Novel Agricultural Products, University of York, Heslington, York YO10 5DD, UK)

in Plant J 69: 679688 – doi: 10.1111/j.1365-313X.2011.04822.x –

PubMed Abstract | CrossRef Full Text | Google Scholar – CrossRef Medline

http://onlinelibrary.wiley.com/doi/10.1111/j.1365-313X.2011.04822.x/abstract

Summary

Malate, along with potassium and chloride ions, is an important solute for maintaining turgor pressure during stomatal opening. Although malate is exported from guard cells during stomatal closure, there is controversy as to whether malate is also metabolised.

We provide evidence that phosphoenolpyruvate carboxykinase (PEPCK), an enzyme involved in malate metabolism and gluconeogenesis, is necessary for full stomatal closure in the dark.

Analysis of the Arabidopsis PCK1 gene promoter indicated that this PEPCK isoform is specifically expressed in guard cells and trichomes of the leaf. Spatially distinct promoter elements were found to be required for post-germinative, vascular expression and guard cell/trichome expression of PCK1.

We show that pck1 mutant plants have reduced drought tolerance, and show increased stomatal conductance and wider stomatal apertures compared with the wild type.

During light–dark transients the PEPCK mutant plants show both increased overall stomatal conductance and less responsiveness of the stomata to darkness than the wild type, indicating that stomata get ‘jammed’ in the open position.

These results show that malate metabolism is important during dark-induced stomatal closure and that PEPCK is involved in this process.

 

Oscillations in stomatal conductance in the light and dark.

 

 

Oscillations in stomatal conductance of hybrid poplar leaves in the light and dark.

by Reich P. B. (1984)

Peter B. Reich

in Plant Physiology 1984;61:541-548 –DOI: 10.1111/j.1399-3054.1984.tb05167.x –

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http://onlinelibrary.wiley.com/doi/10.1111/j.1399-3054.1984.tb05167.x/full

Abstract

Cycling of stomatal conductance in three hybrid poplar (Populus sp.) cultivars was observed under a variety of conditions. Illumination of plants kept previously in the dark induced very large oscillations with a period of about 40 min and large oscillations with a shorter period (< 10 min) were superimposed on the longer cycles. During these oscillations, large changes in conductance could occur very rapidly (1.0 cm s−1 in 3 min).

Plants in constant light also displayed both long and short term cycles in conductance, but these were smaller in amplitude than those induced by sudden illumination.

Stomatal oscillations were also observed in darkness and after darkening of previously illuminated plants. These oscillations had shorter (< 30 min) and less regular periods than those observed in the light. Such cycling in the dark is rare.

Cycling of the two leaf surfaces was sometimes in synchrony in the light, and more so after a perturbation. Little synchrony between the two surfaces was observed in the dark.

Stomatal movements of different leaves on a plant were usually relatively independent. Transient stomatal opening occurred following leaf excision in the light or dark, and often after sudden darkening of intact leaves. Also, stomata of intact leaves sometimes transiently closed following illumination.

Stomatal response and water status of Picea abies

 

Photo credit: Google

Picea abies – Norway Spruce

Dynamics of change in stomatal response and water status of Picea abies during a persistent drought period: a contribution to the traditional view of plant water relations

by Maier-Maercker U. (1998)

Lehrstuhl für Forstbotanik, Universität München, Am Hochanger 13, D-85354 Freising, Germany.

in Tree Physiology 1998, 18: 211- 222 –

Google Scholar CrossRef PubMed

https://www.ncbi.nlm.nih.gov/pubmed/12651375

Abstract

Four experiments on the simulation of a persistent drought period were carried out with cloned Picea abies (L.) Karst. trees: two in the field under varying weather conditions and two in a climate chamber under variously manipulated humidity conditions.

Patterns of diurnal dynamics in gas exchange rates and water potential were monitored and analyzed. The first phase of the drought was characterized by relatively high daily maxima for photosynthesis and transpiration. With decreasing humidity during the day, the values dropped steeply, and the declines were larger and occurred earlier on each passing day of the drought period. When soil water potential was lower than -2000 hPa, maximum stomatal aperture was greatly reduced despite a humid atmosphere.

Under these conditions, rates of photosynthesis and transpiration decreased less steeply from the daily maxima and differences between maxima and minima were small. In the field, the daily sums of transpiration and photosynthesis were more dependent on atmospheric conditions than on soil water potential. In the growth chamber experiments, the daily sums of transpiration and photosynthesis decreased continuously as the soil dried, at first steeply until a soil water potential of -2000 hPa was reached, then slowly.

Predawn water potential values fluctuated under field conditions, but tended to decrease with time, whereas needle osmotic potential increased slightly. Because relative humidities did not reach 100% in the growth chamber, predawn water potentials of plants in the growth chamber were never higher than -1.0 MPa although the soil was saturated.

In the experiment with a high average air humidity during the daily stress period, relatively high predawn water potentials were maintained until lower soil water potentials of -8000 hPa were reached.

Results were used to assess the importance of evaporative demand versus soil drying on stomatal responses within the context of current concepts of plant water relations. The observed trends in diurnal dynamics can be explained solely by the interdependency of leaf conductance and water potential.

Stomata react directly to the ratio of water supply to demand. The central role of peristomatal transpiration in this system is emphasized.