The concept that photosynthetic flux is influenced by the accumulation of photo-assimilate persisted for 100 years before receiving any strong experimental support. Precise analysis of the mechanisms of photosynthetic responses to sink activity required the development of a battery of appropriate molecular techniques and has benefited from contemporary interest in the effects of elevated CO2 on photosynthesis. Photosynthesis is one of the most highly integrated and regulated metabolic processes to maximize the use of available light, to minimize the damaging effects of excess light and to optimize the use of limiting carbon and nitrogen resources. Hypotheses of feedback regulation must take account of this integration. In the short term, departure from homeostasis can lead to redox signals, which cause rapid changes in the transcription of genes encoding photosystems I and II. End-product synthesis can exert short-term metabolic feedback control through Pi recycling. Beyond this, carbohydrate accumulation in leaves when there is an imbalance between source and sink at the whole plant level can lead to decreased expression of photosynthetic genes and accelerated leaf senescence. In a high CO2 world this may become a more prevalent feature of photosynthetic regulation. However, sink regulation of photosynthesis is highly dependent on the physiology of the rest of the plant. This physiological state regulates photosynthesis through signal transduction pathways that co-ordinate the plant carbon : nitrogen balance, which match photosynthetic capacity to growth and storage capacity and underpin and can override the direct short-term controls of photosynthesis by light and CO2. Photosynthate supply and phytohormones, particularly cytokinins, interact with nitrogen supply to control the expression of photosynthesis genes, the development of leaves and the whole plant nitrogen distribution, which provides the dominant basis for sink regulation of photosynthesis.

Sink regulation of photosynthesis

Alkalization of the Chloroplast Stroma Caused by Light-Dependent Proton Flux Into the Thylakoid Space

SUMMARY
Chloroplast preparations capable of rapid rates of photosynthesis contain large numbers of intact (Class A) chloroplasts and smaller numbers of ruptured (Class C) chloroplasts. It is suggested that there is also a third or intermediate class in which the envelope has re-sealed following rupture and release of stromal protein. The number of re-sealed chloroplasts seems to be lowest in preparations containing the largest proportion of Class A chloroplasts. Assays for intactness based on the ability of Class C chloroplasts to utilize ferricyanide as a Hill oxidant are quick and convenient but do not distinguish between Class A and re-sealed chloroplasts. If it is assumed that there is an inverse linear relationship between percentage intactness and ability to react with ferricyanide, such assays over-estimate the proportion of intact chloroplasts and, therefore, underestimate their photosynthetic activity and protein content when these are expressed on a chlorophyll basis.

https://www.jstor.org/stable/pdfplus/2431135.pdf

Criteria of intactness and the photosynthetic activity of spinach chloroplast preparations

Summary
The construction, operation and calibration of an improved form of a Clark oxygen electrode are described in detail The electrode shows a rapid response (1–5 seconds) to change in oxygen concentration and is capable of measuring rates of oxygen evolution (or uptake) of up to 4 μmoles oxygen per minute The use of a pair of electrodes to measure the oxygen evolution of choloroplasts at high intensity of illumination is described

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.1972.tb04068.x

An improved cathode for the measurement of photosynthetic oxygen evolution by isolated chloroplasts

The role of pH in the regulation of carbon fixation in the chloroplast stroma. Studies on CO2 fixation in the light and dark.

Some effects of inorganic phosphate on O2 evolution by isolated chloroplasts.

1. The orthophosphate inhibition of photosynthesis by isolated spinach chloroplasts can be reversed by 3-phosphoglycerate, dihydroxyacetone phosphate, glyceraldehyde 3-phosphate, fructose 6-phosphate and fructose 1,6-diphosphate. 2. Metabolically related compounds such as ribulose 1,5-diphosphate, glucose 6-phosphate, 6-phosphogluconate and phosphoenolpyruvate are ineffective. 3. The kinetics of reversal are characteristic of the intermediate used, but, in each instance, the onset of oxygen evolution is accompanied by a carbon dioxide fixation and except with 3-phosphoglycerate the stoicheiometry is close to unity. 4. The nature of orthophosphate inhibition and its reversal is discussed in relation to metabolic control of photosynthesis.

/pdf/photosynthesis-by-isolated-chloroplasts-reversal-of-5as95iisig.pdf

W. Cockburn

Papers

Some effects of inorganic phosphate on O2 evolution by isolated chloroplasts.

Photosynthesis by isolated chloroplasts. Reversal of orthophosphate inhibition by Calvin-cycle intermediates

Oxygen evolution by isolated chloroplasts with carbon dioxide as the hydrogen acceptor. A requirement for orthophosphate or pyrophosphate.

Inhibition, by sulphate, of the oxygen evolution associated with photosynthetic carbon assimilation

Photosynthetic induction phenomena in spinach chloroplasts in relation to the nature of the isolating medium.