Sunflower: a potential fructan-bearing crop?

Presence of inulin in sunflower (Helianthus annuus L.) grown under high irradiance

Fructans are important polysaccharides synthesized from sucrose which are present in about 12-15% of angiosperms. Sunflower (Helianthus annuus L.) is considered a non-fructan bearing plant even though its close relative, Helianthus tuberosus, accumulates the inulin type of the polymer in large amounts. Previous work suggested that putative fructan-synthesizing enzymes may be expressed in sunflower, but only very limited amounts of the trisaccharide isokestose were found in stems of plants storing high levels of sucrose due to capitulum removal. The present work is aimed at investigating whether intact sunflower plants may indeed synthesize fructans in any of its parts when grown in conditions that favor sucrose availability. Plants were grown in the field at a low density, resulting in a high light availability and low competition for resources, in comparison with controls (usual crop planting density). Plants were harvested at anthesis. Thinned treatment led to an increase in carbohydrates level especially in the capitulum. Carbohydrates analysis of this tissue in thinned plants revealed, for the first time in this species, the presence of inulin-type fructans. The amount of each member of the series appeared to decline starting from isokestose, being DP = 15 the longest fructan detected. Results suggest that, in sunflower, fructans could be synthesized only when sucrose availability exceeds a high threshold, which may not be attained under usual growing conditions. Given the relationship between fructans and tolerance to abiotic stresses including drought, the present finding opens a new perspective for breeding and management of this crop.

Abscisic acid crosstalk with auxin and ethylene in biosynthesis and degradation of inulin-type fructans in chicory

The effect of different hormones on fructan accumulation and the genes regulating biosynthesis and degradation is known; however, information on hormonal interaction mechanisms for fructan content and mean degree of polymerization (mDP) is limited. Cell suspension cultures of chicory were prepared and treated with abscisic acid (ABA), auxin (AUX), ethylene (ETH), ABA + AUX or ABA + ETH, then inulin concentration, mDP of inulin and expression of FAZY genes was determined. A low concentration of AUX and ETH increased fructan content, while a high concentration of AUX and ETH decreased it. Exogenous ABA increased mDP of inulin and this coincided with the low expression of 1-FEHII. In hormone interactions, ABA changed and adjusted the effect of both AUX and ETH. ABA, together with a low level of AUX and ETH, resulted in a decrease in inulin content and increase in mDP, which coincided with low expression of FEHII. ABA together with a high level of AUX and ETH caused an increase in inulin content with a lower mDP, which coincided with high expression of biosynthesis (1-FFT) and degradation (1-FEHII) genes. The effect of both AUX and ETH was almost the same, although the effect of ETH was more severe. ABA had a modulating role in combinations with AUX and ETH. Among biosynthesis and degradation genes, the expression of 1-FEHII was more affected by these hormones.

Metabolomic characterization of sunflower leaf allows discriminating genotype groups or stress levels with a minimal set of metabolic markers

INTRODUCTION

Plant and crop metabolomic analyses may be used to study metabolism across genetic and environmental diversity. Complementary analytical strategies are useful for investigating metabolic changes and searching for biomarkers of response or performance.

METHODS AND OBJECTIVES

The experimental material consisted in eight sunflower lines with two line status, four restorers (R, used as males) and four maintainers (B, corresponding to females) routinely used for sunflower hybrid varietal production, respectively to complement or maintain the cytoplasmic male sterility PET1. These lines were either irrigated at full soil capacity (WW) or submitted to drought stress (DS). Our aim was to combine targeted and non-targeted metabolomics to characterize sunflower leaf composition in order to investigate the effect of line status genotypes and environmental conditions and to find the best and smallest set of biomarkers for line status and stress response using a custom-made process of variables selection.

RESULTS

Five hundred and eighty-eight metabolic variables were measured by using complementary analytical methods such as 1H-NMR, MS-based profiles and targeted analyses of major metabolites. Based on statistical analyses, a limited number of markers were able to separate WW and DS samples in a more discriminant manner than previously published physiological data. Another metabolic marker set was able to discriminate line status.

CONCLUSION

This study underlines the potential of metabolic markers for discriminating genotype groups and environmental conditions. Their potential use for prediction is discussed.