Early seedling growth and morphogenesis in the <Emphasis Type="Italic">xantha1</Emphasis> mutant of sunflower with alteration of chloroplast biogenesis

In the xantha1 (xan1) mutant of sunflower (Helianthus annuus L.), the effects on organ anatomy and seedling growth did correlate to the alteration of chloroplast biogenesis. The xan1 seedlings grown under 165 μmol(photon) m⁻² s⁻¹ revealed a severely altered chloroplast ultrastructure in cotyledons and leaves. Cross-sections or clarified tissues of the xan1 cotyledons did not show evident alterations with respect to normal cotyledons suggesting that the impairment of chloroplast biogenesis has negligible consequences on embryonic leaves. By contrast, the analysis of xan1 leaves showed that the defects in chloroplast biogenesis were correlated to a drastic reduction of organ size and to a clear enhancement of the trichome growth. The differentiation of palisade and spongy parenchyma in cotyledons and leaves of the xan1 mutant was normal but both organs displayed a drastic reduction in the plastid number with respect to wild type. In addition, xan1 hypocotyls showed a reduced development of the main vascular bundles in comparison with normal seedlings and an undersized central cylinder of the primary root. The exogenous supply of sucrose was not sufficient to revert in vitro the deficit of xan1 growth and the constraints in morphogenetic processes.     

CYCLOIDEA 2 Clade Genes: Key Players in the Control of Floral Symmetry,Inflorescence Architecture,and Reproductive Organ Development

Undoubted lines of evidence point out that members of CYCLOIDEA (CYC) 2 clade are essential players to control flower symmetry and, amusingly, also are determinants of capitula architecture (pseudanthium). In several species, CYC-like genes influence the androecium patterning, but to date, the function of these genes in the development of gynoecium organs is less clear. In this review, we first reported details about floral symmetry and an overview of genes and molecular mechanisms regulating the development of zygomorphism in different angiosperm lineages (e.g., basal and core eudicots and monocots). Then, we paid emphasis on the role of CYC-like genes in the development of heterogamous inflorescence of sunflower as well as other Asteraceae and some species within the Dipsacaceae family. Helianthus annuus is particularly attractive because it represents a useful model to study the role of CYC-like genes on shaping floral corolla as well as the differentiation of reproductive organs in different flowers of pseudanthia. A special attention was reserved to inflorescence morphology mutants of sunflower (i.e., Chrysanthemoids2 and tubular ray flower) because they provide useful information on the role of CYC-like genes in the radiate capitulum evolution. Finally, we discuss data from literature to suggest that CYC-like genes are also co-opted to regulate stamen and carpel differentiation likely throughout their interaction with the cell cycle and flower organ identity genes. The recruitment of reproductive organs in ray flowers also supports the phylogenetic origin of a radiate inflorescence of sunflower from a discoid capitulum and suggests that in sterile zygomorphic ray flower primordia the latent identity to differentiate both microsporangium and macrosporangium was conserved.     

Alpha-tryptophan synthase of Isatis tinctoria: gene cloning and expression.

Indole producing reaction is a crux in the regulation of metabolite flow through the pathways and the coordination of primary and secondary product biosynthesis in plants. Indole is yielded transiently from indole-3-glycerol phosphate and immediately condensed with serine to give tryptophan, by the enzyme tryptophan synthase (TS). There is evidence that plant TS, like the bacterial complex, functions as an alpha beta heteromer. In few species, e.g. maize, are known enzymes, related with the TS alpha-subunit (TSA), able to catalyse reaction producing indole, which is free to enter the secondary metabolite pathways. In this contest, we searched for TSA and TSA related genes in Isatis tinctoria, a species producing the natural blue dye indigo. The It-TSA cDNA and the full-length exons/introns genomic region were isolated. The phylogenetic analysis indicates that It-TSA is more closely related to Arabidopsis thaliana At-T14E10.210 TSA (95.7% identity at the amino acid level) with respect to A. thaliana At-T10P11.11 TSA1-like (63%), Zea mays indole-3-glycerol phosphate lyase (54%), Z. mays TSA (53%), and Z. mays indole synthase (50%). The It-TSA cDNA was also able to complement an Escherichia coli trpA mutant. To examine the involvement of It-TSA in the biosynthesis of secondary metabolism compounds, It-TSA expression was tested in seedling grown under different light conditions. Semi-quantitative RT-PCR showed an increase in the steady-state level of It-TSA mRNA, paralleled by an increase of indigo and its precursor isatan B. Our results appear to indicate an involvement for It-TSA in indigo precursor synthesis and/or tryptophan biosynthesis.     

Characterization of a wilty sunflower (Helianthus annuus L.) mutant II. Water relations, stomatal conductance, abscisic acid content in leaves and xylem sap of plants subjected to water deficiency

The response of w-1, a wilty sunflower (Helianthus annuus L.)mutant, to water stress is described in comparison with thecontrol line (W-1). Detached leaves of w-1 strongly dehydratedduring the first 30 min without significant changes in leafconductance, whereas W-1 responded rapidly to water loss byreducing stomatal aperture. After 2 h stress ABA increased slightlyin w-1, while W-1 leaves showed a 20-fold increase. When waterstress was imposed to potted plants by water withholding, w-1quickly dehydrated, and lost turgor, while W-1 maintained positiveturgor values for a longer period. Wild-type plants respondedto small changes in leaf water potential by accumulating ABAand by closing stomata, whereas in the mutant significant changesin ABA content and in stomatal conductance were found only atvery low water potentials. In another experiment in which waterwas withheld under high relative humidity, when soil water contentstarted to decrease W-1 rapidly closed stomata in the absenceof any change in leaf water status and the reduction in conductancewas paralleled by a rise in xylem sap ABA concentration. Bycontrast the mutant started to accumulate ABA in the xylem sapand to close stomata when soil water content and leaf waterpotential were dramatically reduced. The low endogenous ABAlevels and the inability to synthesize the hormone rapidly eitherin the leaves or in the roots seem to be responsible for thehigh sensitivity of w-1 to water stress. Key words: ABA, Helianthus annuus L, water relations, stomatal conductance, drought, wilty mutant     

Role of luteinizing hormone in changes in concentrations of progesterone and luteal blood flow during the hours of a simulated pulse of 13,14-dihydro-15-keto-prostaglandin F(2alpha) (PGFM) in heifers

A bolus treatment (e.g., 25 mg) of prostaglandin F(2alpha) (PGF) in the study of luteolysis in cattle results in dubious interpretations. Therefore, in experiment 1 of the present study, a 13,14-dihydro-15-keto-PGF (PGFM) pulse was simulated by incremental intrauterine (IU) infusion of PGF for 2.7 h on Day 14 postovulation. Concentrations of PGFM during the first hour of infusion and at the maximum were not different between simulated (n = 7) and spontaneous (n = 7) pulses. In experiment 2, four groups (n = 6 per group) were treated at Minute 0 (beginning of infusion) as follows: saline (infused IU), PGF (infused IU), acyline/saline, and acyline/PGF. Two hours before Minute 0, each heifer was given flunixin meglumine to inhibit endogenous PGF secretion, and heifers in the acyline/saline and acyline/PGF groups were given acyline to inhibit luteinizing hormone (LH). Plasma progesterone concentrations were similar among groups during Minutes 0 to 60, with no indication of an initial transient progesterone increase in the two PGF groups. Progesterone began to decrease in the PGF groups at Minute 60 and to rebound at Minute 135 after the PGFM peak at Minute 120. The rebound was complete in association with an increase in LH in the PGF group, but it was not complete when LH was inhibited in the acyline/PGF group. Luteal blood flow increased during PGF infusion in the two PGF groups and remained elevated for approximately 2 h after the PGFM peak in the PGF group but not in the acyline/PGF group. Novel findings were that an initial transient increase in progesterone did not occur with the simulated PGFM pulse and that LH stimulated a progesterone rebound and maintained the elevated luteal blood flow after the PGFM peak.