Cytokinin production by Asparagus shoot apex cultured in vitro

The cytokinin producing capacity of asparagus (Asparagus officinalis L.) shoot apex was examined by means of shoot apex culture in vitro, where adventitious roots were never formed. The cultured shoot apices continued to diffuse a small but constant amount of cytokinin into the medium throughout five passages of subculture. The cytokinin content in the apices at the end of the subculture was not different from that at the beginning of the subculture. These results indicate a production of cytokinin by the apices. However, the finding is not in conflict with the hypothesis that the root tip is the major source of cytokinin supply, because the root tip of asparagus produced more cytokinin than the shoot apex and the decline of shoot growth observed during the subculture was partially restored by an application of zeatin into the medium.     

Callus Formation and Embryogenesis of Endosperm Tissues of Parsley Seed Cultured on Hormone-Free Medium

Archegonial differentiation in light-grown gametophytes of Lygodium japonicum was partially inhibited by exogenously applied gibberellin A₃ (GA₃) at a concentration of 10^?6M, and fully prevented at 10^?5M. The inhibitory effect was nullified by transferring the GA₃-treated samples onto fresh media omitting GA₃, so that the archegonial formation became discernible 6 days after the transplantation. The application of 10^?4M GA₃ to younger gametophytes brought about a complete inhibition of archegonial differentiation, whereas the same concentration applied to older gametophytes did not influence the process at all, indicating the timing of archegonial differentiation during the ontogeny. Activity spectrum of authentic gibberellins on the basis of concentrations inducing 50% inhibition of archegonial formation was obtained as follows: GA₄= GA₉ > GA₇ > GA₃ > GA₁= GA₅= GA₈.     

Germline-specific Antigens Identified by Monoclonal Antibodies in the Nematode Caenorhabditis elegans1

Of 27 monoclonal antibodies identified to react, by indirect immunofluorescent antibody staining, with specific cells and tissues of the nematode Caenorhabditis elegans, we report here three monoclonal antibodies pertaining to the gonadal tissues. One antibody defines an antigen that is distributed over the entire embryo at earlier development and later becomes unique to the gonad, including mature oocytes. The antigens recognized by the other two are distributed asymmetrically in the posterior region of the fertilized egg's cytoplasm destined to become the germline precursor cell. Each antigen is successively segregated only to the germline precursor cells of the developing embryo and, postembryonically, is uniquely localized around the germline cell nuclei of the larvae and adults.     

Cytokinin Production by Tomato Root: Occurrence of Cytokinins in Staled Medium of Root Culture

Cytokinins were released into the medium by cultures of excised tomato (Lycopersicon esculentum Mill.) root tips. A large portion was directly released from the proximal cut-end of the roots. The most active substance was found to co-chromatograph with zeatin riboside in both paper and Sephadex column chromatographies. The cytokinin activity after 7 days of growth was found about eight times higher in the medium as compared with that in the root tissues. When freshly excised root tips were subcultured throughout eight passages, the accumulation of cytokinin in the medium of each passage was approximately the same. These results show that the root tip is a main site of cytokinin synthesis.