Magnetic Iron Oxide Nanoparticles: Synthesis and Surface Functionalization Strategies

Surface functionalized magnetic iron oxide nanoparticles (NPs) are a kind of novel functional materials, which have been widely used in the biotechnology and catalysis. This review focuses on the recent development and various strategies in preparation, structure, and magnetic properties of naked and surface functionalized iron oxide NPs and their corresponding application briefly. In order to implement the practical application, the particles must have combined properties of high magnetic saturation, stability, biocompatibility, and interactive functions at the surface. Moreover, the surface of iron oxide NPs could be modified by organic materials or inorganic materials, such as polymers, biomolecules, silica, metals, etc. The problems and major challenges, along with the directions for the synthesis and surface functionalization of iron oxide NPs, are considered. Finally, some future trends and prospective in these research areas are also discussed

PRODUCTION OF 2N GAMETES IN DIPLOID SUBSPECIES OF DACTYLIS-GLOMERATA L .2. OCCURRENCE AND FREQUENCY OF 2N EGGS

Whereas polyploidy has been found in more than half the Gramineae, the occurrence of 2n gametes, a potentially major mechanism of polyploid production, has been rarely studied. In the present work, the frequency of 2n egg production in nine diploid (n = 2x = 14) subspecies of the polyploid complex Dactylis glomerata has been estimated by determining the ploidy level of the progeny in 98 2X-4X crosses. The 2n egg origin of the 4X offspring was verified using enzyme markers. The frequency of 2n egg production in each subspecies was estimated from the number of 4X offspring, the number of florets in the seed plant and the fertility of the subspecies. The ploidy level of the progeny was determined by chromosome counts or nuclear DNA quantification using flow cytometry. Plants producing 2n eggs were detected in 47% of the fertile crosses, involving eight subspecies. Variability was related to individuals and not to subspecies. Average 2n egg frequency was 0·49% for all crosses, and 1·53% for crosses where 2n egg production was detected. Individual frequencies did not exceed 3·5%, with the exception of 26% in one plant. Triploid block was higher and fertility, frequency of high 2n gamete producers and average 2n gamete frequency were lower in the 2X-4X crosses than in the opposite 4X-2X crosses involving the same plants, previously studied. Diplogynous and diplandrous gamete production were not correlated with each other. However, the widespread occurrence of plants producing both kinds of 2n gametes in almost all the studied subspecies, as well as the presence of several individuals able to produce high rates of 2n eggs or 2n pollen, support the hypothesis that tetraploids can be formed anywhere and anytime by sexual polyploidization in diploid populations of Dactylis glomerata L

PRODUCTION OF 2N GAMETES IN DIPLOID SUBSPECIES OF DACTYLIS-GLOMERATA L .1. OCCURRENCE AND FREQUENCY OF 2N POLLEN

The occurrence of plants producing 2n pollen was ascertained in nine diploid (2n = 2x = 14) subspecies of the polyploid grass complex Dactylis glomerata by determining the ploidy level of the progeny in 100 tetraploid (4X) × diploìd (2X) crosses. The possibility of using pollen size to screen for plants which produce large quantities of 2n pollen was tested by comparing the frequency distributions of pollen diameter in plants which did and did not produce 4X progeny in an interploidy cross. The ploidy level of the progeny was determined by chromosome counts or nuclear DNA quantification using flow cytometry. Parental genotypes of known constitution at different loci coding for enzymes were crossed and the offspring genotypes determined by electrophoresis to identify progeny produced by cross and self-fertilization. Depending on the subspecies, from 20 to 75% of the tested plants produced 4X cross progeny. The average 2n pollen frequency was 0·98% for all crosses, and 3·02% for crosses where 2n pollen was detected. Variability among individuals was greater than that among subspecies. Six genotypes produced exceptionally high frequencies of 2n pollen, ranging from 8.04 to 14·35%. Pollen diameter varied significantly among subspecies. Within subspecies of similar pollen size, the pollen diameter of plants which did or did not produce 4X cross-progeny were not statistically different, although the frequency distribution was biased towards the highest classes of 2n pollen producers. By fixing an arbitrary threshold to normal pollen diameter in each group of subspecies with similar pollen size distribution, 73% of 2n pollen producers could be detected