Photosynthetic characteristics of two hybrid rice combinations, Peiai 64S/E32 and Shanyou 63, were compared at the panicle differentiation stage. As compared with Shanyou 63, the new combination Peiai 64S/E32 showed a significantly higher net photosynthetic rate (PN), apparent quantum yield of carbon assimilation (Φc), carboxylation efficiency (CE), and photorespiratory rate (RP) as well as leaf chlorophyll content, but a significantly lower dark respiration rate (RD) and compensation irradiance (Ic). It also showed a slightly higher photochemical efficiency (Fv/Fm and ΔF/Fm') of photosystem 2, a lower non-photochemical quenching (qN), and a similar CO2 compensation concentration (Γ) as compared to Shanyou 63. and Hua Jiang ... [et al.].
After saturating irradiation for 3 h (SI), the original fluorescence F0 increased while the photosystem 2 (PS2) photochemical efficiency (Fv/Fm) declined significantly. These parameters could largely recover to the levels of dark-adapted leaves after 3 h of subsequent dark recovery. No net loss of the D1 proteins occurred after SI. Soybean and pumpkin leaves had different responses to SI. Low temperature fluorescence parameters, F685 and F685/F735, decreased significantly in soybean leaves but not in pumpkin leaves. Part of the light-harvesting complex LHC2 dissociated from PS2 complexes in soybean leaves but not in pumpkin leaves, as shown by sucrose density gradient centrifugation and SDS-PAGE. The photon-saturated PS2 electron transport activity declined significantly in pumpkin thylakoids but not in soybean thylakoids. In addition, a large amount of phosphorylated D1 proteins was found in dark-adapted soybean leaves but not in dark-adapted pumpkin leaves. Hence at excessive irradiance soybean and pumpkin have the same protective strategy against photo-damage, reversible down-regulation of PS2, but two different mechanisms, namely the reversible down-regulation is related to the dissociation of LHC2 in soybean leaves but not in pumpkin leaves. and Hai-Bo Zhang, Da-Quan Xu.
Significant differences in net photosynthetic rate (PN) of leaves between two maize (Zea mays L.) strains (Shuang 105 and 40×44) grown in the field were observed. At several growth stages, PN of 40×44 was higher than that of Shuang 105 (from 10.3 to 32.5 %). Moreover, the strain 40×44 had a higher plant height, larger leaf area, lower chlorophyll content, and higher photochemical efficiency of photosystem 2 (PS2) (Fv/Fm and ΔF/Fm') than strain Shuang 105. Shuang 105, which showed lower PN, had lower stomatal conductances (gs) but slightly higher intercellular CO2 concentrations (Ci) than those of 40×44. Hence the differences in
PN between the two strains did not result from the difference in gs, but probably from that in light reaction system. and Hua Jiang, Da-Quan Xu.
The protective role of light-harvesting complex 2 (LHC2) dissociation from photosystem 2 (PS2) complex was explored by the 5'-p-fluorosulfonylbenzoyl adenosine (FSBA, an inhibitor of protein kinase) treatment at saturating irradiance (SI) in soybean leaves and thylakoids. The dissociation of some LHC2s from PS2 complex occurred after SI treatment, but FSBA treatment inhibited the dissociation as demonstrated by analysis of sucrose density gradient centrifugation of thylakoid preparation and low-temperature (77 K) chlorophyll (Chl) fluorescence. A significant increase in F0 and decrease in Fv/Fm occurred after SI, and the two parameters could largely recover to the levels of dark-adapted leaves after subsequent 3 h in the dark, but they could not recover in the FSBA-treated leaves at SI. Neither the electron transport activity of PS2 nor the D1 protein amount in vivo had significant change after SI without FSBA, whereas FSBA treatment at SI could result in significant decreases in both the PS2 electron transport activity and the D1 protein amount. When thylakoids instead of leaves were used, the PS2 electron transport activity and the D1 protein amount declined more after SI with FSBA than without FSBA. The phosphorylation level of PS2 core proteins increased, while the phosphorylation level of LHC2 proteins was reduced after SI. Also, the phosphorylation of PS2 core proteins could be greatly inhibited by the FSBA treatment at SI. Hence in soybean leaf the LHC2 dissociation is an effective strategy protecting PS2 reaction centres against over-excitation and photodamage by reducing the amount of photons transferred to the centres under SI, and the phosphorylation of PS2 core proteins plays an important role in the dissociation. and Hai-Bo Zhang, Da-Quan Xu.
The oligomeric state of photosystem 2 (PS2) complex in soybean leaves treated with saturating irradiance was studied by non-denaturing polyacrylamide gel electrophoresis (PAGE) and gel filtration chromatography. PS2 dimers resolved by non-denaturing PAGE accounted for about 75 % of total PS2 complex and there was no significant difference in the ratio of PS2 dimer to monomer between samples from saturating irradiance-treated and fully dark-adapted leaves. Furthermore, BBY particles were resolved into four chlorophyll-enriched fractions by gel filtration chromatography. From their molecular masses and protein components, these fractions were deduced to be PS2 dimer, PS2 monomer, oligomeric light-harvesting complex 2 (LHC2), and monomeric LHC2. Also, no change in the proportion of PS2 dimer in total PS2 was observed in the granal region of thylakoid membranes from soybean leaves after saturating irradiation. Hence the dimer is the predominant natural form of PS2 in vivo and no monomerisation of PS2 dimer occurs during saturating irradiance-induced photoinhibition in soybean leaves. and Shi-Qing Cai ... [et al.].
To explore the cause of difference in photosynthetic performance between different cultivars of crops, leaf net photosynt rate (PN) and photosystem 2 (PS2) photochemical efficiency (Fv/Fm), apparent quantum yield of carbon assimilation (φc), electron transport rate, photophosphorylation activity, etc. were measured in two soybean cultivars, Heinong 42 and Heinong 37. At pod setting and filling, significant differences in PN between them were observed. The former with a higher PN (from 7 to 38 %) had a significantly higher leaf thickness, leaf dry mass/area (LMA), chlorophyll content, soluble protein content, apparent quantum yield of electron transport through PS2 (φe), carboxylation efficiency (CE), and ribulose-1,5-bisphosphate carboxylase (RuBPC) activity. The significantly higher PN of Heinong 42 is mainly due to its higher content and activity of RuBPC. and Hua Jiang, Da-Quan Xu.