angbi Li

Development and Application of EST-Based Markers Specific for Chromosome Arms of Rye (Secale cereale L.)

To develop a set of molecular markers specific for the chromosome arms of rye, a total of 1,098 and 93 primer pairs derived from the expressed sequence tag (EST) sequences distributed on all 21 wheat chromosomes and 7 rye chromosomes, respectively, were initially screened on common wheat ‘Chinese Spring’ and rye cultivar ‘Imperial’. Four hundred and fourteen EST-based markers were specific for the rye genome. Seven disomic chromosome addition lines, 10 telosomic addition lines and 1 translocation line of ‘Chinese Spring-Imperial’ were confirmed by genomic in situ hybridization and fluorescencein situ hybridization, and used to screen the rye-specific markers. Thirty-one of the 414 markers produced stable specific amplicons in ‘Imperial’, as well as individual addition lines and were assigned to 13 chromosome arms of rye except for 6RS. Six rye cultivars, wheat cultivar ‘Xiaoyan 6’ and accessions of 4 wheat relatives were then used to test the specificity of the 31 EST-based markers. To confirm the specificity, 4 wheat-rye derivatives of ‘Xiaoyan 6 × German White’, with chromosomes 1RS, 2R and 4R, were amplified by some of the EST-based markers. The results indicated that they can effectively be used to detect corresponding rye chromosomes or chromosome arms introgressed into a wheat background, and hence to accelerate the utilization of rye genes in wheat breeding.

Relationship between leaf photosynthetic function at grain filling stage and yield in super high-yielding hybrid rice (Oryza sativa. L)

The characteristics of dry matter production before and after heading and the relationships between photosynthesis of flag leaves and dry matter accumulation in panicles were investigated on super high-yielding rice cv. Xieyou 9308 (the yield of up to 12 t/ha) with rice cv. Xieyou 63 as a control. The results showed that (i) the capacity of dry matter production before and after heading in Xieyou 9308, i.e. biomass and daily dry matter production, was remarkably higher than that in Xieyou 63, especially after heading; (ii) CO2 assimilation capacity in flag leaves in Xieyou 9308, namely Leaf Source Capacity (LSC), was also significantly higher than that in Xieyou 63, and the supply of photosynthate in leaves and the demand of grain filling were completely synchronous in Xieyou 9308, but photosynthetic function in flag leaves in Xieyou 63 declined sharply 20 days after heading and it was not enough to meet the demand of grain filling. These results confirmed that high efficient photosynthetic function in leaves after heading and its complete synchronization with grain filling are the key approaches to super high yield of rice.

New structure model of oxygen-evolving center and mechanism for oxygen evolution in photosynthesis

So far, many important questions and problems concerning the structure and mechanism of photosynthetic oxygen evolution are still unsolved. On the basis of recent achievements in this field, a new structure model is proposed whereby two H2O molecules bind asymmetrically to two manganese ions (Mn1II and Mn4III) at the open end of “C” shaped cluster and keep rather large distance. Two histidine residues coordinate to the other two manganese ions in higher oxidation state (Mn2IV and Mn3IV) through their nitrogen atoms of the imidazole. CI bound as terminal ligand to Mn4III is connected to Ca, and the latter is needed to maintain the special configuration of two Mn2O2 units by bridged-oxo and bridged-carboxylate ligands. The whole structure of oxygen evolution center is asymmetry. A new mechanism for oxygen evolution invokes predictions of asymmetric oxidation of two H2O molecules, dynamic structural changes of oxygen evolving center and indirect proton transport, etc. Only in S2 state, could Mn1IV = O, intermediate with high oxidation potential be formed. The S2→ S3 process occurs with significant structural changes, as well as intramolecular and intermolecular hydrogen transfer. The S3 state corresponds to intermediate of Mn1IV-O … H … O-Mn4IV. During S3 → [S4] → S0, the 0-0 bond is formed only in S4 state. The change of nucleophilic interaction between Cl and manganese ions different oxidation states has consequence for the significant structural changes in H2O oxidation process.

Theoretical study on primary reaction of photosynthetic bacteria.

Theoretical calculation was carried out on the primary electron donor P870 of photosynthetic bacteria. The results show that: (i) the bimolecular structure of the primary electron donor is more advantageous in energy than monomolecular structure; (ii) the initial configuration of primary electron donor is no longer stable and changes to the configuration with lower energy and chemical reactivity after the charge separation. In the P870, such structural change is completed through the rotation of C3 acetyl, so the oxygen atom of acetyl interacts with the magnesium atom of another bacterio-chlorophyll molecule, and the total energy and chemical reactivity are reduced evidently. It is suggested that the structural change of the primary electron donor is important in preventing the occurrence of charge recombination during the primary reaction and maintaining the high efficiency of the conversion of sun-light to chemical energy. A new mechanism of primary reaction has been proposed, which can give reasonable explanations to the results of kinetic and site mutation studies.

Responses of photosystem II of white elm to UV-B radiation monitored by OJIP fluorescence transients

Photosystem II (PSII) activities in both samara and leaf of white elm (Ulmus pumila L.) were significantly inhibited by enhanced UV-B radiation (UVBR). UVBR disturbed both the donor and acceptor sides of PSII. The plastoquinone (PQ) pool size on the acceptor side, the trapped excited energy for complete reduction of QA, and the proportion of closed PSII reaction centers (RCs) increased, with PSII RCs being transformed into dissipative sinks for excitation energy under UVBR. However, samara and leaf responded to UVBR in different ways. A decrease in the F0 for leaf induced by UV-B radiation suggests the formation of fluorescence-quenching centers. An increase in the VI for leaf under UVBR might mean the accumulation of reduced QA and PQ. F0 and VI for samara showed opposite change pattern. Leaf has the mechanism of regulation of the amount of light reaching the RC through decreasing the number of light-harvesting chlorophyll molecules under UVBR while samara may be unable to regulate the light-harvesting capacity. PSII in samara was more susceptible to UVBR than that in leaf, with PIABS for samara decreasing more rapidly by a factor of 6.4 than that for leaf. Samara can recover more easily from UVBR-induced damage to PSII than the leaf.

33 ku protein associated several polypeptides with nearly the same molecular weight but not the same isoelectric point

The 33 ku protein, prepared from NaCl-treated PS II particles, has shown an single band by SDS-PAGE. After being dialyzed against the low-osmotic medium at 4°C, it has been found that the 33 ku protein degraded into several small fragments. This result suggests that the preparations of 33 ku protein probably contain some latent proteinases. It has also been found, by the 2-D electrophoresis and IEF, that the preparations of 33 ku protein not dialyzed against the low-osmotic medium contain several polypeptides with nearly the same molecular weight but not the same isoelectric point as the 33 ku protein.

Ultrafast spectroscopy studies on the mechanism of electron transfer and energy conversion in the isolated pseudo ginseng, water hyacinth and spinach chloroplasts

The spectroscopy characteristics and the fluorescence lifetime for the chloroplasts isolated from the pseudo ginseng, water hyacinth and spinach plant leaves have been studied by absorption spectra, low temperature steady-state fluorescence spectroscopy and single photon counting measurement under the same conditions and by the same methods. The similarity of the absorption spectra for the chloroplasts at room temperature suggests that different plants can efficiently absorb light of the same wavelength. The fluorescence decays in PS II measured at the natural QA state for the chloroplasts have been fitted by a three-exponential kinetic model. The three fluorescence lifetimes are 30, 274 and 805 ps for the pseudo ginseng chloroplast; 138, 521 and 1494 ps for the water hyacinth chloroplast; 197, 465 and 1459 ps for the spinach chloroplast, respectively. The slow lifetime fluorescence component is assigned to a collection of associated light harvesting Chl a/b proteins, the fast lifetime component to the reaction center of PS II and the middle lifetime component to the delay fluorescence of recombination of P+ 680 and Pheo-. The excitation energy conversion efficiency(η) in PS II RC is defined and calculated on the basis of the 20 ps electron transfer time constant model, 60%, 87% and 91% for the pseudo ginseng, water hyacinth and spinach chloroplasts, respectively. This interesting result is in unconformity with what is assumed to be 100% efficiency in PS II RC. Our result in this work stands in line with the 20 ps electron transfer time constant in PS II rather sound and the water hyacinth plant grows slower than the spinach plant does as envisaged on the efficiency. But, our results predict that those plants can perform highly efficient transfer of photo-excitation energy from the light-harvesting pigment system to the reaction center (closely to 100%). The conclusion contained in this paper reveals the plant growth characteristics expressed in the primary processes of photosynthesis and a relationship between a plant growing rate and its spectroscopy characteristics and fluorescence lifetimes, namely, the slower a plant grows, the less excitation energy conversation efficiency used might be anticipated.

Theoretical investigation on peripheral ligands of oxygen-evolving center in photosystem II.

The interaction between the Mn-cluster and its peripheral ligands in oxygen-evolving center is still unclear. Theoretical investigation on the coordination of histidine, H2O, and CI to Mn2O2 units in OEC is conducted. The following conclusions are obtained: (i) both histidine and H2O molecule, bound to the two Mn ions, respectively, are vertical to the Mn2O2 plane, and maintain a large distance; (ii) the two H2O molecules cannot bind to the same Mn2O2 unit. Based on Mn-cluster structure in OEC, we theoretically predict that two H2O molecules bind to the two Mn ions at the “C”-shaped open end in S0 state, while two His residues at the closed end. Cl ion can only terminally ligate at the open end. Individual valence for the four Mn ions in S0 state is assigned.

Effect of phosphatidylglycerol on conformation and micro-environment of tyrosyl residue in photosystem II

The structural aspects in the interaction of phosphatidylglycerol (PG) with photosystem II (PSII), mainly the effect of PG on conformation and microenvironment of tyrosine residues of PSII proteins were studied by Fourier transform infrared (FTIR) spectroscopy. It was found that the binding of PG to PSII particle induces changes in the conformation and micropolarity of phenol ring in the tyrosine residues. In other words, the PG effect on the PSII results in blue shift of the stretch vibrational band in the phenol ring from 1620 to 1500 cm−1 with the enhancement of the absorbance intensity. Additionally, a new spectrum of hydrogen bond was also observed. The results imply that the hydrogen-bond formation between the OH group of phenol and one of PG might cause changes in the structures of tyrosine residues in PSII proteins.

The Theoretical Investigation of the Electronic Structure of the Primary Electron Donor in Rhodopseuodomonas Virid

Since the X-ray crystal structure of photosynthetic reaction center (RC) of purple bacteria was reported at 2.3-A resolution[1] ten years ago, the studies on the mechanism of electron transfer (ET) in the RC have been achieved a new atomic mlecular level. The protein cofactor of RC consists of four bacteriochlorophylls (Bchl), two bacteriopheophytins (Bpheo), two quinines and one non-heme iron Fe. Among them, two Bchls, named PL and PM, are close juxtaposed with their pyrrsole ring I overlapping at an average inter-macrocycle separation of ~ 3.3 A, and form the “special pairs” P. When P is excited by solar energy, an electron is transferred from P to the Bpheo molecule on the L branch rapidly (in ~ 3 Ps at room temperature). The fast ET is followed by two slower ET, first to the nearby quinine QA, then to a quinine on the M branch QB[2–3]. Why the ET proceeds only along the L branch of the pseduo-two-fold symmetry in the RC of photosynthetic bacteria? Although many papers focused on this problem, it is still not fully understood.