Search

The photosynthetic, optical, and morphological characteristics of a chlorophyll-deficient (Chl-deficient) "yellow" soybean mutant (MinnGold) were examined in comparison with 2 green varieties (MN0095 and Eiko). Despite the large difference in Chl content, similar leaf photosynthesis rates were maintained in the Chl-deficient mutant by offsetting the reduced absorption of red photons by a small increase in photochemical efficiency and lower non-photochemical quenching. When grown in the field, at full canopy cover, the mutants reflected a significantly larger proportion of incoming shortwave radiation, but the total canopy light absorption was only slightly reduced, most likely due to a deeper penetration of light into the canopy space. As a consequence, canopy-scale gross primary production and ecosystem respiration were comparable between the Chl-deficient mutant and the green variety. However, total biomass production was lower in the mutant, which indicates that processes other than steady state photosynthesis caused a reduction in biomass accumulation over time. Analysis of non-photochemical quenching relaxation and gas exchange in Chl-deficient and green leaves after transitions from high to low light conditions suggested that dynamic photosynthesis might be responsible for the reduced biomass production in the Chl-deficient mutant under field conditions., (© 2018 John Wiley & Sons Ltd.)

Ion beams are powerful mutagens that can induce novel mutants in plants. We previously established a system for producing a mutant population of soybean via ion-beam irradiation, isolated plants that had chlorophyll deficiency, and maintained their progeny via self-fertilization. Here we report the characterization of the progeny plants in terms of chlorophyll content, flowering time and isoflavone content in seeds. Chlorophyll deficiency in the leaf tissues was linked with reduced levels of isoflavones, the major flavonoid compounds accumulated in soybean seeds, which suggested the involvement of metabolic changes associated with the chlorophyll deficiency. Intriguingly, flowering time was frequently altered in plants that had a reduced level of chlorophyll in the leaf tissues. Plant lines that flowered either earlier or later than the wild-type plants were detected. The observed coincidental changes were presumed to be attributable to the following origins: structural changes of DNA segments leading to the loss of multiple gene functions, or indirect effects of mutations that affect one of these traits, which were manifested as phenotypic changes in the background of the duplicated composition of the soybean genome.

Leaf colour regulation is important in photosynthesis and dry material production. Most of the reported chlorophyll-deficient loci are recessive. The dominant locus is rarely reported, although it may be more important than the recessive locus in the regulation of photosynthesis efficiency. During the present study, we mapped a chlorophyll-deficient dominant locus (CDE1) from the ethyl methanesulfonate-mutagenized Brassica napus line NJ7982. Using an F2 population derived from the chlorophyll-deficient mutant (cde1) and the canola variety 'zhongshuang11', a high-density linkage map was constructed, consisting of 19 linkage groups with 2,878 bins containing 13,347 SNP markers, with a total linkage map length of 1,968.6 cM. Next, the CDE1 locus was mapped in a 0.9-cM interval of chromosome C08 of B. napus, co-segregating with nine SNP markers. In the following fine-mapping of the gene using the inherited F2:3 populations of 620 individuals, the locus was identified in an interval with a length of 311 kb. A bioinformatics analysis revealed that the mapping interval contained 22 genes. These results produced a good foundation for continued research on the dominant locus involved in chlorophyll content regulation.

A yellow-leaf mutant (yl11) with chlorophyll-deficient in rice (Oryza sativa L.) was selected from the progeny of a japonica rice variety "Jiahua 1" treated with 60Co γ-radiation. In comparison with the wild-type parent, "Jiahua 1", the mutant had yellow-leaves at whole growth stages and displayed significantly decreased in chlorophyll content and net photosynthetic rate. Underdeveloped chloroplast and alterations of the major agronomic traits, such as plant-heights, were also observed in the mutant. Genetic analysis confirmed that the yellow-leaf mutant trait was controlled by a single recessive nuclear gene (yl11). Using SSR and In/Del molecular markers and 920 F2 and F3 plants from the cross of yl11 with the indica variety Peiai 64S, the yl11 was mapped between the molecular markers MM2199 and InDel21039 with a physical distance of 110 kb on the long arm of chromosome 11, in which no known functional genes for chlorophyll synthesis or chloroplast development in rice has been found. These findings will provide a foundation for the cloning and functional analysis of this gene in the future.

In order to analyze mutations induced by gamma irradiation in higher plants, we irradiated rice with gamma rays and screened for mutations expressing phenotypes of glutinous endosperm (wx), chlorophyll b deficiency, endosperm protein deficiency, gibberellin-related dwarfism, and shortened plastochron-in order to clarify types of mutations. Nucleotide sequence analysis showed that the most frequent mutation induced by gamma rays was deletion, particularly small deletion. Of the 24 mutations, 15 were small deletions (1-16 bp), four were large deletions (9.4-129.7 kbp), three were single-base substitutions, and two were inversions. Deletions 100 bp-8 kbp in length were not found, suggesting that gamma irradiation is unlikely to induce deletions of 100 bp to 8 kbp but is more likely to induce deletions between 1 and several ten bp or those of around 10 kbp or more. Based on the results, reverse genetics applications may be possible for gamma irradiation-induced deletions in rice by mismatch cleavage analysis used in Targeting Induced Local Lesions IN Genomes (TILLING) to detect small deletions and base substitutions or by using array comparative genomic hybridization (aCGH) to detect large deletions.

Leaves of the two new chlorophyll b-less rice mutants VG28-1, VG30-5 and the wild type rice cv. Zhonghua 11 were subjected to temperatures 28, 36, 40, 44 and 48 degrees C in the dark for 30 min or gradually elevated temperature from 30 degrees C to 80 degrees C at 0.5 degrees C/min. The thermostability of photosynthetic apparatus was estimated by the changes in chlorophyll fluorescence parameters, photosynthetic rate and pigment content, chloroplast ultrastructure and tissue location of H2O2 accumulation. There were different patterns of F(o)-temperature curves between the Chl b-less mutants and the wild type plant, and the temperature of F(o) rising threshold was shifted 3 degrees C lower in the Chl b-less mutants (48 degrees C) than in the wild type (51 degrees C). At temperature up to about 45 degrees C, chloroplasts were swollen and thylakoid grana became misty accompanied with the complete loss of photosynthetic oxygen evolution in the two Chl b-less mutants, but chloroplast ultrastructure in the wild type showed no obvious alteration. After 55 degrees C exposure, the disordered thylakoid and significant H2O2 accumulation in leaves were found in the two Chl b-less mutants, whereas in the wild type plant, less H2O2 was accumulated and the swollen thylakoid still maintained a certain extent of stacking. A large extent of the changes in qP, NPQ and Fv/Fm was consistent with the Pn decreasing rate in the Chl b-less mutants during high temperature treatment as compared with the wild type. The results indicated that the Chl b-less mutants showed a tendency for higher thermosensitivity, and loss of Chl b in LHC II could lead to less thermostability of PSII structure and function. Heat damage to photosynthetic apparatus might be partially attributed to the internal oxidative stress produced at severely high temperature.

Heavy-ion irradiation is a new method of mutation breeding to produce new cultivars. We established the application of this method in rice plants to obtain mutants. Rice seeds were irradiated by C or Ne ions (135MeV/u) with a LET (linear energy transfer) of 22.7 or 64.2 keV/microm, respectively. Chlorophyll-deficient mutants (CDM) segregated in M2 progeny were albino, pale-green, yellow or striped-leave phenotypes. The highest rate of CDM with C-ion irradiation, 7.31%, was obtained at 40 Gy among the doses examined. Ne-ion irradiation gave the highest rate, 11.6%, at 20 Gy. We used the RLGS (Restriction Landmark Genomic Scanning) method to analyze DNA deletion in an albino mutant genome. Not I-landmark RLGS profiles detected about 2000 spots in rice. We found that one of the polymorphic spots was strongly linked to the albino phenotypic mutant derived from deleting of a DNA fragment, and demonstrated the high ability to detect of polymorphic regions by the RLGS method.

Of the three isomers of the aromatic amine phenylenediamine (PDA), only o-PDA, but not m- and p-PDA, induced DNA damage (as measured by the Comet assay), and somatic mutations in the leaves of the chlorophyll-deficient tester strain Nicotiana tabacum var. xanthi. With increasing light intensity (0, 30, 80 or 140 micromol m(-2)s(-1) photosynthetic photon fluence rate) during a 72h mutagenic treatment of tobacco seedlings, o-PDA-induced DNA damage and the yield of somatic mutations were significantly increased. The peroxidase inhibitor diethyldithiocarbamate (DEDTC) repressed o-PDA-induced DNA damage. The effect of light is caused by the light-dependent increase of peroxidase activity and the accumulation of hydrogen peroxide, which participate in the metabolic activation of the promutagen o-PDA to mutagenic product(s). In contrast, DNA damage induced by the direct-acting alkylating mutagen ethyl methanesulphonate was the same whether treatment was in the light or in the dark, and was not repressed by the peroxidase inhibitor DEDTC.

Analyses of a series of allelic chlorina mutants of wheat (Triticum aestivum L.), which have partial blocks in chlorophyll (Chl) synthesis and, therefore, a limited Chl supply, reinforce the principle that Chl is required for the stable accumulation of Chl-binding proteins and that only reaction centers accumulate when the supply of Chl is severely limited. Depending on the rate of Chl accumulation (determined by the severity of the mutation) and on the rate of turnover of Chl and its precursors (determined by the environment in which the plant is grown), the mutants each reach an equilibrium of Chl synthesis and degradation. Together these mutants generate a spectrum of phenotypes. Under the harshest conditions (high illumination), plants with moderate blocks in Chl synthesis have membranes with very little Chl and Chl-proteins and membrane stacks resembling the thylakoids of the lethal xantha mutants of barely grown at low to medium light intensities (which have more severe blocks). In contrast, when grown under low-light conditions the same plants with moderate blocks have thylakoids resembling those of the wild type. The wide range of phenotypes of Chl b-deficient mutants has historically produced more confusion than enlightenment, but incomparable growth conditions can now explain the discrepancies reported in the literature.