Tomato: a crop species amenable to improvement by cellular and molecular methods

Tomato is a crop plant with a relatively small DNA content per haploid genome and a well developed genetics. Plant regeneration from explants and protoplasts is feasable which led to the development of efficient transformation procedures. In view of the current data, the isolation of useful mutants at the cellular level probably will be of limited value in the genetic improvement of tomato. Protoplast fusion may lead to novel combinations of organelle and nuclear DNA (cybrids), whereas this technique also provides a means of introducing genetic information from alien species into tomato. Important developments have come from molecular approaches. Following the construction of an RFLP map, these RFLP markers can be used in tomato to tag quantitative traits bred in from related species. Both RFLP's and transposons are in the process of being used to clone desired genes for which no gene products are known. Cloned genes can be introduced and potentially improve specific properties of tomato especially those controlled by single genes. Recent results suggest that, in principle, phenotypic mutants can be created for cloned and characterized genes and will prove their value in further improving the cultivated tomato.

Experimental considerations for the calibration of personnel dosimeters with photons

The criteria for irradiating radiation dosimeters for test purposes are defined quite clearly in Draft ANSI Standard N13.11. In this Draft the use of phantoms, constructed of a near tissue equivalent material, is prescribed for backing the dosimeters while being irradiated, thus simulating a dosimeter being irradiated while attached to a person. When the phantom is placed in the photon beam it becomes a major source of scattered radiation. The scatter component into the dosimeter is a function of the energy of the photon beam and must be defined for each effective energy used. In addition, it is usually cost effective to irradiate more than one dosimeter at the same time, which may result in mutual interference from the dosimeters themselves. The effects of these parameters upon a centrally positioned dosimeter in the presence of a phantom are studied

Leucines on a roll

Several proteins have recently been found to consist of repetitive structural units in a superhelical arrangement. The structure of the leucine-rich repeat variant protein represents an unexpected addition to the list of such proteins, with the repetitive unit consisting of antiparallel alpha- and 3(10)-helices