Correlation between the Carbon Isotope Discrimination in Leaf Starch and Sugars of C₃ Plants and the Ratio of Intercellular and Atmospheric Partial Pressures of Carbon Dioxide

Abstract

Carbon isotope discrimination (Av) was analyzed in leaf starch and soluble sugars, which represent most of the recently fixed carbon. Plants of three C3 species (Populus nigra L. x P. deltoides Marsh., Gossypium hirsutum L. and Phaseolus vulgaris L.) were kept in the dark for 24 hours to decrease contents of starch and sugar in leaves. Then gas exchange measurements were made with constant conditions for 8 hours, and subsequently starch and soluble suprs were extracted for analysis of carbon isotope composition. The ratio of intercellular, pi, and atmospheric, p., partial pressures of C02, was calculated from gas exchange measurements, integrated over time and weighted by assimilation rate, for comparison with the carbon isotope ratios in soluble sugars and starch. Carbon isotope discrimination in soluble sugars correlated strongly (r = 0.93) with pdp. in all species, as did A in leaf starch (r = 0.84). Starch was found to contain significantly more 13C than soluble sugar, and possible explanations are discussed. The strong correlation found between A and p/p. suggests that carbon isotope analysis in leaf starch and soluble sugars may be used for monitoring, indirectly, the average of pip, weighted by C02 assimilation rate, over a day. Because p,/p. has a negative correlation with transpiration efficiency (mol C02/ mol H20) of isolated plants, A in starch and sugars may be used to predict differences in this efficiency. This new method may be useful in ecophysiological studies and in selection for improved transpiration efficiency in breeding programs for C3 species.During photosynthetic CO2 fixation, plants discriminate against the naturally occurring stable isotope 13C. In C3 species, fractionation ofcarbon in plant material is caused by the primary carboxylating enzyme, ribulose-1,5-bisphosphate carboxylase, which discriminates against 13C (24) and by diffusion from the atmosphere to the sites of CO2 fixation (12,23,28). Farquhar et al. (12) developed a model which predicts a linear relationship between A2 and the ratio of intercellular (pi) to atmospheric (pa) partial pressure of CO2 for C3 plants.

The ?13C of Scots pine (Pinus sylvestris L.) needles: spatial and temporal variations

“…As calculated from gas exchange [3], discrimination against 13 C during primary assimilation in Scots pine needles can vary by up to 9‰, leading to a large range of d 13 C for primary assimilatory products. It has been shown for several species, that the d 13 C of soluble sugars and starch are closely related to gas exchange parameters and that the starch d 13 C is less negative than the d 13 C of soluble sugars [5]. An isotopic mass balance illustrates the plausible influence of leaf starch d 13 C and concentration on bulk d 13 C. Assuming reasonable increases in leaf starch in spring of 15% of needle dry weight (starch in Scots pine needles can rise to values over 25% [12]) and a medium change in starch d 13 C of 5‰ (compared to 9‰ variation observed for instantaneous discrimination [3]), bulk needle d 13 C would change by 5‰´0.15 = 0.75‰ to less negative values.…”

Carbon-Isotope Composition of Biochemical Fractions and the Regulation of Carbon Balance in Leaves of the C3-Crassulacean Acid Metabolism Intermediate Clusia minor L. Growing in Trinidad

“…106, 1994 ratory COz), the 613C nomenclature was preferred to A nomenclature, which is independent of source COz (Farquhar et al, 1989). Analyses of carbohydrates has been used to provide an integrated measure of the carbon-isotope discrimination expressed on a daily basis in C3 plants (Brugnoli et al, 1988). Using 613C analyses and mass balance interconversions of organic acid and carbohydrate fractions associated with CAM, one can now calculate the carbon-isotope discrimination expressed during the dark period.…”

“…The solid residue was washed once with distilled water before 2 X 10 cm3 of 20% HCl were added for 1.5 h to hydrolyze the remaining carbohydrates, i.e. glucans and starch (Brugnoli et al, 1988). An aliquot of this acid extract was kept foi analysis of carbohydrates (i.e.…”

Effects of Salinity on Stomatal Conductance, Photosynthetic Capacity, and Carbon Isotope Discrimination of Salt-Tolerant (Gossypium hirsutum L.) and Salt-Sensitive (Phaseolus vulgaris L.) C3 Non-Halophytes

“…Typically, ka was -8.4 x I0V. Carbon isotope analysis of air and of plant material was as previously described (4 Statistical analysis was based on one-way analysis of variance and on Student-Newman-Keuls test for multiple comparisons among means (27). Regression analysis was performed according to the least squares method.…”

“…It has been demonstrated in ABA-treated leaves (8,28) that stomatal heterogeneity and consequent nonuniform photosynthesis cause a systematic overestimation ofthe intercellular CO2 partial pressure (pi) calculated by gas exchange. Nonuniform photosynthesis has also been observed in water-stressed plants (6,9,22,25), and it has been concluded that the primary effect of water stress on photosynthesis is mediated by stomatal closure and that chloroplast reactions are not affected until after other plant processes have become strongly affected (26 15,21), in leaf sugars and starch (4), and from correlation between concurrent short term measurements ofPi/Pa and the isotope composition of the air in gas exchange measurements (1 1). Measurement of A gives an estimation of the assimilation-rate-weighted value of pi, whereas gas exchange gives a conductance-weighted value of pi (15).…”