Turn-final intonation in English

<div><p>The aim of this study was to determine whether transgenic birch (<i>Betula platyphylla</i>) ectopic overexpressing a late embryogenesis abundant (<i>LEA</i>) gene and a basic leucine zipper (<i>bZIP</i>) gene from the salt-tolerant genus <i>Tamarix</i> (salt cedar) show increased tolerance to salt (NaCl) stress. Co-transfer of <i>TaLEA</i> and <i>ThbZIP</i> in birch under the control of two independent CaMV 35S promoters significantly enhanced salt stress. PCR and northern blot analyses indicated that the two genes were ectopically overexpressed in several dual-gene transgenic birch lines. We compared the effects of salt stress among three transgenic birch lines (L-4, L-5, and L-8) and wild type (WT). In all lines, the net photosynthesis values were higher before salt stress treatment than afterwards. After the salt stress treatment, the transgenic lines L-4 and L-8 showed higher values for photosynthetic traits, chlorophyll fluorescence, peroxidase and superoxide dismutase activities, and lower malondialdehyde and Na⁺ contents, compared with those in WT and L-5. These different responses to salt stress suggested that the transcriptional level of the <i>TaLEA</i> and <i>ThbZIP</i> genes differed among the transgenic lines, resulting in a variety of genetic and phenotypic effects. The results of this research can provide a theoretical basis for the genetic engineering of salt-tolerant trees.</p></div

ANOVA analysis of SOD, POD, MDA and Na⁺ Concentration among different lines and time under salt stress.

<p>ANOVA analysis of SOD, POD, MDA and Na⁺ Concentration among different lines and time under salt stress.</p

The phenotypes of WT on day 8 under different concentrations of NaCl.

<p>From left to right were WT, the treatment of 2 g L^-1, 4 g L^-1, 6 g L^-1 and 8 g L^-1 of salt stress, respectively.</p

Pn values of WT under different concentrations salt stress.

<p>Pn values of WT under different concentrations salt stress.</p

Average POD, SOD, MDA and Na⁺ content of different lines in different time under salt stress.

<p>Average POD, SOD, MDA and Na⁺ content of different lines in different time under salt stress.</p

NaCl stress-tolerance test of transgenic birch ectopic overexpressing <i>TaLEA</i> and <i>ThbZIP</i>.

<p>Stems of transgenic and wild type plants were cultured on WPM medium containing 2 g L^-1 (A), 4 g L^-1 (B) or 6 g L^-1 NaCl (C). Shoots of transgenic and wild type plants were transferred to 1/2 MS root medium containing 4 g L^-1 NaCl (D), or 6 g L^-1 NaCl (E). Photographs were taken 20 d following stress treatment. WT, wild type; L-4, transgenic line 4; L-8, transgenic line 8.</p

Northern blot analysis of <i>TaLEA</i> and <i>ThbZIP</i> expression in transgenic birches.

<p>Total RNA was extracted from the aerial tissues of one-month-old wild type and transgenic lines. The full length <i>TaLEA</i> and <i>ThbZIP</i> genes labeled with DIG-dUTP were used as probes. rRNA, ribosomal RNAs from different samples; <i>TaLEA</i>, target band of <i>TaLEA</i> gene; <i>ThbZIP</i>, target band of <i>ThbZIP</i> gene; L-4, 5, 8, three transgenic lines both containing <i>TaLEA</i> and <i>ThbZIP</i> genes; WT, wild type plantlet, respectively.</p

ANOVA analysis of photosynthetic traits and Fv/Fm among different lines and time under salt stress.

<p>ANOVA analysis of photosynthetic traits and Fv/Fm among different lines and time under salt stress.</p

Fv/Fm values of different lines after different days salt stress.

<p>Fv/Fm values of different lines after different days salt stress.</p

Map of the T-DNA construct and identification of overexpressing <i>TaLEA</i> and <i>ThbZIP</i> transgenic birches with PCR.

<p>(A) Schematic of the T-DNA region of the binary vector pROKII-<i>TaLEA</i>-<i>ThbZIP</i>. RB, right border; Pnos, nopaline synthase promoter; <i>NptII</i>, kanamycin resistance gene; Tnos, nopaline synthase terminator; P35S, CaMV 35S promoter; <i>Sma</i> I, <i>Sac</i> I, <i>Bam</i>H I, and <i>Kpn</i> I, four different restriction enzyme sites; <i>TaLEA</i>, <i>TaLEA</i> gene; <i>ThbZIP</i>, <i>ThbZIP</i> gene; LB, left border. Agarose gel electrophoresis of PCR products from wild type and transgenic lines with the primer of <i>NptII</i> (B), <i>TaLEA</i> (C), <i>ThbZIP</i> (D). M, DNA marker; PC, positive control; 1–11, eleven Km resistant lines; L-4, 5, 7, 8, 9, five transgenic lines both containing <i>TaLEA</i> and <i>ThbZIP</i> genes; WT, wild type plantlet; H₂O, double-distilled water as negative control.</p