Two new yellow rice chlorophyll (Chl) b-less (lack) mutants VG28-1 and VG30-5 differ from the other known Chl b-less mutants with larger amounts of soluble protein and ribulose-1,5-bisphosphate carboxylase/oxygenase small sub-unit and smaller amounts of Chl a. We investigated the altered features of Chl-protein complexes and excitation energy distribution in these two mutants, as compared with wild type (WT) rice cv. Zhonghua 11 by using native mild green gel electrophoresis and SDS-PAGE, and 77 K Chl fluorescence in the presence of Mg2+. WT rice revealed five pigment-protein bands and fourteen polypeptides in thylakoid membranes. Two Chl b-less mutants showed only CPI and CPa pigment bands, and contained no 25 and 26 kDa polypeptides, reduced amounts of the 21 kDa polypeptide, but increased quantities of 32, 33, 56, 66, and 19 kDa polypeptides. The enhanced absorption of CPI and CPa and the higher Chl fluorescence emission ratio of F685/F720 were also observed in these mutants. This suggested that the reduction or loss of the antenna LHC1 and LHC2 was compensated by an increment in core component and the capacity to harvest photon energy of photosystem (PS) 1 and PS2, as well as in the fraction of excitation energy distributed to PS2 in the two mutants. 77 K Chl fluorescence spectra of thylakoid membranes showed that the PS1 fluorescence emission was shifted from 730 nm in WT rice to 720 nm in the mutants. The regulation of Mg2+ to excitation energy distribution between the two photosystems was complicated. 10 mM Mg2+ did not affect noticeably the F685/F730 emission ratio of WT thylakoid membranes, but increased the ratio of F685/F720 in the two mutants due to a reduced emission at 685 nm as compared to that at 720 nm. and Zhu-Fang Lin ... [et al.].
Cotyledonary leaves of Cucumis sativus cv. Poinsette exhibited senescence-induced losses in chlorophyll (Chl) and protein contents within three weeks since germination. Chl and protein concentrations in cotyledonary leaves approached maximum on 6th d after germination and they declined to 50 and 41 %, respectively, by the 20th day of growth. Activities of both photosystem (PS) 2 and PS1 decreased by 33 and 31 %, respectively, on the 20th day, compared to the control 6th day. Changes in sensitivity of PS2 to inhibitors like atrazine and dibromothymoquinone and sensitivity of PS1 to KCN accompanied the changes in PS2 and PS1 activities. Hence both the acceptor side of PS2 and the donor side of PS1 are affected by senescence-induced changes in cucumber cotyledonary leaves. and J. S. S. Prakash, M. A. Baig, Prasanna Mohanty.
In comparison to cv. Torsdag, in leaves of low-productive Pisum sativum L. chlorophyll mutants the decrease in chlorophyll content was caused by the decrease in cell number per unit volume. Qualitative changes in activities of photosystem (PS) 1 in mutant M2004, and quantitative changes of PS1 and PS2 in mutants M2004 and M2014 and in hybrids were also found. However, the activity of ribulose-1,5-bisphosphate carboxylase (RuBPC) in M2014, and those of RuBPC and glyceraldehyde phosphate dehydrogenase in M2004 and hybrids were higher than in cv. Torsdag. The hybrids inherited the normal structure of photosynthetic apparatus of standard genotype in parallel with the compensatory gene complex of M2004, which was expressed at many levels of organization. This may be the basis of hybrid vigour in this case. and O. B. Vaishlya ... [et al.].
Greenhouse-grown susceptible 20-d-old seedlings of Theobroma cacao genotypes Catongo and tolerant genotype SCA6xCatongo were inoculated with a mixture of isolates of Crinipellis perniciosa, the causal agent of witches' broom. The characteristics of chlorophyll a fluorescence emission were monitored during leaf ontogeny using a portable system PAM-2000. In both inoculated and non-inoculated genotypes, significant differences were found for the effective quantum yield values of photosystem (PS) 2 (ΔF/Fm') at the B (7 to 14-d-old), D (21 to 30-d-old), and E (>30-d-old) stages of leaf development, and in quantum yield of the non-cyclic photosynthetic electron transport between PS2 and PS1 [qp(Fv/Fm)] and quencher efficiency [(Fm-Ft)/F0] at the B, C (15 to 20-d-old) and D stages. Intergenotypic differences were found only for the [qp(Fv/Fm)] and [(Fm-Ft)/F0] values at the E stage, and for fluorescence quenching (Fm-Ft) at the B and E stages. Highly significant inter- and intragenotype relationships were found between the rate of photosynthetic electron transport to PS2 (Amax) and maximum fluorescence during actinic irradiation (Fm'). Also, each of the highly significant relationships between (Fm-Ft) and Amax, [(Fm-Ft)/F0] and ΔF/Fm', and between [(Fm-Ft)/F0] and Amax were represented by a general model, independent of treatments. Therefore, alterations in energy distribution in the radiant energy collector complex interior of PS2 and reduction in absorption of photosynthetically active radiation were observed in the infected plants, mainly in the hybrid at the C stage. Also, variations were found in the noncyclic photosynthetic electron transport at the B and C stages in the infected Catongo. and I. C. F. Santos, A.-A. F. de Almeida, R. R. Valle.
A unified multibranched chlorophyll (Chl) biosynthetic pathway is proposed. The proposed pathway takes into account the following considerations: (a) that the earliest putative precursor of monovinyl Chl b that has been detected in higher plants is monovinyl protochlorophyllide b, (b) that in most cases, Chl b biosynthesis has its roots in the Chl a biosynthetic pathway, (c) that the Chl a biosynthetic pathway exhibits extensive biosynthetic heterogeneity, (d) that Chl biosynthesis may proceed differently at different stages of greening and in different greening groups of plants. Integration of the Chl a and b biosynthetic pathways into a unified multibranched pathway offers the functional flexibility to account for the structural and biosynthetic complexity of photosynthetic membranes. In this context, it is proposed that the unified, multibranched Chl a/b biosynthetic pathway represents the template of a Chl-protein biosynthesis center where photosystem (PS) 1, PS2, and light-harvesting Chl-protein complexes are assembled into functional photosynthetic units. The individual biosynthetic routes or groups of two to three adjacent biosynthetic routes may constitute Chl-protein biosynthesis subcenters, where specific Chl-protein complexes are assembled. and C. A. Rebeiz ... [et al.].
Forty-four genotypes from the rice germplasm were identified under photoinhibition/photooxidation and shade conditions and divided into four basic types: (1) cultivars tolerant to both photooxidation and shading, (2) cultivars tolerant to photooxidation but sensitive to shading, (3) cultivars tolerant to shading but sensitive to photooxidation, and (4) cultivars sensitive to both photooxidation and shading. Photosynthetic characteristics of a cultivar tolerant (cv. Wuyugeng 3) and a cultivar sensitive (cv. Xiangxian) to photooxidation and shading were compared. The photochemical efficiency (Fv/Fm) of photosystem 2 (PS2) and the content of PS2-D1 protein in the tolerant cultivar Wuyugeng 3 decreased less under photooxidative conditions as compared with Xiangxian. Under similar conditions, superoxide dismutase was induced rapidly to a higher activity and the active oxygen (O-) built up to a lower level in Wuyugeng 3 than in Xiangxian. Net photosynthetic rate (PN) decreased by 23 % in Wuyugeng 3 vs. 64 % in Xiangxian. Shading (80 %) during the booting stage caused only small decreases (7-13 %) in ribulose-1,5-bisphosphate carboxylase activity and PN in Wuyugeng 3 but severe decreases (57-64 %) were observed in Xiangxian which corresponded to the decreases in grain yield of the two cultivars (38 and 73 %, respectively). We described a simple and effective screening method and physiological basis for breeding crops for enhanced tolerance to both high and low irradiance. and Demao Jiao, Xia Li.
In canopy shade leaves of grapevine (Vitis vinifera L. cv. Moscato giallo) grown in the field the contents of chlorophyll (Chl), carotenoids (Car), and soluble protein per fresh mass were lower than in sun leaves. RuBPC activity, in vivo nitrate reductase activity (indicator of nitrate utilisation), apparent electron transport rate, and photochemical fluorescence quenching were also significantly reduced in canopy shade leaves. When various photosynthetic activities were followed in isolated thylakoids, canopy shade leaves exerted a marked inhibition of whole chain and photosystem (PS) 2 activity. Smaller inhibition of PS1 activity was observed even in high-level canopy shade (HS) leaves. The artificial exogenous electron donors, DPC and NH2OH, significantly restored the loss of PS2 activity in HS leaves. Similar results were obtained when Fv/Fm was evaluated by Chl fluorescence measurements. The marked loss of PS2 activity in canopy shade leaves was due to the loss of 47, 43, 33, 28-25, 23, 17, and 10 kDa polypeptides. and M. Bertamini, N. Nedunchezhian.
Photosynthetic acclimation to reduced growth irradiances (650 and 200 µmol m-2 s-1) in Eleusine coracana (L.) Garten, a nicotinamide adenine dinucleotide-malic enzyme (NAD-ME) C4 species and Gomphrena globosa L., a nicotinamide adenine dinucleotide phosphate-malic enzyme (NADP-ME) C4 species were investigated. E. coracana plants acclimated in 4 and 8 d to 650 and 200 µmol m-2 s-1, respectively, whereas G. globosa plants took 8 and 10 d, respectively, to acclimate to the same irradiances. The acclimation to reduced irradiance was achieved in both species by greater partitioning of chlorophyll towards the light-harvesting antennae at the expense of functional components. However, magnitude of increase in the light-harvesting antenna was higher in E. coracana as compared to G. globosa. Superior photosynthetic acclimation to reduced irradiance in G. globosa was due to the smaller change in functions of the cytochrome b 6/f complex, photosystem (PS) 1 and PS2 leading to the higher carbon fixation rates compared to E. coracana. and M. V. Sailaja, V. S. Rama Das.
Cyamopsis tetragonoloba L. seedlings were subjected to continuous ultraviolet (UV)-B radiation for 18 h and post-irradiated with "white light" (WL) and UV-A enhanced fluorescent radiations. UV-B treatment alone reduced plant growth, pigment content, and photosynthetic activities. Supplementation of UV-A promoted the overall seedling growth and enhanced the synthesis of chlorophyll and carotenoids with a relatively high photosystem 1 activity. Post UV-B irradiation under WL failed to photoreactive the UV-B damage whereas a positive photoregulatory effect of UV-A was noticed in electron transport rates and low temperature fluorescence emission spectra. and K. Lingakumar, G. Kulandaivelu.
In field-grown Cyamopsis seedlings, distinct changes were found in the rates of photosystems (PS) 2 and 1 activities at different time of the day. Maximum PS2 activity was at around 11:00 h and decreased thereafter. On the contrary, PS1 activity continued to increase up to 14:00 h and declined in evening hours. Significant energy transfer from PS2 to PS1 was evident during the morning and evening hours of the day whereas a slow excitation of PS2 and energy transfer was favoured during noon hours. and K. Lingakumar, G. Kulandaivelu.