Structure of rapidly frozen gap junctions

The structure of gap junctions in the rabbit ciliary epithelium, corneal endothelium, and mouse stomach and liver was studied with the freeze-fracturing technique after rapid freezing to near 4 degrees K from the living state. In the ciliary epithelium, the connexons were randomly distributed, separated by smooth membrane matrix. In the corneal endothelium, both random and crystalline arrangements of the connexons were observed. In the stomach and liver, the connexons were packed but not crystalline. Experimental anoxia or lowered pH caused crystallization of the connexons within 20-30 min. In the ciliary epithelium, the effects of prolonged anoxia or low pH could not be reversed . In addition, invaginated or annular gap junctions increased in number, but their connexons were usually distributed at random. Rapid freezing thus demonstrates that gap junctions of different tissues are highly pleiomorphic in the living state, and this may explain their variations in structure after chemical fixation. The slow time-course and irreversibility of the morphological changes induced by prolonged anoxia or low pH suggest that connexon crystallization may be a long-term consequence rather than the morphological correlate of the switch to high resistance.     

Plantlet formation from isolated protoplasts ofSolanum melongena L.

Summary Mesophyll protoplasts were isolated from axenic shoot cultures ofSolanum melongena by the one-step enzymatic method. Of the different media employed for the culture of protoplasts, a medium modified fromKao andMichayluk (1975) supported sustained mitotic cycles most effectively. Organogenesis from protoplast-derived callus was achieved on transfer toMurashige andSkoog'S (1962) medium supplemented with an appropriate auxin and a cytokinin.     

Alteration in the Geotropic Response of Allium Seedlings by Growth Regulators

Indoleacetic acid (1AA) brings about a striking alteration in the normal geotropic response in the seedlings of onion and several other species of Allium. The seedlings which are normally positively geotropic, become ageotropic. Besides IAA several other auxins like IBA, NAA and 2,4-D also showed a similar response. An anti-auxin like triiodobenzoic acid (TIBA) enhanced the auxin-effect instead of reversing it. A marked enhancement of the auxin-effect was also brought about when sucrose (in the culture medium) was replaced by L-arabinose which appeared to act synergistically with the auxin.     

Simultaneous utilization of glucose and sucrose by thermophilic fungi.

The utilization of mixtures of glucose and sucrose at nonlimiting concentrations was studied in batch cultures of two common thermophilic fungi, Thermomyces lanuginosus and Penicilium duponti. The sucrose-utilizing enzymes (sucrose permease and invertase) in both fungi were inducible. Both sugars were used concurrently, regardless of their relative proportion in the mixture. At the optimal growth temperature (50 degrees C), T. lanuginosus utilized sucrose earlier than it did glucose, but at a suboptimal growth temperature (30 degrees C) the two sugars were utilized at nearly comparable rates. The coutilization of the two sugars was most likely possible because (i) invertase was insensitive to catabolite repression by glucose, (ii) the activity and affinity of the glucose transport system were lowered when sucrose was included in the growth medium, and (iii) the activity of the glucose uptake system was also subject to repression by high concentrations of glucose itself. The concurrent utilization of the available carbon sources by thermophilic fungi might be an adaptive strategy for opportunistic growth in nature under conditions of low nutrient availability and thermal fluctuations in the environment.     

The formation of a defective small subunit of the mitochondrial ribosomes in petite mutants of Saccharomyces cerevisiae

The involvement of mitochondrial protein synthesis in the assembly of the mitochondrial ribosomes was investigated by studying the extent to which the assembly process can proceed in petite mutants of Saccharomyces cerevisiae which lack mitochondrial protein synthetic activity due to the deletion of some tRNA genes and/or one of the rRNA genes on the mtDNA. Petite strains which retain the 15-S rRNA gene can synthesize this rRNA species, but do not contain any detectable amounts of the small mitochondrial ribosomal subunit. Instead, a ribonucleoparticle with a sedimentation coefficient of 30 S (instead of 37 S) was observed. This ribonucleoparticle contained all the small ribosomal subunit proteins with the exception of the var1 and three to five other proteins, which indicates that the 30-S ribonucleoparticle is related to the small mitochondrial ribosomal subunit (37 S). Reconstitution experiments using the 30-S particle and the large mitochondrial ribosomal subunit from a wild-type yeast strain indicate that the 30-S particle is not active in translating the artificial message poly(U). The large mitochondrial ribosomal subunit was present in petite strains retaining the 21-S rRNA gene. The petite 54-S subunit is biologically active in the translation of poly(U) when reconstituted with the small subunit (37 S) from a wild-type strain. The above results indicate that mitochondrial protein synthetic activity is essential for the assembly of the mature small ribosomal subunit, but not for the large subunit. Since the var1 protein is the only mitochondrial translation product known to date to be associated with the mitochondrial ribosomes, the results suggest that this protein is essential for the assembly of the mature small subunit.     

Melt solidification technique: Incorporation of higher wax content in ibuprofen beads

The purpose of this study was to achieve incorporation of a higher amount of wax during the preparation of ibuprofen beads by a melt solidification technique for better integrity and prolonged drug release by using a combination of waxes. A mixture of cetyl alcohol (CA) and palmitic acid (PA) was used to improve the matrix integrity and drug release. The effect of variables such as CA, PA, and speed of agitation were studied using 3³ factorial design. Yield, crushing strength, and drug release were analyzed using response surface methodology. The in vitro dissolution test did not show any significant improvement in the drug release. Scanning electron microscopy (SEM) showed that beads were spherical with a smooth surface, but after dissolution became rough and porous. Differential scanning calorimetry (DSC) studies showed that different solidification and erosion properties of waxes are responsible for the inability of waxes to retard drug release even at higher concentration.     

Aflatoxin content and number of fungi in poultry feedstuffs from Indonesia

The content of aflatoxin and associated fungi was determined in 56 samples, including 34 of corn, 10 of soybean meal, nine of rice bran and three of broken rice, collected from different poultry farms and poultry feedmills situated around Jakarta-Bogor, Indonesia.
Ninety-one per cent of the corn samples contained aflatoxins and the total concentration ranged from 22 to 6171 μ g/kg. With rice bran, 100% of the samples were positive for aflatoxin B₁, ranging from 36 to 71 μ g/kg. No aflatoxin was detected in samples of soybean meal or broken rice. All the samples were contaminated by several fungi (8 times 10³–5 times 10⁶cfu/g) and further identification was limited to Aspergillus flavus and A. parasiticus. The dominant species was A. flavus (2 times 10³–4 times 10⁶cfu/g in corn samples, 1·0 times 10³–1·0 times 10⁵cfu/g in soybean meal, 2 times 10⁴–4·4 times 10⁵cfu/g in rice bran and 2 times 10⁴–6 times 10⁴cfu/g in broken rice). Some of the corn samples also contained A. parasiticus (2 times 10³–9·5 times 10⁴cfu/g).