Phorbol esters inhibit chondrogenesis in limb mesenchyme by mechanisms independent of PGE2 or cyclic AMP

Effects of the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) on chondrogenesis and concentrations of prostaglandin E₂ (PGE₂) and cyclic AMP (cAMP) were investigated in micromass cultures of chick limb mesenchyme derived from the distal tip of stage 25 limb buds. TPA completely inhibited Chondrogenesis during the first 4 days of culture; however, a few small cartilage nodules formed by day 6. Relative to control cultures, both PGE₂ and cAMP concentrations were altered by TPA treatment during the 6-day period of cell culture. Concentrations of both compounds increased in control cells during the first 24 h of culture and then declined during the remaining 5 days. In TPA-treated cells both PGE₂ and cAMP levels increased progressively during the 6 days of cell culture, each being elevated at day 6 by twofold over control cells. The results suggest the presence of regulatory pathways important in Chondrogenesis which occur independent of those initiated by PGE₂ and the cAMP system.     

Metabolism of cyclic AMP in isolated renal tubules: Effects of prostaglandins and parathyroid hormone

Concentrations of cyclic AMP (cAMP) were increased in isolated renal cortical tubules from hamsters by both parathyroid hormone (PTH) and prostaglandin E₁ (PGE₁) with maximal effects of PGE₁ being 6–8 fold greater than those of PTH during a 10 min period. However, cAMP concentrations in cells treated with 1-methyl-3-isobutylxanthine (MIX) were increased with maximal concentrations of either hormone to the same degree. Similar effects of both hormones were observed on adenylate cyclase activity in renal homogenates. Simultaneous addition of hormones produced changes in both cAMP concentrations in intact tubules as well as adenylate cyclase activity of homogenates which were not completely additive. Degradation of cAMP, estimated in intact tubules as the difference in cAMP levels in the presence and absence of MIX, was increased by both hormones, however, changes were 2–3 fold greater in tubules exposed to PTH than to PGE₁. Neither hormone directly altered cAMP phosphodiesterase (PDE) activity in either 30,000 x g supernatant or pellets from renal cortical homogenates.The results suggest that both hormones increase the production of cAMP in renal cortical tubules and may share a common target cell type in this response. Degradation of cAMP, however, is differentially effected by the two hormones, probably reflecting differences exerted on intracellular mechanisms regulating the enzymatic hydrolysis of cAMP.     

Comparative effects of cytosine arabinoside and a prostaglandin E2 antagonist, AH6809, on chondrogenesis in serum-free cultures of chick limb mesenchyme

The present study was designed to compare effects of an established inhibitor of cell proliferation and growth, cytosine arabinoside (Ara C), with that of a prostaglandin E2 (PGE2) antagonist, AH6809, on chondrogenesis in cultured mesenchyme derived from stage 25 chick limb buds. Continuous treatment of cell cultures with 10(-4) M AH6809 prevented completely the twofold increases in DNA content of control cultures which occurred between Day 1 and Day 5 of culture and also produced 90% inhibition of chondrogenesis occurring in control cultures during this same period. Treatment of cells with Ara C (0.1-0.5 microgram/ml) produced equivalent inhibition of DNA content during the same time period; however, chondrogenesis, as evaluated on Day 5 of cell culture, remained at approximately 90% of control cultures. These results indicate that the inhibitory effect of PGE2 receptor blockade on cell growth in these cultures cannot account for the potent inhibitory effects observed on differentiation of cartilage and provide further evidence in support of the notion that PGE2 plays an important initiating role in the process of chondrocyte differentiation within limb mesenchyme.     

Review of wheat improvement for waterlogging tolerance in Australia and India: the importance of anaerobiosis and element toxicities associated with different soils

Background and Aims

The lack of knowledge about key traits in field environments is a major constraint to germplasm improvement and crop management because waterlogging-prone environments are highly diverse and complex, and the mechanisms of tolerance to waterlogging include a large range of traits. A model is proposed that waterlogging tolerance is a product of tolerance to anaerobiosis and high microelement concentrations. This is further evaluated with the aim of prioritizing traits required for waterlogging tolerance of wheat in the field.

Methods

Waterlogging tolerance mechanisms of wheat are evaluated in a range of diverse environments through a review of past research in Australia and India; this includes selected soils and plant data, including plant growth under waterlogged and drained conditions in different environments. Measurements focus on changes in redox potential and concentrations of diverse elements in soils and plants during waterlogging.

Key Results

(a) Waterlogging tolerance of wheat in one location often does not relate to another, and (b) element toxicities are often a major constraint in waterlogged environments. Important element toxicities in different soils during waterlogging include Mn, Fe, Na, Al and B. This is the first time that Al and B toxicities have been indicated for wheat in waterlogged soils in India. These results support and extend the well-known interactions of salinity/Na and waterlogging/hypoxia tolerance.

Conclusions

Diverse element toxicities (or deficiencies) that are exacerbated during waterlogging are proposed as a major reason why waterlogging tolerance at one site is often not replicated at another. Recommendations for germplasm improvement for waterlogging tolerance include use of inductively coupled plasma analyses of soils and plants.Key words: Waterlogging, microelements, toxicity, redox potential, wheat, anaerobiosis

‘No grain is ever produced without water, but too much water tends to spoil the grain and inundation is as injurious to growth as dearth of water.’ Narada Smriti XI, 19; circa 3000 bc.‘Waterlogging’ is defined as a condition of the soil where excess water limits gas diffusion; while ‘waterlogging tolerance’ is defined as survival or the maintenance of high growth rates, biomass accumulation or grain yield under waterlogging relative to non waterlogged (usually drained soil) conditions (Setter and Waters, 2003).

     

The photosynthetic action spectrum of the bean plant

The photosynthetic action spectrum of the bean plant leaf, Phaseolus vulgaris L. (variety Red Kidney), has been determined with a diffraction grating illuminated by a 6500-watt xenon arc. An infrared CO₂ analyzer was used to determine the gross photosynthetic rate of the terminal leaflet of the first trifoliate leaf. The rate was measured as a function of the light intensity at steps of 12.5 nanometers which approximates the length of the leaflet used. Twenty-five curves between 400 and 700 nanometers were used to establish the action spectrum. All light curves were some linear function of the incident intensity, and all were extrapolated to zero. The action spectrum shows the following features. (a) there are two peaks (i.e., at about 670 and 630 nanometers) and a shoulder between 600 and 612 nanometers in the red region where the highest rate of photosynthesis is found. Lower peaks in descending order are found in the blue (at about 437 nanometers) and the green (at about 500 nanometers) regions. (b) There are two small minima at about 650 nanometers and between 470 and 480 nanometers, and a broad minimum is found between 540 and 530 nanometers. (c) The photosynthetic rate declines rapidly above 680 nanometers, reaching the lowest value at 700 nanometers. (d) At wave lengths below the blue maximum, the rate decreases progressively to 400 nanometers.     

Effects of prostaglandins on cyclic AMP levels in isolated cells from developing chick limbs

Effects of prostaglandins (PGs) on accumulation of cyclic AMP (cAMP) in the presence of a phosphodiesterase inhibitor were investigated in cells isolated from avian limb buds at various stages of development. Cells were responsive to PGE2 at the earliest stage investigated (stage 20-21) which was well in advance of specific cytodifferentiation of limb tissues. At three later stages (24-25; 26-28; 30-32), the responsiveness of cells isolated from the developing skeletal anlagen of the limb progressively increased coincident with the differentiation and maturation of the cartilage phenotype. Cells isolated from stage 26-28 cartilage rods were responsive also to prostacyclin (PGI2); however, the response produced was only about 50% of the response to an equivalent concentration of PGE2. Cells were not responsive to either PGF2 alpha or 6-keto PGF1 alpha, at concentrations of 30-33 micrograms/ml demonstrating a degree of specificity for PGE2 and PGI2. In the absence of the phosphodiesterase inhibitor, PGE2 increased cAMP accumulation two-fold over the controls and produced a concentration-dependent response between 0.3-30 micrograms/ml. The results demonstrate that PGs are capable of modulating cAMP levels of undifferentiated limb mesenchymal cells as well as embryonic cartilage cells and suggest a role for these compounds in limb chondrogenesis.     

Interactions between parathyroid hormone and prostaglandins on renal cortical cyclic AMP

Effects of parathyroid hormone (PTH) and several prostaglandins (PGs) on cyclic AMP (cAMP) metabolism were studied and compared in isolated renal cortical tubules from male hamsters. Both production and intracellular degradation of cAMP were increased by PTH and each of the PGs tested (PGE₂, PGE₁, PGI₂). Production of cAMP was increased to similar levels by maximal concentrations of PTH and each PG, however, degradation of cAMP was significantly higher in response to PTH than with any of the PGs. This difference in intracellular degradation of cAMP was responsible for the much higher concentrations of cAMP in renal cortical tubules exposed to PGs (PGE₁, PGE₂, PGI₂) than to PTH. Submaximal amounts of each PG produced additive increases in cAMP concentrations in the presence of maximal amounts of PTH. Additivity of the combined responses was lost, however, as the PGs concentrations reached their maximas. The results suggest that renal PGs (PGE₂ and PGI₂) may modulate the effects of PTH on cAMP concentrations in renal cortical tubules.