Limits...
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.

Show MeSH

Related in: MedlinePlus

Relative expression levels of LeSUT1 genes in leaves of plants grown under control and saline conditions for short (A) and long (B) periods. (A) Leaves were sampled at 0.5, 1, 3, 6, 12, and 24 h after the start of exposure to salinity stress. (B) Leaves were sampled 5 d and 10 d after the start of exposure to salinity stress. Open and shaded columns indicate control (0 mM NaCl) and salinity treatments (160 mM NaCl), respectively. Values are means ±SE (n=4). The asterisks indicate statistical significance of the means estimated using Fisher's PLSD test (*P <0.05, **P <0.01).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig5: Relative expression levels of LeSUT1 genes in leaves of plants grown under control and saline conditions for short (A) and long (B) periods. (A) Leaves were sampled at 0.5, 1, 3, 6, 12, and 24 h after the start of exposure to salinity stress. (B) Leaves were sampled 5 d and 10 d after the start of exposure to salinity stress. Open and shaded columns indicate control (0 mM NaCl) and salinity treatments (160 mM NaCl), respectively. Values are means ±SE (n=4). The asterisks indicate statistical significance of the means estimated using Fisher's PLSD test (*P <0.05, **P <0.01).

Mentions: To elucidate the sugar loading activity in source leaves under salinity stress, transcriptional levels of LeSUT1 were investigated (Fig. 5). This gene encodes the major isoform of a sucrose transporter in photosynthetic source leaves that functions in phloem loading of sucrose in tomato plants (Kühn et al., 1997). At the transcriptional level, LeSUT1 exhibited diurnal cycles under control and the salinity conditions, and the setting time-course shown in Fig. 5. In plants exposed to salt stress for 6–24 h, although LeSUT1 expression decreased in the first 3 h, it was up-regulated 1.98–4.19 times compared to the control at the same time point (Fig. 5A). The LeSUT1 transcription was enhanced for at least 10 d after the onset of salinity stress (Fig. 5B), when the prominent starch accumulation was observed in the fruit (Figs 3, 4).


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)

Relative expression levels of LeSUT1 genes in leaves of plants grown under control and saline conditions for short (A) and long (B) periods. (A) Leaves were sampled at 0.5, 1, 3, 6, 12, and 24 h after the start of exposure to salinity stress. (B) Leaves were sampled 5 d and 10 d after the start of exposure to salinity stress. Open and shaded columns indicate control (0 mM NaCl) and salinity treatments (160 mM NaCl), respectively. Values are means ±SE (n=4). The asterisks indicate statistical significance of the means 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

fig5: Relative expression levels of LeSUT1 genes in leaves of plants grown under control and saline conditions for short (A) and long (B) periods. (A) Leaves were sampled at 0.5, 1, 3, 6, 12, and 24 h after the start of exposure to salinity stress. (B) Leaves were sampled 5 d and 10 d after the start of exposure to salinity stress. Open and shaded columns indicate control (0 mM NaCl) and salinity treatments (160 mM NaCl), respectively. Values are means ±SE (n=4). The asterisks indicate statistical significance of the means estimated using Fisher's PLSD test (*P <0.05, **P <0.01).
Mentions: To elucidate the sugar loading activity in source leaves under salinity stress, transcriptional levels of LeSUT1 were investigated (Fig. 5). This gene encodes the major isoform of a sucrose transporter in photosynthetic source leaves that functions in phloem loading of sucrose in tomato plants (Kühn et al., 1997). At the transcriptional level, LeSUT1 exhibited diurnal cycles under control and the salinity conditions, and the setting time-course shown in Fig. 5. In plants exposed to salt stress for 6–24 h, although LeSUT1 expression decreased in the first 3 h, it was up-regulated 1.98–4.19 times compared to the control at the same time point (Fig. 5A). The LeSUT1 transcription was enhanced for at least 10 d after the onset of salinity stress (Fig. 5B), when the prominent starch accumulation was observed in the fruit (Figs 3, 4).

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
Related in: MedlinePlus