A rapid gravitational effect on the translocation of fluorescein in mung bean hypocotyl sections

Geotropic stimulation of excised stems of dark-grown mung bean seedlings (Vigna radiata L., Wilczek) results in a rapid increase in the movement of fluorescein in phloem cells of the hypocotyl. A significant effect is observed after subjecting stems to geotropic stimulation for 2.5 min. Maximum increase occurs after about 15 or more min of geotropic stimulation. The increase is confined to the lower side of the hypocotyl. Pretreatment with a 5x10^-4 M concentration of 2,4-dinitrophenol prevents the gravity-induced increase in fluorescein movement. It is suggested that the increased movement of fluorescein is due to the generation of a positive electrostatic charge in the plasma membrane of receptor cells by some unknown action of gravity on membrane molecules. The charge is presumed to be the causative factor that increases the movement of auxin and other negatively-charged substances into receptor cells.     

The effect of the antigen-induced splenic suppressor factor on the immune response to different antigens

Quick-frozen spleen of mice immunized with sheep red blood cells was homogenized and centrifuged. Supernatant was used as a source of suppressor factor (SF). It was shown that SF inhibited antibody immune response to thymus-dependent antigens and delayed hypersensitivity reaction. SF did not inhibit antibody formation to thymus-independent antigen. SF activity disappeared after its treatment with anti-Ig immunosorbent.     

The effect of the seasonal cycle on the splenic leukocyte functions in the turtle Mauremys caspica

The reptile immune system is strikingly affected by seasonal variations, which induce changes in the structure of the lymphoid organs and in the function of the leukocytes. The aim of this work is to study several functions of splenic leukocytes from the turtle Mauremys caspica along its seasonal cycle. The functions assayed were adherence to substrate, mobility directed to a chemoattractant gradient (chemotaxis), lymphoproliferative response to mitogens, antibody-dependent cellular cytotoxicity, and natural killer-like cell-mediated cytotoxicity. Splenic leukocytes showed a positive response in all the assays, and this response was similar to that of mammals. In regard to the effect of the seasonal cycle, we have observed in winter a low adherence to substratum and high chemotaxis and cytotoxic activity, whereas in spring, only lymphoproliferation induced by mitogens showed high values except with lipopolysaccharide, which did not induce any seasonal variation in proliferation percentages. In summer, a high chemotaxis and cytotoxicity were observed, while in autumn, adherence to substratum was increased, but chemotaxis, cytotoxicity, and proliferation were clearly diminished. Our results demonstrate that splenic leukocyte functions are affected by the seasonal cycle, which induces a different pattern of response depending on the function studied.