Separation and Measurement of Direct and Indirect Effects of Light on Stomata

Abstract

Conductance for water vapor, assimilation of C02, and intercellular CO2 concentration of leaves of five species were determined at various irradiances and ambient CO2 concentrations. Conductance and assimilation were then plotted as functions of irradiance and intercellular CO2 concentration. The slopes of these curves allowed us to estimate infinitesimal changes in conductance (and assimilation) that occurred when irradiance changed and intercellular CO2 concentration was constant, and when CO2 concentration changed and irradiance was constant. On leaves ofXanthium stumarium L., Gossypium hirsutum L., Phaseolis vulgaris L., and Perilla frutescens (L.), Britt., the stomatal response to light was determined to be mainly a direct response to light and to a small extent only a response to changes in intercellular CO2 concentration. This was also true for stomata of Zea mays L., except at irradiances < 150 watts per square meter, when stomata responded primarily to the depletion of the intercellular spaces of CO2 which in turn was caused by changes in the assimilation of CO2.Stomata responded to light even in leaves whose net exchange of CO2 was reduced to zero through application of the inhibitor of photosynthetic electron transport, cyanazine (2-chloro-4l-cyano-l-methylethylaminoljethylamino-S-triazine). When leaves were inverted and irradiated on the abaxial surface, conductance decreased in the shaded and increased in the illuminated epidermis, indicating that the photoreceptor pigment(s) involved are located in the epidermis (presumably in the guard cells). In leaves of X. strwmariwn, the direct effect of light on conductance is primarily a response to blue light.Stomatal responses to CO2 and to light opposed each other. In X.stumariwn, stomatal opening in response to light was strongest in CO2 free air and saturated at lower irradiances than in CO2 containing air. Conversely, stomatal closure in response to CO2 was strongest in darkness and it decreased as irradiance increased. In X. strwnarin, P. vulgaris, and P. frutescens, an irradiance of 300 watts per square meter was sufficient to eliminate the stomatal response to CO2 altogether. Application of abscisic acid, or an increase in vapor pressure deficit, or a decrease in leaf temperature reduced the stomatal conductance at light saturation, but when the data were normalized with respect to the conductance at the highest irradiance, the various curves were congruent.result of the photosynthetic production of osmotica. In 1908, Lloyd (9) showed that stomata respond to light in C02-free air, from which he concluded that "photosynthesis, even in stomata, whose plastids are well supplied with chlorophyll, plays a secondary role in their physiology, and is connected only indirectly with their movements." An alternative view was proposed in 1932 by Scarth (20). He believed that stomata do not open in response to light absorbed in the guard cells but only in response to the changes in the concentration of CO2 inside the leaf that resulted from changes in th...

Evidence for Involvement of Photosynthetic Processes in the Stomatal Response to CO2

“…These results suggest that DCMU should cause stomata to close in intact leaves and are therefore consistent with our data. Our results appear contradictory to those of Sharkey and Raschke (1981b), who found little effect of DCMU and cyanazine (a herbicide that blocks photosynthetic electron transport at PSII) on g s in cocklebur. However, in Gossypium hirsutum, Sharkey and Raschke (1981b) found a reduction in g s and a change in the response of conductance to c i in response to cyanazine, and these effects were qualitatively similar to our results (compare their Fig.…”

“…Specifically, the RL response saturates at fluences similar to those for photosynthetic saturation. In addition, the action spectra for mesophyll photosynthesis and for the stomatal response to RL are similar to one another (Sharkey and Raschke, 1981a), and the RL response is abolished by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), a PSII inhibitor (Sharkey and Raschke, 1981b;Schwartz and Zeiger, 1984;Tominaga et al, 2001;Olsen et al, 2002). For these reasons, chlorophyll is commonly assumed to be the RL receptor (Assmann and Shimazaki, 1999;Zeiger et al, 2002).…”

Ecosystem CO2/H2O fluxes are explained by hydraulically limited gas exchange during tree mortality from spruce bark beetles

“…Engelmann spruce reduce their needle conductance in response to drought [Brodersen et al, 2006;Kaufmann, 1979]. Stomatal conductance, light (the most significant driver), and photosynthesis are all interconnected [Sharkey and Raschke, 1981] such that hydraulic failure can signal a reduction in photosynthesis as observed in other conifers found in the Rocky Mountains [Hubbard et al, 2001]. Thus, the 14% decrease in the g c response to PPFD during epidemic I (Table 2) may reflect a reduction in photosynthesis from limited gas exchange due to sapwood occlusion and hydraulic failure.…”

Stomatal Size, Speed, and Responsiveness Impact on Photosynthesis and Water Use Efficiency

“…In general, stomata open in response to light (with the exception of Crassulacean Acid Metabolism stomata), low CO 2 concentration, high temperatures, and low VPD, while closure is driven by low light or darkness, high CO 2 , and high VPD (Outlaw, 2003). In the natural environment, these factors exert compound effects on stomatal movements (Sharkey and Raschke, 1981;Zeiger and Zhu 1998;Talbott et al, 2003;; therefore, stomata must respond to multiple signals in an integrated and sometimes hierarchical manner (Lawson et al, 2010). Short-term stomatal responses to changes in VPD (and to some extent temperature) are often considered to be related to the water status of the plant rather than the in situ photosynthetic carbon demand, while responses to CO 2 concentration and irradiance are closely associated and correlated with mesophyll CO 2 demand.…”