Cold tolerance of potato plants transformed with yeast invertase gene

Our study was carried out with potato plants (<i>Solanum tuberosun</i> L.,cv. Désirée) transformed with the yeast invertase gene under the control of the B33 class I patatin promoter and with the proteinase inhibitor II leader peptide sequence providing for the apoplastic enzyme localization (B33-<i>inv</i> plants) and with the plants transformed with the reporter gene encoding bb-glucuronidase under the control of the 35S CaMV promoter (control plants). Exposure to 5°C during 6 days caused an increase in invertase activity and sugar content in B33-<i>inv</i> leaves in comparison with the control plants. Cell membranes of B33-<i>inv</i> plant cells showed greater cold tolerance under low temperature conditions than control plants that was recorded by electrolyte release. We supposed that higher cold tolerance of B33-<i>inv</i> plants was caused by stabilizing effect of sugar on the membranes, because B33-<i>inv</i> plants differ from the control plants in higher invertase activity, induced by expression of yeast invertase gene, and high content of sugars.

Role of tobacco vacuolar invertase regulated by patatin promoter in potato tuber resistance to cold sweetening

To slow down the accumulation of reducing sugar in potato tubers exposed to low-temperature storage, an expression vector, pBICNI, including Nt-VIF (Nicotiana tabacum vacuolar inhibitor of beta fructosidase, a vacuolar invertase inhibitor from Nicotiana tabacum) gene regulated by potato tuber specific promoter class I patatin promoter (CIPP) was constructed and transformed into potato (Solanum tuberosum L.) cultivar E-potato 3 (E3). Detection by polymerase chain reaction (PCR), Northern and Southern hybridizations indicated that the full-length Nt-VIF cDNA was transformed successfully into cv. E3. After storing potato tubers of 14 transgenic lines at 4 or 20°C for 30 days, their activities of vacuolar invertase (VI) and reducing sugar (RS) content were analysed. The results showed that there were no significant differences in RS content between transgenic and untransformed (control) tubers stored at 20°C. However, RS content of transgenic lines was obviously reduced at 4°C compared to the control, from 34.0% (line B-13) to 76.8% reduction (line B-1), implying that VI activity was inhibited by Nt-VIF cDNA expression and RS content was reduced. Further analysis revealed a positive linear relationship between VI activity and RS content (VI=0.308RS+0.067), and lines B-1, B-2, B-6, B-9 and B-14 could meet the requirements of potato chips in terms of their low RS content after cold storage.

Characterization of transgenic potato (Solanum tuberosum) tubers with increased ADPglucose pyrophosphorylase*

The aim of the work described in this paper was to characterize the tubers of potato (Solanum tuberosum var. Prairie) plants that had been transformed with the Escherichiacoli ADPglucose pyrophosphorylase (EC 2.7.7.27) gene, glgC-16, under the control of a patatin promoter. Over 30 lines of transformed plants with increased ADPglucose pyrophosphorylase activity were obtained. The tubers of six of these lines were compared with those of control plants expressing the gene for β-glucuronidase. The average increase in pyrophosphorylase activity was 200%, and the highest was 400%. Western immunoblotting of tuber extracts showed that the amounts of glgC-16 protein were linearly related to the extractable activity of the ADPglucose pyrophosphorylase. Cell fractionation studies showed that the increased activity of the pyrophosphorylase in the glgC-16 tubers had a similar intracellular location, the amyloplast fraction, to that found in the control tubers. No pleiotropic changes in the maximum catalytic activities of the following enzymes could be detected in the glgC-16 tubers: sucrose synthase, fructokinase, UDPglucose pyrophosphorylase, phosphofructokinase, soluble starch synthase, starch branching enzyme, phosphoglucomutase and alkaline inorganic pyrophosphatase. The glgC-16 tubers are held to be suitable for the study of the role of ADPglucose pyrophosphorylase in the control of starch synthesis.