ABSTRACT
The present study investigated the significance of serine biosynthetic genes for salt stress in sugar beet (Beta vulgaris). We isolated a total of four genes, two each encoding D-3-phosphoglycerate dehydrogenase (BvPGDHa and BvPGDHb) and serine hydroxymethyl transferase (BvSHMTa and BvSHMTb). mRNA transcriptional expression for BvPGDHa was significantly enhanced under salt stress conditions in both leaves and roots of sugar beet, whereas it was reduced for BvPGDHb. On the other hand, BvSHMTa was expressed transiently in leaves and roots under salt stress, whereas expression level of BvSHMTb was not altered. PGDH activity was high in storage root. After salt stress, PGDH activity was increased in leaf, petiole, and root. Recombinant proteins were expressed in Escherichia coli. The K m values for 3-phosphoglycerate in PGDHa and PGDHb were 1.38 and 2.92 mM, respectively. The findings suggest that BvPGDHa and BvSHMTa play an important role during salt stress in sugar beet.
Subject(s)
Beta vulgaris/enzymology , Glycine Hydroxymethyltransferase/metabolism , Phosphoglycerate Dehydrogenase/metabolism , Plant Proteins/metabolism , Gene Expression , Glycine Hydroxymethyltransferase/chemistry , Glycine Hydroxymethyltransferase/genetics , Glycine Hydroxymethyltransferase/isolation & purification , Hydrogen-Ion Concentration , Kinetics , Phosphoglycerate Dehydrogenase/chemistry , Phosphoglycerate Dehydrogenase/genetics , Phosphoglycerate Dehydrogenase/isolation & purification , Plant Proteins/chemistry , Plant Proteins/genetics , Plant Proteins/isolation & purification , RNA, Messenger/genetics , RNA, Messenger/metabolism , Salt Tolerance , Stress, PhysiologicalABSTRACT
Proline transporters (ProTs) originally described as highly selective transporters for proline, have been shown to also transport glycinebetaine (betaine). Here we examined and compared the transport properties of Bet/ProTs from betaine accumulating (sugar beet, Amaranthus, and Atriplex,) and non-accumulating (Arabidopsis) plants. Using a yeast mutant deficient for uptake of proline and betaine, it was shown that all these transporters exhibited higher affinity for betaine than proline. The uptake of betaine and proline was pH-dependent and inhibited by the proton uncoupler carbonylcyanide m-chlorophenylhydrazone (CCCP). We also investigated choline transport by using a choline transport-deficient yeast mutant. Results revealed that these transporters exhibited a higher affinity for choline uptake rather than betaine. Uptake of choline by sugar beet BvBet/ProT1 was independent of the proton gradient and the inhibition by CCCP was reduced compared with that for uptake of betaine, suggesting different proton binding properties between the transport of choline and betaine. Additionally, in situ hybridization experiments revealed the localization of sugar beet BvBet/ProT1 in phloem and xylem parenchyma cells.
