SEED DORMANCY IN ISANTHUS BRACHIATUS (LABIATAE)

Seed dormancy and its ecological aspects were investigated in Isanthus brachiatus, a summer annual plant of limestone outcrops in southeastern United States. Freshly matured seeds are dormant and exhibit physiological polymorphism with respect to the conditions necessary to overcome dormancy. Fifteen to thirty-five percent of the seeds in a seed crop require only one stratification treatment and germinate the first spring following their dispersal in autumn. The remainder of the seeds require two, three, or more stratification treatments and thus do not germinate until after two, three, or more overwintering periods in the field. In those seeds that require more than one stratification treatment to overcome dormancy, the stratification periods must be separated by a “rest” period, which in nature corresponds to summer. The ecological significance of this type of seed dormancy mechanism in I. brachiatus is discussed in relation to adaptation to its habitat.     

Replacement of chilling requirement in seeds of Ruellia humilis by gibberellic acid

Summary Gibberellic acid (GA₃) completely replaced the chilling requirement of intact, dormant seeds of Ruellia humilis. At 30° 100 and 1000 mg/l completely replaced the chilling requirement, while in seeds germinated at 25° 100 mg/l GA₃ was ineffective but 1000 mg/l entirely replaced the after-ripening requirement at low temperature.This work was supported by an NIH Biomedical Sciences Support Grant to the University of Kentucky.     

Age of maturity and life span in herbaceous, polycarpic perennials

A review of age of maturity in herbaceous, polycarpic perennials found that the most common year of earliest maturity for wild and cultivated conditions was the second year of life, followed by the first year and then the third year. A comparison of age of maturity in wild and cultivated conditions for individual taxa confirmed the assumption that perennials generally do not mature sooner in the wild than in cultivation. This validated use of the pattern for maturity in cultivation (second year or later) against which to judge that for maturity in the wild. For plants of the same age of maturity, those with clonal growth had longer life spans than did those with little or no clonal growth. This difference in life span was more pronounced for plants of first- and second-year maturity than it was for those of later maturity. Herbaceous, polycarpic perennials in the wild generally were either short-lived with first-year maturity or long-lived with later maturity. These results were also true for nonclonal taxa only. For application to the real world, theoretical plant-population models must take these results into account.     

Standardization of tritium-sensitive film for quantitative autoradiography

A method for the calibration of plastic tritium standards for use with LKB Ultrofilm is described and validated. This method uses 12-microns cryostat slices of frozen liver which have been labeled with [3H]-formaldehyde and extracted with chloroform-methanol to remove lipids. Quantitative autoradiographic measurement of 3H radioactivity in the liver slices was underestimated by 35% when lipids were not extracted. Plastic sections impregnated with tritium were calibrated in terms of lipid-extracted, tissue-equivalent radioactivity content. Calibrated standard curves for these plastic standards were closely fit (p = 0.99) by second order polynomial equations for exposures of 1, 4, 7, 13, 28, and 104 days. The equations are generally useful for any plastic tritium standards.     

Correlates of SIV encephalitis in rhesus monkeys.

Necropsy records from 204 SIV-infected rhesus monkeys that had been inoculated with various strains of SIV and had died of SIV-related disease were reviewed. The relationship of SIV encephalitis with other parameters was evaluated. Encephalitis was associated with the presence of syncytial cells in other tissues, with persistent or early recurrent antigenemia, with a selective decrease in CD4+CD29+ blood lymphocytes, and with a shortened time of survival. Monkeys whose lymphocytes produced high levels of virus in culture also had a higher incidence of encephalitis. SIV was more frequently isolated from the brains of animals with encephalitis. No other clear associations were detected.