The objective of the current study is to investigate the effects of different stages of shading after anthesis on grain weight and quality of maize at cytology level. The shading experiments were conducted in the field from 2005 to 2006, with a common maize cultivar （TY2） as the experimental material. Plants were given stress using horizontal shading net and the light intensity was reduced by 55%. Field-grown maize plants were shaded at 1-14 d （S1）, 15-28 d （$2）, and 29-42 d （$3） after pollination, respectively. Control plants （SO） were grown under natural light. Grain weight, quality, endosperm cell proliferation, cob sugar content, and grain pedicel vascular bundle cross section area were measured. The ultrastructural changes of endosperm ceils and endosperm transfer cells were observed after pollination. The result indicated that the grain weight, starch content, endosperm cell number, and volume were declined after shading. On the contrary, the proportion of embryo and endosperm, protein content, and fat content in grain increased. Shading treatments significantly delayed the development of the starch granules and remarkably reduced the endosperm filling status. Among the three treatments, the number of the grain endosperm was the least under shading stress at 1-14 d after pollination. However, the volume of starch granules and the substantiation of endosperm under shading treatment at 15-28 d after pollination were the worst. Compared with the control （natural sunlight without shading）, the soluble sugar of maize cob increased significantly, while there was no obvious change in vascular structure of small cluster stalk. The number of protein body in maize endosperm was influenced markedly by low light at different stages after pollination. Low light decreased the volume of the grain endosperm transfer and the cell wall extensions of the basal transfer ceils became thinner and shorter under shading treatment than those of the control. Furthermore, the degree of connection and the capac
The high-affinity K＋ （HAK） transporter gene family is the largest family in plant that functions as potassium transporter and is important for various aspects of plant life. In the present study, we identified 27 members of this family in rice genome. The phylogenetic tree divided the land plant HAK transporter proteins into 6 distinct groups. Although the main characteristic of this family was established before the origin of seed plants, they also showed some differences between the members of non-seed and seed plants. The HAK genes in rice were found to have expanded in lineage-specific manner after the split of monocots and dicots, and both segmental duplication events and tandem duplication events contributed to the expansion of this family. Functional divergence analysis for this family provided statistical evidence for shifted evolutionary rate after gene duplication. Further analysis indicated that both point mutant with positive selection and gene conversion events contributed to the evolution of this family in rice.
Vernalization, the process of a long exposure to low temperature to induce flowering in plants, is essential for plants to adapt to cold winters. The presence of vernalization genes Vrn-A1, -B1, and -D1 in four cornerstone breeding parents of wheat in China （Funo, Mentana, Yanda 1817, and Bima 4） and 322 derivative varieties （mostly winter wheat） from these parents were determined using PCR based molecular method. The frequencies of the VRN-1 genes in these derivative varieties were in order of Vrn-Dl（67.1%）〉 Vrn-Bl（19.6%）〉 Vrn-Al（5.3%）, which are similar as the former conclusion that Vrn-D1 is associated with the latest heading time, Vrn-A1 the earliest, and Vrn-B1 intermediate values. The frequencies of Vrn-Al and Vrn-B1 loci in the derivative varieties from winter wheat zones were higher than that from spring winter zones. Based on the wheat breeding history in China and the fact of non-random distribution of Vrn-A1 and Vrn-B1 in the derivative varieties from the four parents, there could be a strong selective effect on VRN-1 genes in different regions where the derivative varieties were cultivated.
Better understanding of genotype-by-environment interaction （GEI） is expected to provide a solid foundation for genetic improvement of crop productivity especially under drought-prone environments. To elucidate the genetic basis of the plant and ear height, 2 F2：3 populations were derived from the crosses of Qi 319 × Huangzaosi （Q/H） and Ye 478 × Huangzaosi （Y/H） with 230 and 235 families, respectively, and their parents were evaluated under 3 diverse environments in Henan, Beijing, and Xinjiang, China during the year of 2007 and 2008, and all the lines were also evaluated under water stress environment. The mapping results showed that a total of 21 and 12 QTLs were identified for plant height in the Q/H and Y/H population, respectively, and 24 and 13 QTLs for ear height, respectively. About 56 and 73% of the QTLs for 2 traits did not present significant QTL-by-environment interaction （QE1） in the normal joint analyses for Q/H and Y/H population, respectively, and about 73% of the QTLs detected did not show significant QEI according to joint analyses for stress condition in Q/H. Most of the detected major QTLs exhibited high stability across different environments. Besides, several major QTLs were detected with large and consistent effect under normal condition （Chr. 6 and 7 in Q/H; Chr. 1, 3 and 9 in Y/H）, or across 2 water regimes （Chr. 1, 8 and 10 for in Q/H）. There were several constitutive QTLs （3 for Q/H and 1 for Y/H） with no or minor QTL-by-environment for the 2 populations. Finally, we found several genomic regions （Chr. 1, 10, etc.） to be co-located across the populations, which could provide useful reference for genetic improvement of these traits in maize breeding programs. Comparative genomic analysis revealed that 3 genes/genetic segments associated with plant height in rice were orthologous to these 3 identified genomic regions carrying the major QTLs for plant and ear height on Chr. 1, 6, and 8, respectively.
