Sink regulation of photosynthesis

Abstract

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.

A complete ferredoxin/thioredoxin system regulates fundamental processes in amyloplasts

“…The amount of photosynthate produced and exported by leaves has long been known to be greatly enhanced by light (54). In addition to providing energy and essential building blocks, metabolites transported in the phloem, such as sucrose and hexoses, have more recently been shown to be part of a signaling network whereby source and sink tissues communicate (55,56). The current study provides new insight into how these metabolites could regulate processes of heterotrophic plastids.…”

Increased Phytochrome B Alleviates Density Effects on Tuber Yield of Field Potato Crops

“…The primary effect could be on tuber formation and the increased demand of photo-assimilates by the larger number of tubers. Control of maximum photosynthesis by the availability of sinks is well established (Paul and Foyer, 2001), and in some cases, it has been related to changes in stomatal conductance (Setter and Brun, 1980). In favor of this interpretation, tuber number increased more than tuber yield with the consequent reduction in weight per tuber.…”

Stress-Induced Cytokinin Synthesis Increases Drought Tolerance through the Coordinated Regulation of Carbon and Nitrogen Assimilation in Rice

“…[See online article for color version of this figure. ] and Foyer, 2001), and N metabolism . Previously, we showed that the induction of CK synthesis in transgenic P SARK ::IPT rice influenced changes in source-sink interactions that resulted in the improvement of yield and grain quality .…”