Localization of chitin in algal and fungal cell walls by light and electron microscopy.

Chitin was visualized in cell walls after hydrolysis with potassium hydroxide and subsequent postfixation of the deacetylated polysaccharide (chitosan) in OsO4. Areas of chitin deposition appeared dark borwn by light microscopy and electron dense in the electron microscope. With this method, the presence of chitin was demonstrated in the cell walls of the green alga Pithophora oedogonia (Montagne) Wittrock and two fungi, Ceratocystis ulmi Buism. (C. Moreau) and Blastocladiella emersonii Cantino and Hyatt. Most of the chitin in P. oedogonia ws found in the crosswall disk and small amounts occurred in the outer longitudinal walls. The septal disk of C. ulmi also contained chitin, but significant amounts were present in the inner and outer regions of longitudinal walls as well. Chitin was present throughout the walls of B. emersonii. Small amounts of chitin were not easily demonstrated by this technique, but removal of chitosan by exposure to dilute acetic acid before osmium fixation disrupted cell wall integrity, suggesting that small amounts of the structural polysaccharide had been removed.

beta-Glucan Synthetases of Plasma Membrane and Golgi Apparatus from Onion Stem.

Biosynthesis of glucans occurred in cell-free fractions isolated from onion stem (Allium cepa L.) enriched in either dictyosomes or plasma membranes. beta-1,3- and beta-1, 4-Glucans were synthesized in differing proportions and at different rates as the concentration of uridine diphosphoglucose or the proportion of dictyosomes or plasma membrane varied. At low (1.5 mum) UDP-glucose concentrations synthesis of alkali-insoluble glucan was correlated with abundance of dicytosomes; most of the substrate utilized by plasma membrane was for glycolipid synthesis. At high (1 mm) UDP-glucose concentration, the synthesis of alkali-insoluble glucans correlated with the abundance of plasma membrane. Substrate enhancement of beta-1, 4-glucan synthesis in dictyosome fractions was less than proportional to increases in substrate concentration. In contrast, beta-1, 4-glucan synthesis by plasma membrane was more than proportionately increased. At high substrate concentrations the synthesis of beta-1, 3-glucans predominated in both dictyosome and plasma membrane fractions. The results show that the capacity to synthesize glucans resides in both Golgi apparatus and plasma membranes of onion stem, but that the plasma membrane has the greatest capacity for synthesis of alkali-insoluble glucans at high UDP-glucose concentrations.

Enhancement of RNA polymerase activity by a factor released by auxin from plasma membrane.

Using recently developed techniques for solubilization of RNA polymerase from soybean chromatin and isolation of plasma membrane fractions from plants we can show the presence of a transcriptional factor specifically released from the membranes by auxin, 2,4-dichlorophenoxyacetic acid. The nonauxin, 3,5-dichlorophenoxyacetic acid, does not release the factor, but subsequent exposure of the membranes to auxin results in its release. Factor activity could not be demonstrated in fractions devoid of plasma membranes. The presence of a regulatory factor for RNA polymerase associated with plant plasma membrane and specifically released by auxin provides a mechanism whereby both rapid growth responses and delayed nuclear changes could be derived from a common auxin receptor site associated with plasma membrane.

N-1-napthylphthalamic-acid-binding activity of a plasma membrane-rich fraction from maize coleoptiles.

Plasma membrane-rich fractions were prepared from maize coleoptiles by low-shear homogenization and differential and sucrose-gradient centrifugation. Plasma membrane fragments were identified using a specific cytochemical stain based on phosphotungstic acid prepared in chromic acid. In a comparison of 10 different cell fractions of varying plasma membrane content, the N-1-napthylphthalamic-acid (NPA)-binding activity of the fractions was directly proportional to the content of plasma membrane. The NPA binding appears to be strong K M between 10(-8) and 10(-7) M) but non-covalent. NPA is known to inhibit auxin transport efficiently and quickly. Thus, the results are consistent with the localization of auxin transport sites at the plasma membrane of plant cells.

INTERCONNECTIONS BETWEEN CYTOPLASMIC MICROTUBULES AND BASAL BODIES OF TETRASPORALEAN PSEUDOCILIA.

Ultrastructural investigations of the development and structure of pseudocilia in Tetraspora lubrica and Schizochlamys sp. have disclosed interconnections between cytoptasmic microtubules and pseudo-cilial basal bodies heretofore unreported. Connections between elements of the basal bodies and the proximal connecting fibers are also described. The possible significance of the interconnections in correlating structure and function of these organelles is discussed.