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Differential regulation of alanine aminotransferase homologues by abiotic stresses in wheat (Triticum aestivum L.) seedlings.

Kendziorek M, Paszkowski A, Zagdańska B - Plant Cell Rep. (2012)

Bottom Line: Nitrogen deficiency has little effect on the activity of GGAT.Both AlaAT and GGAT activities were present in etiolated wheat seedlings but their activity was half of that observed in light-grown seedlings.It is proposed that hypoxia-induced AlaAT1 and light-induced peroxisomal GGAT1 appears to be crucial for the regulation of energy availability in plants grown under unfavourable environmental conditions.

View Article: PubMed Central - PubMed

Affiliation: Biochemistry Department, Warsaw University of Life Sciences, Nowoursynowska 159, 02-776 Warsaw, Poland.

ABSTRACT
Wheat (Triticum aestivum L.) seedlings contain four alanine aminotransferase (AlaAT) homologues. Two of them encode AlaAT enzymes, whereas two homologues act as glumate:glyoxylate aminotransferase (GGAT). To address the function of the distinct AlaAT homologues a comparative examination of the changes in transcript level together with the enzyme activity and alanine and glutamate content in wheat seedlings subjected to low oxygen availability, nitrogen and light deficiency has been studied. Shoots of wheat seedlings were more tolerant to hypoxia than the roots as judging on the basis of enzyme activity and transcript level. Hypoxia induced AlaAT1 earlier in roots than in shoots, while AlaAT2 and GGAT were unaffected. The increase in AlaAT activity lagged behind the increase in alanine content. Nitrogen deficiency has little effect on the activity of GGAT. In contrast, lower activity of AlaAT and the level of mRNA for AlaAT1 and AlaAT2 in wheat seedlings growing on a nitrogen-free medium seems to indicate that AlaAT is regulated by the availability of nitrogen. Both AlaAT and GGAT activities were present in etiolated wheat seedlings but their activity was half of that observed in light-grown seedlings. Exposure of etiolated seedlings to light caused an increase in enzyme activities and up-regulated GGAT1. It is proposed that hypoxia-induced AlaAT1 and light-induced peroxisomal GGAT1 appears to be crucial for the regulation of energy availability in plants grown under unfavourable environmental conditions. Key message In young wheat seedlings, both AlaAT and GGAT are down-regulated by nitrogen deficiency, whereas AlaAT1 is upregulated by hypoxia and GGAT1 by light.

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Alanine and glutamate concentration quantified by RP-HPLC in shoots and roots of wheat seedlings subjected to hypoxia. Amino acids were extracted from shoots and roots of control seedlings and seedlings harvested 24, 48, 72, 96 and 120 h after induction of hypoxia. Results are the mean of three replicates ± SD
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Fig7: Alanine and glutamate concentration quantified by RP-HPLC in shoots and roots of wheat seedlings subjected to hypoxia. Amino acids were extracted from shoots and roots of control seedlings and seedlings harvested 24, 48, 72, 96 and 120 h after induction of hypoxia. Results are the mean of three replicates ± SD

Mentions: To analyze the involvement of AlaAT in alanine accumulation during oxygen deficiency, the changes in alanine and glutamate contents were investigated. Alanine concentration in seedling shoots decreased by about 50% after 48 h of hypoxia and then started to increase and was about twofold higher after 120 h of hypoxia as compared to control seedlings (Fig. 7). Glutamate concentration remained practically unchanged in seedling roots upon hypoxia but it varied considerably in seedling shoots and increased 1.5-fold after 120 h of hypoxia. As a result, alanine accumulated rapidly in roots under hypoxia. After 24 h of hypoxia treatment alanine content was about tenfold higher and continued to increase reaching maximum after 72 h hypoxia and then started to decrease. Glutamate concentration, however, decreased by about 42% after 48 h hypoxia treatment and started to reach the final concentration twice as high as in control plants.Fig. 7


Differential regulation of alanine aminotransferase homologues by abiotic stresses in wheat (Triticum aestivum L.) seedlings.

Kendziorek M, Paszkowski A, Zagdańska B - Plant Cell Rep. (2012)

Alanine and glutamate concentration quantified by RP-HPLC in shoots and roots of wheat seedlings subjected to hypoxia. Amino acids were extracted from shoots and roots of control seedlings and seedlings harvested 24, 48, 72, 96 and 120 h after induction of hypoxia. Results are the mean of three replicates ± SD
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3351597&req=5

Fig7: Alanine and glutamate concentration quantified by RP-HPLC in shoots and roots of wheat seedlings subjected to hypoxia. Amino acids were extracted from shoots and roots of control seedlings and seedlings harvested 24, 48, 72, 96 and 120 h after induction of hypoxia. Results are the mean of three replicates ± SD
Mentions: To analyze the involvement of AlaAT in alanine accumulation during oxygen deficiency, the changes in alanine and glutamate contents were investigated. Alanine concentration in seedling shoots decreased by about 50% after 48 h of hypoxia and then started to increase and was about twofold higher after 120 h of hypoxia as compared to control seedlings (Fig. 7). Glutamate concentration remained practically unchanged in seedling roots upon hypoxia but it varied considerably in seedling shoots and increased 1.5-fold after 120 h of hypoxia. As a result, alanine accumulated rapidly in roots under hypoxia. After 24 h of hypoxia treatment alanine content was about tenfold higher and continued to increase reaching maximum after 72 h hypoxia and then started to decrease. Glutamate concentration, however, decreased by about 42% after 48 h hypoxia treatment and started to reach the final concentration twice as high as in control plants.Fig. 7

Bottom Line: Nitrogen deficiency has little effect on the activity of GGAT.Both AlaAT and GGAT activities were present in etiolated wheat seedlings but their activity was half of that observed in light-grown seedlings.It is proposed that hypoxia-induced AlaAT1 and light-induced peroxisomal GGAT1 appears to be crucial for the regulation of energy availability in plants grown under unfavourable environmental conditions.

View Article: PubMed Central - PubMed

Affiliation: Biochemistry Department, Warsaw University of Life Sciences, Nowoursynowska 159, 02-776 Warsaw, Poland.

ABSTRACT
Wheat (Triticum aestivum L.) seedlings contain four alanine aminotransferase (AlaAT) homologues. Two of them encode AlaAT enzymes, whereas two homologues act as glumate:glyoxylate aminotransferase (GGAT). To address the function of the distinct AlaAT homologues a comparative examination of the changes in transcript level together with the enzyme activity and alanine and glutamate content in wheat seedlings subjected to low oxygen availability, nitrogen and light deficiency has been studied. Shoots of wheat seedlings were more tolerant to hypoxia than the roots as judging on the basis of enzyme activity and transcript level. Hypoxia induced AlaAT1 earlier in roots than in shoots, while AlaAT2 and GGAT were unaffected. The increase in AlaAT activity lagged behind the increase in alanine content. Nitrogen deficiency has little effect on the activity of GGAT. In contrast, lower activity of AlaAT and the level of mRNA for AlaAT1 and AlaAT2 in wheat seedlings growing on a nitrogen-free medium seems to indicate that AlaAT is regulated by the availability of nitrogen. Both AlaAT and GGAT activities were present in etiolated wheat seedlings but their activity was half of that observed in light-grown seedlings. Exposure of etiolated seedlings to light caused an increase in enzyme activities and up-regulated GGAT1. It is proposed that hypoxia-induced AlaAT1 and light-induced peroxisomal GGAT1 appears to be crucial for the regulation of energy availability in plants grown under unfavourable environmental conditions. Key message In young wheat seedlings, both AlaAT and GGAT are down-regulated by nitrogen deficiency, whereas AlaAT1 is upregulated by hypoxia and GGAT1 by light.

Show MeSH
Related in: MedlinePlus