PHYSIOLOGISCHE UNTERSUCHUNGEN ZUR REIFETEILUNG

[The pollen tube growth of Pisum mutants under consideration of the free amino acids]

The germination of the pollen grains and the growth rate of the pollen tubes of eight mutants of Pisum sativum were compared with the parent line by in vitro investigations. All of the mutants studied showed a retardation of pollen tube growth as compared to the parent line, resulting in competitive elimination of some of the gametes in plants heterozygous for the respective mutant genes. The deficit of recessive plants in the progenies of heterozygous mutant strains of peas can be attributed to this retardation. Marked differences between the various mutants with regard to the levels of various free amino acids in their pollen grains were found. Certain amino acids may be present in greatly reduced concentration or may be present in excess. In some genotypes pollen tube growth can be stimulated by adding the deficient amino acid. This is especially true for proline, valine and threonine. As far as the other amino acids are concerned, the mutants studied showed varying reactions. The germination rate of the pollen grains is reduced by proline and threonine; germination is completely inhibited by glutamine. The amino acids isoleucine, histidine and cysteine retard pollen tube growth in all the mutants investigated. This is also true for leucine which, however, has a stimulating effect in one of the chlorophyll mutants.

[Changes of flavonol and anthocyanin content during microsporogenesis]

The changes in the content of flavonols, anthocyanins, and carotenoids which can be observed in the anther during microsporogenesis were followed in Narcissus pseudonarcissus and in the Darwin tulip "Apeldoorn".The investigations revealed a distinct relationship between the process of pigmentation and the cytologic development in the anther. A marked increase in the production of flavonols occurs during and immediately after the separation of the microspores of the tetrad and seems to be connected in some specific manner with the presence of the immature pollen. In Narcissus, the total flavonol content of the anthers and their pollen and tapetum fraction reaches its highest value during the enclosure of the bud by the bulb and remains more or less unchanged until the flowers open. In contrast, an intense synthesis of flavonols does not begin in the tulip before the flower-bud has left bulb; then the flavonol content increases continuously until anthesis is reached.The colouring of the pollen by anthocyanins does not occur until the final stages of maturation.Without exceptions the production of carotenoids takes place after the separation of the microspores of the tetrad.

Meiosis and sporulation induced in sporophytes of Ulva mutabilis ("slender") with synchronous mitosis

Sporulation preceded by meiosis was induced in young, diploid plants of Ulva mutabilis, mutant "slender" (FöYN). The induction was brought about either by replacement of the old culture medium (sea water plus soil extract) with new, or by the addition of a mixture of seven vitamins to old medium. The new chemical environment seems to induce a shift from presumptive mitosis to presumptive meiosis.

[Variations in the protein and enzyme pattern during pollen meiosis and pollen development]

During pollen development and meiosis in Lilium henryi the protein pattern was analysed by disc electrophoresis, the microsporocytes and the tapetal fractions, being taken seperately. The pattern undergoes a phase-specific variation: every cytological stage shows a specific protein pattern.The fractions could be partially identified by incubation with substrate and by specific enzyme staining of some of the enzymes (phosphorylase, acid phosphatase, peroxydase, thiamine pyrophosphatase, malate dehydrogenase, lactate dehydrogenase). The enzyme pattern also has a high phase specificity. Iso-enzymes were found in various numbers and activity, especially in the case of peroxydase and lactat dehydrogenase. The results are interpreted as a series of phase-specific gene transcriptions which coordinate the sequence of biochemical events essential for the normal pollen meiosis and the subsequent development of the pollen.

Nucleic Acids and Survival of Excised Anthers in vitro

Excised anthers of Allium cepa and Rhoeo discolor have been successfully cultured in modified White's medium supplemented with various concentrations of ribonucleic acid and deoxyribonucleic acid. Ribonucleic acid proved to be much more useful than deoxyribonucleic acid and reduced the time required for the completion of meiosis from 48 hours to 24 hours. The role of nucleic acids in the control of nuclear divisions has been indicated.