No abstract

Sugarcane juice contains a lot of sucrose associated with several monosaccharides, defined as low molecular mass carbohydrates (LMMC), as well as some polysaccharides and glycoproteins, which are defined as mid and high molecular mass carbohydrates (MMMC and HMMC, respectively). These three categories of carbohydrates can be separated by size-exclusion chromatography through Sephadex G-10 and Sephadex G-50 columns, but elution profiles change drastically after juice clarification performed by adjusting the pH value of the juice to 8.0. In addition, polyamines and some phenolics are currently associated with carbohydrate preparations, and the distribution pattern of these conjugates also changes after clarification. Polyamine levels generally decrease after juice clarification. Cadaverine is completely removed from the different carbohydrate preparations, whereas spermidine is the main polyamine occurring in association with sugarcane carbohydrates, as free or acid-soluble form in LMMC preparation or as acid-soluble and -insoluble forms in both MMMC and HMMC preparations. Polyamines, presumably spermidine, conjugate to p-hydroxybenzoic acid in LMMC, mostly to caffeic acid in MMMC, and to syringic acid in HMMC preparations. HMMC-associated polyamines appear in both acid-soluble and -insoluble fractions. Syringic acid also occurs in the LMMC preparation, but juice clarification changes it from acid-soluble to free form, and it coelutes with sucrose.

The accumulation of soluble and cell wallbound phenolics in the sugarcane stems of young plants from highly resistant cv. My 5514 and susceptible cv. B 42231, inoculated or not inoculated with smut sporidia, was studied. The ratio of inoculated to uninoculated plants of some cell wallbound phenolics, such as ferulic, caffeic, and syringic acids increased for the resistant cv. My 5514, whereas it was maintained more or less constantly for the susceptible cv. B 42231. The highest increase of this ratio in the resistant cv. My 5514 corresponded to both caffeic and syringic acids. This could result in a better capacity to cv. My 5514 for an increase in the frequency of bridges between lignin fragments through ester-ether linkages for reinforcing the cell wall and major resistance to the disease. This reinforcement of the cell wall could provide an effective barrier to pathogen entry and spread. Soluble sub-fractions of all phenolics detected showed non-stable patterns. Caffeic acid, that regulates phenylalanine ammonia-lyase activity in sugarcane, showed a significant decrease in its titre at 24 h in the resistant cultivar, principally in the free soluble fraction, whilst the susceptible cultivar enhanced it. We hypothesise that the pathway of hydroxybenzoic acids is only activated once the level of p-coumaric acid justifies the accumulation of hydroxycinnamic acids required for reinforcing the cell wall after inoculation.

This study describes a method for determining cinnamyl alcohol dehydrogenase activity in sugarcane stems using reverse phase (RP) high-performance liquid chromatography to elucidate their possible lignin origin. Activity is assayed using the reverse mode, the oxidation of hydroxycinnamyl alcohols into hydroxycinnamyl aldehydes. Appearance of the reaction products, coniferaldehyde and sinapaldehyde is determined by measuring absorbance at 340 and 345 nm, respectively. Disappearance of substrates, coniferyl alcohol and sinapyl alcohol is measured at 263 and 273 nm, respectively. Isocratic elution with acetonitrile:acetic acid through an RP Mediterranea sea C18 column is performed. As case examples, we have examined two different cultivars of sugarcane; My 5514 is resistant to smut, whereas B 42231 is susceptible to the pathogen. Inoculation of sugarcane stems elicits lignification and produces significant increases of coniferyl alcohol dehydrogenase (CAD) and sinapyl alcohol dehydrogenase (SAD). Production of lignin increases about 29% in the resistant cultivar and only 13% in the susceptible cultivar after inoculation compared to uninoculated plants. Our results show that the resistance of My 5514 to smut is likely derived, at least in part, to a marked increase of lignin concentration by the activation of CAD and SAD.

Caffeic acid (CA) sometimes behaves as a potent phytotoxin affecting plant and fungi growth and physiology. The aim of the present study was to investigate whether CA at a concentration range similar to that found in sugarcane leaves, had any effect against different phases of Sporisorium scitamineum growth cycle. Leaf CA concentration from two different sugarcane cultivars, Mayari (My) 55-14, resistant, and Barbados (B) 42231, susceptible to smut, was chromatographically quantified by HPLC. A smut elicitor promoted an increase of CA concentration in the resistant cv. while no effect was produced in the susceptible one. The effect of CA upon S. scitamineum growth cycle showed to be dependent of both concentration and time. At 5.0 mg ml (1 , CA produced and inhibition of teliospore germination, haploid sporidia production and dikaryotic mycelium appearance. At 30 mg ml (1 , CA produced similar effects to these just described. Inhibition was more evident after 24 h or 28 h incubation of teliospores in CA solution than after 48 h. CA at 20 mg ml (1 reduced both germination of teliospores and production of haploid sporidia but it had no significant effect on dikaryotic mycelium appearance after 24-h incubation.