Photoperiodic requirements for flowering of the long-day duckweed, Lemna gibba G3

The min-LD estimation by the log. flower number vs. the cultureperiod curve provides a unique method of judging whether a givenphotoperiodic schedule is a long day or not for Lemna gibbaG3. Duckweeds in M-sucrose medium are exposed to the test scheduleat 26°C on either the first or second day of a continuouslight culture. If the min-LD (48 hr for control cultures) isnot changed, the inserted schedule is considered to have functionedas a long day. If, however, the min-LD is extended by 24 hr,the inserted schedule is judged to have functioned as a shortday. Examinations using this method of orderly designed light-darkschedules disclosed two critical phases in the light requirement;the initial and terminal 1 hr portions (designated the L1- andL2-phases) of the subjective day. Thus, a given day became along or short day when both the L1- and L2-phases were illuminatedor when either or both of the two phases were darkened. Thecritical daylength (11.5 hr) was just long enough to cover boththe L1- and L2-phases and the inductive phase (L2-phase) waslocated at the end of the subjective day. (Received June 9, 1975; )     

Growth of fetal rat gastro-intestinal epithelial cells is region-specifically controlled by growth factors and substrata in primary culture

The mammalian gastro-intestinal tract can be divided into three parts: esophagus and forestomach, glandular stomach, and intestine. We have previously reported primary culture systems for duodenal and glandular stomach epithelial cells in which the cells express tissue-specific marker proteins. However, the effects of growth factors and substrata on cell growth have not been fully investigated. In this study a primary culture system was established for forestomach epithelial cells and the mechanism by which the growth of gastro-intestinal epithelial cells is controlled in primary culture was examined. Forestomach, glandular stomach and duodenal epithelial cells proliferated rapidly in culture, increasing their numbers about 30-, 20-and 10-fold, respectively, in the first 5 days. Scanning electron microscopy showed that these three types of epithelial cells exhibited region-specific morphologies in culture. Results on the effects of growth factors and substrata on the proliferation of the epithelial cells revealed that the culture conditions required to induce maximal epithelial growth differed. Forestomach and glandular stomach epithelial cells required similar combinations of growth factors to proliferate, and these were quite different from those required for duodenal epithelial cells. Glandular stomach and duodenal epithelial cells could proliferate in a serum-free condition while forestomach epithelial cells could not. Thus, glandular stomach epithelial cells exhibited intermediate characteristics between forestomach and duodenal epithelial cells regarding their growth factor requirement. Glandular stomach and duodenal epithelial cells could not proliferate on plastic without collagen substrata while forestomach epithelial cells could. Duodenal epithelial cells proliferated faster on collagen gels than on collagen films, and forestomach epithelial cells faster on collagen films than on collagen gels. Glandular stomach epithelial cells proliferated similarly on both substrata. Thus again, glandular stomach epithelial cells exhibited intermediate characteristics between forestomach and duodenal epithelial cells regarding their substratum dependency. We conclude that the growth of gastro-intestinal epithelial cells is affected by both growth factors and substrata, and that glandular stomach epithelial cells exhibit intermediate characteristics between forestomach and duodenal epithelial cells in responding to these factors. These results suggest that a head-to-tail gradient exists in the gastro-intestinal tract which controls the epithelial response to growth factors and substrata.     

Studies on chlorophyllase of Chlorella protothecoides III. Purification and catalytic properties

Chlorophyllase was extracted from green cells of Chlorella protothecoidesby n-butanol treatment and purified 600-fold, as measured byenzyme activity in chlorophyll a hydrolysis, by ammonium sulfateprecipitation, chromatography on TEAE-cellulose column and gelfiltration with Sephadex G-200. At each purification step the following activities were compared:hydrolyses of chlorophyll a and methyl chlorophyllide a, methanolysisof chlorophyll a and transphythylation of methyl chlorophyllidea to chlorophyll a. The ratio of activities of chlorophyll a hydrolysis to chlorophylla methanolysis changed on purification and partial inactivationby heat, PCMB and phytol, as well as by varying the reactiontemperature, thus suggesting that the two reactions are notcatalyzed by a single enzyme. In contrast, the activity ratio of chlorophyll a methanolysisto transphytylation of methyl chlorophyllide a remained unaltered,indicating that these reactions can be forward and backwardreactions catalyzed by one enzyme. Results of kinetic studies also indicated that the chlorophyllaseof Chlorella protothecoides consists of at least two enzymes.One enzyme catalyzes chlorophyll a hydrolysis and the other,chlorophyll a methanolysis and the reverse reaction, transphytylationof methyl chlorophyllide a. (Received May 24, 1973; )     

Identification of the Region Required for Monomerization of the Rolling Circle Plasmid pKYM

Plasmid pKYM, isolated from the Gram-negative bacterium Shigellasonnei, is a small multicopy plasmid which replicates by a rollingcircle mechanism. The formation of multimers has been observedin a derivative of pKYM which lost a part of the origin region,and the loss of the monomerization mechanism would have ledto these multimers. By analyzing the constructs of several mutants,we discovered that a DNA region required for monomerizationwas present upstream of the RepK binding site in the replicationorigin. As either of the T-rich sequence or the inverted repeatsequences which were seen in that region have been lost in themultimer-forming plasmids, these sequences may be necessaryfor monomerization.