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Heterogeneous binding of high mobility group chromosomal proteins to nuclei 总被引:7,自引:5,他引:2 下载免费PDF全文
A dramatic difference is observed in the intracellular distribution of the high mobility group (HMG) proteins when chicken embryo fibroblasts are fractionated into nucleus and cytoplasm by either mass enucleation of cytochalasin-B-treated cells or by differential centrifugation of mechanically disrupted cells. Nuclei (karyoplasts) obtained by cytochalasin B treatment of cells contain more than 90 percent of the HMG 1, while enucleated cytoplasts contain the remainder. A similar distribution between karyoplasts and cytoplasts is observed for the H1 histones and the nucleosomal core histones as anticipated. The presence of these proteins, in low amounts, in the cytoplast preparation can be accounted for by the small percentage of unenucleated cells present. In contrast, the nuclei isolated from mechanically disrupted cells contain only 30-40 percent of the total HMGs 1 and 2, the remainder being recovered in the cytosol fraction. No histone is observed in the cytosol fraction. Unike the higher molecular weight HMGs, most of the HMGs 14 and 17 sediment with the nuclei after cell lysis by mechanical disruption. The distribution of HMGs is unaffected by incubating cells with cytochalasin B and mechanically fractionating rather than enucleating them. Therefore, the dramatic difference in HMG 1 distribution observed using the two fractionation techniques cannot be explained by a cytochalasin-B-induced redistribution. On reextraction and sedimentation of isolated nuclei obtained by mechanical cell disruption, only 8 percent of the HMG 1 is released to the supernate. Thus, the majority of the HMG 1 originally isolated with these nuclei, representing 35 percent of the total HMG 1, is stably bound, as is all the HMGs 14 and 17. The remaining 65 percent of the HMGs 1 and 2 is unstably bound and leaks to the cytosol fraction under the conditions of mechanical disruption. It is suggested that the unstably bound HMGs form a protein pool capable of equilibrating between cytoplasm and stably bound HMGs. 相似文献
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Copper Supply in Relation to Content and Redistribution of Copper Among Organs of the Wheat Plant 总被引:2,自引:0,他引:2
The relationship of copper supply to the content and movementof copper among organs of wheat plants was examined at sevenstages in their growth from seedlings to maturity on a copperdeficient sand. In the absence of copper (Cu0), plants becameseverely copper deficient and produced no grain; developmentof tillers, leaves, stems, and inflorescences was delayed andgrowth of roots strongly depressed; leaf senescence was retardedand tiller growth was prolonged. Application of a marginal supplyof copper (Cu1) overcame all symptoms and promoted growth andgrain production. Increasing copper supply eightfold (Cu2) didnot change vegetative or grain production. Copper concentrations in stems, individual leaves, and wholetops were highest and responded most strongly to copper supplywhen they were young. As they aged, Cu1 and Cu2 leaves lostcopper rapidly; the first Cu0 leaves retained their copper andremained healthy for more than 7 weeks even though younger leavesdeveloped severe copper deficiency. In all treatments, lossof copper from the oldest leaf paralleled senescence and theloss of nitrogen. It is suggested that copper does not move out of plant leavesuntil they lose organic nitrogen compounds. As a result, copperbehaves in non-senescent leaves as if it is not mobile in plantphloem. But under conditions favouring senescence, copper ishighly mobile: in the present experiment, 67 per cent of thecopper present in vegetative organs of the Cu2 primary shootat flowering moved from them during grain development and thiscould account for all of the copper found in the grain at maturity. The retention of copper by leaves before senescence, its rapidloss during senescence, and the effect of copper deficiencyin delaying senescence resulted in the oldest leaf of severelydeficient Cu0 plants in the present experiment having a highercopper concentration than that of copper adequate Cu1 and Cu2plants. This behaviour could account for the many reports ofanomalous C-shaped Piper-Steenbjerg curves inthe relationship of yield to copper concentrations in planttops. The coupling of copper movement from leaves to nitrogenmovement can also account for the unusually high values reportedfor critical concentrations of copper in tops of plants givenhigh levels of nitrogen fertilizers. Old organs should not be included in samples for diagnosis ofcopper deficiency. Only young organs should be used. In thepresent experiment, the copper concentration of young leavesgave a good indication of the copper status of wheat: a valueof 1 µg g1 in young leaves indicated copper deficiency. copper, nitrogen, phloem transport, mineral transport, deficiency diagnosis, wheat, Triticum aestivum L. 相似文献
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The aim of these experiments was to determine whether uninhibitedroot growth is possible in a soil lacking Mg, provided thatthe plant is adequately supplied with Mg from another regionwithin the soil. Two experiments were undertaken using splitroot systems in free-draining sand or gravel irrigated dailywith nutrient solution. Magnesium supply to one half of theroot system was varied and root growth in the deficient partof the system was measured. Magnesium redistribution was comparedto that of calcium, phosphorus and potassium. Magnesium content of the roots grown in the compartment withno Mg supply increased, but only when the shoots had an adequateto luxury Mg status. Even under these conditions root growthwas inhibited compared to roots with an adequate external supplyin both compartments. Similarly potassium was transferred tothe roots with no external supply, but root growth was retardedin this compartment. Roots proliferated in the compartment suppliedwith phosphate and did so at the expense of growth in the non-supplycompartment. The shoots had a barely adequate phosphorus statusand there was no transfer of phosphorus to the root with noexternal supply. Magnesium, phosphorus, potassium, root growth, split root systems, subterranean clover, Trifolium subterraneum L. 相似文献
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The assimilation of carbon (C) by, and distribution of 14C from,leaves at each end of an unbroken sequence of ten mature leaveson the main stolon of clonal plants of white clover (Trifoliumrepens L.) were measured to identify intra-plant factors determiningthe direction of C movement from leaves. Leaves at two intermediatepositions were also measured. Localized movement of 14C to sinks at the same node as, or atthe one to two nodes immediately behind, the fed leaf accountedfor 4050% of the total 14C exported by all measured leaves.A further 5060% of exported 14C was therefore availablefor more-distant sinks, and the direction of translocation ofthis C was determined by the relative total strength or demand(number x size x rate of activity or growth) of sinks forwardof, or behind, the leaf in question. Thus 85% of the 14C exportedfrom the youngest measured leaf moved toward the base of thestolon, while about 60% of the 14C exported from the oldestleaf moved acropetally. Defoliating plants to leave just one mature leaf on the mainstolon (at any one of the same four positions studied in undefoliatedplants), and no leaves on branches, resulted in: (1) increasednet photosynthetic rate in all residual leaves: (2) increased%export of fixed C from one of the four leaves; (3) increasedexport to the main stolon apex from all except the eldest leaf;(4) increased export to branches from three of the four leaves;and (5) decreased export to stolon tissue and roots from allleaves, within 3 d of defoliation. These responses would seemto ensure the fastest possible replacement of lost leaf areaand, thus, restoration of homeostatic growth. The observed patternsof C assimilation and distribution in both undefoliated anddefoliated white clover plants are consistent with the generalrules of source-sink theory; the distance between sources andcompeting sinks, and relative sink strength, emerge as the mostimportant intra-plant factors governing C movement. These resultsemphasize the need to consider plant morphology, and the modularnature of plant growth, when interpreting patterns of resourceallocation in clonal plants, or plant responses to stressessuch as partial defoliation. Trifolium repens L, white clover, photosynthesis, assimilate translocation, defoliation 相似文献
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