GROWTH OF MAIZE SEEDLINGS AS AFFECTED BY GLUCOKININ AND INSULIN

1. Solutions of glucokinin and insulin, particularly those from which the easily dialyzable substances had been removed, increased the growth of roots and tops of young maize seedlings, as shown by comparisons with untreated seedlings grown in distilled water. 2. Strong solutions of crude glucokinin or of crude insulin repressed growth. 3. Seedlings from which the tips of the primary roots had been removed just before placing the plants in the test solutions made greater gains in both top growth and root growth than seedlings with uncut roots treated with solutions of the same strength. Control experiments showed that this difference in growth was not the result of cutting the roots, and that crude glucokinin and crude insulin contained several substances some of which were more readily absorbed by the plant than others. 4. Purification of crude glucokinin and crude insulin by dialysis showed that the residue of relatively non-dialyzable substance was the growth-promoting fraction. 5. The dialysate of crude glucokinin contained at least three types of material, one of which repressed growth. 6. Ammonium sulfate, one of the possible impurities of glucokinin, repressed the growth of seedlings but did not produce the other changes in metabolism shown by seedlings treated with dialysate of onion glucokinin. 7. The endosperm of plants treated with growth-promoting solutions of purified insulin did not lose weight as rapidly as the endosperms of untreated plants, indicating that the treated plants made their greater gains in growth by more efficient utilization of the endosperm, or as a result of greater photosynthetic activity, or by a combination of these. 8. Experiments with albino seedlings suggested that the greater gain in weight made by plants treated with insulin was the result in part of increased photosynthetic activity.     

Contractility of rat testicular seminiferous tubules in vitro: Prostaglandin F1α and indomethacin

The frequency of spontaneous in vitro contractions of seminiferous tubules of the rat appeared to be increased in a dose-dependent manner by prostaglandin F_1α. PGF_1α treatment increased the tonus of the smooth muscle cells in the wall of the tubules as indicated by a reduction in the diameter of the tubules. When the tubules were rinsed successively with fresh Tyrode's solution, the contractile frequency was diminished. Returning the original bathing medium to the tubules restored their contractile frequency, as did treatment of the rinsed tubules with PGF_1α (10⁻⁷ M). Pre-injecting the rats with indomethacin tended to reduce the contractile frequency of the extirpated tubules. Treating the tubules with a solution of indomethacin for 90 min. in vitro was more effective than pretreatment in vivo in reducing contractile frequency, but a combination of these two procedures produced the greatest inhibition. PGF_1α restored the contractile frequency of the indomethacin-treated tubules. Our results indicate that PGs modulate the in vitro contractility of the tubules.     

Mortality and birth weight in Philadelphia Blacks: an example of stabilizing selection

It has been suggested that as a result of the action of natural selection the mean value of any biological measurement would be the most normal value and associated with the most favorable survival rate. Selection is said to be stabilizing (or normalizing or balancing) if individuals with intermediate values for a given quantitative trait have the highest fitness. Birth weight is perhaps the most clear-cut example of a human character subject to stabilizing selection. This paper presents the distribution of birth weights among 8382 Philadelphia Black infants and the rate of perinatal mortality for the birth weight classes. Using these data, several analyses of stabilizing selection are made. The data were taken from the Collaborative Study on Cerebral Palsy, Mental Retardation, and other Neurological and Sensory Disorders of Infancy and Childhood.