[Dynamics of carbon and nitrogen balance during leaf senescence of maize seedlings induced by low nitrogen stress]. / 低氮诱导玉米幼苗叶片衰老过程中碳氮平衡的动态变化.

Timing of leaf senescence is important to ensure maize yield. In this study, we investigated the dynamics of carbon and nitrogen balance during leaf senescence in two maize inbred lines PH6WC and PH4CV under normal (4 mmol·L-1, CK) and low nitrogen (0.04 mmol·L-1, LN) treatments. Leaf phenotype, photosynthetic characteristics, nitrogen and sugar contents, and carbon to nitrogen ratio of the second and third leaves were analyzed after 2, 4, 6 and 8 days of cultivation. Results showed that leaf size, biomass, relative chlorophyll content, net photosynthetic rate, soluble sugar content, and starch content of the second and third leaves were decreased, while nitrogen production capacity was increased under low nitrogen treatment compared to the control, with the changes of the second leaf being earlier than that of the third leaf. For all the leaf traits, the variation scales of PH6WC were larger than that of PH4CV under low nitrogen stress, and only the C/N ratio in the seedling leaves was significantly increased. In addition, leaf senescence of PH4CV was slower than PH6WC due to its stronger ability in maintaining carbon and nitrogen balance. In conclusion, low nitrogen could induce leaf senescence of maize seedlings. High C/N ratio could promote leaf senescence. There are significant differences in carbon and nitrogen balance ability of seedling leaves between two maize genotypes under low nitrogen stress.

[Progress and application prospects of glutamine synthase in plants].

Nitrogen is one of the most important nutrient elements for plants and a major limiting factor in plant growth and crop productivity. Glutamine synthase (GS) is a key enzyme involved in the nitrogen assimilation and recycling in plants. So far, members of the glutamine synthase gene family have been characterized in many plants such as Arabidopsis, rice, wheat, and maize. Reports show that GS are involved in the growth and development of plants, in particular its role in seed production. However, the outcome has generally been inconsistent, which are probably derived from the transcriptional and post-translational regulation of GS genes. In this review, we outlined studies on GS gene classification, QTL mapping, the relationship between GS genes and plant growth with nitrogen and the distribution characters, the biological functions of GS genes, as well as expression control at different regulation levels. In addition, we summarized the application prospects of glutamine synthetase genes in enhancing plant growth and yield by improving the nitrogen use efficiency. The prospects were presented on the improvement of nitrogen utility efficiency in crops and plant nitrogen status diagnosis on the basis of glutamine synthase gene regulation.

Comparative proteomic analysis of embryos between a maize hybrid and its parental lines during early stages of seed germination.

In spite of commercial use of heterosis in agriculture, the molecular basis of heterosis is poorly understood. It was observed that maize hybrid Zong3/87-1 exhibited an earlier onset or heterosis in radicle emergence. To get insights into the underlying mechanism of heterosis in radicle emergence, differential proteomic analysis between hybrid and its parental lines was performed. In total, the number of differentially expressed protein spots between hybrid and its parental lines in dry and 24 h imbibed seed embryos were 134 and 191, respectively, among which 47.01% (63/134) and 34.55% (66/191) protein spots displayed nonadditively expressed pattern. Remarkably, 54.55% of nonadditively accumulated proteins in 24 h imbibed seed embryos displayed above or equal to the level of the higher parent patterns. Moreover, 155 differentially expressed protein spots were identified, which were grouped into eight functional classes, including transcription & translation, energy & metabolism, signal transduction, disease & defense, storage protein, transposable element, cell growth & division and unclassified proteins. In addition, one of the upregulated proteins in F1 hybrids was ZmACT2, a homolog of Arabidopsis thaliana ACT7 (AtACT7). Expressing ZmACT2 driven by the AtACT7 promoter partially complemented the low germination phenotype in the Atact7 mutant. These results indicated that hybridization between two parental lines can cause changes in the expression of a variety of proteins, and it is concluded that the altered pattern of gene expression at translational level in the hybrid may be responsible for the observed heterosis.