Monoploids in Zea mays L. following crosses with untreated and X-rayed pollen

Monoploids in Zea mays L. occur spontaneously among individual diploid seedlings. Plants with the gametic chromosome number have also been detected among members of multiple seedlings of maize and numerous other species of angiosperms. Previous reports disclosed that Xirradiation of the pollen successfully stimulated reduced parthenogenesis in some other angiosperms, but the results of X-ray treatment were inconclusive in maize. Therefore, a tester stock of maize homozygous for lg _land gl _l was crossed with pollen from inbred CI3A, carrying the dominant alleles. The pollen was exposed to 0, 1000, 2000, and 4000r units of X rays. chromosome counts were made from root tips of plants exhibiting both recessive phenotypes to establish the frequencies of monoploids in the control and X₁ populations.Monoploids were more abundant among the individual seedlings from crosses with untreated pollen than in the X₁ populations. X irradiation of the pollen is not a feasible method for the induction of monoploids in maize. The X-ray treatments greatly increased the frequency of multiple seedlings, and deficiencies were numerous among them. The members of a set of multiple seedlings were always genetically identical, and no monoploid members occurred. It is concluded that the induced deficiencies caused atypical development resulting in zygotic or embryonic cleavage.Scientific Article No. A2070, Contribution No. 5023 of the Maryland Agricultural Experiment Station, Department of Botany.     

Abalone I: Analyzing Mark-Recapture-Recovery Data Incorporating Growth and Delayed Recovery

Abalone are semimobile marine gastropods that form the basis of Australia's second most valuable fishery. A site off the coast of Port Arthur, Tasmania, was visited on six occasions. On each occasion, any unmarked live abalone found were marked with a unique identification number and were recorded. Any previously marked abalone found had its identification number and whether or not it was still alive recorded. This results in integrated mark-recapture-recovery data, as in Catchpole et al. (1998, Biometrics 54, 33-46). During the study period, abalone grew in size, and we model the survival of individuals as a function of their size, estimated from a fitted growth curve. The shells of dead animals are long lasting, and we extend existing methodology to allow for the possibility that an animal found dead may have been dead but overlooked for several visits.     

Receptor-mediated endocytosis of transferrin and ferritin by guinea-pig reticulocytes. Uptake by a common endocytic pathway

Earlier studies have shown that transferrin binds to specific receptors on the reticulocyte surface, clusters in coated pits and is then internalized via endocytic vesicles. Guinea-pig reticulocytes also have specific receptors for ferritin. In this paper ferritin and transferrin endocytosis by guinea-pig reticulocytes was studied by electron microscopy using the natural electron density of ferritin and colloidal gold-transferrin (AuTf). At 4 degrees C both ligands bound to the cell surface. At 37 degrees C progressive uptake occurred by endocytosis. AuTf and ferritin clustered in the same coated pits and small intracellular vesicles. After 60 min incubations the ligands colocalized to large multivesicular endosomes (MVE), still membrane-bound. MVE subsequently fused with the plasma membrane and released AuTf, ferritin and inclusions by exocytosis. All endocytic structures labelled with AuTf contained ferritin, but 23 to 35% of ferritin-labelled endocytic structures contained no AuTf. These data suggest that ferritin and transferrin are internalized through the same pathway involving receptors, coated pits and vesicles, but that these proteins are recycled only partly in common.     

Improved methods of estimating root length using a photocopier,a light box and a bar code reader

Photocopying was found to be a rapid method of making a permanent record of a root sample. The method used produced a copy with white roots against a black background. Manual estimates of root length were made from photocopies using a light box. The number of intersections visible when laid over a copy of a white on black regular square grid was counted. Automated estimates of root length were made by scanning a photocopy with a bar code reader in place of a pen in a computer-driven graph plotter. Roots >0.2 mm diameter were resolved with precision and speed.