OsSIZ1 Regulates the Vegetative Growth and Reproductive Development in Rice

SAP and MIZ (SIZ) is a small ubiquitin-related modifier (SUMO) E3 ligase that facilitates conjugation of SUMO to protein substrates. Although there have been a number of reports about the functions of SIZ1 in Arabidopsis in the regulation of diverse life processes, no information regarding the role of SIZ in other plants is available yet. In this work, two homologous genes from rice (Oryza sativa) were isolated and designated as OsSIZ1 and OsSIZ2 based on amino acid sequence homology to AtSIZ1 and their phylogenetic relationship. The function in the vegetative growth and reproductive development in rice was investigated using OsSIZ1 mutants containing a T-DNA insertion. The results showed that the mutant Ossiz1 exhibited the significant changes in several growth and developmental parameters, including primary root length, adventitious root number, plant height, leaf and panicle length, flower formation, and seed-setting rate compared with wild type. Taking together these results indicate that OsSIZ1 plays an important role in regulating growth and development in rice.     

Genetic Dissection of the Relative Roles of Auxin and Gibberellin in the Regulation of Stem Elongation in Intact Light-Grown Peas

Exogenous gibberellin (GA) and auxin (indoleacetic acid [IAA]) strongly stimulated stem elongation in dwarf GA1-deficient le mutants of light-grown pea (Pisum sativum L.): IAA elicited a sharp increase in growth rate after 20 min followed by a slow decline; the GA response had a longer lag (3 h) and growth increased gradually with time. These responses were additive. The effect of GA was mainly in internodes less than 25% expanded, whereas that of IAA was in the older, elongating internodes. IAA stimulated growth by cell extension; GA stimulated growth by an increase in cell length and cell number. Dwarf lkb GA-response-mutant plants elongated poorly in response to GA (accounted for by an increase in cell number) but were very responsive to IAA. GA produced a substantial elongation in lkb plants only in the presence of IAA. Because lkb plants contain low levels of IAA, growth suppression in dwarf lkb mutants seems to be due to a deficiency in endogenous auxin. GA may enhance the auxin induction of cell elongation but cannot promote elongation in the absence of auxin. The effect of GA may, in part, be mediated by auxin. Auxin and GA control separate processes that together contribute to stem elongation. A deficiency in either leads to a dwarfed phenotype.     

Cytokinins in Vegetative and Reproductive Buds of Pseudotsuga menziesii

Immunoaffinity techniques using columns of immobilized antibodies raised against zeatin riboside and isopentenyladenosine were found to be effective in isolating cytoklnins from vegetative, female, and male buds of Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco). The purified cytokinins were separated by reverse phase high performance liquid chromatography and analyzed by radioimmunoassay. Confirmation of cytokinin identities was by gas chromatography-mass spectrometry. Immediately prior to bud burst, all bud types contained three major cytokinins: isopentenyladenosine, zeatin riboside, and a hexose conjugate of zeatin riboside (not zeatin riboside O-glucoside). Zeatin-type cytokinins were present in relatively high concentration in vegetative and female buds. In male buds, however, relatively high levels of isopentenyladenosine were found together with low levels of zeatin-type cytokinins.     

Temporal and Spatial Requirement of EMF1 Activity for Arabidopsis Vegetative and Reproductive Development

EMBRYONIC FLOWER （EMF） genes are required to maintain vegetative development via repression of flower homeotic genes in Arabidopsis. Removal of EMF gene function caused plants to flower upon germination, producing abnormal and sterile flowers. The pleiotropic effect of ernfl mutation suggests its requirement for gene programs involved in diverse developmental processes. Transgenic plants harboring EMF1 promoter：：glucuronidase （GUS） reporter gene were generated to investigate the temporal and spatial expression pattern of EMF1. These plants displayed differential GUS activity in vegetative and flower tissues, consistent with the role of EMF1 in regulating multiple gene programs. EMFI：：GUS expression pattern in emf mutants suggests organ-specific auto-regulation. Sense- and antisense （as） EMF1 cDNA were expressed under the control of stage- and tissue-specific promoters in transgenic plants. Characterization of these transgenic plants showed that EMF1 activity is required in meristematic as well as differentiating tissues to rescue emf mutant phenotype. Temporal removal or reduction of EMF1 activity in the embryo or shoot apex of wild-type seedlings was sufficient to cause early flowering and terminal flower formation in adult plants. Such reproductive cell memory is reflected in the flower MADS-box gene activity expressed prior to flowering in these early flowering plants. However, temporal removal of EMF1 activity in flower meristem did not affect flower development. Our results are consistent with EMF1＇s primary role in repressing flowering in order to allow for vegetative growth.     

气孔在四季秋海棠营养器官和繁殖器官上的发育及相关性分析

主要观察了气孔在四季秋海棠营养器官和繁殖器官上的分布和发育情况,并分别对叶片和翅上气孔簇大小、气孔簇密度等指标的相关性进行了研究、结果表明:在叶片的下表皮、雌花和雄花的花被片、苞片、小苞片和翅上有气孔分布,而在茎、花梗上却未见气孔分布.叶片下表皮和翅上气孔通常成簇分布.在叶片的下表皮,气孔簇大小与气孔簇密度呈显著的负相关(P<0.05);气孔簇密度与叶片长度呈极显著的负相关(P<0.01).而翅上的气孔簇密度、气孔簇大小与子房长度无显著相关性(P>0.05).在四季秋海棠中,不同器官表皮的气孔簇大小是不同的,这可能与生理功能的不同有关.     

The Control of Apical Bud Growth and Senescence by Auxin and Gibberellin in Genetic Lines of Peas

Pea (Pisum sativum L.) lines G2 (dwarf) and NGB1769 (tall) (Sn Hr) produce flowers and fruit under long (LD) or short (SD) days, but senesce only under LD. Endogenous gibberellin (GA) levels were inversely correlated with photoperiod (over 9-18 h) and senescence: GA20 was 3-fold and GA1 was 10- to 11-fold higher in flowering SD G2 shoots, and the vegetative tissues within the SD apical bud contained 4-fold higher levels of GA20, as compared with the LD tissues. Prefloral G2 plants under both photoperiods had GA1 and GA20 levels similar to the flowering plants under LD. Levels of indole-3-acetic acid (IAA) were similar in G2 shoots in LD or SD; SD apical bud vegetative tissues had a slightly higher IAA content. Young floral buds from LD plants had twice as much IAA as under SD. In NGB1769 shoots GA1 decreased after flower initiation only under LD, which correlated with the decreased growth potential. We suggest that the higher GA1 content of G2 and NGB1769 plants under SD conditions is responsible for the extended vegetative growth and continued meristematic activity in the shoot apex. This and the increased IAA level of LD floral buds may play a role in the regulation of nutrient partitioning, since more photosynthate partitions of reproductive tissue under LD conditions, and the rate of reproductive development in LD peas is faster than under SD.     

Relative Rates of Nucleotide Substitution in Frogs

Accurate estimation of relative mutation rates of mitochondrial DNA (mtDNA) and single-copy nuclear DNA (scnDNA) within lineages contributes to a general understanding of molecular evolutionary processes and facilitates making demographic inferences from population genetic data. The rate of divergence at synonymous sites (K_s) may be used as a surrogate for mutation rate. Such data are available for few organisms and no amphibians. Relative to mammals and birds, amphibian mtDNA is thought to evolve slowly, and the K_s ratio of mtDNA to scnDNA would be expected to be low as well. Relative K_s was estimated from a mitochondrial gene, ND2, and a nuclear gene, c-myc, using both approximate and likelihood methods. Three lineages of congeneric frogs were studied and this ratio was found to be approximately 16, the highest of previously reported ratios. No evidence of a low K_s in the nuclear gene was found: c-myc codon usage was not biased, the K_s was double the intron divergence rate, and the absolute K_s was similar to estimates obtained here for other genes from other frog species. A high K_s in mitochondrial vs. nuclear genes was unexpected in light of previous reports of a slow rate of mtDNA evolution in amphibians. These results highlight the need for further investigation of the effects of life history on mutation rates. Current address (Andrew J. Crawford): Smithsonian Tropical Research Institute, Apartado 2072, Balboa, Ancon, Republic of Panama     

Role of Plants in the Vegetative and Reproductive Growth of Saprobic Basidiomycetous Ground Fungi

Non-symbiotic microorganisms engineered or expensively selected to degrade xenobiotic hydrocarbons or modify heavy-metal uptake of plants in soil remediations die back after their introduction into the target soils. Mycelia of saprobic basidiomycetes were therefore inoculated into soil samples of 1 l in glass vessels to record mycelial growth and reproduction in the immediate rhizosphere of up to 11 herbaceous plant species, or to study their responses to the separate volatiles from whole plant swards or their root balls whose emanations had been collected in 1.5-l plastic bags fixed to the glass vessels. Excess CO₂ was controlled with NaOH solution. Volatiles from root balls of parsley and pea but not wheat, from unplanted soils, from the fungus-permeated, unplanted substrate soil itself, and from the rooting soil of whole wheat sward increased mycelial densities in Clitocybe sp. more than in Agaricus macrocarpus and indicated thus a higher nutrient state of the mycelia. Organic volatiles proved therefore to be a significant carbon source for certain basidiomycetes in poor natural soils. The contemporary decline in the number of basidiocarp initials to 0 to 36% in both fungi relative to the unplanted and aerated controls was caused by volatiles from rooted and unplanted soil and pointed thus to their ecological role as antibiotics, fumigants, toxins, and hormonal compounds. Aqueous extracts from root balls of wheat stimulated mycelial density and fruiting in A. macrocarpus contemporarily because of their contents in soil-derived macronutrients. They suppressed once more fruiting in the more sensitive Clitocybe sp. by active agents in the aqueous phase. Within plant rhizospheres, densities of Clitocybe sp. mycelia were stimulated in the presence of alfalfa, carrot, red clover, ryegrass, and spinach, whereas those of A. macrocarpus were halved by 7 of 10 plant species including alfalfa, red clover, ryegrass, and spinach. Mycelia of A. macrocarpus may thereby have responded to differences in concentration and composition of volatile compounds. The contemporary repression of fruiting in both fungi and in nearly all treatments was not due to plant competition for macronutrients. Mycelia of basidiomycetes over-compensated for losses in macronutrients to the plant by decomposing soil matrix constituents. It is concluded that organic volatiles emitted by several plant organs and natural soils improved the nutritional state of A. macrocarpus and Clitocybe sp. but not of Agaricus bisporus mycelia and could therefore help establish certain ground fungi in the field. The contemporary and general suppression of fruiting by constituents of the gaseous (and liquid) phase in all fungi examined suggests interference with basic physiological processes and recommends an urgent re-examination of the degradative ability of basidiomycetes in the presence of volatiles.     

Genetic and Chromosomal Control of Development

The last decade has been characterized by extraordinary progress in studies of the molecular mechanisms underlying the gene control of development: complexes of genes with a hierarchic principle of functioning have been identified, evolutionary-conservative systems of genes have been studied that ensure the transmembrane regulatory signaling between cells and play a key role in morphogenesis, and a concept of gene networks that coordinate gene interaction was introduced. Note that temporal and tissue-specific parameters of gene expression are correctly realized only in terms of chromosomes and are largely determined by the gene position on a chromosome and in the interphase nucleus. The epigenetic inheritance of gene status in cell generations is realized at the chromosomal level alone due to the cellular or chromosomal memory. This ontogenetic memory is an immanent property of a chromosome and cis-regulation plays a key role in its maintenance.     

Genetic Diversity and Linkage Disequilibrium in Drosophila melanogaster with Different Rates of Development

We have examined eight enzyme polymorphisms in groups of Drosophila melanogaster flies with fast, intermediate and slow development. The allelic frequencies are similar in all three developmental classes, but the distribution of the genotypes among the classes is significantly heterogenous for the three loci on the second chromosome. When the total sample of 300 individuals is examined, significant gametic disequilibrium appears in 3 out of 13 pairs of genes located on the same chromosome and in 4 out of 15 pairs of genes located on different chromosomes. This 25% incidence of disequilibrium between pairs of genes is larger than previously observed in other natural populations (but similar to the incidence observed in laboratory populations). The greater frequency of significant gametic disequilibrium in our study is probably due to the larger number of genomes sampled.-Some models specifically predict that individuals with faster rates of development (i.e., greater fitness) should be more heterozygous (and exhibit more linkage disequilibrium) than individuals with slower development. This hypothesis is not supported by our results.     

Relationship between Chloroplast Development and ent-Kaurene Biosynthesis in Peas

Treatment of etiolated pea (Pisum sativum (L. cv. Alaska) seedlings with 2′-isopropyl-4′-(trimethylammonium chloride)-5′-methylphenyl piperidine-1-carboxylate (Amo-1618) prior to irradiation with white light inhibits photomorphogenesis and formation and stacking of thylakoid membranes in the chloroplasts, as well as (−)-kaur-16-ene (ent-kaurene)biosynthesis. Exogenous gibberellic acid also inhibits greening. A crudely determined action spectrum for the photoinduction of ent-kaurene biosynthesis shows two peaks, one in the blue region at 458 to 490 nanometers and another in the red region at 606 to 678 nanometers. The possible participation of phytochrome in the photoinduction of ent-kaurene biosynthesis is indicated by comparative effects of red, far red, and alternating red/far red irradiations on enhancement of enzyme activity. The activity of blue light as well as red shows a similarity of the photoinduction of ent-kaurene synthesis activity to the high irradiance responses, and indicates probable participation of a second photoreceptor. From these observations, it is concluded that photoinduction of ent-kaurene biosynthesis and chloroplast development in shoots are closely linked processes.     

The Development of Stomata in Vegetative and Reproductive Organs ofBupleurum tenue Buch.-Ham. ex D. Don

InBupleurum tenue stomata have been observed on leaf, stem,stalk of compound umbel and umbellet, bract of involucre andinvolucel, pedicel of flower, both surfaces of petal, outerepidermis of pericarp, and the stylopodium. Their developmentis of the syndetocheilic type in vegetative as well as the reproductiveorgans. In the stylopodium the stomata are anomocytic whilein the rest of the organs they are anisocytic.     

Development of Pyrimidine-metabolizing Enzymes in Cotyledons of Germinating Peas

Mechanisms controlling conversion of orotic acid-6-¹⁴C to uridine-5′-phosphate in cotyledons of germinating Alaska peas (Pisum sativum L.) were investigated. The content of 5-phosphoribosyl-1-pyrophosphate was very low in dry seeds, increased to a maximum after about 12 hours of imbibition, and then rapidly declined. Orotidine-5′-phosphate pyrophosphorylase and orotidine-5′-phosphate decarboxylase activities more than doubled during the first 24 hours of germination and then also decreased. These results do not account for the continuous increases of orotate anabolism in such cotyledons as we observed previously. The initial increases in activities of these two enzymes were unaffected by cycloheximide, while the subsequent decreases were less rapid in the presence of this inhibitor. Activities of cotyledonary cytidine deaminase and uridine hydrolase also increased during imbibition, but the activity of only the latter showed a decrease after imbibition was completed. Cycloheximide inhibited the initial rapid increase in uridine hydrolase activity but had little effect on its subsequent decline. Cycloheximide had only slight inhibitory effects on the development of cytidine deaminase activity during the first 62 hours. The evidence suggests that uridine hydrolase might be synthesized de novo during the first few days of germination, but that the other three enzymes might not be.     

Description of the Photoperiodic Control of Larval Burrowing in the Blowfly Lucilia Cuprina: a Novel Index for Photoperiodic Research

The photoperiodic control of larval burrowing depth in the Australian sheep blowfly Lucilia cuprina (Wiedemann) (Diptera: Calliphoridae) was investigated by measuring burrowing depth under controlled laboratory photo-periods. The results demonstrated that larvae exposed to long photoperiods (LD 18:6) burrowed to deeper depths than those in shorter photoperiods (LD 12:12), and that this behavior was induced during the third instar stage. The ecological significance of this behavior is discussed, as are the ways in which daylength is measured and depth assessed. The use of burrowing depth could prove to be a novel index of a photoperiodic response and provide a far simpler approach to the study of photoperiodism in certain insect species. (Chronobiology International, 14(3), 247–252, 1997)     

Carbon Transfer and Partitioning between Vegetative and Reproductive Organs in Pisum sativum L

Assimilate partitioning was studied in the common pea (Pisum sativum L.) by feeding ¹⁴CO₂ to whole plants and measuring radioactivity in different organs 48 hours after labeling. Two experimental protocols were used. For the first, one reproductive node was darkened with an aluminum foil, to prevent photosynthesis during labeling. The aim was to study assimilate translocation among nodes. The second was carried out to assess any priority among sinks. Whole plants were shaded, during labeling, to reduce carbon assimilation. Various developmental stages between the onset of flowering and the final stage in seed abortion of the last pod were chosen for labeling. When all photosynthetic structures at the first reproductive node were darkened at any stage of development after the formation of the first flower, the first pod was supplied with assimilates from other nodes. In contrast, later developed pods, when photosynthetic structures at their node were darkened, received assimilates from other nodes only when they were beyond their final stage in seed abortion. Reducing illumination to 30% did not change distribution of assimilated carbon between vegetative and reproductive structures, nor among pods. It appears that the relative proportion of ¹⁴C allocated to any one pod, compared to other pods, depends on the dry weight of that pod as a proportion of the total reproductive dry weight. When the plant was growing actively, following the start of the reproductive phase until a few days before the end of flowering, the top of the plant (i.e., all the organs above the last opened flower) had a higher sink strength and a higher relative specific activity than pods, suggesting that it was a more competitive sink for assimilates. The pattern of assimilate distribution described here provides an explanation for pod and seed abortion.     

Genetic Change and Rates of Cladogenesis

Models are introduced which predict ratios of mean levels of genetic divergence in species-rich versus species-poor phylads under two competing assumptions: (1) genetic differentiation is a function of time, unrelated to the number of cladogenetic events and (2) genetic differentiation is proportional to the number of speciation events in the group. The models are simple, general, and biologically real, but not precise. They lead to qualitatively distinct predictions about levels of genetic divergence depending upon the relationship between rates of speciation and amount of genetic change. When genetic distance between species is a function of time, mean genetic distances in speciose and depauperate phylads of equal evolutionary age are very similar. On the contrary, when genetic distance is a function of the number of speciations in the history of a phylad, the ratio of mean genetic distances separating species in speciose versus depauperate phylads is greater than one, and increases rapidly as the frequency of speciations in one group relative to the other increases. The models may be tested with data from natural populations to assess (1) possible correlations between rates of anagenesis and cladogenesis and (2) the amount of genetic differentiation accompanying the speciation process. The data collected in electrophoretic surveys and other kinds of studies can be used to test the predictions of the models. For this purpose genetic distances need to be measured in speciose and depauperate phylads of equal evolutionary age. The limited information presently available agrees better with the model predicting that genetic change is primarily a function of time, and is not correlated with rates of speciation. Further testing of the models is, however, required before firm conclusions can be drawn.