Biochemical alterations of cellular membranes in chilling-sensitive mung bean (Vigna radiata [L.] Wilczek) hypocotyls were invesfigated with reference to chilling injury. Reversible decreases in activities of tonoplast H+-ATPase and in vivo respiration became manifest within 24 hours of chilling when tissues suffered no permanent injury as assessed by electrolyte leakage and regrowth capacity. These changes were found to be the earliest cellular responses to chilling. A density-shift on a sucrose density gradient was observed in Golgi membranes early in the chilling treatment, suggesting that Golgi function and/or membrane biogenesis via the Golgi may have been altered upon chilling. After chilling more than 2 days, irreversible changes were generally produced in cellular membranes including the plasma membrane, endoplasmic reticulum, and mitochondria. Respiratory functions remained intact in mitochondria isolated from tissues prechilled for 24 hours, but were impaired after prechilling for 3 days. Given the important role of the tonoplast H+-ATPase in the active transport of ions and metabolites, the early decline in the tonoplast H+-ATPase activity may give rise to an alteration of the cytoplasmic environment and, consequently, trigger a series of degenerative reactions in the cells. uncertainty as to how the chill-induced physical changes in those membranes can be sequentially transduced into cell injury. Furthermore, there seems to be no specific reason to assume that those organelles are exclusive cellular sites for sensing low temperatures.In our earlier studies, using extremely chill-sensitive cultured cells (27), degeneration ofcell structures occurred within a short period of chilling, i.e., 6 to 12 h at 0°C. Partial dilation and microvesiculation of RER and other deteriorative changes were followed by marked morphological changes in the intramembranous particles on the tonoplast fracture faces. Furthermore, the chilled cells retained the capacity to grow after transfer to a warm temperature until the onset of the structural alteration in the tonoplast. It is assumed that chillinduced structural and functional deterioration in the tonoplasts is also involved in the earliest cellular events triggered by chilling. In the present study, we have attempted to analyze the biochemical changes in various cellular membranes, which take place during chilling in the cells in chill-sensitive mung bean seedlings. Special attention was paid to determining the earliest changes manifested in intact cells immediately upon chilling and to distinguish them from the secondarily transduced ones.Although a number of studies have been carried out to elucidate the mechanisms involved in chilling injury in plants, many problems remain to be explained. For a better understanding of the mechanisms, it is important to identify the cellular site(s) and the physical features of the primary reaction(s) sensing low temperatures and to determine the physiological transducers transmitted from the low temperature sensing reaction...
Staphylococcal protein A (SpA) is a cell-bound protein which has a high affinity for the Fc portion of immunoglobulins from various mammalian species (7), and many researchers have been using it as a useful tool in immunoglobulin-associated experiments. We have studied the mode of reaction between immunoglobulins and SpA molecules produced by mutants derived from the Cowan I strain which releases SpA into culture medium (10, 11). These soluble SpA molecules were assumed to have different valencies for the binding to immunoglobulins in proportion to their molecular weights. It was considered interesting to investigate the mode of binding of these SpA molecules to mammalian immunoglobulins by hemagglutination test which might reflect differences in the number of binding sites or steric structure of SpA molecules.The hemagglutination test with sheep erythrocytes (SRBC) sensitized with rabbit antiserum has been considered one of the most sensitive methods for the detection of soluble SpA (1, 4, 6,13,14). In the present communication we describe hemagglutination patterns of SRBC sensitized with antisera from several mammalian species by soluble SpA which has possibly two, three, or four binding sites to immunoglobulins in one molecule. We also propose a new hemagglutination test using SRBC sensitized with guinea pig antiserum, which is more sensitive and stable in detecting SpA activity than using SRBC sensitized with rabbit antiserum.The SpA molecules were purified from the culture supernatant of mutants (UV-2, LH-IV, UV-1, V-11, and V-21) by a column of human IgG-conjugated Sepharose CL 4B according to the procedure of Hjelm et al (5) with a slight modification. The mutants, UV-2, LH-IV, and UV-1, were isolated previously (11). For the present investigation, V-11 and V-21 were newly isolated by the cosedimentation technique from independent bacterial clones (9). As previously reported V-11 and V-21 (V type mutants) were easily distinguished from usual LH mutants on an agar plate containing dog serum because V type mutants develop vague halos compared with usual LH mutants. The molecular weights of UV-2, LH-IV, UV-1, V-11, and V-21 SpA molecules were estimated to be 41
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