[SSR linkage map construction and QTL mapping for leaf area in maize].

Maize (Zea mays L.) leaf is the main organ for photosynthesis. The area of leaves (especially the ear-leaf and the two leaves above and below the ear-leaf) plays a vital role in dry matter accumulation and grain yield. Therefore, genetic information on leaf area has a theoretical significance for breeding maize with high yield. In this study, a genetic linkage map composing of 184 simple sequence repeat (SSR) markers was constructed based on an F8 recombinant inbred line (RIL) population, which was derived from a cross between 478 and W312. The parents showed a significant difference in leaf area. The map covers 2084.1 cM with an average interval of 11.3 cM. QTLs for leaf area were identified under two-year's field experiments. Totally 7 QTLs were detected in two years, among which 4 QTLs were detected in 2006 and 3 QTLs in 2007. A major QTL on chromosome 2 (between umc1542 and umc1518) were detected in both 2006 and 2007. It explains 12.5% and 17.3% of the phenotypic variation, respectively. This locus can be used as a potental marker for improving maize leaf growth through marker assisted selection (MAS) approach.

[Effects of multifunctional plant rhizosphere promoting bacteria on maize growth in black soil areas in Northeast China]. / å¤šåŠŸèƒ½æ¤ç‰©æ ¹é™ ä¿ƒç”ŸèŒå¯¹ä¸œåŒ—é»‘åœŸåŒºçŽ‰ç±³çš„ä¿ƒç”Ÿæ•ˆæžœ.

The application of microbial fertilizer plays an important role in improving soil restoration and fertilizer utilization. The effects of microbial fertilizer are greatly affected by crop genotypes and ecological conditions. Little is known about the effects of microbial fertilizers on maize production in Northeast China. To develop microbial fertilizer specific to the black soil and the climate characteristics of Northeast China, we isolated five plant rhizosphere-promoting bacteria (PGPR), named as MZ1, MZ2, MZ3, MZ4 and MZ5, with different degrees of biological functions such as IAA synthesis, phosphate-solubilizing, potassium-solubilizing and siderophore-releasing, from the rhizosphere of maize field. The analysis of ecological adaptability showed that those five strains differed in salt resistance, drought tolerance, acid and alkali resistance, pesticide resistance. The 16S rRNA gene sequences analysis showed that the strains MZ1, MZ2, MZ3, MZ4 and MZ5 belonged to the genus of Sphingomonas, Enterobacter, Pseudomonas, Bacillus and Rhizobium, respectively. In maize field experiment with 50% nitrogen fertilizer reduction, the inoculation with MZ1, MZ3 and MZ5 increased grain yield by 19.9%-25.0%. MZ1, MZ3, and MZ5 could be used as microbial fertilizers for maize in Northeast China.

[Effect of NO3- supply on lateral root growth in maize plants].

Growth of lateral roots is regulated by both environmental factors and nitrate (NO(-)(3)) content of the plant. The mechanism involved is not clearly understood. Two maize (Zea mays L.) inbred lines (478 and Wu312) were used to study the effect of different nitrate supply on lateral root (LR) growth by a whole plants agar culture. The results showed that increasing NO(-)(3)concentration in nutrient solution from 0.01 to 1.0 mmol/L significantly increased the LR length and root biomass. Lateral root density changed little with NO(-)(3) increase up to 5x10(-3) mol/L (for Wu312) - 10x10(-3) mol/L (for 478), then decreased significantly with increasing NO(-)(3). The inhibitory effect of high NO(-)(3) on root growth was weaker in 478 than in Wu312. The growth of lateral roots in Wu312 was completely inhibited by NO(-)(3) at a concentration of 10x10(-3) mol/L, whereas LR density of 478 could reach 30% (axial) and 50% (radicle) of its maximum even at NO(-)(3) 20x10(-3) mol/L. Both the shoot total N and shoot nitrate content increased with increasing NO(-)(3) level. They had similar mathematic functions with shoot/root ratio (Exponential Decay), LR density (Gaussian) and LR length (Parabola). When shoot N content exceed about 1.6 mol/kg and NO(-)(3) content exceed 0.22 mol/kg, shoot/root ratio increased rapidly; when the shoot N content exceed about 1.5 and NO(-)(3) exceed 0.16 mol/kg, LR densities began to decrease; when shoot N content reached about 1 mol/kg and NO(-)(3) content reached 0.10 mol/kg, the LR lengths began to decrease. The possible relationship between shoot NO(-)(3) content and lateral root growth was discussed.

Cloning and characterization of cDNA for the Oryza sativa phosphate transporter.

A putative high-affinity phosphate (Pi) transporter gene in rice (Oryza sativa), OsLPT1, was isolated by RT-PCR from the leaves of the plants. The 1635-bp nucleotide sequence of OsLPT1 spans an open reading frame encoding a polypeptide of 535 amino acids with sequence similarity to phosphate transporters from other plant species. Southern blot analysis showed that the OsLPT1 gene might be present in three transcripts in the rice genome. RT-PCR analysis demonstrated the expression of OsLPT1 in both leaves and roots. The expression of OsLPT1 in the roots was enhanced by Pi deprivation. In situ hybridization revealed OsLPT1 expression in mesophyll cells, xylem parenchyma and phloem cells in the leaves, and in the epidermis, exodermis, and in the vasculature surrounding metaxylem vessels in the roots. The data suggests that the OsLPT1 protein may be involved in enhancing phosphate uptake under conditions of Pi starvation, and in the translocation of Pi among cells in shoots to increase the efficiency of internal Pi use.