Fructan degradation and hydrolytic activity in tuberous roots of Viguiera discolor Baker (Asteraceae), a herbaceous species from the cerrado

Abstract

-(Fructan degradation and hydrolytic activity in tuberous roots of Viguiera discolor Baker (Asteraceae), a herbaceous species from the cerrado). Fructans of the inulin type are the major reserve carbohydrates in tuberous roots of Viguiera discolor, a perennial herb native to the cerrado. Changes in molecular mass of the polymer, followed by releasing free fructose suggested that hydrolysis could be related to the sprouting of the buds after the dormant period, when aerial parts of the plant are naturally absent. Excision of aerial parts resulted in the increase of fructan 1-exohydrolase (1-FEH) activity in tuberous roots after sprouting. 1-FEH was partially purified from this material by binding to ConA-Sepharose and the highest activity was detected at pH 5.4 and between 20 and 40 °C. Values of K m for V. discolor inulin could not be determined since no saturation was observed up to 10%. The study of the kinetics of the 1-FEH activity showed that it does not follow MichaelisMenten and apparently presents allosteric behaviour, as data fits in the Hill equation. The 1-FEH from V. discolor is a glycoprotein, more active on low molecular mass fructans than on high molecular mass inulin from the same species.Key words -Asteraceae, cerrado, fructan 1-exohydrolase, inulin RESUMO -(Degradação de frutanos e atividade hidrolítica em raízes tuberosas de Viguiera discolor Baker, uma espécie herbácea de Asteraceae do cerrado). Frutano do tipo inulina é o principal carboidrato de reserva das raízes tuberosas de Viguiera discolor, uma espécie herbácea nativa do cerrado. Variações na massa molecular do polímero, acompanhadas de altas proporções de frutose livre sugeriram que a hidrólise do mesmo poderia estar associada à brotação das plantas, após o período de dormência, quando toda a parte aérea é naturalmente eliminada. Após indução experimental de brotação e estímulo da atividade hidrolítica, por eliminação da parte aérea, o extrato enzimático foi parcialmente purificado por adsorção em Sepharose ConA, sendo a maior atividade detectada em pH 5,4 e entre 20 e 40 °C. Não foi possível determinar os valores de K m para a inulina, uma vez que até a concentração de 10% não houve a saturação do substrato. O estudo da cinética da atividade de frutano 1-exohidrolase mostrou que a mesma não corresponde à cinética de Michaelis-Menten, apresentando um comportamento aparentemente alostérico, uma vez que os dados se enquadram na equação de Hill. A 1-FEH de V. discolor é uma glicoproteína, mais ativa sobre oligofrutanos do que sobre inulina de alta massa molecular, como a encontrada em outras Asteráceas, e principalmente na própria espécie.Palavras-chave -Asteraceae, cerrado, frutano 1-hexohidrolase, inulina

Hydrolase and fructosyltransferase activities implicated in the accumulation of different chain size fructans in three Asteraceae species

“…The presence of an hDP 1-FFT activity in V. discolor [22], in addition to a very low growth rate of the plant and a low demand of carbon source for growth [24], and a low hydrolytic activity [21], confirmed in the present work (Fig. 3), is consistent with the predominance of high DP fructans stored in the tuberous roots of this species.…”

“…The high 1-FEH activity found in S. sonchifolius as opposed to the low activity of this enzyme generally found in other Asteraceae presenting higher DP fructans [11,13,21] was also suggested to contribute to the predominance of low DP over high DP fructans in its tuberous roots [12]. Therefore, although 1-FFT alone greatly contributes to the fructan chain size characteristic of each species [18,22], the influence of 1-SST/1-FFT ratio and of 1-FEH activity must also be considered.…”

“…The seasonal growth pattern of V. herbacea and V. discolor was previously described and shown to be related to variations in contents and composition of fructans and to changes in the relative activities of the fructan metabolizing enzymes [15e17,21]. Fructan biosynthesis and accumulation in the cerrado species occur predominantly from the vegetative phase throughout dormancy while fructan degradation occurs during natural sprouting in spring and more markedly after induced sprouting by excision of aerial organs [13,17,21].…”

Fructan stability in strawberry sorbets in dependence on their source and the period of storage

“…They are the main reserve carbohydrates in Asteraceae and in many other economically important families [14]. Fructans are a very good example of compounds with proven beneficial effect on the organism [15][16][17][18][19][20], as well as positive impact on the organoleptic attributes [21].…”

Biossíntese e degradação de frutanos em diferentes regiões do rizóforo de Vernonia herbacea (Vell.) Rusby (Asteraceae)

“…Fukai et al (1997) (Mino et al 1978;Fukai et al 1997;Marx et al 1997a;Morvan et al, 1997;Pavis et al, 1998;Degasperi et al 2003;Asega & Carvalho, 2004 (Crowe et al, 1996;Tsvetkova et al, 1998;Hincha et al, 2000). Estresses ambientais induzem um complexo de respostas nas plantas, tanto em nível celular, como fisiológico e de desenvolvimento (Levitt, 1980).…”