The Cell Cycle and Cell Population Kinetics in the Programmed Cell Death in the Limb-Buds of Normal and 5-Bromodeoxyuridine- Treated Chick Embryos

The cell cycle and cell population kinetics have been analyzed in the interdigital regions of chick limb-buds during the course of programmed cell death both in normal and the 5-bromodeoxyuridine (BrdU)-treated embryos. Our previous study has shown that a single administration of BrdU at day 6 1/3 inhibited the programmed cell death occurring in normal development of limb-buds.
Pulse- as well as continuous labelings with tritiated thymidine (³H-TdR) were used. The results obtained from the analyses made on both normal and experimental embryos have demonstrated the presence of a particular DNA-synthetic period, around day 6 1/3, closely related to the programmed death occurring on day 7 1/3. In normal embryos, new cell populations, which did not belong to any phases of normal cell cycle, made their appearances in the process of programmed cell death. A possible correlation between programmed cell death and the cell cycle has been discussed in relation to the morphogenesis of limbs in both normal and BrdU-treated embryos.     

The Effect of Hydrocortisone on the Epidermal Proliferation in an Organ Culture of Chick Embryonic Skin

Hydrocortisone is regarded as an initiator of keratinization in embryonic skin. The present investigation dealt with the effect of hydrocortisone on the proliferation of epidermal cells during early development: Cell kinetic analyses using ³H-thymidine autoradiography were applied to a skin organ culture prepared from a 13-day chick embryo.
Hydrocortisone at a concentration between 0.01 and 1.0 μg/ml was effective in initiating a morphological change leading to the epidermal keratinization in vitro and caused a marked decrease in the mitotic and labeling indices of epidermal basal cells, the decrease being maximum at 2 days of culture previous to the morphological change.
During continuous labeling with ³H-thymidine, the number of labeled basal cells reached 100% within 2 days in the control and 4 days in the culture treated with hydrocortisone. This confirmed that the growth fraction of epidermal basal cells was 1.0 even after the administration of hydrocortisone.
The duration of each cell cycle phase at 2 days of culture was determined by percent labeled mitoses and double-labeling analyses. It was concluded that hydrocortisone extended the generation time of epidermal basal cells at this time point about three fold over the control. This extension was mainly due to the elongation of the G ₁ phase.     

Effects of NO2 and O3 Alone or in Combination on Kidney Bean Plants (Phaseolus vulgaris L.): Growth, Partitioning of Assimilates and Root Activities

Ten-day old kidney bean plants (Phaseolus vulgaris L. cv. Shin-edogawa)were exposed to 2.0 and 4–0 parts 10^–6 NO2, and0.1, 0.2, and 0.4 parts 10^–6 O3 alone or in combinationfor 2, 4, and 7 d. The effects of these air pollutants wereexamined with respect to the growth, partitioning of assimilates,nitrogen uptake, soluble sugar content, and root respiration. Decreased dry matter production was significant with all treatmentsexcept 2.0 parts 10^–6 NO₂ and 0.1 parts 10^–6 O₃.Exposure to mixtures of the gases produced more severe suppressionof growth than exposure to the single gases. Root/shoot ratiowas significantly lowered at 7 d by the gas treatments otherthan 2.0 parts 10^–6 NO₂ and 0.1 parts 10^–6 O₃. Thetotal nitrogen content of plants was increased by all treatments;the higher percent of nitrogen found with O₃ exposure will resultfrom the growth retardation which increases the concentrationof nitrogen in the plants because the absorption of nitrogenby roots was unaffected. The combination of O₃ with NO₂ significantlydecreased the assimilation of NO₂ by the plants. The concentration of soluble sugars in roots was decreased bythe gas treatments. There was a strong positive correlationbetween soluble sugar content and dry weight of the roots harvestedat 7 d. Root respiration was relatively unchanged until 5 dand then decreased significantly at 7 d by 2.0 parts 10^–6NO₂ and 0–2 parts 10^–6 O₃. Retarded growth of theroots and the decreased root respiration may be due to diminishedtranslocation of sugars from leaves to roots caused by exposureto air pollutants. The uptake of soil nitrogen was not closelyrelated with root respiration in the case of O₃ exposure. Key words: NO₂, O₃, Phaseolus vulgaris, Growth, Sugars, Root respiration     

Studies on chloroplast development in Chlamydomonas reinhardtii I. Effect of brief illumination on chlorophyll synthesis

When dark grown cells of Chlamydomonas reinhardtii y-1 mutantwere exposed to continuous light, an immediate transformationof small amounts of protochlorophyll(ide), which had been presentin the dark grown cells, to chlorophyll was observed. Afterthis, there was a slow accumulation of chlorophyll lasting for2.5-3 hr before the start of exponential synthesis. Initialaccumulation of chlorophyll was distinctly slower at a highlight intensity (13,000 lux) than it was at moderate intensitiesof light (2,000–5,000 lux). However, the exponential synthesisof chlorophyll started after the same 2.5–3 hr of illumination. A brief pre-illumination of cells followed by incubation indarkness was effective in promoting chlorophyll synthesis undersubsequent continuous illumination at high, as well as moderatelight intensities. Pretreatment alleviated retardation of theinitial chlorophyll accumulation by light of high intensity.The promoting effect of preillumination on chlorophyll synthesiswas sufficient, even when a light impulse as short as 10 secwas given. However, the effect was dependent on length of thedark period after the short pre-illumination. The full extentof this effect was observed when the dark period was about 2.5–3hr long. Further dark incubation gradually decreased the effect. On the basis of these findings, it is assumed that a factor(s)responsible for promotion of chlorophyll (or chloroplast) synthesisin the process of greening of dark grown cells is produced duringthe dark period after a brief pre-illumination, and that thefactor is turned over at a relatively fast rate. The possiblenature of the presumed factor is discussed in relation to chloroplastdevelopment. ¹Present address: Department of Biology, Faculty of Science,Kobe University, Nada-ku, Kobe, Japan. (Received August 18, 1970; )     

Function of the <Emphasis Type="Italic">rel</Emphasis> Gene in <Emphasis Type="Italic">Escherichia coli</Emphasis>

Sokawa et al. suggest that rel^- strains of Escherichia coli possess abnormal protein synthesizing machinery, which cannot carry out normal protein synthesis when the supply of amino-acids is limited.     

The relation between calcium and cell wall in growing rice leaf

The percentage of pectic substances in the cell wall of riceleaf decreased with the ageing of the leaf but other componentsin the cell wall changed little during leaf growth. Cell wallcomponents were not affected by a nutritional deficiency ofcalcium. At the beginning of the growth of rice leaf, calciumin the cell wall existed only in the pectic substance fractionboth in the calcium sufficient and deficient leaves. However,in the cell wall of the mature leaf, a considerable amount ofcalcium was found in the lignin fraction. The amount of calciumin this form was larger in calcium sufficient leaves than indeficient leaves. Calcium seems to occur in two forms in the cell wall, combinedwith pectic substances and with ligneous substances. This assumptionwas further supported by calcium distribution in enzymaticallydegradated fractions of the cell wall. Calcium seems to be combined with pectic substances by a strongerchemical bond than with the ligneous substances. ¹Present address: Tohoku Agricultural Experiment Station, Omagari,Akita.     

Effects of after-ripening and gibberellic acid on the thermoinduction of seed germination in Solarium melongena

Daily alternating temperatures or a short exposure to low orhigh temperatures were necessary for the germination of eggplantseeds at the initial stage of after-ripening. But requirementsbecame less strict with the progress of after-ripening, andafter 4 to 8 months of afterripening, germination occurred easilyboth at constant (20 and 25) and daily alternating temperatures(30 for 16hrs and then 20 for 8hrs). With further progress in after-ripening, however, daily alternatingtemperatures or a short exposure to low or high temperaturesbecame again indispensable for attaining a high percentage ofgermination. The progress of after-ripening was greatly influencedby the degree of seed ripening, that is, by the period beforethe seeds were sampled from fruits after anthesis (ripening). The effect of GA on the germination of egg plant seeds varieddepending on the concentration of GA, temperature and the degreeof maturity (ripening and after-ripening) of the seeds. (Received March 8, 1968; )     

EFFECT OF LIGHT ON THE CHLOROPHYLL FORMATION IN THE "GLUCOSE-BLEACHED" CELLS OF CHLORELLA PROTOTHECOIDES

1. Previous studies have shown that when Chlorella protothecoidesis grown in a medium rich in glucose and poor in nitrogen source(urea), apparently chlorophyll-less cells with profoundly degeneratedplastids—referred to as "glucose-bleached cells—areproduced either in the light or in darkness. When the glucose-bleachedcells are incubated in a medium enriched with the nitrogen sourcebut without added glucose, an active formation of chlorophylloccurs after a certain lag period under illumination, whilein darkness a very small amount of chlorophyll is formed atabout the same time as in the light. The stimulating effectof light on the chlorophyll formation is not appreciably affectedwhen the photosynthetic CO₂-fixation of greening algal cellsis blocked by the addition of CMU. In the present study, itwas further found that the light-enhanced chlorophyll formationproceeds, although at a somewhat lower rate, under aerationof CO₂-free air. All the experiments in this work were doneunder these non-photosynthetic conditions to exclude any influenceof photosynthates.
2. The effect of light (from daylight fluorescentlamps) on thechlorophyll formation in the glucose-bleachedalgal cells wassaturating at about 1,000 lux. Blue light wasfound to be mosteffective; yellow, green and red light followingin the orderof decreasing effectiveness.
3. When the bleachedalgal cells were illuminated for a short periodin the lag phaseof chlorophyll formation and subsequently incubatedin darkness,there occurred an appreciable enhancement of chlorophyllformationin the dark. When the short illumination was appliedat differenttimes of the lag phase, the enhancement was inducedto almostthe same extent. But the longer the duration of theilluminationduring the lag phase, the greater was the enhancementof chlorophyllformation in the subsequent dark incubation.In such experimentsblue light was most effective and red lightleast, as it wasthe case in the experiments of continuous illumination.An intervenientillumination of the bleached cells at lowertemperatures orunder the atmosphere of N2 produced little orno enhancementof the chlorophyll formation in the subsequentdark incubation.
4. Based on these results, it was concluded that the light enhancementof chlorophyll formation in the glucose-bleached algal cellsis mediated by a non-chlorophyllous photoreceptor(s), absorbingmaximally blue and yellow light, and that a light-induced changeof the photoreceptor is immediately followed by a certain dark(temperaturedependent and aerobic) process(es) which is connected,directly or indirectly, to the chlorophyll synthesis.

(Received August 10, 1967; )     

The Presence of Tyrosinase and Related Proteins in Human Epidermis and Their Relationship to Melanin Type

The present study was carried out to investigate the abundance of tyrosinase and related proteins (TRP-1 and TRP-2) in human epidermis and their relationship to melanin type. Positive immunocytochemical staining was seen for all three proteins in epidermal melanocytes. For each protein the numbers of positively stained melanocytes were similar in all subjects studied irrespective of skin type. Following 5 daily suberythemal doses of UVB the melanocytes were larger, more dendritic, and increased in number. With TRP-1 and TRP-2 the increase in number in response to UVB was unrelated to skin type and, hence, with melanin type but with tyrosinase there was a much greater increase in skin types III and IV than in skin type I and II. The enhanced numbers of tyrosinase-positive melanocytes were accompanied by increased staining intensity, suggesting a greater expression of tyrosinase in the melanocytes from skin types III and IV compared with skin types I and II. This increase in tyrosinase could be related to the greater levels of eumelanin found in skin types III and IV, and this is in keeping with the view that higher levels of tyrosinase are associated with the production of eumelanin than phaeomelanin.