Li Tianzhong

Isolation and preliminary function analysis of a Na + /H + antiporter gene from Malus zumi

A full-length cDNA Na+/H+ antiporter gene (MzNHX1) was isolated from Malus zumi according to the homologous Na+/H+ antiporter gene region in plants. Sequence analysis indicated that the cDNA was 2062 bp in length, including an open reading frame (ORF) of 1629 bp, which encoded a predicted polypeptide of 542 amino acids. The MzNHX1 protein shared high identity with other reported plant vacuolar Na+/H+ antiporters. Southern blot analysis detected multiple copies of MzNHX1 in the M. zumi genome. Northern blot analysis showed negligible expression of the gene in roots, but expression was detected in stems and leaves. To test the function of MzNHX1, we expressed the gene in the saltsensitive AXT3 yeast mutant. No differences in yeast cell growth were detected given the presence or absence of MzNHX1 on a NaCl free medium. However, on a 70 mM NaCl medium, growth in the control transformant was noticeably suppressed, and yeast overexpression of MzNHX1 showed increased population growth rates. These results indicated that the MzNHX1 protein increased AXT3 salt tolerance. Alignments of the deduced Na+/H+ antiporter amino acid sequence of different plants from NCBI revealed that MzNHX1 shared high identity (>86%) with vacuolar Na+/H+ antiporters, including RhNHX1 from rose, cNHX1 from citrus, and AtNHX1 from Arabidopsis thaliana. However, MzNHX1 shared very low identity ( thaliana. These results indicated that MzNHX1 was localized to the vacuolar membrane.

Influx Pathways and Key Stages of Phosphorus and Potassium Transport into Grape Fruits

ABSTRACT Using radioisotope tracer determination of 32P and 86Rb and fruit stalk micro-girdling, the influx pathways and key stages of phosphorus (P) and potassium (K) transport to grape fruits were studied. After fruit stalk micro-girdling, only 5.4% of P and 7.3% of K was transported from leaves to fruits via the xylem, compared with 46.75 and 38.67% from roots via phloem. The influx of 32P and 86Rb into fruits from treated leaves varied significantly according to stage of fruit development. For 32P, the variation was in the order: first stage > third stage > fruit veraision > second stage, while for 86Rb the order was: third stage > first stage > second stage > fruit veraision stage. The above results indicated that both first and third stages of grape fruit development had the greatest requirement for P or K from leaves, and the phloem was the dominant influx pathway for their transport into fruits from leaves.