Nitric oxide (NO) has been recently characterized as an important signal molecule that mediates many developmental and physiological processes in plant cells . NO can be generated from nitrite by nitrate reductase (NR) and arginine by NO synthaselike enzymes. NO induces various processes in plants, including seed germination, root development, inflorescence initiation, stomatal closure and abiotic and biotic stress responses . The redox chemistry of NO allows it to react with the haem groups, cysteine and tyrosine residues on target proteins, which result in post-translational protein modification, metal nitrosylation, S-nitrosylation, and tyrosine nitration. Intracellular signaling responses to NO also include generation of cyclic guanosine monophosphate, elevation of cytosolic calcium, and activation of mitogen-activated protein kinases. However, divergence and crosstalk of reactive oxygen species and NO signaling pathways occur in the plant response to hormone and stresses. Here, we provide a brief summary of new insights into NO signaling in plants and the cross-talk between reactive oxygen species and NO signaling.

To identify quantitative trait loci (QTL) related to oil, protein and glucosinolate content and elucidate the relations among them, we analyzed several traits of two F₂ populations derived from the original cross and a reciprocal cross betw een high-oilcontent lines 8908B and R1 in Brassica napus. Oil and protein content showed a significant correlation in both populations (r = -0.68 and r = -0.81, respectively; P<0.01). Protein and glucosinolate content showed a significant correlation (r = -0.45; P<0.01) in the F₂ population of the reciprocal cross but not in the F₂ population of the original cross. We constructed a genetic linkage map on the basis of 118 F₂ plants of the original cross. The map was made up of 21 linkage groups, including 121 markers, covering 1 298.7 cM. A composite interval mapping method was used to map QTL related to the three quality traits. Two QTLs related to oil content were detected on LG8 and LG10 and accounted for 4.8% and 13.7%, respectively, of the phenotypic variation, and R1 had a positive effect on both loci. Two QTLs related to protein content, pro1 and pro2, were identified on LG1 and LG3 and accounted for 15.2% and 14.1%, respectively, of the phenotypic variation. 8908B had a positive effect on pro1 loci, and R1 had a positive effect on pro2 loci. Four QTLs related to glucosinolate content were detected. Among these, glu1 and glu2 located on LG20, glu3 located on LG4, and glu4 located on LG8 accounted for 1.9%-25.4% of the phenotypic variation. R1 had a positive effect on glu1, and 8908B had a positive effect on the other three loci.

In this study, we selected 83 cultivars, including Hefeng 25, from 13 breeding units of Heilongjiang Province. We amplified 43 of 100 simple sequence repeats (SSRs), which distributed on 20 linkage groups of the soybean genetic map. In total, 157 polymorphic alleles were detected in 43 pairs of SSR primers. For each primer , 2 to 7 alleles (mean 3.65 alleles) were detected in all cultivars. Cluster analysis revealed most of the varieties bred by the same breeding unit with high genetic similarity. Pairwise genetic similarity coefficients ranged from 0.216 to 0.937 (mean 0.638 4), which indicated that the genetic basis of soybean varieties from Heilongjiang province were narrow. The genetic composition can be broadened by introducing diverse and distant cultivars as parents in soybean breeding.

Megasporogenesis of Beta vulgaris (2n=18) is of the Polygonum type. Megasporocytes contain nuclear vacuoles before meiosis and synaptonemal complexes at the early stage of meiosis. Redifferentiation of cytoplasmic components occurs, and callose is deposited in the wall during meiosis. The dyad formed in Meiosis I was wrapped by thick callose. The chalazal cell in the dyad contains many organelles, and mitochondria and plastids showing regular shapes, considered a sign of the end of redifferentiation. The micropylar cell in a dyad always degenerates quickly, and only chalazal one finished meiosis II to form two unequal-sized megaspores . The two unequal-sized megaspores plus a micropylar cell in the dyad formed a triad, and the callose disappeared in the chalazal end of the megaspore cell that developed into a functional megaspore.

This study focused on the changes in chlorophyll content, soluble protein content, O₂ ^.- generating rate, MDA content and activity of protective enzymes (SOD, CAT, POD) in leaves of Nymphoides peltatum under different concentrations of Cd²⁺ stress with 0.01 mmol.L^-1 exogenous spermidine. Transmission electron microscopy revealed that Cd²⁺ imposed injury on the ultrastructure of chloroplasts, with swelling, breakage and disappearance of the chloroplast envelope and reduced chlorophyll content. Spermidine treatment effectively protected the ultrastructure of chloroplasts against Cd²⁺ stress and maintained the arrangement of thylakoids. Under single Cd²⁺ stress, with Cd²⁺ increase, chlorophyll content in N. peltatum increased then decreased quickly, whereas soluble protein content decreased gradually. The content was much higher with the addition of sprayed spermidine than with only a single Cd²⁺ treatment, and the trend of decrease was lower. Under single Cd²⁺ stress, the maximal SOD, CAT and POD content appeared at 1, 1 and 2 mg.L^-1 Cd^2+_, respectively, and decreased gradually thereafter ; the activities of these protective enzymes were markedly increased under spermidine treatment, by 5.8%, 37.5%, and 3.3%, respectively, and therefore decreased the generation rate of reactive oxygen species such as O₂ ^-. and MDA content.

We examined the net photosynthetic rate (Pn), the maximal photochemical efficiency of PSII (Fv/Fm) and the activities of antioxidant isoenzymes in cucumber (Cucumis sativus) w ith or without photosynthetic bacteria (PSB) application. PSB spraying resulted in a significant increase in fresh weight and leaf area for both genotypes of cucumber plants, accompanied by a marked increase of Pn. However, Fv/Fm showed negligible changes. Exogenous PSB also increased activities of total superoxide dismutase (SOD) and ascorbate peroxidase (APX) , and a general increase of their isoenzymes. The increased level in Cu/Zn-SOD, Fe-SOD
and stroma APX (sAPX) was most significant in chloroplasts. These results implied that PSB played a favorable role in growth and photosynthesis and improved hardiness in cucumber by enhancing antioxidant enzyme activities.

Zinc malnutrition has been one of most essential causes of harm to human health. Quantitative trait loci (QTL) for zinc content in rice grains is of great significance to the study of zinc-rich rice genetics and in zinc breeding programs. We used 145 F₂ lines from the cross between Fengxinhongmi and Minghui100 rice to detect QTL as sociated with zinc content with 92 simple sequence repeat markers covering the whole rice genome. A total of 3 QTL for zinc content were detected on chromosome 3, 6, and 11 and accounted for 4.97%, 12.75% and 7.74% of the phenotypic variance, respectively. Among them, QZN3 was located between RM186 and RM168 on chromosome 3 and contributed the most to phenotypic variation. The favorable alleles of QZN3 for zinc content originated from Minghui100, with partial dominant effects. The total contribution of the 3 QTL was 25.46%. This study has laid a foundation for mapping and cloning QTL and molecular-marker-assisted selection of zinc content in rice.

Phytochromes, which receive and transmit signals generated by red and far- red light, can regulate a wide range of developmental and physiological responses during plant development. Their PHY-PAS1 domain is critical for tuning spectroscopic properties of the bound bilin and signal transduction and exists in all members of the gymnosperm phytochrome gene family created by gene duplication. Gene duplications can play significant roles in speciation. The PHYP gene occurs from the first gene duplication event, as a single copy. To further test whether PHY-PAS1 domains in PHYP have experienced the same constraint or positive selection during their evolution in distinct gymnosperm species , we assayed the molecular evolution of 31 gymnosperm PHY-PAS1 domain sequences under the branch, site and branch-site models. Most lineages are highly conserved, with w< 1, but 14 lineages evolved under positive selection, with w> 1; among them 13 lineages are of co-generic species. By contrast, such selective pressure is not detected in more distantly related species.

Sphingolipids are ubiquitous membrane components in eukaryotic cells and in a few bacteria. Recent information indicated that sphingolipids are an impor tant class of messenger molecules involved in many significant signal trans duction pathways, regulating cell growth, differentiation, senescence, and apoptosis in mammals and yeast. However, the biological function of sphingolipids in plants has been explored only recently and remains elusive. Increasing investigation has shown that sphingolipids and their metabolites play an important role in plants. In this review, we describe the structure, metabolic pathway and biological function of sphingolipids.

Seed dormancy is an adaptation to environmental changes that plants acquire during long-term phylogenesis. Dormancy may ensure that the species can survive natural catastrophes, decrease competition between individuals of the same species, or prevent germination out of season. Here, we review a classification scheme of seed dormancy; its development and continuum, regulation and evolution; as well as proteins associated with the induction, maintenance and release of dormancy. We also describe topics for future study of seed dormancy.