Irregular segregation at the Pr locus controlling plastid inheritance in Pelargonium: gametophytic lethal or incompatibility system?

Summary Two distinct segregation patterns are recognized after G X W plastid crosses in Pelargonium. Type I parents produce offspring in which maternal zygotes are frequent, biparental intermediate, and paternal zygotes rare (MZ>BPZ>PZ), as defined by the presence or absence of green or white plastids in the young embryos into which the zygotes develop. Type II parents produce offspring in which maternal and paternal zygotes are frequent with biparental zygotes the least frequent class (MZ>BPZPr₁Pr₁. Type II plants, which do not breed true, are regarded as heterozygotes — Pr₁Pr₂. The nuclear gene is symbolized as Pr as it is presumed to control alternative patterns of plastid segregation through an effect on plastid replication.Selfs and intercrosses of heterozygous plants segregate in an unexpected 1:1 ratio and not the expected 3:1 (1:2:1). The alternative homozygote — Pr₂Pr₂ — could not be detected. Reciprocal crosses between heterozygotes (Pr₁Pr₂) and homozygotes (Pr₁Pr₁) give the expected 1:1 ratio when the Pr₂ allele is derived from the male, whereas there is often, but not always, a highly significant deviation from 1:1 when the Pr₂ allele is derived from the female.A simple explanation, which is not wholly satisfactory, is to assume that Pr₂ is a gametophytic lethal on the female side. An alternative, or additional, explanation is that an incompatibility mechanism is involved in which Pr₁ is a self-compatible allele, Pr₂ a self-incompatible allele, and Pr₁-Pr₂ cross-compatible alleles. Successful fertilization is then determined by sporophytic control on the male side and gametophytic control on the female side.     

Critical Notice: Cycles of Contingency – Developmental Systems and Evolution

The themes, problems and challenges of developmental systems theory as described in Cycles of Contingency are discussed. We argue in favor of a robust approach to philosophical and scientific problems of extended heredity and the integration of behavior, development, inheritance, and evolution. Problems with Sterelny's proposal to evaluate inheritance systems using his `Hoyle criteria' are discussed and critically evaluated. Additional support for a developmental systems perspective is sought in evolutionary studies of performance and behavior modulation of fitness.     

Alloplasmic male sterility in AD allotetraploid Gossypium hirsutum upon replacement of its resident A cytoplasm with that of D species G. harknessii

Summary Alloplasmic male sterile (cms) and restoration-of-fertility (Rf) lines of the AD allotetraploid Gossypium hirsutum were earlier derived from the presumed introgression of the cytoplasm of the D species G. harknessii. To confirm that this happened and address its significance, cytoplasms of the maternal progenitor, backcross intermediates, derived breeding lines, related A, D, and F species, and a synthetic AD tetraploid were examined by agarose and polyacrylamide gel electrophoresis of 140 restriction enzyme fragments of chloroplast DNA. Length mutations of 10–50 nucleotides predominate over site loss/gain mutations. Chloroplast DNA is maternally inherited and that of G. harknessii has been maintained in the cms lines for at least 13 successive generations without detectable alteration. Chloroplast DNA divergence is consistent with current nuclear genome classification and shows that the A progenitor was the maternal parent of the AD tetraploids. As predicted from incompatability models of cms, the degree of male sterility in alloplasmic Gossypium tetraploids is correlated with the extent of evolutionary divergence of their cytoplasms. It is suggested that the A genome in the AD tetraploids dominates those nuclear-cytoplasm interactions reflected by male fertility.     

Plastid development in seedlings of Echinochloa crus-galli var. oryzicola under anoxic germination conditions

Plastid development in the primary leaf of Echinochloa crus-galli (L.) Beauv. var. oryzicola (Vasing.) Ohwi was followed during 5 d of anoxic germination and growth. Plastids develop slowly from simple spheroidal proplastids into larger pleomorphic plastids with several stromal membranes and many peripheral membrane vesicles. A small prolamellar body is present at 96 h with perforated (pro)thylakoids extending into the stroma. Changes in starch grains and plastoglobuli are evidence of carbohydrate and lipid metabolism. Plastid division is indicated by dumbbell plastid profiles after 4 d of anoxia. These results demonstrate that plastids not only maintain their integrity during anaerobic germination but also show developmental changes involving an increase in internal membrane complexity, although to a lesser extent than in etiolated shoots.Abbreviation PLB prolamellar body Scientific paper No. 6167. College of Agriculture, Washington State University, Pullman     

Selective disappearance of maternal centrioles after fertilization in the anisogamous brown alga Cutleria cylindrica (Cutleriales, Phaeophyceae): Paternal inheritance of centrioles is universal in the brown algae

The behavior of centrioles in zygotes and female gametes developing parthenogenetically in the anisogamous brown alga Cutieria cyiindrica Okamura was studied using electron and immunofluorescence microscopy. Two pairs of centrioles, detected using anti-centrin antibody, were observed in the vicinity of the male and female nuclei, respectively, just after plasmogamy. The fluorescence intensity of one of the two centrin foci became weak 6 h after plasmogamy and finally disappeared. It was impossible to determine whether the male- or female-derived centrioles disappeared in zygotes, because there was nothing to detect morphological differences between the two centrioles. However, a prominent anti-centrin staining focus was located at the condensed male nucleus in zygotes in which karyogamy had not occurred yet. As a result, it was considered that the maternally inherited centrioles had selectively disappeared during development in C. cylindrica. The paternal inheritance of centrioles in zygotes was also confirmed by electron microscopy. Considering previous observations from oogamous and isogamous species of brown algae, we concluded that the paternal inheriance of centrioles could be universal in the brown algae.     

About a transmissible influence through several generations in a clone of the rotifer notommata copeus EHR

Over ten years, the individuals of an orthoclone of Notommata copeus gradually lost their sensitivity to photoperiod. This loss is transmissible but reversible in three generations. It is endogenous but not chromosomal. The hypothesis is forwarded that it is induced by external factors, and quite possibly crowding.