single cotyledon (sic) mutants of pea and their significance in understanding plant embryo development

Angiosperms are divided into two distinct classes—the dicotyledons (dicots) and monocotyledons (monocots)—based in part on the number of cotyledons in mature embryos. In this paper, we describe single‐cotyledon pea mutants, termed sic (single cotyledon), all of which show a degree of fusion between the cotyledons. The fusion in sic1 is along the margin of one cotyledon and is less complete than in sic2 embryos, but the effects of the mutations are additive in the double mutant. Occasionally sic2 mutants will show fusion of the two cotyledons into one cylindrical embryo in which the shoot apex becomes surrounded by the cotyledons. Both sic1 and sic2 mutants produce fertile plants. In the sic3 embryo, a single cotyledon is generated under the shoot apex that breaks the vascular connection between root and shoot, causing embryo lethality. The pattern of cotyledon development in all these mutants is identified by in situ mRNA hybridization and antibody labeling, using the storage protein vicilin as a cotyledon‐specific marker. These patterns indicate that the joining of the cotyledons was due to zonal growth. The results indicate that there are genes in pea that influence the positioning and the morphology of the cotyledon. A model for cotyledon development in pea is proposed that is based on the regulation of the positioning of cell clusters by the sic genes. Dev. Genet. 25:11–22, 1999. © 1999 Wiley‐Liss, Inc.     

ABA调控种子发育的研究进展

种子发育是一个复杂的生物学过程，受各种遗传和外界因素的调节，显著影响农作物特别是禾谷类作物的种子活力和产量与质量。脱落酸(ABA)是调控种子发育和萌发最重要的植物激素之一，其活性水平、信号转导及其LAFL网络在种子发育包括胚胎发生和成熟过程的调控中起关键作用。该文主要综述了近年来ABA调控种子发育的研究取得的重要进展，包括ABA代谢和信号转导对种子发育的调控，ABA与种子成熟转录因子(AFL-B3、FUS3、ABI3、LEC2等)的作用，以及ABA在种子发育中的作用机制，并提出了需要进一步研究的科学问题，为深入理解种子发育的分子机制提供参考，从而提高种子的活力、产量和质量。     

Analogues of auxin modifying growth and development of some monocot and dicot plants

The dependence of morphogenetic processes in the formation of vegetative and generative organs in spring oilseed rape and barley on exogenously applied physiological analogues of auxin: 2,4-D (2,4-dichlorphenoxyacetic acid), NAA (naphthalene-1-acetic acid), TA-12 (1-[2-chloroethoxycarbonyl-methyl]-4-naphthalenesulfonic acid calcium salt) and TA-14 (1-[2-dimethylaminoethoxicarbonylmethyl]naphtalene chlormethylate) were investigated. The experiments were performed with hypocotyl tissue cultures of oilseed rape and barley microspores in vitro. The auxin analogues applied revealed differences of morphogenetic competence in dedifferentiation-redifferentiation processes that occurred in oilseed rape cultures. TA-12 and TA-14 applied together with NAA and BA (6-benzylaminopurine) caused more intensive callus growth in comparison with 2,4-D. Rhizogenesis was induced when 2,4-D was substituted by TA-12. Compound TA-14, unlike TA-12, facilitated the appearance and development of cotyledons in callus tissues. Hower the compounds TA-12 and TA-14 have no positive effect in monocot plant — barly anther culture for callogenesis and regeneration in comparison to indole-3-acetic acid (IAA). TA-14 and TA-12 showed similar but not identical auxin properties and demonstrated high efficiency as modifiers of rape-dicot plant growth and morphogenesis.     

Seedling diversity in Hydatellaceae: implications for the evolution of angiosperm cotyledons

BACKGROUND AND AIMS: Cotyledon number has long been a primary morphological feature distinguishing monocots from other angiosperms. Recent placement of Hydatellaceae near the early-divergent angiosperm order Nymphaeales, rather than in the monocot order Poales, has prompted reassessment of seedling morphology in this poorly known family. METHODS: Seedlings of six species representing all eco-geographical groups of Hydatellaceae are described using light and scanning electron microscopy. KEY RESULTS: Two seedling types were discovered. Material examined of Trithuria submersa, T. bibracteata, T. austinensis and T. filamentosa possess a transparent bilobed sheathing structure that surrounds the main axis below the first foliage leaf. The seed coat is attached to the sheathing structure. Seedlings of Trithuria lanterna and T. konkanensis lack a sheathing structure, and the seed coat is attached to a short, narrow lateral outgrowth on the main axis of the seedling. CONCLUSIONS: The sheathing structure that is present in seedlings of some Hydatellaceae could be homologized with the two united cotyledons of water lilies. It also resembles the single cotyledon of some monocots, and hence demonstrates a possible pathway of the origin of a monocot-like embryo, though no homology is implied. The sheathing structure is reduced in Trithuria lanterna and T. konkanensis, and the short, narrow outgrowth of its seedling could represent a single cotyledon. This synapomorphy suggests that the only Indian species of Hydatellaceae, T. konkanensis, is closer to the northern Australian T. lanterna than to the south-western Australian T. bibracteata.     

Changes in the factor of safety within the superstructure of a dicot tree

The objective of this study was to determine whether the factor of safety for mechanical stability varied among stems differing in size and age within the superstructure of a large dicot tree. Two factors of safety were selected for study: the quotient of the critical buckling height and the actual length of stems, Hcrit/L, and the quotient of the modulus of rupture (the force per unit area required to break a stem) and the working stress (the force per unit area resulting from the biomass measured distal to a stem), M_R/σ_w. These two dimensionless safety factors were determined for a total of 420 shoot segments comprising much of the aboveground biomass of a Robinia pseudoacacia (Fabaceae) tree measuring 18.7 m in height and 1347 kg in mass, and 0.46 m in diameter (40 yr old) at 1.2 m from the ground. An S-shaped trend was observed when each of the two factors of safety was plotted as a function of stem age. Each factor decreased from a local maximum for the most distal (peripheral) stems in the canopy to a local minimum value for stems ∼10 yr old; each factor increased again to another local maximum for stems 11–18 yr old, and then decreased steadily toward the base of the trunk. This trend was the result of the allometric relationships among stem diameter, length, biomass, and material properties (stiffness and strength) with respect to stem age. Although they were disproportionately more slender than their older counterparts, peripheral stems were sufficiently stiff and strong to sustain the stresses resulting from their weight and that of foliage without deflecting under these loads, yet they were sufficiently flexible to easily bend and thereby presumably provide a mechanism to reduce the drag forces acting on the entire tree. In contrast, the internally imposed mechanical forces acting on progressively older stems increased at a greater rate than the observed rate of increase in stem stiffness, strength, or diameter. The probability of mechanical failure, which must be considered from a demographic perspective (i.e., an age-dependent phenomenon), thus increased from older branches to the base of the trunk. Reports of similar allometric trends based on interspecific comparisons among diverse dicot species comply with the allometry observed for the R. pseudoacacia tree and suggest that the S-shaped trend for the factor of safety holds for stems differing in age drawn from individual trees and for the trunks of conspecifics differing in age drawn from a dense population.     

转录因子对B细胞发育的调控作用

Ｂ细胞同其他血细胞一样,也是由多能造血干细胞发育为祖细胞,再发育成 末成熟细胞的。发育过程中,向Ｂ细胞发育的前 细胞逐渐推动向其他谱系发育的潜能,Ｂ细胞谱系特征性基因开始表达。近来的研究表明,Ｂ细胞发育过程中有多种转录因子参与,它们调节多种重要基因的转录,保证Ｂ细胞的正常发育。本文综述了与Ｂ细胞发育相关转录因子的最新研究进展。     

Isolation and characterization of cDNAs encoding mitochondrial phosphate transporters in soybean,maize, rice,and Arabidopsis

cDNA clones encoding mitochondrial phosphate transporters were isolated from four herbaceous plants. The cDNAs for the soybean, maize and rice transporters contained entire coding regions, whereas the Arabidopsis cDNA lacked the 5 portion. The hydropathy profiles of the deduced amino acid sequences predicted the existence of six membrane-spanning domains which are highly conserved in the mitochondrial transporter family. In soybeans, the mRNA level for the transporter was high in tissues containing dividing cells. It was suggested that there are multiple copies of transporter genes in both dicots and monocots. The soybean transporter was expressed as inclusion bodies in Escherichia coli, solubilized with detergents, and then reconstituted into liposomes. The resulting proteoliposomes exhibited high phosphate transport activity. The activity was inhibited by N-ethylmaleimide, like those of mammalian phosphate transporters.     

The factors affecting the evolution of the anthocyanin biosynthesis pathway genes in monocot and dicot plant species

Background

The available data demonstrate that even in universal metabolic pathways, some species-specific regulatory features of structural genes are present. For instance, in the anthocyanin biosynthesis pathway (ABP), genes may be regulated by ABP-specific regulatory factors, and their expression levels may be strongly associated with anthocyanin pigmentation, or they may be expressed independently of pigmentation. A dataset of orthologous ABP genes (Chs, Chi, F3h, F3’h, Dfr, Ans) from monocot and dicot plant species that have distinct gene regulation patterns and different types of pollination was constructed to test whether these factors affect the evolution of the genes.

Results

Using a maximum likelihood approach, we demonstrated that although the whole set of the ABP genes is under purifying selection, with greater selection acting on the upstream genes than on the downstream genes, genes from distinct groups of plant species experienced different strengths of selective pressure. The selective pressure on the genes was higher in dicots than in monocots (F3h and further downstream genes) and in pollinator-dependent plants than in pollinator-independent species (Chi and further downstream genes), suggesting an important role of pollination type in the evolution of the anthocyanin biosynthesis gene network. Contrasting effects of the regulation patterns on evolution were detected for the F3h and Dfr genes, with greater selective pressure on the F3h gene in plant species where the gene expression was not strongly associated with pigmentation and greater selective pressure on Dfr in plant species where the gene expression was associated with pigmentation.

Conclusions

We demonstrated the effects of pollination type and patterns of regulation on the evolution of the ABP genes, but the evolution of some of the genes could not be explained in the framework of these factors, such as the weaker selective pressure acting on Chs in species that attract pollinators or the stronger selective pressure on F3h in plant species where the gene expression was not associated with pigmentation. The observations suggest that additional factors could affect the evolution of these genes. One such factor could be an effect of gene duplication with further division of functions among gene copies and relaxed selective pressure acting on them. Additional tests with an appropriate dataset combining data on duplicated gene sequences and their functions in the flavonoid biosynthesis pathway are required to test this hypothesis.

     

Diversification of the RAB Guanosine Triphosphatase Family in Dicots and Monocots

RAB guanosine triphosphatases （GTPases） are key regulators of vesicle trafficking and are essential to the growth and development of all eukaryotic cells. During evolution, the RAB family has expanded in different patterns to facilitate distinct cellular, developmental and physiological adaptations. Yeast has only 11 family members, whereas mammalian RABs have expanded to 18 RAB subfamilies. Plant RABs have diversified primarily by duplicating members within a single subfamily. Plant RABs are divided into eight subfamilies, corresponding to mammalian RAB1, RAB2, RAB5, RAB6, RAB7, RAB8, RAB11 and RAB18. Functional diversification of these is exemplified by the RAB1 ls, orthologs of which are partitioned into unique cell compartments in plants where they function to transport vesicles during localized tip growth. Similarly, the RAB2 family in grasses is likely involved in vesicle secretion associated with wall expansion, as determined by analysis of over-expression mutants. We propose that dicots and monocots have also diverged in their RAB profiles to accommodate unique cellular functions between the two groups. Here we present a bioinformatics analysis comparing the RAB sub-families of rice, maize and Arabidopsis. These results will guide future functional studies to test for the role of diversification of subfamilies unique to monocots compared to dicots.