Electron transport and chloroplast ultrastructure of a chlorophyll deficient mutant of wheat

ABSTRAC1As compared with normal wheat leaves, the chlorina wheat mutant, designated CD3, has a high chlorophyll a/b ratio and a deficiency in the light harvesting chlorophyll protein (LHCP) complex. Applications of 200 micrograms per milliliter of D-threo-chloramphenicol to etiolated seedlings decreased the chlorophyll a/b ratio and increased the accumulation of the 27 kilodalton LHCP polypeptide and the LHCP complex in thylakoids of the mutant during greening. These data led to the suggestion that a protein encoded in chloroplast genes impaired either transcriptional, translational, or posttranslational events in CD3 wheat limiting the accumulation of the LHCP complex. The LHCP complex which accumulated in chloramphenicol treated wheat appeared functional even though chlorophyll protein complex accumulations were altered greatly in the wheat thylakoids. LHCP polypeptides were phosphorylated by action of a membrane protein kinase but yet photosystem II electron transport was impaired. The chloramphenicol treatment increased the photosystem 1/photosystem II ratio of electron transport and the fluorescence emission ratio at 740 to 686 nanometers relative to those of untreated wheat. Chloramphenicol prevented development of normal granal thylakoids in normal wheat chloroplasts but not in those of the CD3 mutant. Elongated stacked thylakoids were observed in normal wheat. Net-like membranes and vesicles were noted in the stroma of chloroplasts from treated mutant seedlings.

Section: Methodsmentioning

confidence: 87%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Chloramphenicol Stimulation of Light Harvesting Chlorophyll Protein Complex Accumulation in a Chlorophyll b Deficient Wheat Mutant

Duysen¹,

Freeman²,

Williams³

et al. 1985

“…Mutants 2 Permanent address: Zentralinstitut fur Genetik und Kulturpflanzenforschung der Akademie der Wissenschaften der DDR, DDR-4325 Gatersleben, Corrensstrasse 3,DDR. normally contain approximately half the total amount of Chl as the normal parent, or those which contain somewhat reduced amounts of Chl b, normally having ratios of Chl a/b >5 versus values of approximately 3 for the normal plants. Such mutants have been described in barley (Hordeum vulgare) (14), pea (Pisum sativum) (15,27), maize (Zea mays) (16,25), wheat (Triticum aestivum) (10,12), sweetclover (Melilotus alba) (13,21,22,26,30), Chlamydomonas reinhardii (24), and other species. Such mutants are usually selected on the basis of decreased pigment content and the major physiological effect is that the fluence rate of light needed to saturate photosynthetic electron transport is increased (15,16).…”

mentioning

confidence: 99%

A Temperature-Sensitive Chlorophyll b-Deficient Mutant of Sweetclover (Melilotus alba)

Markwell¹,

Danko²,

Bauwe³

et al. 1986

The ch4 mutant of sweetclover (Melilotus alba) has previously been demonstrated to be partially deficient in chlorophyll and to have a higher ratio of chlorophyll a to b than normal plants. We were able to substantiate these findings when plants were grown at 23°C and lower (permissive temperatures). However, when grown at 26°C (nonpermissive temperature) the plants produced small yellow leaves which exhibited onetwentieth the chlorophyll content of normal plants. Affected

“…However, mutants have been described which are able to photosynthesize and grow normally. Although pigment mutants may differ widely in photosynthetic characteristics, most display higher Chl a/b ratios, greater photosynthetic rates on a Chl basis, but equivalent or slightly lower rates on a leaf area basis when compared to the wild type (1,7).…”

mentioning

confidence: 99%

Photosynthesis, Ribulose-1,5-bisphosphate Carboxylase, Electron Transport, and Ribulose 1,5-Bisphosphate of Virescent and Normal Green Wheat Leaves

Tomarchio¹,

Triolo²,

DiMARCO³

1983

CO2 gas exchange, ribulose-1,5-bisphosphate, and electron transport have been measured in leaves ofa yellow-green mutant of wheat (Triticum durum var Cappelli) and its wild type strain grown in the field. All these parameters, expressed on leaf area basis, were similar in both genotypes except electron transport which was more than double in the wild type. These results, treated according to a recent photosynthesis model for C3 plants, seem to indicate that the electron transport rate of mutant leaves is not sufficient to support the carboxylation derived through both the assimilation rate and the in vitro ribulose-1,5-bisphosphate carboxylase activity. It is suggested that under our experimental conditions photosynthetic electron transport is not the sole energy-dependent determinant of ribulose-1, is not limiting it is possible to relate electron transport to the rate ofphosphoglyceric acid production and to carboxylation velocity (6).To test the practical application of this model, we have investigated some photosynthetic parameters of a Chl-deficient mutant of Triticum durum which grows normally in the field. Young seedlings show the same photosynthetic rate at saturating irradiances as the wild type (10).In this communication, we report on the correlation between net photosynthesis, uncoupled electron transport rate, and RuBP and RuBPCase content measured in the flag leaf of field grown mutant and wild type plants. MATERIALS AND METHODSPlants of a yellow-green mutant derived from a commercial variety of Triticum durum (var Cappelli) and its wild type strain were grown in a field near Rome. The crop was sown in January with a density of 500 plants/m2. Normal cultivation practices were applied, and irrigation was not necessary. Flag leaves were harvested on clear days starting in May when the leaves were fully expanded.Net photosynthesis was measured in a CO2 assimilation chamber in an open system connected with a Beckmann model 865 CO2 analyzer. Three or four detached leaves were enclosed in the ventilated chamber. Irradiance at leaf surface was 700 ,umol quanta m-2 s-', corresponding to light saturation of CO2 uptake. Leaf temperature, measured using a copper-constantan thermocouple in contact with the lower surface of one of the leaves, was 25 ± 1'C. Gas entering the chamber was saturated with water.RuBPCase activity was assayed using 2 g of fresh tissue taken from the material obtained by cutting five leaves in small pieces. The extraction was performed immediately after harvesting as previously described (3). The enzymic activity of the extract was measured by end-point titration of formed D-3-phosphoglycerate in a 60-s assay at 25'C as reported elsewhere (4).RuBP was determined by 14C incorporation into phosphoglycerate using commercial RuBPCase. Ten flag leaves, frozen in liquid N2 within 2 s from the harvest, were finely powdered and lyophilized. The dry powder was then treated according to the procedure of Latzko and Gibbs (8)