First Stages Of Growth Research Articles

Developmental Physiology of Sugar Beet: I. THE INFLUENCE OF LIGHT AND TEMPERATURE ON GROWTH

Sugar beet plants were grown for 12 weeks from emergence in growth rooms at temperatures of 10, 17, 24 and 31 °C and 20, 50, 80, and 110 cal visible radiation cm-2d-1, and the changes with time in their dry weight, leaf area, leaf numbers, and storage root sugar determined. The first stage of growth was dominated by the development of the shoot, but the storage root gradually assumed increasing importance and eventually grew at a faster rate and to a greater weight than the shoot. The relative growth rate and final yield of dry matter of the shoot were greatest at 24 °C and of the root between 17 and 24 °C. The relative rate of expansion and the final area of the leaf surface were also greatest at 24 °C, whilst the rates of production and of unfolding of leaves were greatest at about 17 °C. All these attributes were increased with increased radiation. Net assimilation rate increased almost proportionately with radiation and was not significantly affected by temperature.The relationships of total leaf area with plant dry weight, root dry weight with shoot dry weight, and total leaf number with plant dry weight were scarcely affected by changes in radiation, but were much influenced by temperature. Plants of the same dry weight generally had bigger roots and smaller areas of leaf surface as temperatures departed from 24 °C and had most leaves at 17 °C. Sugar concentrations in the storage root were greatest at 17 °C, but the total amount of sugar was about the same at 17 and 24 °C. The concentration of sugar in the storage root depended on root size.Thus, temperature affected both the rate and pattern of development, and radiation affected the rate but not the pattern of development.

Changes in dry weight, protein, deoxyribonucleic acid, ribonucleic acid and reserve and structural carbohydrate during the aerobic growth cycle of yeast.

1. Changes in dry weight, DNA, RNA, protein and reserve and structural carbohydrate were measured during the aerobic growth of yeast on 0.9% glucose in an aerobic synthetic medium. 2. After glucose had been consumed and during the growth of yeast on ethanol and acetate, the rate of formation of DNA remained about the same but the rate of increase of dry weight was greatly diminished. 3. During the second stage of growth the ratios dry weight/DNA, protein/DNA, RNA/DNA and carbohydrate/DNA decreased to about 30% of the corresponding values during the first stage of growth. 4. A higher fraction of the dry weight of the yeast cells could be accounted for by the reserve carbohydrate content of the cells during the second stage of growth. 5. By the end of the first stage of growth an increase in the reserve carbohydrate content of the cells was observed. Part of this reserve carbohydrate was consumed by the cells in the beginning of the second stage of growth. The possibility of adaptation of cells at the expense of their reserves is discussed.

The ecological genetics of growth in Drosophila 6. The genetic correlation between the duration of the larval period and body size in relation to larval diet.

1. The low but regular positive correlation between body-size and the duration of the larval period in populations ofD. melanogasterhas been studied by selecting for large size or shorter development time on aseptic defined diets deficient in RNA and comparing the results with parallel selection on unrestricted yeast diets or on media in which RNA is not a limiting factor.2. There is a striking contrast according to the nature of the diet during selection. On unrestricted diets and where RNA is adequate there is little or no evidence of correlation between the two characters, but on low RNA media there is a striking correlation whether selection is for large body size or shorter development time.3. This contrast is accounted for in terms of particular changes in larval growth which can be divided into a first stage of growth to a critical size in the early 3rd instar and a second stage thereafter. The duration of the first stage can be greatly prolonged by inadequate diet but the duration of the later stage appears to be virtually unaffected by such variation although the amount of growth and hence final body-size, may be drastically reduced. The different diets which lead to presence or absence of correlation have enabled selection either to extend the growing period, so that the critical stage is reached later at a larger larval size, or to accelerate the growth rate in the later stage.4. Variation in the final stage of growth predominates on unrestricted diets and is responsible for the greater part of the variation in body size in unselected populations. Stabilization of body-size about an intermediate optimum refers especially to growth in this later stage.5. Lines selected for fast development on low RNA media are especially sensitive to minor nutritional variation. Probably only under rather special conditions is it possible to shorten the duration of the larval period and this is compatible with the importance of development time in fitness generally.6. There is evidence that the restriction of early growth, in the 2nd instar, reduces the size of the 3rd instar mouth-parts. Such reduction is correlated with changes in adult size probably because smaller mouth-parts restrict food intake.7. The pattern of larval growth suggests a flexible system which can be adjusted to different ecological conditions since the same body-size can be attained by adjusting the amount of growth effected before or after the critical stage. Differ ences in this respect will involve characteristic differences in reaction to environ mental variation and particular nutritional conditions are likely to influence the way in which adaptive changes are realized.

Acides nucléiques et phosphatases au cours de phénomènes de croissance provoqués par l'oestradiol et la prolactine

The considerable synthesis of proteins occuring in the vagina and uterus of castrated Mice as a result of oestradiol injection, is accompanied by an accumulation of ribonucleic acid and alkaline phosphomonoesterase in these organs. The equally rapid protein synthesis in the mucosa of the gizzard of pigeons treated with prolactin is accompanied by the first phenomenon only; the amount of alkaline phosphomonoesterase present remains very low during the whole process. Pancreas also contains but little alkaline phosphomonoesterase although a very active synthesis of proteins takes place in this organ. There is a constant relation between the amounts of proteins and ribonucleic acid formed during the first stages of growth. No such relation exists for desoxyribosenucleic acid. The accumulation of alkaline phosphomonoesterase in growing vagina and uterus might bear relation to the formation of fibrous proteins that are not synthesised by the gizzard gland or pancreas.

The production of a hemolytic substance in young liquid cultures of Cl. botulinum.

A clear zone of hemolysis is usually noted around each colony of Cl. botulinum when the organism is grown anaerobically on blood agar medium at 35° C. for 3 to 4 days. The blood cells within the hemolyzed area are entirely dissolved. Preliminary experiments to demonstrate the production of a soluble hemolytic substance in 24 hour sheep's serum veal broth cultures were unsuccessful. Subsequent tests indicate that the hemolytic substance is formed during the first stages of growth; it is in all probability destroyed by the 24th hour.The demonstration of the lytic substance depends on (1) the composition of the culture medium, (2) the age of the culture, and (3) the strain. Plain veal infusion broth is unfavorable for production of the lytic agent. The addition of small amounts of glucose or of 20 percent heated (56° C.—30°) sterile sheep's serum stimulates its formation. The first visible signs of growth in a 1 percent glucose veal broth medium, inoculated with spore forms (3-4 day beef heart cultures heate...

The Development of the Cape Species of Peripatus

The Development of the Cape Species of Peripatus