CAM-idling in Hoya carnosa (Asclepiadaceae)

In the leaf succulent Asclepiad Hoya carnosa (L.) R. Br., CAM photosynthesis occurred under well-watered conditions, as characterized by diurnal gas exchange and changes in titratable acidity. Following 10–12 days of severe water stress, the plants shifted from CAM to a modified CAM-idling mode of metabolism. CAM-idling was characterized by complete or almost complete stomatal closure accompanied by CAM-like diurnal changes in titratable acidity. H. carnosa plants maintained this CAM-idling mode of photosynthesis for at least 8 weeks. Upon reirrigation, the plants returned to the original CAM mode within 1 week. These results suggested that CAM-idling is a reversible, intermediate form of sustained metabolism which enables plant survival under conditions of extended drought.This work was supported in part by NSF Grant PCM 8200366 and in part by the Science and Education Administration of the United States Department of Agriculture under Competitive Grant 5901-0420-8-0018-0.     

Purified N-cadherin is a potent substrate for the rapid induction of neurite outgrowth

N-cadherin is the predominant mediator of calcium-dependent adhesion in the nervous system (Takeichi, M. 1988. Development (Camb.). 102: 639-655). Investigations using antibodies to block N-cadherin function (Bixby, J.L., R.L. Pratt, J. Lilien, and L.F. Reichardt. 1987. Proc. Natl. Acad. Sci. USA. 84:2555-2569; Bixby, J.L., J. Lilien, and L.F. Reichardt. 1988. J. Cell Biol. 107:353-362; Tomaselli, K.J., K.N. Neugebauer, J.L. Bixby, J. Lilien, and L.F. Reichardt. 1988. Neuron. 1:33-43) or transfection of the N-cadherin gene into heterologous cell lines (Matsunaga, M., K. Hatta, A. Nagafuchi, and M. Takeichi. 1988. Nature (Lond.). 334:62-64) have provided evidence that N-cadherin, alone or in combination with other molecules, can participate in the induction of neurite extension. We have developed an affinity purification procedure for the isolation of whole N-cadherin from chick brain and have used the isolated protein as a substrate for neurite outgrowth. N-cadherin promotes the rapid extension of neurites from chick ciliary ganglion neurons, which extend few or no neurites on adhesive but noninducing substrates such as polylysine, tissue culture plastic, and collagens. N-cadherin is extremely potent, more so than the L1 adhesion molecule, and comparable to the extracellular matrix protein laminin. Compared to laminin, however. N-cadherin promotes outgrowth from ciliary ganglion neurons extremely rapidly and with a distinct morphology. These results provide a direct demonstration that N-cadherin is sufficient to induce neurite outgrowth when substrate bound and suggest that the mechanism(s) involved may differ from that induced by laminin.     

Insulin suppresses hepatitis B surface antigen expression in human hepatoma cells

The human hepatoma Hep3B cells contain integrated hepatitis B viral genome and continually secret hepatitis B surface antigen (HBsAg). The production of HBsAg (but not alpha-fetoprotein) was suppressed by addition of low concentrations (0.1-1 nM) of insulin into serum-free medium. In addition, the suppression of HBsAg production by insulin was paralleled with the decrease in HBsAg mRNA abundance. Insulin also cause a rapid rate of disappearance of HBsAg mRNA (t 1/2, 2 h) in Hep3B cells. The Hep3B cells carry specific receptor with high affinity for insulin (Kd = 1.8 nM). The receptor showed an insulin-dependent protein tyrosine kinase activity. The half-maximal insulin concentration for the activation of the receptor kinase was about 5 nM. Only very high concentrations of insulin-like growth factor I and human proinsulin can compete for the insulin receptor binding and suppress HBsAg production, this suggests that insulin may act through its receptor binding to suppress HBsAg expression in human hepatoma Hep3B cells.     

Phosphorus concentration in barley (Hordeum vulgare L.) seed: Influence on seedling growth and dry matter production

The effect of phosphorus (P) concentration in barley seed on seedling growth has not been much investigated. Consequently, two experiments were conducted in the greenhouse to determine the effect of P concentration in barley seed (Hordeum vulgare L., cv. Empress) on the seedlings grown in sand-filled boxes receiving a culture solution without P. Seeds were selected with three P concentrations: high-P (113.0 mmol P kg⁻¹), medium-P (80.7 mmol P kg⁻¹) and low-P (54.9 mmol P kg⁻¹). At 21 days after sowing, the shoot and root yield or shoot height was the least with seedlings from low-P seed. In the other experiment, high-P and low-P seeds were wetted with distilled water or with a solution of 25.8 cmol L⁻¹ of NaH₂PO₄ for 24 h, and then grown for 31 days. Solution P had been imbibed by seeds whether low or high in native P, but only the imbibed P held by low native P seed benefited seedling dry matter accumulation and shoot elongation. The lack of benefit from seed-imbibed P on seedlings grown from high-P barley seed was associated with low recovery of the imbibed P in those seedlings.     

Generation of hydroxyl radical by crocidolite asbestos is proportional to surface [Fe3+].

Differences among fibrous silicates to effect injury in biological systems have been postulated to reflect oxidant generation by structural iron within the crystal lattice of amphiboles. Iron is also coordinated to the surface of all silicates in concentrations which depend on the density of acidic functional groups. We tested the hypothesis that oxidant generation by crocidolite is proportional to surface-complexed iron rather than variance in the lattice concentrations of this transition metal. Surface iron was quantified after its reduction to Fe2+ and chelation by citrate. Thiobarbituric acid (TBA) reactive products and dihydroxybenzoic acid products of salicylate were employed as indices of nonspecific oxidant and hydroxyl radical generation, respectively. Surface iron, TBA reactive products, and dihydroxybenzoic acid products all diminished after pretreatment of crocidolite with the metal chelator deferoxamine in concentrations varying from 0 to 250 mM. Inclusion of deferoxamine in the reaction mixture provided similar results of diminishing both TBA reactive products and dihydroxybenzoic acid generation. We conclude that oxidant generation by crocidolite is proportional to surface concentrations of iron which can be chelated using deferoxamine. The design of synthetic fibers without health effects after exposure will likely necessitate decreasing the number of surface acidic functional groups to diminish the capacity to complex iron (i.e., minimize the percentage SiO2).     

Parametric study of diethyl phthalate biodegradation

Summary The effects of temperature, dissolved oxygen, and other environmental parameters under both aerobic and anaerobic conditions were investigated using one aerobic and one facultative strain isolated from wastewater treatment plant sludge. Among other results, we found that low dissolved oxygen levels and low temperatures decreased the rate of DEP degradation and the growth rate, and that the facultative strain was much less affected by the lower DO concentrations than the aerobic strain.     

农业生态系统中新物种引进的初步探讨

在现有的农业生态系统中,引进某些新物种,往往可以使整个系统的功能发生变化。如果新物种引进得当,则可产生良好的效果,系统功能得以改善,效益提高;反之,则会造成人力、物力、财力的损失,削弱系统的功能,甚至可能遗患无穷。因此,对农业生态系统中     

以淀粉珠为载体的亲和层析法分离纯化高温α淀粉酶

 以淀粉珠为载体的亲和层析法分离纯化高温α淀粉酶张学忠,宋伦,王群,吴晓霞,唐锌进（吉林大学酶工程国家重点实验室,长春１３００２３;南京师范大学生物系,南京２１００２４）金凤燮等人从酒曲中筛选出高产热稳定α淀粉酶的菌株,命名为Ｂａｃｉｌｌｕｓｓｐ－ＪＦ...     

Bi（Ⅲ）与金属硫蛋白作用性质研究

 Ｂｉ（Ⅲ）与金属硫蛋白作用性质研究张保林,黄辉,朱凌燕,岳晟,唐雯霞（南京大学配位化学研究所,配位化学国家重点实验室,南京２１００９３）如何降低顺铂或其它抗癌铂的毒性,一直是癌症化疗中的重要课题之一,最近研究发现预先给大鼠或肺癌病人服用铋盐,可以极大...