Harvest index, a parameter conditioning responsiveness of wheat plants to elevated CO2

Abstract

The expansion of the world's population requires the development of high production agriculture. For this purpose, it is essential to identify target points conditioning crop responsiveness to predicted [CO2]. The aim of this study was to determine the relevance of ear sink strength in leaf protein and metabolomic profiles and its implications in photosynthetic activity and yield of durum wheat plants exposed to elevated [CO2]. For this purpose, a genotype with high harvest index (HI) (Triticum durum var. Sula) and another with low HI (Triticum durum var. Blanqueta) were exposed to elevated [CO2] (700 µmol mol(-1) versus 400 µmol mol(-1) CO2) in CO2 greenhouses. The obtained data highlighted that elevated [CO2] only increased plant growth in the genotype with the largest HI; Sula. Gas exchange analyses revealed that although exposure to 700 µmol mol(-1) depleted Rubisco content, Sula was capable of increasing the light-saturated rate of CO2 assimilation (Asat) whereas, in Blanqueta, the carbohydrate imbalance induced the down-regulation of Asat. The specific depletion of Rubisco in both genotypes under elevated [CO2], together with the enhancement of other proteins in the Calvin cycle, revealed that there was a redistribution of N from Rubisco towards RuBP regeneration. Moreover, the down-regulation of N, NO3 (-), amino acid, and organic acid content, together with the depletion of proteins involved in amino acid synthesis that was detected in Blanqueta grown at 700 µmol mol(-1) CO2, revealed that inhibition of N assimilation was involved in the carbohydrate imbalance and consequently with the down-regulation of photosynthesis and growth in these plants.

Fig. 1.

Effect of elevated [CO2] (700 µmol mol^–1 versus 360 µmol mol^–1) exposure (A) in total dry matter (DM, g plant^–1), grain DM (g plant^–1), and harvest index (HI, g g^–1), and (B) thousand kernel weight (TKW, g plant^–1) and number of grains (no. grains plant^–1) of durum wheat Sula and Blanqueta genotypes determined during the grain maturity stage. Each value represents the mean of eight replicates ±SE. Two-factor analysis of variance (ANOVA) was used to test significance. When significant differences were detected in ANOVA, LSD analysis was applied. Means that differed significantly (P > 0.05) are followed by a different letter according to the LSD test parameters.

Fig. 2.

Effect of elevated [CO₂] (700 µmol mol^–1 versus 360 µ mol mol^–1) exposure (A) on starch (g m^–2) and soluble sugars (sucrose, glucose, and fructose; mmol m^–2) and (B) organic acid (citrate, malate, oxalacetate, α-ketoglutarate, and succinate; mg m^–2) content of durum wheat Sula and Blanqueta genotypes determined in flag leaves 2 weeks after anthesis. Each value represents the mean of four replicates ±SE. Otherwise as for Fig. 1.

Fig. 3.

Effect of elevated [CO₂] (700 µmol mol^–1 versus 360 µmol mol^–1) exposure on amino acid (glutamate, glutamine, aspartate, threonine, glycine, serine, asparagine, cysteine, alanine, proline, valine, arginine, γ-aminobutyric acid, tyrosine, histidine, isoleucine, lysine, phenylalanine, leucine, methionine and tryptophan) content (10^–5 mol m^–2) of durum wheat Sula and Blanqueta genotypes determined in flag leaves 2 weeks after anthesis. Each value represents the mean of four replicates ±SE. Otherwise as for Fig. 1.