The use of P32 in studies on the uptake of phosphorus by plants

Summary A fertilizer experiment with calcium phosphates labelled with P³² was carried out in pots with barley as a test plant. By determining the ratio of P³² in fertilizer and plant phosphorus after more than 7 weeks the content of exchangeable phosphate in the soil could be calculated. The results of the calculation were independent of the amount of phosphate added providing it was soluble.     

The influence of ammonia in nutrient solution on growth and metabolism of cucumber plants

Summary Shoot yield of cucumber plants grown 18 days in nutrient solution with 0.06 mM NH₃ was decreased. Root yield was diminished at 0.09 mM NH₃ The ammonia treatment caused heavy chlorosis increasing with age of leaves. This chlorosis was not due to any nutrient deficiency. Ammonia also influenced the morphology of roots. They were clearly shorter caused by a much smaller size of root cells.The decrease of yield was linked to a reduction of assimilation occurring not only after a long influence of ammonia lasting 14 days, but also within one hour after starting the NH₃ treatment. The decline of assimilation was probably caused by a higher resistance of stomata against CO₂ influx in leaf tissue as can be concluded from the observation that transpiration was decreased in the same way as assimilation.The effect of ammonia in nutrient solution could also be due to the occurrence of higher NH₃ concentrations in leaf tissue, because both, pH of plant press sap as well as NH₄ concentration of plant tissue, were increased.Furthermore, it is shown that the nitrate content of plant tissue was diminished by ammonia whereas ammonium and amide content were raised. Regulation of nitrate uptake of plants by means of ammonium and amide content of tissue is discussed.     

Membrane lipids composition and metabolism during early embryonic development. Phospholipid subcellular distribution and 32P labeling

Phospholipid composition and 32P metabolism were studied in oocytes and early developing embryos of the toad, Bufo arenarum, Hensel. The content and distribution of phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, phosphatidic acid, sphingomyelin, phosphatidylserine, and diphosphatidylglycerol in embryos, whole oocytes, and the subcellular fractions of both were determined. Phosphatidylcholine and phosphatidylethanolamine were the major constituents of yolk platelet. Diphosphatidylglycerol was confined to the mitochondrial fraction, where it represented about 7% of the total phosphoacylglycerols. Relatively large amounts of sphingomyelin were found in microsomal and postmicrosomal supernatants. After in vivo labeling with 32P, the early development of individual phospholipids in subcellular fractions and in whole eggs was followed. The greatest uptake was found in mitochondrial and yolk platelet fractions. A steady increase in the amount of 32P present in phosphatidylethanolamine, phosphatidylcholine, and phosphatidylinositol was seen in the whole embryo from oocyte to late gastrula stage and in all subcellular fractions. Phosphatidic acid exhibited a slight decrease in specific activity, except in the yolk platelet fraction. This high 32P incorporation would indicate a rapid and uneven polar headgroup turnover determined by phospholipid class and subcellular fraction. At the same time, the phospholipid content of the subcellular fractions studied remained unchanged during early embryogenesis. Moreover, 32P was actively incorporated into the individual phospholipids in the absence of measurable net synthesis.     

P32 distribution in phosphorus fractions of phosphorus-sensitive and -tolerant soybeans

Summary P³² incorporation into various phosphorylated compounds of roots, stems, and leaves was studied with P-sensitive (Clark) and P-tolerant (L9) varieties of soybeans. With increasing P concentration in the pretreatment solution, more P³² was incorporated into the inorganic phosphate fraction, mainly in which form P seemed to be transported from roots to leaves. P³² percentage of inorganic phosphate also showed a continuous decrease with absorption time. The rate of phosphorylation, as manifested by the ratio of P³² percentage or specific activities of the organic acid-soluble P to that of inorganic-P, was higher with the P-tolerant variety than with the P-sensitive one. The rate of RNA synthesis also seemed to be higher with the tolerant variety. Paper No. 7082, Scientific Journal Series, Minnesota Agricultural Experiment Station.     

Effect of short-term geo-stimulation on the distribution of32P in decapitated pea seedlings

Three-leaf pea (Pisum sativum L. cv. ‘Alaska’) seedlings were oriented horizontally and³²P was applied to leaf-2 for 6 h period, at the end of which the distribution of isotopes in the seedlings was determined. It was found that (i) isotope accumulation in the apices of the vertical and horizontal seedlings remained almost the same; (ii) on decapitation almost all the isotopes in the apex diverted to the roots in the vertical seedlings; (iii) among the horizontal seedlings³²P was retained in the hanging treated leaf and the rest moved to the roots via shoots; (iv) the dry weight of the hanging treated leaf was slightly greater than the above-axis one; (v) the position of buds on the axis had no effect on the initial³²P accumulation in them, however, a trend of greater isotope accumulation was noted in the above-axis basal buds; (vi) geo.stimulation had no effect on the total dry weight of the seedlings; and (vii) in geo-stimulated seedlings decrease in the dry weights of shoots and its concomittant increase in roots was primarily the result of the movement of substances.     

The uptake and metabolism of [32P]pyrophosphate by mouse calvaria in vitro

In order to study the uptake and metabolism of PP(i) by bone, (32)PP(i) was added to the medium surrounding explanted mouse calvaria maintained in organ culture. Most of the PP(i) was hydrolysed during incubation, but there was a measurable entry of intact PP(i) into bone. When (32)P(i) was added to the medium, synthesis of PP(i) and organic phosphates from P(i) was observed in bone. There was no detectable passage of PP(i) from bone into the medium. These results are discussed in terms of two models of pyrophosphate hydrolysis and exchange. Some quantitative estimates about the fate of PP(i) in bone were made.     

The distribution of 32P in ribonucleic acid from nucleate and anucleate half cells of Amoeba proteus

Nucleate and anucleate half cells of Amoeba proteus were labelled with [³²P]orthophosphate and the distribution of ³²P among the labelled nucleotides was examined. Both nucleate and anucleate half cells were capable of incorporating orthophosphate into RNA. The anucleate half cell, however, incorporated ³²P at a slower rate than did the nucleate half cell and there was a diminution in the relative rate of ³²P incorporation into the anucleate half cell with time after enucleation. Irrespective of the rate of ³²P incorporation the distribution of ³²P label among the nucleotides of RNA following alkaline degradation was not significantly different between the ribonucleotides in anucleate and nucleate half cells.Several methods of RNA preparation demonstrated that the orthophosphate incorporation was in fact attributable to a polyribonucleotide. It was further shown that the radioactivity was primarily associated with 2′,3′-nucleotides following alkaline degradation of the labelled RNA, ruling out the possibility of a nucleotide-binding phenomenon. Filtration experiments suggested that the labelled cytoplasmic RNA was not bound to stable particles of a diameter greater than 50 mμ.Finally the half cells were fractionated by centrifugation and the distribution of ³²P in RNA of these fractions was analyzed. The fractionation experiments led us to conclude that RNA associated with the microsomes contains much of the label in nucleate and anucleate half cells. The RNA of the microsomes has similar distributions of ³²P in both nucleate and anucleate half cells and these distributions were similar to the total half-cell distributions of ³²P. The soluble fractions of both half cells had distinctly different distributions of ³²P from the microsomal fractions and the soluble fractions of nucleate and anucleate half cells were different from each other.     

Effects of fungicide timing on control of Rhynchosporium secalis in barley plants

Sprays of captafol, carbendazim, carbendazim + tridemorph + maneb, diclobutrazol, triadimefon or triadimefon + carbendazim all completely protected barley plants in a glasshouse against R. secalis for at least 30 days. However, their effectiveness in preventing disease development when applied after inoculation differed: triadimefon, traidimefon + carbendazim, or diclobutrazol were the most effective, completely preventing symptom development when applied up to 5 days after inoculation to plants grown above 16 °C, and up to 8 days below 8 °C. All the fungicides decreased the number of viable conidia produced by leaf blotch lesions, and when applied to infected plants at G. S. 30, greatly decreased the upward spread of the disease under simulated rain conditions; the most effective fungicides in these respects were triadimefon and triadimefon + carbendazim. The above fungicides and fungicide mixtures, together with the recently introduced materials fenpropimorph and propiconazole were applied to diseased winter barley crops in winter or in spring. All treatments decreased leaf blotch development and increased yields. In most cases, a winter application was more effective than spring applications, particularly if applied in mid-November. The most effective fungicides were triadimefon and propiconazole. The field trials data fitted well with the predictions of performance indicated by the glasshouse investigations.     

Effects of secretagogues on [32P]phosphatidylinositol 4,5-bisphosphate metabolism in the exocrine pancreas.

Experiments were carried out to assess the effects of secretagogues on the polyphosphoinositides phosphatidylinositol 4-phosphate (PtdIns4P) and phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] on preparations of exocrine pancreas in vitro. Carbachol and caerulein provoked a rapid (less than 1 min) breakdown of 15-20% of [32P]PtdIns(4,5)P2 in isolated pancreatic acini, but did not affect [32P]PtdIns4P. In contrast, the Ca2+ ionophore ionomycin had no immediate effect on the levels of either inositide but caused a parallel fall in both lipids after 5-10 min. A similar decrease in [32P]PtdIns(4,5)P2 due to carbachol was obtained with isolated acini and isolated cells, despite the fact that the secretory response of isolated cells was considerably less than that of isolated acini. Loss of [32P]PtdIns(4,5)P2 elicited by carbachol or caerulein was unaffected either by the addition of EGTA in excess of extracellular Ca2+ or when a protocol was employed that eliminated caerulein-induced intracellular Ca2+-release. These results suggest that agonist-induced PtdIns(4,5)P2 breakdown in the exocrine pancreas may be an early step in the stimulus-response coupling pathway and also suggest that this breakdown is not dependent on Ca2+-mobilization.