Chlorophyll a Fluorescence Yield as a Monitor of Both Active CO₂ and HCO₃⁻ Transport by the Cyanobacterium Synechococcus UTEX 625

Abstract

Simultaneous measurements have been made of inorganic carbon accumulation (by mass spectrometry) and chlorophyll a fluorescence yield of the cyanobacterium Synechococcus UTEX 625. The accumulation of inorganic carbon by the cells was accompanied by a substantial quenching of chlorophyll a fluorescence. The quenching occurred even when CO2 fixation was inhibited by iodoacetamide and whether the accumulation of inorganic carbon resulted from either active CO2 or HCO3-transport. Measurement of chlorophyll a fluorescence yield of cyanobacteria may prove to be a rapid and convenient means of screening for mutants of inorganic carbon accumulation.We have shown that the cyanobacterium Synechococcus UTEX 625 can actively transport both CO2 and HCO3- (5,6,10,11,21). Other cyanobacteria, both unicellular and filamentous, have similar abilities (1,2,6,8,13,14,16,17, 22). The active transport of CO2 can be unambiguously monitored by mass spectrometry (2, 3). Unfortunately, HCO3-transport can be monitored by mass spectrometry only in the presence of carbonic anhydrase (2, 3), which is known to stimulate CO2 transport (10). The transport and accumulation of DIC2 can be monitored under some circumstances by the centrifugal filtration of cells through a layer of silicone fluid after they have been incubated in 14C-DIC (8, 13). This is a very useful method, especially for the study of HCO3-transport. It does, however, have a number of drawbacks. It is a rather laborious technique, not well suited to screening a large number of samples, as is necessary in a search for DIC transport mutants. Also, the cells cannot be separated fast enough from the incubation solution to allow proper monitoring of CO2 transport in many cases (AG Miller, GS Espie, DT Canvin, unpublished data). DIC transport can be monitored by IR gas analysis (16,18), but the method is restricted to the study of cell suspensions at pH 7.5 or below.We

Utilization of inorganic carbon in the edible cyanobacterium Ge‐Xian‐Mi (Nostoc) and its role in alleviating photo‐inhibition

“…It is possible that the low-CO 2 -inducible system is supported by PSI activity that depends on electrons donation from PSII whereas the constitutive system is partially supported by cyclic PSI electron transport (Ogawa & Kaplan 2003). It has been shown that DIC accumulation in Synechococcus UTEX 625 dramatically increased electron flow from PSII to PSI and resulted in the quenching of chlorophyll fluorescence (Miller & Canvin 1987;Miller, Espie & Canvin 1988a, b, 1991Crotty, Tyrrell & Espie 1994). Much excitation energy will be used to transport DIC under C i limititation because the operation of CCM is dependent on the supply of photosynthetic energy.…”

Active Transport of Inorganic Carbon Increases the Rate of O2 Photoreduction by the Cyanobacterium Synechococcus UTEX 625

“…The active transport of HC03-or CO2 causes quenching of Chl a fluorescence in Synechococcus UTEX 625 even when CO2 fixation is inhibited by iodoacetamide (14,16). Quenching does not occur in the presence of DCMU which suggests that the quenching is due to oxidation of the acceptor QA of PSII (14).…”

“…Quenching does not occur in the presence of DCMU which suggests that the quenching is due to oxidation of the acceptor QA of PSII (14). In the presence ofiodoacetamide, CO2 reduction cannot be a means for oxidation of QA (14,16), but it is well established that 02 can also be reduced by noncycic electron transport (1,4,6). Addition of 02 can cause Q-quenching (qQ2) even in the absence of CO2 (7).…”

Selective and Reversible Inhibition of Active CO2 Transport by Hydrogen Sulfide in a Cyanobacterium

“…Changes in Chl a fluorescence yield, which occurred as a consequence of DIC transport (15,18) were measured with a pulse modulation fluorometer described in (Fig. 1A).…”