Embryological Studies on Narcissus tazetta var. chinensis

Chinese narcissus (Narcissus tazetta var.chinensis Roem) blooms but has no seeds.Embryological studies on the species were conducted to discover the causes of its sterility.Its anther wall is composed of four layers of cells,and its tapetum is of the secretory type.The cytokinesis of microspore mother cells is of the successive type,and the tetrad is tetrahedral.During meiosis of microspore mother cells,some chromosomes lagged,and several micronuclei were found in tetrads.Only 27.7% of the pollen grains contained full cytoplasm,and 1.3% of them germinated in culture medium.No pollen grain,however,could germinate on the stigma.The ovary is trilocular with axile placenta,and the ovules are bitegmic,tenuinucellate,and anatropous.Its embryo sac is of the polygonum type.Most embryo sacs degenerated,and only about 4.5% of the ovules contained a normal embryo sac with an egg cell,two synergids,three antipodal,and a central cell containing two polar nuclei.One reason for the sterility of Chinese narcissus is the abnormality of microsporogenesis and megasporogenesis,in which only a few functional pollen grains and embryo sacs are produced.The other reason is that the pollen grains cannot germinate on the stigma.     

Guiding Neuronal Cell Migrations

Neuronal migration is, along with axon guidance, one of the fundamental mechanisms underlying the wiring of the brain. As other organs, the nervous system has acquired the ability to grow both in size and complexity by using migration as a strategy to position cell types from different origins into specific coordinates, allowing for the generation of brain circuitries. Guidance of migrating neurons shares many features with axon guidance, from the use of substrates to the specific cues regulating chemotaxis. There are, however, important differences in the cell biology of these two processes. The most evident case is nucleokinesis, which is an essential component of migration that needs to be integrated within the guidance of the cell. Perhaps more surprisingly, the cellular mechanisms underlying the response of the leading process of migrating cells to guidance cues might be different to those involved in growth cone steering, at least for some neuronal populations.The migration of newly born neurons is a precisely regulated process that is critical for the development of brain architecture. Neurons arise from the proliferative epithelium that covers the ventricular space throughout the neural tube, an area named the ventricular zone (VZ). From there, newly born neurons adopt two main strategies to disperse throughout the central nervous system (CNS), designated as radial and tangential migration (Hatten 1999; Marín and Rubenstein 2003). During radial migration, neurons follow a trajectory that is perpendicular to the ventricular surface, moving alongside radial glial fibers expanding the thickness of the neural tube. In contrast, tangentially migrating neurons move in trajectories that are parallel to the ventricular surface and orthogonal to the radial glia palisade (Fig. 1). Besides their relative orientation, some of the basic mechanisms underlying the movement of cells using each of these two modes of migration are also different. For example, radially migrating neurons often use radial glial fibers as substrate, whereas tangentially migrating neurons do not seem to require their support to migrate. Even so, neurons may alternate from radial to tangential movement and vice versa during the course of their migration. This suggests that both types of migrations share common principles, in particular those directly related to the cell biology of movement (Marín et al. 2006).Open in a separate windowFigure 1.Representative migrations in the developing CNS. Multiple migrations coexist during embryonic development at different areas of the central nervous system. This schema summarizes some of these migrations during the second week of the embryonic period in the mouse. Neurons use tangential and radial migration to reach their final destination; both strategies are used by the same neurons at different stages of development (i.e., cortical interneurons in the forebrain and precerebellar neurons in the hindbrain). (IML) intermediolateral region of the spinal cord; (IO) inferior olive nucleus; (LGE) lateral ganglionic eminence; (LRN) lateral reticular nucleus; (MGE) medial ganglionic eminence; (NCx) neocortex; (OB) olfactory bulb.One of the structures that better illustrates how both types of migrations are integrated during brain development is the cerebral cortex, and so we will primarily refer to studies performed on cortical neurons for this review. The adult cerebral cortex contains two main classes of neurons: glutamatergic cortical projection neurons (also known as pyramidal cells) and GABAergic interneurons. Pyramidal cells are generated in the ventricular zone (VZ) of the embryonic pallium—the roof of the telencephalon—and reach their final position by radial migration (Rakic 2007). In contrast, cortical interneurons are born in the subpallium—the base of telencephalon—and reach the cerebral cortex through a long tangential migration (Corbin et al. 2001; Marín and Rubenstein 2001).The earliest cortical neurons form a transient structure known as the preplate, around embryonic day 10 (E10) of gestation age in the mouse. This primordial layer consists of Cajal-Retzius cells and the first cohort of pyramidal neurons, which will eventually populate the subplate. Cajal-Retzius cells, which play important roles during neuronal migration, arise from discrete pallial sources and colonize the entire surface of the cortex through tangential migration (Bielle et al. 2005; Takiguchi-Hayashi et al. 2004; Yoshida et al. 2006). The next cohort of pyramidal cells forms the cortical plate (CP) by intercalating in the preplate and splitting this primitive structure in a superficial layer, the marginal zone (MZ or layer I), and a deep layer, the subplate. The development of the neocortex progresses with new waves of neurons that occupy progressively more superficial positions within the CP (Gupta et al. 2002; Marín and Rubenstein 2003). Birth dating studies have shown that layers II–VI of the cerebral cortex are generated in an “inside-out” sequence. Neurons generated earlier reside in deeper layers, whereas later-born neurons migrate past existing layers to form superficial layers (Angevine and Sidman 1961; Rakic 1974). In parallel to this process, GABAergic interneurons migrate to the cortex, where they disperse tangentially via highly stereotyped routes in the MZ, SP, and lower intermediate zone/subventricular zone (IZ/SVZ) (Lavdas et al. 1999). Interneurons then switch from tangential to radial migration to adopt their final laminar position in the cerebral cortex (Ang et al. 2003; Polleux et al. 2002; Tanaka et al. 2003).     

Abscisic acid-triggered guard cell l-cysteine desulfhydrase function and in situ hydrogen sulfide production contributes to heme oxygenase-modulated stomatal closure

Recent studies have demonstrated that hydrogen sulfide (H₂S) produced through the activity of l -cysteine desulfhydrase (DES1) is an important gaseous signaling molecule in plants that could participate in abscisic acid (ABA)-induced stomatal closure. However, the coupling of the DES1/H₂S signaling pathways to guard cell movement has not been thoroughly elucidated. The results presented here provide genetic evidence for a physiologically relevant signaling pathway that governs guard cell in situ DES1/H₂S function in stomatal closure. We discovered that ABA-activated DES1 produces H₂S in guard cells. The impaired guard cell ABA phenotype of the des1 mutant can be fully complemented when DES1/H₂S function has been specifically rescued in guard cells and epidermal cells, but not mesophyll cells. This research further characterized DES1/H₂S function in the regulation of LONG HYPOCOTYL1 (HY1, a member of the heme oxygenase family) signaling. ABA-induced DES1 expression and H₂S production are hyper-activated in the hy1 mutant, both of which can be fully abolished by the addition of H₂S scavenger. Impaired guard cell ABA phenotype of des1/hy1 can be restored by H₂S donors. Taken together, this research indicated that guard cell in situ DES1 function is involved in ABA-induced stomatal closure, which also acts as a pivotal hub in regulating HY1 signaling.     

Biosystematic Studies on Adenophora potaninii Korsh. Complex (Campanulaceae). Ⅰ. Phenotypic Plasticity

Phenotypic plasticity is the environmental modification of genotypic expression and an important means by which individual plants respond to environmental heterogeneity. The study of phenotypic plasticity in the genus Adenophora, which is very complicated taxo nomically because of great morphological variation, proves to be helpful in both investigating the phenotypic variation so as to evaluate potential taxonomic value of their characters and providing important sources of information on the variation, adaptation and evolution of the genus. Twenty-three populations representing all the six species in Adenophora potaninii complex were transplanted into the garden. Of them six populations were selected for study ing their performance in the field and in the garden, in addition to cultivation experiment under different treatments. The results show that there exists considerable developmental plasticity in some leaf, floral and capsule characters. In particular, the leaf shape and length of calyx lobe display significant developmental variation with the maximum being three times as great as the minimum, which is noteworthy because they were previously considered as diagnostic. The characters of root, caudex, stem and inflorescence are found to be very plastic, especially the root diameter, the number of stems, stem height and inflorescence length with great environmental plasticity. In addition, the populations from different habi tats show distinct amounts of plasticity. On the contrary, the characters of leaf, floral, cap sule and seed are less influenced by environments. It seems that the considerable variation in the characters of leaf is attributed mainly to genetic differences. Finally, the phenotypic plasticity of morphological characters of A. potaninii complex and its taxonomic significanceis discussed.     

Highly sensitive chemiluminescence immunoassay on chitosan membrane modified paper platform using TiO2 nanoparticles/multiwalled carbon nanotubes as label

A highly sensitive chemiluminescence (CL) immunoassay was incorporated into a low‐cost microfluidic paper‐based analytical device (μ‐PAD) to fabricate a facile paper‐based CL immunodevice (denoted as μ‐PCLI). This μ‐PCLI was constructed by covalently immobilizing capture antibody on a chitosan membrane modified μ‐PADs, which was developed by simple wax printing methodology. TiO₂ nanoparticles coated multiwalled carbon nanotubes (TiO₂/MWCNTs) were synthesized as an amplification catalyst tag to label signal antibody (Ab₂). After sandwich‐type immunoreactions, the TiO₂/MWCNTs were captured on the surface of μ‐PADs to catalyze the luminol‐p‐iodophenol‐H₂O₂ CL system, which produced an enhanced CL emission. Using prostate‐specific antigen as a model analyte, the approach provided a good linear response range from 0.001 to 20 ng/mL with a low detection limit of 0.8 pg/mL under optimal conditions. This μ‐PCLI showed good reproducibility, selectivity and stability. The assay results of prostate‐specific antigen in clinical serum samples were in good agreement with that obtained by commercially used electrochemiluminescence methods at the Cancer Research Center of Shandong Tumor Hospital (Jinan, Shandong Province, China). This μ‐PCLI could be very useful to realize highly sensitive, qualitative point‐of‐care testing in developing or developed countries. Copyright © 2013 John Wiley & Sons, Ltd.