Starch synthesis in strawberry fruit

E. Souleyre, P. Iannetta, M. Taylor, G. Duncan, and H. Davies ¨ Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, Scotland, UK Scottish Crop e. mail:[email protected] Research Institute

Introduction Results

The physiology and biochemistry underlying Frozen strawberry fruit (-80°C) were Sugar content in ripening strawberry fruit (year 1999) In contrast starch Starch content in ripening strawberry fruit (year 1999) 90 16 80 carbohydrate metabolism in ripening strawberry fruits ground and soluble sugars were extracted levels decreased by ca. 14 70 Glucose Fructose 12 60 Sucrose has not been addressed in detail. Likewise, the role of with 80% ethanol. Sucrose and hexose Total sugar 50% between RS 1 10 [Sugar] 50 mg/fruit [Starch] starch and its contribution to strawberry fruit quality sugar concentrations were quantified from 40 and RS 2, then mg/g FW 8 30 6 has not been the supernatant by High Performance 20 reduced dramatically 4 Pre-anthesis Anthesis Post-anthesis 10 2 0 to a low level well investigated. Anion Exchange Chromatography. The 123456 0 12 1 23456 Ripening stage The research remaining insoluble pellet was gelatinised before visible Ripening stage presented here and digested by amyloglucosidase for ripening. aims to understand measurement of starch. Results revealed that the concentration of glucose, the potential role fructose and sucrose increased during fruit ripening.

of starch synthesis 2 34 and breakdown in Starch specific staining (using Lugol solution) The examination of Lugol stained fruit sections under low magnification (11.5 fold) by contributing to the was carried out on the cut surface of halved light microscopy revealed that starch was localised mainly in the fruit cortex at RS 1. overall quality and fresh strawberry fruits at different ripening Higher magnification sweetness of the stages. The staining intensity was highest at the (100 fold) indicated end product. immature stage and decline as fruit ripened. starch was Achene Achene 5 5 6 predominantly near Six different 1RS 34 5 6 6 the achenes in the ripening stages (RS) Lugol cells layers of Strawbwerry cv. + immediately below the epidermis. Elsanta were 0.3mm Starch 0.3mm examined covering - the range from immature green fruit (RS 1, c. 5 mm Ripening stage 1 (11.5 fold) Ripening stage 1 (100.5 fold) diameter, 7 days after anthesis) through to small green (RS 2, 12 days), mature green (RS 3, 18 days), white (RS 4, 22 days), pink (RS 5, 31 days) and red ripe stages (RS 6, 40 days). Scanning electron microscopy (SEM) studies of frozen microtome fruit sections Labelled starch precursors [U-14C] glucose and [U-14C] show that starch granules are present within the cells of immature fruits at RS 1, sucrose were supplied to strawberry fruit discs to monitor RS 2 and RS 3. These granules were of a circular form (5-10 µm diameter). the rate of starch Starch synthesis in ripening strawberry fruit Of all the cells examined 90% of the fruit cells at RS 1 and 2 contained synthesis. 30 Conclusion U-14C Sucrose 25 granules, compared to 25% of the RS 3 fruit cells. In addition, the number of The percentage of U-14C Glucose 14 granules per aggregate in the cells of RS 3 was also decreased. 20 [U- C] glucose Percentage of radioactivity 15 From the starch measurement studies, it can be incorporated into incorporated into starch estimated on all fruit basis that starch breakdown starch was greater than 10 could contribute up to 2.5% of the sugar from sucrose. The rate 5 0 accumulation in ripe strawberry fruit. Light of starch biosynthesis 1236 Ripening stage microscopy also revealed that the highest density of for [U-14C] glucose 14 starch granules is located in the cortex of the immature 20µm 20µm 20µm and [U- C] sucrose did not alter significantly as fruit fruit. 14C-labelling experiments revealed that decline ripened. Ripening stage 1 Ripening stage 2 Ripening stage 3 in starch appear to be independent of the rate of synthesis. Further work on the regulation of turnover is imperative. ADP-glucose pyrophosphorylase and fructokinase proteins, key enzymes of carbohydrate To assess the presence or absence of enzymes on the starch biosynthetic pathway, Western blot and enzymatic analyses were performed. µ metabolism are present at all stages. In contrast Fructokinase and sucrose synthase activity patterns are supported by western blot analysis (lanes loaded on g (gFW)). ADP-glucose sucrose synthase activity increased to mature green pyrophosphorylase protein was detected in all fruit ripening stages. ADP-glucose pyrophosphorylase fruit and then declined as ripening progressed. This protein work shows, for the first time, the ripening stage- RS Marker 1 3 4 6 RSMarker 1 3 4 6 RS Marker 1 3 4 6 specific accumulation and utilisation of starch reserves Sucrose synthase activity in ripening strawberry fruit Fructokinase activity in ripening strawberry fruit 40 during strawberry fruit ripening. 14 35 12 30

10 Susy activity 25 (nmol/min/g FW) Fk activity 8 20 (nmol/min/g FW) Acknowledgements 6 15 E. Benson, R. Hancock, Alison Roberts, R Viola, B. Williamson. 4 10 The work is funded by SERAD 2 5 0 0 123456 12 3456 Ripening stage Ripening stage