Effects of elevated CO2 concentration and water deficit on fructan metabolism in Viguiera discolor Baker.

Elevated [CO2 ] is suggested to mitigate the negative effects of water stress in plants; however responses vary among species. Fructans are recognised as protective compounds against drought and other stresses, as well as having a role as reserve carbohydrates. We analysed the combined effects of elevated [CO2 ] and water deficit on fructan metabolism in the Cerrado species Viguiera discolor Baker. Plants were cultivated for 18 days in open-top chambers (OTC) under ambient (∼380 ppm), and high (∼760 ppm) [CO2 ]. In each OTC, plants were submitted to three treatments: (i) daily watering (control), (ii) withholding water (WS) for 18 days and (iii) re-watering (RW) on day 11. Analyses were performed at time 0 and days 5, 8, 11, 15 and 18. High [CO2 ] increased photosynthesis in control plants and increased water use efficiency in WS plants. The decline in soil water content was more distinct in WS 760 (WS under 760 ppm), although the leaf and tuberous root water status was similar to WS 380 plants (WS under 380 ppm). Regarding fructan active enzymes, 1-SST activity decreased in WS plants in both CO2 concentrations, a result consistent with the decline in photosynthesis and, consequently, in substrate availability. Under WS and both [CO2 ] treatments, 1-FFT and 1-FEH seemed to act in combination to generate osmotically active compounds and thus overcome water deficit. The proportion of hexoses to sucrose, 1-kestose and nystose (SKN) was higher in WS plants. In WS 760, this increase was higher than in WS 380, and was not accompanied by decreases in SKN at the beginning of the treatment, as observed in WS 380 plants. These results suggest that the higher [CO2 ] in the atmosphere contributed to maintain, for a longer period, the pool of hexoses and of low DP fructans, favouring the maintenance of the water status and plant survival under drought.

Fructan composition in adventitious tuberous roots of Viguiera discolor Baker (Asteraceae) as influenced by daylength.

Short (8-10h) photoperiods stimulated branching, flowering and enlargement of adventitious tuberous roots of Viguiera discolor Baker, a native plant of the Brazilian cerrado. Inulin was mostly accumulated in parenchyma cells associated with secondary xylem of tuberous roots. Accumulation was greater in plants grown under conditions that induce flowering (1) than in plants grown under conditions that do not induce flowering (NI) (photoperiods longer than 12 h), Although total fructan concentration was similar in both conditions [approx. 460 mg (g dry mass)-1 ], the amount of inulin in I was 10 times that of oligosaccharides, whereas in NI it was 6 times greater. In addition, the relative molecular mass of inulin was slightly lower in NI 16600) than in I (18600), but considerably higher than those reported for other Asteraceae (approx. 5500). The results suggest that flower-inductive conditions affect fructan metabolism in Viguiera discolor without altering the total fructose.