The kinetics of P‐700⁺ reduction in leaves : a novel in situ probe of thylakoid functioning

Abstract. The half time (t1/2) of the reduction of P‐700+ in the millisecond time frame is known to be limited by the reaction between plastoquinol and the cytochrome cytb6f complex. This is considered to be the rate limiting reaction of thylakoid electron transport and measurements of it provide a means of analysing how thylakoid election transport is regulated in vivo. The half time for the reduction of photochemically oxidized P‐700 has been measured in vivo using absorbance changes around 820 nm. The results showed that t1/2 is independent of irradiance and decreases as photosynthetic induction progresses. Even with a constant t1/2 the quantum efficiency of PSI declined as irradiance increased. The significance of the concept of photosynthetic control of electron transport is discussed in the light of these observations.</p

Changes in P-700 oxidation during the early stages of the induction of photosynthesis

Following dark adaptation, the response to irradiance of chlorophyll (Chl) fluorescence, the light-induced absorbance change around 820 nm (to measure reaction center Chl of photosystem I [PSI] P-700 oxidation), and CO2 fixation were examined in pea (Pisum sativum L.) leaves under a range of conditions. Initially, P-700 oxidation is restricted by a lack of regeneration of PSI electron acceptors, and the increase of oxidized P-700 (P-700+) that occurs during approximately the first 60 s of irradiation is largely independent of the resistance to electron flow between the two photosystems. Under these conditions, the quantum efficiency for linear electron flow is directly positively related to P-700+ accumulation, which is in contrast to the direct negative correlation that is the most frequently reported relationship between P-700+ accumulation and the quantum efficiency for linear electron flow

A mutation at the rb gene, lowering ADPGPPase activity, affects storage product metabolism of pea seed coats

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