Carbohydrate composition and invertase activity of the leafy liverwort Porella platyphylla

Abstract

The major soluble carbohydrates in the desiccation-tolerant leafy liverwort Porella platyphylla (L.) Lindb. are sucrose and a homologous series of fructans including the trisaccharide 1-kestose. Exogenous glucose and fructose (10 mol m −$ ) did not affect the composition of the soluble carbohydrate pool. Sucrose caused an increase in the fructan pool. Sucrose also inhibited photosynthetic oxygen evolution and respiration. The fructan pool was maintained in preference to sucrose during dark starvation. Low temperature and low water potential increased the fructan pool whereas desiccation increased the proportion of high molecular weight fructan. Acid invertase activity was detected in a taxonomically diverse range of liverworts but was very low or undetectable in a range of mosses. The invertase activity from P. platyphylla was partially purified by ammonium sulphate precipitation. The reaction products of the partially purified enzyme were equimolar glucose and fructose. Kestose and higher DP fructans were not detected suggesting that, at least under the assay conditions used, the enzyme does not have sucrose : sucrose fructosyl transferase activity. The pH optimum was 4n5-5 and the K m for sucrose was 1n7 mol m −$ . Pyridoxal hydrochloride (5 mol m −$ ) caused 50 % inhibition. The coexistence of sucrose and invertase suggests that either the invertase is inactive in vivo or is in a different subcellular compartment from sucrose. The pH response shows that it would have very low activity at cytosolic pH. A large acidic vacuole was detected in P. platyphylla leaf cells by neutral-red staining in which either invertase or sucrose could be sequestered. Rehydrating desiccated P. platyphylla for 10 min resulted in a 60 % loss of extractable invertase activity. By contrast, extractable malate dehydrogenase activity increased during rehydration. Rehydrating desiccated leaves caused an increase in glucose and fructose suggesting that the sucrose pool was susceptible to invertase at this time. It is suggested that the partial inactivation of invertase during rehydration minimizes sucrose hydrolysis while membrane structure and subcellular compartmentation are re-established.

Drought induces fructan synthesis and 1-SST (sucrose: sucrose fructosyltransferase) in roots and leaves of chicory seedlings ( Cichorium intybus L.)

“…This is consistent with a previous report (Sprenger et al 1997) where fructans were initiated in detached chicory leaves upon incubation in Suc. In the leafy liverwort Porella platyphylla desiccation also led to an increase in the fructan pool (Marschall et al 1998) and ®eld-grown Vernonia herbacea exhibit an increase in total fructan concentration during winter when cerrado plants are exposed to temperature and drought stress (Machado de Carvalho and Dietrich 1993).…”

“…Other reports, however, suggest that, during drought, tolerant genotypes accumulate higher levels of fructan than the more sensitive ones (Volaire and LelieÁ vre 1997;Kerepesi et al 1998). In the leafy liverwort Porella platyphylla, drought led to an accumulation of high-molecular-weight fructan (Marschall et al 1998). Transgenic fructan-accumulating tobacco exhibited enhanced resistance to drought stress (Pilon-Smits et al 1995).…”

Polysaccharides from Lower Plants: Bryophytes

“…Even if Sphagnum mosses is the bryophyte group most frequently chosen for polysaccharide research, there are some studies concentrating on other bryophyte groups, such as liverworts (Suleiman et al 1978;Marschall et al 1998;Nagao et al 2006). Studies on the carbohydrate content of the liverwort Plagiochila asplenioides reveal that there are some differences in the carbohydrate content of mosses and liverworts, and the carbohydrate composition can be used as a taxonomic characteristic (Marschall et al 1998). The water-soluble fraction of Plagiochila asplenioides consists of glucose (3 μg * mg of dry weight À1 ), fructose (6 μg * mg of dry weight À1 ), sucrose (6 μg * mg of dry weight À1 ), mannitol (0.93 μg * mg of dry weight À1 ), and volemitol (10.4 μg * mg of dry weight À1 ), which have not been found in Sphagnum mosses (Suleiman et al 1978).…”

“…During cold weather and in the aging process, the fructose and glucose levels decrease, while sucrose does not change greatly (Smirnoff 1991). Even if Sphagnum mosses is the bryophyte group most frequently chosen for polysaccharide research, there are some studies concentrating on other bryophyte groups, such as liverworts (Suleiman et al 1978;Marschall et al 1998;Nagao et al 2006). Studies on the carbohydrate content of the liverwort Plagiochila asplenioides reveal that there are some differences in the carbohydrate content of mosses and liverworts, and the carbohydrate composition can be used as a taxonomic characteristic (Marschall et al 1998).…”

“…The total amount of carbohydrates and polysaccharides in bryophytes vary in a significant range, largely depending on the studied species and the method used (Judina et al 1999;Marschall et al 1998). One of the key groups of bryophyte mosses most abundantly studied to identify the structure-forming polysaccharides is Sphagnum moss, which is placed in a separate class -Sphagnopsidarepresented by 120 different species and being one of the main species forming northern bogs and wetlands as well as the major precursor of raised bog peat (Glime 2007;Judina et al 1999).…”