Translocation hormone

These results suggest that in the short-term collection method basal and apical receivers should be applied simultaneously. By this means, the acropetal component of the transport system is accounted for and the auxin then delivered to basal receivers probably will give a more accurate measure for the density of the basipetal auxin stream. Moreover, the calculation of the acropetal/basipetal ratio may reflect the polarity of hormone translocation. 

Measurements and calculations of velocities, densities, and intensities of transport to characterize hormone translocation usually imply that these quantities be constant and that the hormone moves in a stream. They do not, however, allow for degradation and/or immobilization, i.e., leakage of molecules out of the stream, to take place. Yet such phenomena do take place, and do vary with time and distance from the hormone source. Variations in the density of mobile auxin have been demonstrated even within short transport sections (e.g., Kaldewey 1963 in Fritillaria axes Newman 1965, 1970 in Avena coleoptiles Kaldewey and Kraus 1972 in Gossypium seedlings Kaldewey etal. 1974 in Pisum internodes Kaldewey 1976 in Tulipa axes). The commonly observed decline of mobile auxin as a function of distance from the auxin source indicates that not all auxin molecules move with the same velocity. The same conclusion may be drawn from the tpyical initial gradual increase of hormone flux into basal receivers which occurs before linearity of the time course is reached (e.g., Hertel 1962, Hertel and Leopold 1963, de la Fuente and Leopold 1973 in Helianthus hypocotyls McCready and Jacobs 1963 a, b, in petioles and Smith and Jacobs 1968 in hypocotyls of Phaseolus de la Fuente and Leopold 1966 in Coleus internodes Thornton and Thimann 1967 in Avena coleoptiles Greenwood and Goldsmith 1970 in Pinus embryonic hypocotyls Wilkins and Cane 1970, Wilkins etal. 1972 and Shaw and Wilkins 1974 in Zea roots Kaldewey et al. 1974 in Pisum internodes Tsurumi and Ohwaki 1978 in Vida roots). 

Basically two lines have been followed in the search for the pathways of hormone translocation (1) surgical methods and (2) autoradiographic methods which have come with the advent of radioactive hormones. Phloem-feeding aphids have been used as a speciality to detect translocation in sieve elements (for references see p lOOf.). 

Other oncogenes code for proteins that bind guanine nucleotides, and others code for nuclear proteins. The guanine nucleotide-binding proteins, the so-called G proteins, affect several key reactions. Some G proteins are stimulatory, whereas others are inhibitory. For example, they link hormone receptors to adenylate cyclase, they translocate... 

Understanding of the intracellular localization of steroid receptors has gone through a number of phases, beginning with the view that receptors translocated from cytoplasm to nucleus in the presence of hormone. Indeed, with the exception of thyroid hormone receptors, which are exclusively nuclear in location, cell fractionation studies have revealed that in the absence of hormone, steroid receptors are extracted in the soluble or cytosolic fraction. However, when steroid is present in the cell, many occupied receptors are retained by purified cell nuclei. Histological procedures, such as immunocytochemistry, have confirmed the largely nuclear localization of occupied receptors, but... 

The initial step after cellular uptake of T4 is metabolic transformation to 3,5,3, -tri-iodothyronine (T3) (Fig. 52-8), which interacts with cytosolic and nuclear receptors, as well as with synaptosomal membrane binding sites of unknown function [25], Cytosolic receptors are proteins of 70 kDa that do not appear to undergo translocation to cell nuclei, nor do they appear to be nuclear proteins that have leaked out of cell nuclei during cell rupture nuclear receptors are proteins of 50 70 kDa that have both DNA-and hormone-binding domains [25,26,28],... 

The intracellular distribution of steroid hormone receptors has long been the object of controversy. The first theoretical formulation on the intracellular location of the ERs was elaborated by Jensen in 1968 and is known as the two-step theory. Its execution was based entirely on biochemical observations obtained by means of tritium-marked estradiol. The ERs, in cells not exposed to hormones, are found abundantly in the soluble cell fraction, or cytosol (Fig. 1.1). Treatment with hormones confines the receptors to the particulated or nuclear fraction and causes their disappearance from the cytosol. The two-step theory established that the receptor is found in the cytoplasm naturally and upon the arrival of a hormone it is transformed into a complex hormone-receptor (first step) capable of translocating itself to the nucleus and of modifying gene expression (second step). 

---