Seasonal root growth in the arctic tussock tundra

Summary The quantity of growing root tips per unit of soil volume was analyzed in a central Alaskan tussock tundra site. By June 10, the aboveground fraction of the vegetation had initiated the flush of spring growth and flowering while less than 5 active root tips cm^-3 were found. By June 25 this value had increased to 30 root tips cm^-3. Similar values in July were followed by a complete cessation of root growth after the first week of August. By then, leaf senescence had also become visible. In the spring, low root temperatures were responsible for the time lag between shoot growth initiation and the beginning of root growth. In early August, root growth stopped in spite of adequate soil temperatures and accumulated carbohydrate for root growth. It is proposed that use of reserve carbohydrate for root growth in August would compromise the flush of spring growth in the following year.     

The effects of monocyte-conditioned medium and interleukin 1 on the synthesis of collagenous and non-collagenous proteins by mouse bone and human bone cells in vitro

Cultural adherent human mononuclear cells produce factor(s) which stimulate the release of calcium from new-born mouse calvaria in organ culture. This stimulation of bone resorption is accompanied by an inhibition of the incorporation of [³H]proline into collagen which is independent of increased prostaglandin production by the bone. When human osteoblast-like cells are treated with conditioned medium from human mononuclear cells, collagen accounts for a decreased proportion of the protein synthesised. This effect on matrix synthesis is not accompanied by an inhibitory action of the monocyte-conditioned medium preparations on net cell proliferation. In human osteoblast-like cell cultures, partially purified human interleukin 1 also inhibits the production of the bone-specific protein osteocalcin in a dose-dependent fashion. These observations are consistent with the hypothesis that products of human monocytes similar to, or identical with, human interleukin 1 may be important regulators of bone metabolism and may contribute to the bone loss seen in diseases such as chronic rheumatoid arthritis.     

Optical probe responses on sarcoplasmic reticulum. Merocyanine and oxonol dyes.

The fluorescence and absorbance of merocyanine 540 in suspensions of skeletal muscle microsomes is altered by the binding of Ca2+ and other cations to the membrane. The order of effectiveness of various cations in causing this effect is La greater than Ca congruent to Mg greater than K. Competition between Ca2+, Mg2+, and K+ suggests the involvement of low affinity, relatively nonspecific cation binding sites in the process. Changes in the fluorescence and absorbance of merocyanine were also observed during ATP-dependent accumulation of calcium into sarcoplasmic reticulum. These changes are satisfactorily explained by the binding of accumulated calcium to binding sites on the interior of sarcoplasmic reticulum membrane. The small absorbance response of the oxonol dye bis[1,3-dibutylbarbituric acid-(5)]trimethinoxonol to Ca2+ and ATP is qualitatively similar to that of merocyanine 540 and can be readily explained by the same mechanism. We have found no clear evidence that any of the observed dye responses are due to changes in the diffusion potential across the sarcoplasmic reticulum membrane generated by an electrogenic transport mechanism. The possibility is considered that merocyanine and oxonol dyes respond to changes in electrostatic surface potential caused by the binding of cations.