Metabolism of Glutamic Acid and N-Acetylglutamic Acid in Leaf Discs and Cell-free Extracts of Higher Plants

Radioactive glutamic acid and N-acetylglutamic acid have been incubated with normal and wilted leaf discs and radioactivity recovered in uncombined proline. The discs which had been placed under moisture stress incorporated considerably more label in uncombined proline than did normal discs.     

Analysis of Chlamydomonas reinhardtii histones and chromatin

Chromatin spreads made from isolated nuclei of the unicellular green alga Chlamydomonas reinhardtii show the beaded fibers typical of eukaryotic polynucleosomes. Micrococcal nuclease digestions confirmed the presence of nucleosomes with a repeat length of 189 base pairs, essentially the same as typical mammalian cells. Basic nuclear proteins extracted from isolated nuclei or chromatin with 1 M calcium chloride and 0.3 M hydrochloric acid are resolved into seven major components by electrophoresis in the presence of sodium dodecyl sulfate (SDS). These seven components were subjected to qualitative peptide mapping with V8 protease on SDS gels for comparison with the major histone components of calf thymus. Finally, the C. reinhardtii basic nuclear proteins were fractionated by reversed phase high performance liquid chromatography and their amino acid composition determined. From these studies, we conclude that C. reinhardtii has a full complement of the five histones with properties very similar to those of both higher animals and higher plants.     

Transfusion induces blood donor-specific suppressor cells

Transfusion with blood from the organ donor before transplantation can prolong the survival of renal allografts in the rat. To determine if the beneficial effect of preoperative blood transfusion was due to the generation of donor-specific suppressor cells, in vivo and in vitro adoptive transfer experiments were performed. Lymphoid cells were harvested from transfused and untreated rats. These cells were then either (1) transferred to lightly irradiated (200 R) syngeneic hosts which were subsequently challenged with a kidney allograft (in vivo assay) or (2) titrated as regulator cells into naive unidirectional MLC such that the regulator and responder populations were syngeneic. In the LEW-RT1 to DA-RT1av1 strain combination, the adoptive transfer of thoracic duct lymph (TDL) or lymph node (LN) cells (5 x 10(7) to 7.5 x 10(7) cells) from DA animals transfused with LEW blood, 7 days previously into syngeneic (DA), lightly irradiated (200 R) hosts resulted in the indefinite survival of LEW kidney allografts. The phenomenon was blood donor-specific and dose-dependent. In contrast the adoptive transfer of spleen cells (10(7) to 10(8] from blood transfused hosts 7 days after transfusion had no effect on renal allograft survival. In vitro the addition of LN or TDL regulator cells, harvested from DA rats transfused with LEW blood, to a unidirectional MLC (DA responders, LEW stimulators) resulted in a significant depression of the proliferative response when compared with the proliferation of these same cells without the addition of these regulator cells or with the addition of LN or TDL regulator cells from a DA rat transfused with third party (PVG-RT1c) blood. The depression of the proliferative response observed in vitro, was blood donor specific. When LN or TDL regulator cells from a DA rat transfused with PVG-RT1c blood were added to a unidirectional MLC between DA responders and PVG stimulators, a significant depression in the proliferative response was observed. These in vitro findings were confirmed in two other strain combinations (LEW-PVG, and DA-PVG). Thus a single blood transfusion results in the induction of donor-specific suppressor cells detectable both in vivo and in vitro 7 days after transfusion in some but not all lymphoid compartments.     

Transfer RNA Is the Source of Extracellular Isopentenyladenine in a Ti-Plasmidless Strain of Agrobacterium tumefaciens

Even in the absence of the classical Ti plasmid-encoded cytokinin biosynthetic genes ipt and tzs, Agrobacterium tumefaciens strains still release significant amounts of the cytokinin isopentenyladenine (iP) into the culture medium (R.W. Kaiss-Chapman and R.O. Morris [1977] Biochem Biophys Res Commun 76: 453-459). A potential source of the iP is isopentenylated transfer RNA (tRNA), which, in turn, is synthesized by the activity of tRNA:isopentenyltransferase encoded by the bacterial miaA gene. To determine whether secreted iP had its origin in isopentenylated tRNA, a miaA- deletion/insertion mutant was prepared and reconstructed in Agrobacterium tumefaciens in vivo. The mutant no longer possessed tRNA:isopentenylation activity and no longer released iP into the extracellular medium. Transfer RNA therefore makes a small but significant contribution to the total amount of cytokinin normally secreted by Agrobacterium strains. tRNA-mediated synthesis may also account for cytokinin production by other plant-associated bacteria, such as Rhizobia, that have been reported to secrete similarly low levels of nonhydroxylated cytokinins.