Fructan and fructan‐metabolizing enzymes in the growth zone of barley leaves

Abstract

SUMMARYTo Study the role of fructan in leaf development of barley seedlings, fructan contents and the activities of enzymes involved in fructan metabolism were measured in segments of the third leaf at the stage of maximal growth. Fructans amounted to more than 10% of the d. wt in the growth zone at the base of the developing leaf and decreased sharply in the zone above. The specific activities of sucrose: sucrose 1-fructosyltransferase (1-SST) and sucrose: fructan 6-fructosyltransferase (6-SFT), two key enzymes in fructan synthesis, also peaked in the growth zone but decreased more slowly in the zone above. By contrast, the specific activities of invertase and fructan exohydrolase (FEH) were low in the growth zone at the leaf base and had their peak just above it. The specific activity of fructan: fructan 1-fructosyltransferase (1-FFT) was approx. constant over the whole leaf. These results indicate that transitory accumulation of fructans in the growth zone plays a key role in the development of barley leaves.

Fructans and fructan‐metabolizing enzymes in leaves of Lolium perenne

“…The younger the sheath was, the higher the fructan content. According to the present results and as shown once in barley (Roth et al, 1997), fructans were also heterogenously distributed along the sheath axis, being preferentially accumulated in the basal part. Crude SST and 6G-FT activities were very active in that segment and the activities increased markedly under conditions which allowed carbohydrate accumulation.…”

“…As in the case of Festuca and barley Roth et al, 1997), large fructan stores were deposited temporarily in the basal segment of elongating leaves which comprised most of the growing zone (Morvan-Bertrand et al, 1999). In barley, the two enzymes which use sucrose as fructosyl donor for fructan synthesis, namely the 1-SST and the 6-SFT, were also preferentially active in the growth zone of the elongating leaves (Roth et al, 1997).…”

“…Schnyder & Nelson (1987) have suggested that the fructosyltransferases might facilitate phloem unloading in the growth zone by using sucrose for fructan synthesis in the vacuole to facilitate its removal from the cytosol. In their recent studies, Roth et al (1997) proposed that in the growth zone, fructosyltransferases could replace invertase as the main sucrose-metabolizing enzymes. This hypothesis is based on the fact that invertase activities were minimal in that zone, a result also found by Lüscher & Nelson (1995) in tall fescue.…”

“…Recently, Roth et al . (1997) found that, in barley, the activity of 1-SST and 6-SFT, the two key enzymes in fructan synthesis for that species, peaked in the growth zone, indicating that these enzymes might play an important role in assimilate partitioning during leaf development.…”

Pool sizes of fructans in roots and leaves of mycorrhizal and non‐mycorrhizal barley

“…In leaves of mycorrhizal plants, overall fructan contents were significantly reduced in 35-d-old, non-fertilized plants, very likely to the benefit of the root system. Moreover, the gradient of fructan accumulation, namely high amounts in the youngest to low amounts in the oldest leaves (Roth et al, 1997), was markedly altered in mycorrhizal plants, again irrespective of the fertilization status. Transposed into a field situation, this would mean that the presence of mycorrhizal fungi may not only shape a plant community horizontally by favouring different plant species to different extents (Grime et al, 1987), but also vertically by altering the pattern of accumulation of storage compounds in infected plants (even within a monoculture).…”