Study of Energy Storage Processes in Bundle Sheath Cells of <i>Zea mays</i>

Popovic, Radovan; Beauregard, Marc; Leblanc, Roger M.

doi:10.1104/pp.84.4.1437

Cited by 10 publications

(5 citation statements)

References 17 publications

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“…On the other hand, NADPH has been shown to reduce the plastoquinone pool and P700 + when added to isolated thylakoid membranes (Mills et al 1979;Wieckowski et al 1988;Miyake et al 1994). In this context, it is worth mentioning that, in a study of heated chloroplasts supplied with ascorbate, Sabat et al (1989) have concluded that some sites in the intersystem electron-transport chain are opened in response to heat stress, allowing electron donation by this reductant to PS I. Interestingly, reduction of PSI by ascorbate has been previously inferred from photoacoustic analysis of C4 bundle sheath cells (Popovic et al 1987). 1988) and which are actively transcripted (Berger et al 1993;Matsubayashi et al 1987), thus supporting the existence of a NAD(P)H plastoquinone oxidoreductase in higher-plant chloroplast membranes.…”

Section: Discussionmentioning

confidence: 93%

Short-term responses of Photosystem I to heat stress

Havaux

1996

Photosynth Res

209

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When 23°C-grown potato leaves (Solanum tuberosum L.) were exposed for 15 min to elevated temperatures in weak light, a dramatic and preferential inactivation of Photosystem (PS) II was observed at temperatures higher than about 38°C. In vivo photoacoustic measurements indicated that, concomitantly with the loss of PS II activity, heat stress induced a marked gas-uptake activity both in far-red light (>715 nm) exciting only PS I and in broadband light (350-600 nm) exciting PS I and PS II. In view of its suppression by nitrogen gas and oxygen and its stimulation by high carbon-dioxide concentrations, the bulk of the photoacoustically measured gas uptake by heat-stressed leaves was ascribed to rapid carbon-dioxide solubilization in response to light-modulated stroma alkalization coupled to PS I-driven electron transport. Heat-induced gas uptake was observed to be insensitive to the PS II inhibitor diuron, sensitive to the plastocyanin inhibitor HgCl2 and saturated at a rather high photon flux density of around 1200 μE m(-2) s(-1). Upon transition from far-red light to darkness, the oxidized reaction center P700(+) of PS I was re-reduced very slowly in control leaves (with a half time t1/2 higher than 500 ms), as measured by leaf absorbance changes at around 820 nm. Heat stress caused a spectacular acceleration of the postillumination P700(+) reduction, with t1/2 falling to a value lower than 50 ms (after leaf exposure to 48°C). The decreased t1/2 was sensitive to HgCl2 and insensitive to diuron, methyl viologen (an electron acceptor of PS I competing with the endogenous acceptor ferredoxin) and anaerobiosis. This acceleration of the P700(+) reduction was very rapidly induced by heat treatment (within less than 5 min) and persisted even after prolonged irradiation of the leaves with far-red light. After heat stress, the plastoquinone pool exhibited reduction in darkness as indicated by the increase in the apparent Fo level of chlorophyll fluorescence which could be quenched by far-red light. Application (for 1 min) of far-red light to heat-pretreated leaves also induced a reversible quenching of the maximal fluorescence level Fm, suggesting formation of a pH gradient in far-red light. Taken together, the presented data indicate that PS I responded to the heat-induced loss of PS II photochemical activity by catalyzing an electron flow from stromal reductants. Heat-stress-induced PS I electron transport independent of PS II seems to constitute a protective mechanism since block of this electron pathway in anaerobiosis was observed to result in a dramatic photoinactivation of PS I.

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Section: Discussionmentioning

confidence: 93%

Short-term responses of Photosystem I to heat stress

Havaux

1996

Photosynth Res

209

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“…1984; Buschmann, 1987;Popovic et al, 1987). This approach has the advantage of using the same sample as active and inactive material.…”

Section: Introductionmentioning

confidence: 99%

Simultaneous Saturation of Variable Fluorescence Yield and Photoacoustically Monitored Thermal Emission in Thylakoid Membranes

Carpentier

Owens

Leblanc

1991

Photochem & Photobiology

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Thermal and fluorescence emission from thylakoid membranes were monitored simultaneously in a photoacoustic cell. A close relationship existing between variable fluorescence and variable thermal emissions is demonstrated. The modulated measuring beam of the photoacoustic spectrophotometer was used to study the effect of light intensity on the energy storage yield and on the variable fluorescence yield. The half-saturation light intensities obtained for both parameters were 8.5 and 9.1 W m-2, respectively. The similar sensitivity of energy storage and variable fluorescence yield to light intensity indicates that electron transfer with plastoquinone as last acceptor is probably responsible for the photoacoustically monitored energy storage.

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“…Popovic and coworkers have shown that P S I1 in bundle sheath chloroplasts regulates ("poises") the redox state of PS I and prevents its overoxidation a n d that malate is not serving this reducing function. 164,165,167,168…”

Section: Owens Etmentioning

confidence: 99%