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Salinity induces carbohydrate accumulation and sugar-regulated starch biosynthetic genes in tomato (Solanum lycopersicum L. cv. 'Micro-Tom') fruits in an ABA- and osmotic stress-independent manner.

Yin YG, Kobayashi Y, Sanuki A, Kondo S, Fukuda N, Ezura H, Sugaya S, Matsukura C - J. Exp. Bot. (2009)

Bottom Line: Tracer analysis with (13)C confirmed that elevated carbohydrate accumulation in fruits exposed to salinity stress was confined to the early development stages and did not occur after ripening.The results indicate that salinity stress enhanced carbohydrate accumulation as starch during the early development stages and it is responsible for the increase in soluble sugars in ripe fruit.These results indicate AgpL1 and AgpS1 are involved in the promotion of starch biosynthesis under the salinity stress in ABA- and osmotic stress-independent manners.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki, Japan.

ABSTRACT
Salinity stress enhances sugar accumulation in tomato (Solanum lycopersicum) fruits. To elucidate the mechanisms underlying this phenomenon, the transport of carbohydrates into tomato fruits and the regulation of starch synthesis during fruit development in tomato plants cv. 'Micro-Tom' exposed to high levels of salinity stress were examined. Growth with 160 mM NaCl doubled starch accumulation in tomato fruits compared to control plants during the early stages of development, and soluble sugars increased as the fruit matured. Tracer analysis with (13)C confirmed that elevated carbohydrate accumulation in fruits exposed to salinity stress was confined to the early development stages and did not occur after ripening. Salinity stress also up-regulated sucrose transporter expression in source leaves and increased activity of ADP-glucose pyrophosphorylase (AGPase) in fruits during the early development stages. The results indicate that salinity stress enhanced carbohydrate accumulation as starch during the early development stages and it is responsible for the increase in soluble sugars in ripe fruit. Quantitative RT-PCR analyses of salinity-stressed plants showed that the AGPase-encoding genes, AgpL1 and AgpS1 were up-regulated in developing fruits, and AgpL1 was obviously up-regulated by sugar at the transcriptional level but not by abscisic acid and osmotic stress. These results indicate AgpL1 and AgpS1 are involved in the promotion of starch biosynthesis under the salinity stress in ABA- and osmotic stress-independent manners. These two genes are differentially regulated at the transcriptional level, and AgpL1 is suggested to play a regulatory role in this event.

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Changes in endogenous ABA content in the developing fruits grown under control and saline conditions. Open and shaded columns indicate control (0 mM NaCl) and salinity (160 mM NaCl) treatments, respectively. The horizontal axis indicates fruit developing stages (DAF). Values are means ±SD (n=5). The asterisks indicate statistical significance of means in the same developing stage estimated using Fisher's PLSD test (*P <0.05, **P <0.01).
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fig9: Changes in endogenous ABA content in the developing fruits grown under control and saline conditions. Open and shaded columns indicate control (0 mM NaCl) and salinity (160 mM NaCl) treatments, respectively. The horizontal axis indicates fruit developing stages (DAF). Values are means ±SD (n=5). The asterisks indicate statistical significance of means in the same developing stage estimated using Fisher's PLSD test (*P <0.05, **P <0.01).

Mentions: To elucidate the response of Agp genes to possible physiological effectors in early developing fruit, the fruits at 10 DAF were exposed to exogenous ABA, sucrose, and the same level of osmotic stress given by mannitol. The transcription level of the Agp genes was analysed in fruits at 10 DAF which were cultured for 6 h on agar plates of half-strength MS medium containing 0.01–100 μM ABA, 150 mM sucrose, and 150 mM mannitol as single or multiple effectors. AgpL1 and AgpS1 were significantly up-regulated by sucrose and sucrose+ABA but not by ABA, mannitol, and mannitol+ABA (Fig. 8A, D; see Supplementary Table S2 at JXB online). Results of the two-way repeated measures ANOVA showed the sucrose-response of AgpL1 was affected by ABA; however, there was no interaction effect on AgpS1 expression (see Supplementary Table S2 at JXB online). On the other hand, AgpL2 transcription was slightly up-regulated by mannitol, and AgpL3 was affected by the ABA level with sucrose and mannitol, while these were not effective as single effectors (Fig. 8B, C; see Supplementary Table S2 at JXB online). To ensure the validity of this analysis, the endogenous ABA content in developing fruit was assayed (Fig. 9). Fruit ABA contents ranged from 3 nmol g−1 DW to 16 nmol g−1 DW and peaked at 26 DAF in both growth conditions. However, ABA tended to be lower in the salinity-stressed fruits than control fruits at 10 DAF. Based on the water content ratio in the fruits, 91.4% and 87.6% on average in the control and salinity-stressed fruits, respectively, endogenous ABA concentration in fresh fruit was roughly estimated to be 0.3 μM to 2 μM, which fell within the dose range administered in Fig. 8.


Salinity induces carbohydrate accumulation and sugar-regulated starch biosynthetic genes in tomato (Solanum lycopersicum L. cv. 'Micro-Tom') fruits in an ABA- and osmotic stress-independent manner.

Yin YG, Kobayashi Y, Sanuki A, Kondo S, Fukuda N, Ezura H, Sugaya S, Matsukura C - J. Exp. Bot. (2009)

Changes in endogenous ABA content in the developing fruits grown under control and saline conditions. Open and shaded columns indicate control (0 mM NaCl) and salinity (160 mM NaCl) treatments, respectively. The horizontal axis indicates fruit developing stages (DAF). Values are means ±SD (n=5). The asterisks indicate statistical significance of means in the same developing stage estimated using Fisher's PLSD test (*P <0.05, **P <0.01).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2803223&req=5

fig9: Changes in endogenous ABA content in the developing fruits grown under control and saline conditions. Open and shaded columns indicate control (0 mM NaCl) and salinity (160 mM NaCl) treatments, respectively. The horizontal axis indicates fruit developing stages (DAF). Values are means ±SD (n=5). The asterisks indicate statistical significance of means in the same developing stage estimated using Fisher's PLSD test (*P <0.05, **P <0.01).
Mentions: To elucidate the response of Agp genes to possible physiological effectors in early developing fruit, the fruits at 10 DAF were exposed to exogenous ABA, sucrose, and the same level of osmotic stress given by mannitol. The transcription level of the Agp genes was analysed in fruits at 10 DAF which were cultured for 6 h on agar plates of half-strength MS medium containing 0.01–100 μM ABA, 150 mM sucrose, and 150 mM mannitol as single or multiple effectors. AgpL1 and AgpS1 were significantly up-regulated by sucrose and sucrose+ABA but not by ABA, mannitol, and mannitol+ABA (Fig. 8A, D; see Supplementary Table S2 at JXB online). Results of the two-way repeated measures ANOVA showed the sucrose-response of AgpL1 was affected by ABA; however, there was no interaction effect on AgpS1 expression (see Supplementary Table S2 at JXB online). On the other hand, AgpL2 transcription was slightly up-regulated by mannitol, and AgpL3 was affected by the ABA level with sucrose and mannitol, while these were not effective as single effectors (Fig. 8B, C; see Supplementary Table S2 at JXB online). To ensure the validity of this analysis, the endogenous ABA content in developing fruit was assayed (Fig. 9). Fruit ABA contents ranged from 3 nmol g−1 DW to 16 nmol g−1 DW and peaked at 26 DAF in both growth conditions. However, ABA tended to be lower in the salinity-stressed fruits than control fruits at 10 DAF. Based on the water content ratio in the fruits, 91.4% and 87.6% on average in the control and salinity-stressed fruits, respectively, endogenous ABA concentration in fresh fruit was roughly estimated to be 0.3 μM to 2 μM, which fell within the dose range administered in Fig. 8.

Bottom Line: Tracer analysis with (13)C confirmed that elevated carbohydrate accumulation in fruits exposed to salinity stress was confined to the early development stages and did not occur after ripening.The results indicate that salinity stress enhanced carbohydrate accumulation as starch during the early development stages and it is responsible for the increase in soluble sugars in ripe fruit.These results indicate AgpL1 and AgpS1 are involved in the promotion of starch biosynthesis under the salinity stress in ABA- and osmotic stress-independent manners.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki, Japan.

ABSTRACT
Salinity stress enhances sugar accumulation in tomato (Solanum lycopersicum) fruits. To elucidate the mechanisms underlying this phenomenon, the transport of carbohydrates into tomato fruits and the regulation of starch synthesis during fruit development in tomato plants cv. 'Micro-Tom' exposed to high levels of salinity stress were examined. Growth with 160 mM NaCl doubled starch accumulation in tomato fruits compared to control plants during the early stages of development, and soluble sugars increased as the fruit matured. Tracer analysis with (13)C confirmed that elevated carbohydrate accumulation in fruits exposed to salinity stress was confined to the early development stages and did not occur after ripening. Salinity stress also up-regulated sucrose transporter expression in source leaves and increased activity of ADP-glucose pyrophosphorylase (AGPase) in fruits during the early development stages. The results indicate that salinity stress enhanced carbohydrate accumulation as starch during the early development stages and it is responsible for the increase in soluble sugars in ripe fruit. Quantitative RT-PCR analyses of salinity-stressed plants showed that the AGPase-encoding genes, AgpL1 and AgpS1 were up-regulated in developing fruits, and AgpL1 was obviously up-regulated by sugar at the transcriptional level but not by abscisic acid and osmotic stress. These results indicate AgpL1 and AgpS1 are involved in the promotion of starch biosynthesis under the salinity stress in ABA- and osmotic stress-independent manners. These two genes are differentially regulated at the transcriptional level, and AgpL1 is suggested to play a regulatory role in this event.

Show MeSH