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

Abstract

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)

Characterization and mapping of novel chlorophyll deficient mutant genes in durum wheat

“…Cappelli treated by gamma radiation (Tomarchio et al 1983). The mutant displays yellow-green leaves throughout development.…”

Study of the violaxanthin cycle using a yellow‐green mutant of wheat

“…In spite of these differences, the mutant shows normal survival in the field and produces a good yield. Various characteristic aspects of the mutant have been studied: photosynthetic parameters (Tomarchio et al 1983), ultrastructural characteristics, dark/light germination, and pigment composition and content (Antonielli et al 1985). A different ratio between the xanthophylls, in particular a greater proportion of violaxanthin, was found in the mutant as compared to the wild-type after a period of darkness (Antonielli et al 1987).…”

Expression of nuclear-cytoplasmic interactions on quantitatively inherited traits from interspecific matings of oat (Avena sativa L. and A. sterilis L.)

“…Respiratory and photosynthetic rates both exhibit differential responses to cyto plasmic substitution . Variant forms of Rubisco's large sub-unit have been detected (Hirai and Tsunewaki, 1981), but variability in Rubisco has not been related to variability in photo synthesis or photorespiration (Tomarchio et al, 1983). Different cytoplasms also produce variable mitochondrial protein products (Forde and Leaver, 1980).…”