Stomatal Responses to Illumination

Abstract.Using an open and a closed system of gas analysis, it was found that CO., evolution in light and in darkness from plant leaves (sunflower, soybean, watermelon, eggplant, and jackbean) have a different response to temperature. While the rate of CO, evolution in light increased with incre-asing temperature from 17 to 350 and then declined, the rate of CO, evolution in darkness increased continuously up to 400. The rate of CO, evolution in light was affected by light intensity. At 1800 ft-c and below 350 the rate of CO2 evolution in light was greater than in darkness, but above 350 it beoame lower than in darkness. The Q10 for CO2 evolution in light was consistently lower than that in darkness.Apparent photosynthesis decreased with increasing temperature, from 20 to 400 and its rate was affected 'by both light intensity and oxygen concentration. In leaves of dicotyledonous plants studied 'the decrease in apparent photosynthesis between 20 to 300 at 21 % 02 was shown to be due primarily to an increase in CO. evolution in light with relatively little effect on photosynthesis.In corn which does not evolve CO2 during illumination there was little effect of increasing temperature on the rate of apparent photosynthesis.The different response to temperature of CO., evolution in light and in darkness support the earlier conclusion that these are 2 different processes.It has been reported that the rates of CO2 evolution by green leaves in light are affected by both O, concentration (6, 9, 11, 14, 29) and light intensity (3,6,15, 17,18,27). Decker (3) has shown that the post-illumination CO., outburst from tobacco at 33.5' was 3 times as large as that at 17.50 and Zelitch (34) has also shown that CO., evolution in light increases with a temperature increase from 250 to 350. Further data on the effect of temperature on CO. evolutioni in light is scanity although the response of CO.2 evolution in darkness has been well documented (19). Additional knowledge would be of interest since there is increasing evidence to in.dicate that in green 'leaves the processes leading to the evolution of CO., in light and in darkness mav be different (6,9,11, 17,23 35-day old watermelon and eggplants were used. The closed and the open systems of gas analysis were the same as described previously ( 15, 16). The closed system was used to study the magnitude of the post-illumination CO. outburst, the CO., compen'sation point, and the effect of CO) concen,tration on -the rate of apparent photosynthesis at various temperattures. The open system. was used to studv the effect of temperature on the steadv rates of apparent photosynthesis at 0.03 % CO2 in air anid CO., evolution into CO-free air in light and in darkness.The various leaf temperatures were obtained by circulating water (Hakke temperature controller) of the desired temperature around the leaf chamber.

Section: Discussionmentioning

confidence: 95%

Effects of Temperature on Photosynthesis and CO₂ Evolution in Light and Darkness by Green Leaves

Hew¹,

Krotkov²,

Canvin³

1969

“…The most recent reviews of stomatal physiology (6,9,12,22) generally agree that stomatal opening in light involves an increase in turgor in the guard cell as a result of a decrease in the solute (osmotic) potential (rise in solute concentration). There are however 2 main hypotheses to explain this decrease.…”

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confidence: 99%

“…including light, water deficit and temperature. are considered to affect stomatal aperture by causing changes in the CO., levels around the stomata in the leaf (12).…”

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confidence: 99%

“…the classical hypothesis involving the internal generation of sugar or other solutes from starch, and the more recent speculative ideas on the accumulation of external solute by the guard cells (9,22). It is generally considered that the process of opening is endergonic and that the CO, concentration in the guard cell is a basic factor controlling stomatal movement (12). Several environmental factors.…”

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confidence: 99%

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Stomatal Opening in Isolated Epidermal Strips of Vicia faba. I. Response to Light and to CO₂-free Air

Fischer

1968

Abstract. This paper reports a consistent and large openinig response to light + C0-free air in living stomata of isolated epidermal strips of Vicia faba. The response was compared to that of non-isolated stomata in leaf discs floating on water; stomatal apertures, guard cell solute potentials and starch contents were similar in the 2 situations. To obtain such stomatal behavior, it was necessary to float epidermal strips on dilute KCl solutions. This suggests that solute uptake is necessary for stomatal opening.The demonstration of normal stomatal behavior in isolated epidermal strips provides a very useful system in which to investigate the mechanism of stomatal opening. It was possible to show independent responses in stomatal aperture to light and to CO,-free air.The most recent reviews of stomatal physiology (6,9,12,22) generally agree that stomatal opening in light involves an increase in turgor in the guard cell as a result of a decrease in the solute (osmotic) potential (rise in solute concentration). There are however 2 main hypotheses to explain this decrease. the classical hypothesis involving the internal generation of sugar or other solutes from starch, and the more recent speculative ideas on the accumulation of external solute by the guard cells (9,22). It is generally considered that the process of opening is endergonic and that the CO, concentration in the guard cell is a basic factor controlling stomatal movement (12). Several environmental factors. including light, water deficit and temperature. are considered to affect stomatal aperture by causing changes in the CO., levels around the stomata in the leaf (12).Investigation of the opening mechanism of stomata would be greatly assisted by the development of means to isolate stomata from the leaf without interfering with their ability to respond to natural stimuli. Much work has been done with epidermal strips and sections. Floated under various conditions, stomata in strips have been shown to open in response to inorganic solutes (7,8,21) and varying pH (1,15,17,18,21). Results of these studies tended, however, to be irregular.With regard to more natural environmllental stimuli, Mouravieff (13,14) demonstrated stomatal opening in response to CO,-free air. anid, to some extent, to light in epidermal sections, but only wlhen the sections were replaced in close contact to the mesophyll from which they were taken. Williams and Shipton (21) demonstrated a stomatal response to light in isolated epidermal strips but their results were also irregular. Heath (6) was unable to show such a light resiponse. AMore recently. Kuiper (10) failed to show light-induced opening of stomata in epidermal strips floating on water, but did show the maintenance of opening in light.Criteria for assessing tlle relevance of these results to normal behavior of the stomata on the intact leaf include vitality of the guard cells in strips, responsiveness to light and low CO., levels and changes in aperture and guard cell solute potential comparable to those of stomata on l...

“…Stomatal aperture is regulated by a series of interdependent feedback loops (11,12). Intercellular CO2 concentration is a principle factor controlling gas exchange (5,6,11,12). In light, depletion of intercellular CO2 levels by the light reactions of photosynthesis stimulates opening.…”

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confidence: 99%

Effect of Potassium Levels on the Stomatal Behavior of the Hemi-Parasite Striga hermonthica

Smith¹,

Stewart²

1990

The hemi-parasite Striga hermonthica, exhibits an anomalous pattern of stomatal response, stomata remaining open in darkness and when subjected to water stress. This suggests irregularity in stomatal response due to malfunction of the stomatal mechanism. To test this suggestion guard cells were isolated from the effects of surrounding cells, by incubating epidermal strips at low pH. These stomata responded rapidly to low CO2 concentrations, darkness, and ABA. Thus, a paradox exists between stomatal behavior observed in whole leaves and that in isolated guard cells. However, when incubated in the presence of high potassium concentrations (>200 millimolar KCI) stomatal responses in epidermal strips resembled those found in whole leaves, with enhanced opening and reduced closing responses. It is suggested that the anomalous behavior of stomata in Striga and other leafy hemiparasites can be explained by the modulatory effects of high potassium concentrations which accumulate in the leaves as a consequence of high transpiration rates and the lack of a retranslocation system. High transpiration rates are characteristic of both root and shoot angiosperm parasites (2,10,17,23). The capture of water and solutes from the host requires a gradient ofdecreasing water potential toward the parasite, and high transpiration rates are thought to maintain this gradient (1 9). An anomalous pattern of stomatal behavior has been observed in the root hemi-parasite, Striga hermonthica, which showed little change in the transpiration rate in response to light intensity or water stress (17). The lack of response of Striga to factors which normally control stomatal behavior result in the stomata remaining open almost continuously. The high transpiration rate has been exploited in the development of antitranspirants as a potential control method (9).In general, higher plant transpiration rates are modulated via the stomata, through which gas exchange and water loss are controlled. Stomatal aperture is regulated by a series of interdependent feedback loops (11,12). Intercellular CO2 concentration is a principle factor controlling gas exchange (5,6,11,12). In light, depletion of intercellular CO2 levels by the light reactions of photosynthesis stimulates opening. In the dark, respiration increases internal leaf CO2 concentration and stomata close. Control of water loss is regulated through ABA effects on stomata. As leaf turgor pressure falls to zero ' The work presented here was financed by the Leverhume Trust.ABA synthesis is induced (13,28). ABA then acts on guard cells causing closure of the stomata by inhibition of solute uptake and increased solute efflux (13).The behavior of Striga stomata could be explained by a lack of response in the guard cells to one or more of the effectors which control stomatal aperture. The purpose of this investigation was to examine the fundamental responses of Striga guard cells to changes in their environment. MATERIALS AND METHODS Plant Material and Growth ConditionsSeeds of Sorghum bicolor (1.)...