Sucrose Metabolism in Tubers of Potato (Solanum tuberosum L.)

Abstract

Excision of developing potato (Solanum tuberosum L.) tubers from the mother plant, followed by storage at 10°C, resulted in a rapid, substantial decrease in sucrose synthase activity and considerable increases in hexose content and acid invertase activity. A comparison of the response of three genotypes, known to accumulate different quantities of hexoses in storage, showed that both sucrose synthase activity and the extent to which activity declined following excision were similar in all cases. However, there was significant genotypic variation in the extent to which acid invertase activity developed, with tubers accumulating the highest hexose content also developing the highest extractable activity of invertase. Similar effects were found in nondetached tubers when growing plants were maintained in total darkness for a prolonged period. Furthermore, supplying sucrose to detached tubers through the cut stolon surface prevented the decline in sucrose synthase activity. Maltose proved to be ineffective. Westem blots using antibodies raised against maize sucrose synthase showed that the decline in sucrose synthase activity was associated with the loss of protein rather than the effect of endogenous inhibitors. Although there were indications that maintaining a flux of sucrose into isolated tubers could prevent the increase in acid invertase activity, the results were not conclusive.

Sink- and vascular-associated sucrose synthase functions are encoded by different gene classes in potato.

“…They could encode proteins of 805 amino acids with calculated molecular masses of ~92 kD, which is consistent with the estimated size of 90 kD for potato sucrose synthase (Ross and Davies, 1992 The presence of a long leader intron in the 5' untranslated region is a typical feature of sucrose synthase genes (Werr et al, 1985;Chopra et al, 1992;Wang et al, 1992;Yu et al, 1992;Shaw et al, 1994). A 1612-bp leader intron with a GT/AG splicing boundary was easily identified in Sus4-16 by comparing its sequence with that of the 5' untranslated region of the potato sucrose synthase cDNA Pofssyn (Figure 4).…”

“…In contrast, Sus3 transcripts were not sucrose inducible and were present at relatively constant low levels after incubation with various concentrations of sucrose. Ross and Davies (1992) have shown that tuber excision causes a rapid decrease in both the amount and activity of sucrose synthase. As expected, we found that the Sus4 class transcript level decreased dramatically within 6 hr after tuber excision and was almost undetectable after 12 hr ( Figure 9C).…”

Purification and Characterization of Sucrose Synthase from the Cotyledons of Vicia faba L

“…The tetrameric structure of the native protein is similar to that observed with mung bean seedlings (10), rice grains (15), maize kernels (21), soybean nodules (14), and peach fruit (13). In these instances, the molecular mass of the protein ranges between 360 and 400 kD, with the molecular masses (18). The amino acid sequence data, although only for a small portion of the faba bean SS protein, show distinct homology with potato tuber SS, which itself has a 75% overall identity with maize SS (20).…”

“…Throughout the purification, SS activity was assayed in the cleavage direction (18). Additionally, sucrose cleavage activity with nucleoside diphosphates other than UDP was determined using a stopped assay system.…”

Expression of a yeast-derived invertase in companion cells results in long-distance transport of a trisaccharide in an apoplastic loader and influences sucrose transport

“…2, curve D). Because invertase activity is virtually absent in WT tubers during loading (Ross and Davies 1992), an endogenous invertase cannot be responsible for oligosaccharide synthesis in the rolC invertase/WT combinations, thus ruling out the possibility of oligosaccharide synthesis in the tubers of rolC invertase/WT grafts. This shows that oligosaccharides produced in the companion cells of above-ground plant tissues have been transported via the phloem to the storage organs in an apoplastic loader.…”