From mature needles of white spruce, Picea glauca (Moench) Voss we isolated thylakoids capable of high rates of oxygen evolution. Oxygen-evolving activity of spruce thylakoids was labile in the absence of osmoticum and declined by 40 % during 1 h on ice, compared to a 9 % dechne observed in spinách thylakoids. We compared the relative activity in spruce and spinách of the oxygen evolving complex (OEC) and the reaction centre in Triton X-100 fractionated membranes prepared and stored for 20 or 240 h at 0 or -80 °C in media with different combinations of sucrose (0.3, 0.5 and 1.0 M) and two pH values (6.0 and 7.6). In membranes detergent- fractionated and stored at pH 7.6, photosystem 2 (PS2) activity (H2O -> DCIP) was sensitive to sucrose concentration of the medium. Spruce and spinách membranes prepared and stored in 0.3 M sucrose and pH 7.6, showed 22 and 48 % activity of their respective control membranes, freshly prepared in 1 M sucrose at pH 6.0. In contrast, in membranes prepared and stored at pH 6.0, PS2 activity was less sensitive to sucrose concentration: spruce and spinách membranes in 0.3 M sucrose showed 73 and 88 % (respectively) of the activity of membranes freshly prepared in 1 M sucrose. In both species, the degree of stimulation of DCIP photoreduction by diphenylcarbazide suggested minimal damage to the reaction centre (RC) except during preparation in 0.3 M sucrose, pH 7.6. Since the spruce RCs were not more labile than those of spinách, the extra sensitivity of spruce thylakoids in media of low sucrose concentration was likely due to extra lability of the OEC.
Chlorophyll (Chl) a fluorescence transient and 820-nm transmission kinetic were investigated to explore the development of photosynthetic apparatus in grapevine leaves from emergence to full expansion. In this study, all leaves at various developing stages exhibited typical Chl a fluorescence transient. In newly initiating leaves, the maximum quantum yield of primary photochemistry (ϕP0) was slightly lower (<10 %) than that in fully expanded leaves. Nevertheless, the fluorescence rise from O to J step was clearly speeded up in young leaves compared with that in fully expanded leaves. Additionally, a distinct K step appeared in young leaves at high irradiances. With leaf development, the efficiency that a trapped exciton can move an electron into the electron transport chain further than QA - (Ψ0), the quantum yield of electron transport beyond QA (ϕE0), electron transport flux per excited cross section (ET0/CS0), the amount of active photosystem (PS) 2 reaction centres per excited cross section (RC/CS0), and the performance index on cross section basis (PICS) increased gradually and rapidly. Young leaves had strikingly lower amplitude of transmission at 820 nm. A linear relationship between Ψ0 and the transmission at 820 nm (I30/I0) was evident. Based on these data, we suggest that (1) the primary photochemistry of PS2 may be not the limiting step of the photosynthetic capacity during leaf growth under natural irradiance; (2) oxygen evolving complex (OEC) might be not fully connected to PS2 at the beginning of leaf growth; (3) though there are a few functional PS1 and PS2 at the early stages of leaf development, they match perfectly. and C.-D. Jiang ... [et al.].
Thermal stability of thylakoid membranes isolated from acclimated and non-acclimated wheat (Triticum aestivum L. cv. HD 2329) leaves under irradiation was studied. Damage to the photosynthetic electron transport activity was more pronounced in thylakoid membranes isolated from non-acclimated leaves as compared to thylakoid membrane isolated from acclimated wheat leaves at 35 °C. The loss of D1 protein was faster in non-acclimated thylakoid membrane as compared to acclimated thylakoid membranes at 35 °C. However, the effect of elevated temperature on the 33 kDa protein associated with oxygen evolving complex in these two types of thylakoid membranes was minimal. Trypsin digestion of the 33 kDa protein in the thylakoid membranes isolated from control and acclimated seedlings suggested that re-organisation of 33 kDa protein occurs before its release during high temperature treatment. and A. K. Singh, G. S. Singhal.
Irradiation of thylakoid membranes at 40 °C resulted in complete inhibition of photosystem (PS) 2 activity measured as 2,6-dichlorophenol indophenol (DCIP) photoreduction either in the absence or presence of 1,5-diphenylcarbazide (DPC). Concomitant with the inactivation of PS2 activity, several thylakoid proteins were lost and high molecular mass cross-linking products appeared that cross-reacted with antibodies against proteins of PS2 but not with antibodies against proteins of other three complexes PS1, ATP synthase, and cytochrome b6f. Irradiation of thylakoid membranes suspended in buffer of basic pH or high concentration of Tris at 25 °C resulted in the formation of cross-linking products similar to those in thylakoid membranes irradiated at 40 °C. Presence of radical scavengers and DPC during the high temperature treatment prevented the formation of cross-linking products. These results suggest the involvement of oxygen evolving co mplex (OEC) in the formation of cross-linking between PS2 proteins in thylakoid membrane irradiated at high temperature. and Abhay K. Singh, G. S. Singhal.