Localization of Fe-containing superoxide dismutase in cyanobacteria from the Baltic Sea: depth and light dependency

The abundance and cellular location of Fe-containing superoxide dismutase (Fe-SOD) in trichomes of Nodularia , Aphanizomenon and Anabaena collected from various depths in the Baltic Sea, and in trichomes of a cultured Nodularia strain, BC Nod-9427, isolated from the Baltic Sea, was examined by immunogold labelling. For trichomes collected from natural populations the areal concentration of Fe-SOD labelling decreased with depth: trichomes collected from surface accumulations had between 8 and 11 gold particles μm⁻² whereas trichomes collected from a depth of 18 m were unlabelled. When trichomes collected from a depth of 10 m (mean areal labelling density 0·5 gold particles μm⁻²) were exposed to the higher irradiances present at 1 m, the areal concentration of Fe-SOD increased to 3·5–4 gold particles μm⁻² within 4 h. When cultures of Nodularia strain BC Nod-9427, adapted to low light (10 μmol m⁻² s⁻¹), were transferred to an incident irradiance of 1350 μmol m⁻² s⁻¹, a doubling of the areal concentration of Fe-SOD gold label was observed within 1 h. Addition of 3-(3,4-dichlorophenyl)-1,1'-dimethylurea (DCMU) to cultures immediately before their transfer to increased illumination resulted in a decrease in areal Fe-SOD concentrations whereas addition of CdCl₂ caused an increase over and above that induced by the elevated irradiance. These results suggest that Baltic Sea cyanobacteria are able to modulate their Fe-SOD content but that this might be in response to oxidative stress rather than to light per se .     

Pollen-pistil interactions in Hermodactylus tuberosus Mill. (Iridaceae)

ABSTRACT

Hermodactylus tuberosus Mill. (Iridaceae) is a species with a very short style and a tricarpellar unilocular ovary. For ornamental purposes it is usually reproduced by means of tubers, although both vegetative and seed reproduction occur in nature. However, its capsules do not contain many seeds in comparison to the high number of ovules inside the ovary. To understand this conflicting process a study on H. tuberosus pollen-pistil interaction was carried out. Pollen viability was evaluated by different techniques. Germination rate was tested in vitro and in vivo after stigma, intrastylar and intraovarian pollinations. A high percentage of the pollen grains were found to be viable resulting in a high percentage of in vitro germination and a low rate of germination on the stigma. Indeed, many pollen tubes developed after intrastylar and intraovarian pollinations. Several anomalies characterized pollen germination and pollen tube growth in vitro and in vivo. Observations from field trials indicated that capsules were only produced from open or hand, cross- pollinated flowers, confirming that the plant is self- incompatible and not apomictic. In addition, all the mature capsules contained only a few mature seeds suggesting the existence of pre- and postzygotic seed set inhibition.     

Poly(A) polymerase in Dormant Embryos of Triticum durum

Triticum durum‘Cappelli’ has a ‘relative’dormancy which can be broken by dry after-ripening at room temperature.The breakage of dormancy in the embryos of T. durum , is accompaniedby a decline in content and a different degree of synthesisof poly(A)⁺RNA. This work studies the activity of poly(A) polymerase(E.C. 2.7.7.19), the enzyme which permits polyadenylation. Anincrease in the activity of this enzyme in parallel with theenhanced rate of germination is revealed. Since poly(A) polymeraseactivity is the same in dormant and non-dormant dry embryos,it seems that the activity of the enzyme is not involved inthe breakage of dormancy. The use of cycloheximide and cordycepinshows the presence of enzymes with different origins: a storedenzyme and one bound to a long lived mRNA, present in dormantand non-dormant embryos, plus an enzyme bound to newly synthesizedmRNA which is mainly active in non-dormant embryos. Since dormancycould be the result of an interaction between hormones, thiswork analyses the effects of GA₃and ABA on poly(A) polymerase.GA₃enhanced poly(A) polymerase activity only in dormant embryoswhile ABA inhibited this activity only in non-dormant embryos.Cycloheximide applied to excised wheat embryos represses thestimulatory and inhibitory effects of GA₃and ABA, respectively.The hormone action on poly(A) polymerase activity is thus dependenton de novo protein synthesis. Results using cordycepin suggestthe presence of a stored mRNA for poly(A) polymerase, togetherwith hormonal regulation of enzyme activity at a translationallevel. Copyright 1999 Annals of Botany Company Triticum durum , wheat, dormancy breakage, poly(A) polymerase, GA₃, ABA, germination.     

Polyamines and Protein Metabolism in Maize Inbreds Differing in Seed Protein Content

Polyamine metabolism was evaluated in the embryo and the endosperm,during the early stages of seed germination, of two maize inbreds(Lo5 and B73) differing in the protein nitrogen content of thecaryopscs. On germination, the concentration of buffer-extractableproteins and of polyamines increases more quickly and to greatervalues in Lo5 than in B73. In the caryopses, the embryos havea higher polyamine content than the endosperms and in the seedlings,after three days of growth, the shoots show a higher polyaminecontent than in the case of the scutellum and the roots. Duringseed germination, spermidine is the main polyamine and its contentvaries while the spermine remains virtually constant. The polyaminesand protein pattern in the embryo and the endosperm of the twoinbreds are discussed in relation to the differences in theirgermination energy and early seedling growth.