A yellow leaf colouration mutant (named ycm) generated from rice T-DNA insertion lines was identified with less grana lamellae and low thylakoid membrane protein contents. At weak irradiance [50 μmol(photon) m -2 s -1 ], chlorophyll (Chl) contents of ycm were ≈20 % of those of WT and Chl a/b ratios were 3-fold that of wild type (WT). The leaf of ycm showed lower values in the actual photosystem 2 (PS2) efficiency (Φ PS2 ), photochemical quenching (q P ), and the efficiency of excitation capture by open PS2 centres 1 (F v '⁄F m ') than those of WT, except no difference in the maximal efficiency of PS2 photochemistry (F v /F m ). With progress in irradiance [100 and 200 μmol(photon) m -2 s -1 ], there was a change in the photosynthetic pigment stoichiometry. In ycm, the increase of total Chl contents and the decrease in Chl a/b ratio were observed. Φ PS2 , q P , and F v '⁄F m ' of ycm increased gradually along with the increase of irradiance but still much less than in WT. The increase of xanthophyll ratio [(Z+A)/(V+A+Z)] associated with non-photochemical quenching (q N ) was found in ycm which suggested that ycm dissipated excess energy through the turnover of xanthophylls. No significant differences in pigment composition were observed in WT under various irradiances, except Chl a/b ratio that gradually decreased. Hence the ycm mutant developed much more tardily than WT, which was caused by low photon energy utilization independent of irradiance.Additional key words: β-carotene; chlorophyll; photochemical and non-photochemical quenching; xanthophyll cycle.
Aim: We performed experiments to isolate DNA topoisomerase II gene from Pleurotus ostereatus and to discuss its application as a feasible and credible molecular maker in phylogenitic analysis. Methods and Results: A fragment of PosTopII was amplified from a P. ostreatus cDNA clone by nested polymerase chain reaction (PCR), using degenerate primers and primer walking. The full‐length gene sequence was obtained with 3′ and 5′‐full RACE‐PCR. The PosTopII cDNA is 4808 bp length and contains an open reading frame (ORF) of 4713 bp. The predicted peptide has 1571 amino acids, and exhibits strong sequence homology to other eukaryotic topoisomerase II. The PosTopII sequence was compared with the homologous genes to determine it can be used as a reliable molecular maker for P. ostreatus. Conclusions: The complete sequence of PosTopII cDNA clone was obtained. The phylogenetic relationships were consistent with other classification methods based on the morpological chracteristics and rDNA gene sequences. Significance and Impact of the Study: This is the first report on isolation of a DNA topoisomerse II from P. ostreatus. Findings from this study indicate that the DNA topoisomers II can be applied as a reliable meker for taxonomic distinction in the genus Pleurotus.
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