Relationships between Stomatal Behavior and Internal Carbon Dioxide Concentration in Crassulacean Acid Metabolism Plants

Abstract

Measurements of internal gas phase CO2 concentration, stomatal resistance, and acid content were made in Crassulacean acid metabolism plants growing under The physiological significance of CAM is believed to result from the temporal separation of photosynthetic CO2 reduction and gas exchange with the atmosphere. Gas exchange with the atmosphere is restricted to the hours of darkness when the inevitable associated water loss is likely to be minimized. Photosynthetic CO2 reduction occurs without gas exchange with the atmosphere and hence without water loss. CO2 acquired at night is temporarily stored in malic acid and is consumed in photosynthetic reactions the following day.Earlier work (4, 5) has shown that CO2 may be released to the atmosphere surrounding CAM plants following illumination. This indicates that release of CO2 from malic acid is not directly caused by photosynthetic consumption of CO2 and suggests that there might be an accumulation of CO2 inside illuminated CAM tissues.Since CO2 concentration has effects on photosynthesis, respiration, photorespiration, and stomatal behaviour (1, 3, 6-8, 10) and inasmuch as it has been suggested that CO2 concentration is involved in the regulation of CAM (2) Gas Sampling. Disposable hypodermic syringes (2.0-ml capacity, 22-gauge needle) were used to withdraw gas samples (0.5-2.0 ml) from photosynthetic tissue. The syringe needle was inserted into the tissue through a globule of water standing on the surface of the plant or contained in a cup of Plasticine adhering to the plant. Taking samples by this method ensured, providing that stomata were closed, that any gas entering the syringe came from inside the plant and not from leakage around the needle. Furthermore, as the syringe was withdrawn from the plant this procedure ensured that any partial vacuum in the syringe was filled by water and not by gas from the atmosphere. If the syringe was sealed by plunging the needle deeply into a rubber stopper the sample could be stored for periods of up to 30 min without significant change in CO2 concentration. For the longer periods of storage required for field experiments (up to 30 h) gas samples, usually 1.0 ml, were injected through a serum bottle stopper into small glass vials which contained C02-free N2 and also sand to reduce the internal gas space.Measurement of CO2 Concentration. CO2 was separated from other atmospheric gases by GC of 0.5-ml samples at 70 C on a 2.15-m Porapak Q column using helium at a flow rate of 40 ml/

Succulence and CAM relationships in Aeonium genus

“…three samples in similar position on the plant, were taken from each species for the following determinations: pH measurements at 0.01 unit, rates of dark CO2 uptake in confined environment through variations of the NaHCO3 5 x 10 -s N buffer system [24] in 300cm 3 flasks and acid titrations to a pH 7.00 end point [9,31] with 0.01 N NaOH (data expressed as /~eg/g fresh weight). The pH end point used is halfway between the most habitual in the bibliography [27,3,5,14,13,26,33,22]. The mean values (n = 6) of the three samples are presented in this paper, except for regressions calculations where all the values were used in order to obtain more degrees of freedom (n = 18).…”

Evolution along the crassulacean acid metabolism continuum

“…1). This decarboxylation can lead to generation of internal leaf CO 2 partial pressures greater than 100 times atmospheric levels (Cockburn et al 1979;Spalding et al 1979), reduction in stomatal opening and transpiration and sometimes even release of CO 2 from the leaf despite low stomatal conductance (Frimert et al 1986). Decarboxylation is catalysed by either cytosolic PEP carboxykinase (PEPCK) or cytosolic NADP + -and/or mitochondrial NAD + -malic enzymes (ME) (Smith and Bryce 1992;Christopher and Holtum 1996;Holtum et al 2005).…”

Modulation of Rubisco Activity during the Diurnal Phases of the Crassulacean Acid Metabolism Plant Kalanchoëdaigremontiana

“…Whereas it is clear that decarboxylation generates very high internal partial pressures of CO 2 during phase III (typically 1.8%-8%) (Cockburn et al, 1979;Spalding et al, 1979;Osmond et al, 1999), the low internal conductance of CO 2 from the stomatal cavity to Rubisco active sites results in a very low pCO 2 during atmospheric CO 2 uptake (Maxwell et al, 1997). Therefore, during phases II and IV, the internal partial pressure of CO 2 is limiting for Rubisco carboxylase activity, but is saturating for PEPC (Osmond et al, 1999).…”