SUMMARYMeasurements of photosynthetic CO2 and Oj exchange, and associated chlorophyll fluorescence were made on leaves (from plants grown in complete nutrient medium) while the internal inorganic phosphate concentration was increased or decreased by feeding solutions through the vascular tissue. The data indicate that orthophosphate supply to the chloroplast can, in some circumstances, become the process that limits photosynthesis in vivo.

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ABSTRACIIn spinach (Spinacia okracea) and barley (Hordeum vulgare) leaves, chlorophyll a fluorescence and 02 evolution have been measured simultaneously following re-illumination after a dark interval or when steady state photosynthesis has been perturbed by changes in the ps phase. In high CO2 concentrations, both O°and fluorescence can display marked dampening oscillations that are antiparallel but slightly out of phase (a rise or fall in fluorescence anticipating a corresponding fall or rise in 02 by about 10 to 15 seconds). Infrared gas analysis measurements showed that CO2 uptake behaved like 2 evolution both in the period ofoscillation (about 1 minute) and in its relation to fluorescence. In the steady state, oscillations were initiated by increases in CO2 or by increases or decreases in 02. Oscillations in 02 or CO2 did not occur without associated oscillations in fluorescence and the latter were a sensitive indicator of the former. The relationship between such oscillations in photosynthetic carbon assimilation and chlorophyl a fluorescence is discussed in the context of the effect of ATP or NADPH consumption on known quenching mechanisms.In 1949, Van der Veen (23) described what he called 'irregularities in photosynthesis' during the period when a leaf is suddenly illuminated after a period in darkness. These irregularities during the induction period, i.e. the lag before maximal photosynthesis is achieved following re-illumination (28), included 'secondary peaks' (or increases and decreases in rate which finally gave way to a more or less steady rate of CO2 uptake). Similar but somewhat simpler irregularities associated with re-illumination had already been observed by McAlister and Myers (16) and by Aufdemgarten (2). They were immediately apparent when renewed attempts were made to follow 02 evolution from leaf discs by polarographic methods (26 studied for many years, and many attempts have been made to relate these relatively slow changes (that normally occur after the first few s of illumination), with changes in 02 evolution and/or CO2 uptake (see e.g. Ref. 16). Surprisingly, Van der Veen (24) did not follow the fluorescence changes associated with the more dramatic secondary peaks in CO2 fixation which he had observed (cf Refs 23 and 24) but nevertheless concluded that 'nearly always increase of photosynthesis during adaptation (induction) is correlated with a decrease of fluorescence.' In algae, the relationship seems less clear and Chl fluorescence has been found to rise in parallel with 02 evolution in some circumstances (3) but not in others (18) and Ogawa (19) has recently reported that fluorescence yield and 02 evolution oscillate in phase (in parallel) in Vicia faba leaves under anaerobic conditions. In preliminary experiments with spinach, antiparallel, dampening oscillations in 02 and fluorescence were observed (29). These observations have now been confirmed and further characterization of these phenomena is reported.

A close, immediate and precise relationship between chlorophyll a fluorescence and photosynthetic carbon assimilation in xivo is demonstrated. The examples discussed include kinetics displayed during dark to light transitions plus oscillations and transients observed during changes in the gas phase surrounding the leaf. Remaining uncertainties surrounding the relationship between chlorophyll fluorescence and photosynthesis are attributed to the underlying complexity of the regulatory mechanisms involved. Examples are also given that show how multiple simultaneous measurements of difl'erent aspects of the photosynthetic process may contribute to the resolution of these uncertainties. The practical relevance of these matters is also discussed, particularly in relation to the limitations of the photosynthetic process and to the use of chlorophyll fluorescence as a diagnostic probe of chemical and genetic manipulation and stress,

The structure of a-glucan, isolated from wild-type Escherichia coli B, a glycogen branching enzyme (BE)-deficient E. coli AC71 (glgB-), or from AC71 transformed with genes coding for maize BEI and BEII individually as well as with both genes, was analyzed by high-performance anion-exchange chromatography (HPAEC) with pulsed amperometric detection. Transformation of the maize BE gene(s) in AC71 (glgB-) showed complementation in branching activity. Analysis by HPAEC revealed different structures between glycogen ofE. coli B and a-glucan of AC71 transformed with a different maize BE gene(s). The individual chains of the ci-glucan debranched with isoamylase were distributed between chain length (CL) 3 and > 30 and the chain with CL 6 was the most abundant. In comparison with the glycogen ofE. coli B, the az-glucan of AC71 transformed with the maize BE gene(s) consisted ofa lesser amount of chains with CL 7-9 and a larger amount ofchains with CL > 14. It also showed a broad peak with chains of CL 9-12 as in maize amylopectin. This study provides in vivo evidence that glycogen BE and maize BE isozymes may have different specificities in the length of chain transferred. Furthermore, this study suggests that the specificity of glycogen synthase and starch synthase and their concerted action with BE play an important role in determining the structure of the polysaccharide synthesized.