Short-term responses of Photosystem I to heat stress

Abstract

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.

Genetic engineering of glycine betaine biosynthesis to enhance abiotic stress tolerance in plants

“…It has been demonstrated that PSII is highly affected by severe heat stress when temperature is above 45°C (Havaux 1996). Moderately high temperatures that normally inhibit CO 2 fixation have no lethal effects on PSII (Haldimann and Feller 2004).…”

The chloroplast Ndh complex mediates the dark reduction of the plastoquinone pool in response to heat stress in tobacco leaves

“…E¡ect of heat stress on the rate of re-reduction of P700 + after far-red illumination in the ndh mutant v1 Previous work has shown that mild heat stress of pea [7] and potato [8] leaves induces a dramatic increase in the rate of re-reduction of P700 in the dark after a period of far-red illumination. This type of assay gives a measure of the rate of PSII-independent reduction of PSI and is comprised of both cyclic electron transfer around PSI and electron donation to the intersystem electron transfer chain by stromal reductant [8,12].…”

“…This type of assay gives a measure of the rate of PSII-independent reduction of PSI and is comprised of both cyclic electron transfer around PSI and electron donation to the intersystem electron transfer chain by stromal reductant [8,12]. Fig.…”

Heat Stress Induces an Aggregation of the Light-Harvesting Complex of Photosystem II in Spinach Plants

“…It has been considered for many years that PSII is the primary site of heat damage to the photosynthetic function (Berry and Bjö rkman, 1980;Havaux, 1993Havaux, , 1996. For example, heat stress results in a loss of the oxygen evolving complex activity (Enami et al, 1994;Yamane et al, 1998), an inhibition of electron transfer from primary/ secondary electron-accepting plastoquinone of PSII at the acceptor side (Bukhov et al, 1990;Cao and Govindjee, 1990), and a dissociation of the peripheral antenna complex of PSII from its core complex (Gounaris et al, 1984;Srivastava et al, 1997).…”

“…However, it has been well understood in recent years that PSII activity is not inhibited at temperatures that inhibit whole leaf CO 2 assimilation, suggesting that CO 2 assimilation is most sensitive to heat stress (for review, see Salvucci and Crafts-Brandner, 2004a). It has been shown that PSII is damaged by severely high temperature stress when temperature is normally higher than 45°C (Havaux, 1993(Havaux, , 1996, while CO 2 assimilation is already significantly decreased by moderately high temperature stress (Weis, 1981a(Weis, , 1981bFeller et al, 1998;Crafts-Brandner, 2004a, 2004b). The decreased CO 2 assimilation is associated with the inhibition of activation of Rubisco via a direct effect on Rubisco activase (Feller et al, 1998;Haldimann and Feller, 2004;Salvucci and Crafts-Brandner, 2004b).…”