Role of cell compartments in the redistribution of K and Na ions absorbed by the roots of intact barley plants

Hooymans, J. J. M.

doi:10.1016/s0044-328x(74)80156-x

Cited by 25 publications

(9 citation statements)

References 8 publications

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“…plants were partially relieved of that stress. They have reported, for example, a rapid cessation of Na+ transport to the shoot after its removal from the external medium that appears similar to that reported here (2,12). K+ transport, on the other hand, continued, and a 'special structure or organelle' involved in the transfer of K+ to the xylem was hypothesized (13 as it does in S. marina (3), and that protocols which do not include very short time points cannot indicate, let alone resolve, act S. marina under such exchange (4).…”

Section: Methodssupporting

confidence: 81%

Sodium and Potassium Compartmentation and Transport across the Roots of Intact Spergularia marina

Lazof

Cheeseman²

1988

Plant Physiol.

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ABSTRACIThe Na+ and K+ transport characteristics of Spergularia marina (L.) Griseb. were considered in order to compare the systems by which these two physiologically different cations are managed during initial acquisition and subsequent partitioning in midvegetative plants. Uptake of 22Na and 42K and redistribution of labels in pulse-chase studies were compared under steady state growth conditions or with the concentration of one of the ions elevated. At high external concentrations, the initial 42K+ accumulation and transport to the shoot was associated with a small, rapidly exchanging, cellular compartment similar to that previously indicated for Na+ (D Lazof, JM Cheeseman 1986 Plant Physiol 81: 742-747). At 1 mol m3, K+ was conducted to the shoot through a root compartment, the specific activity of which rose much more slowly than the rapidly exchanging compartment. After a lag of approximately 5 minutes, 42K+ translocation approached a constant rate with a half-time of 14 minutes compared to 5 minutes for 22Na+ or for 42K+ at higher external levels. At all external levels, prolonged translocation of 42K+ was measured when a 10 minute pulse was followed by an unlabeled chase, again suggesting a conducting compartment distinct from that for Na+. It is suggested that the K+ conducting compartment, possibly the 'bulk cytoplasm,' is associated with the active K+ transport system generally found in higher plants.The partitioning of mineral resources between the above and below ground parts of a plant is controlled by the root. It is largely mediated through transmembrane events, with a negligible contribution of apoplastic movements (11,17). The systems responsible for providing a controlled nutrient supply to a rapidly growing shoot and maintaining the ion levels in the root itself, however, are still not well understood. Despite the desirability of 'simple' systems for transport studies, nutrient management is better considered within the complexity of an intact growing plant.Among the difficulties facing organismal transport studies is interpretation of isotope flux studies when unidirectional fluxes cannot be measured. In a previous report (16), we addressed these problems, considering the transport and accumulation of labeled Na+ in Spergularia marina growing at moderate salinity. Using the approach of integrated pulse-chase protocols, transport events related to an internal root compartment other than 'bulk cytoplasm' and 'vacuole' were distinguished.Even in a halophyte, Na+ may well be a special case, particu- larly when the external concentrations to which the plants are exposed are high, both absolutely and relative to other cations. In this report, therefore, we extend our studies to lower salinity conditions and to K+. Our objective is to consider Na+ and K+ transport under comparable conditions, with particular concern for the mechanisms of initial acquisition, for compartmentation within the roots, and for delivery of the ions to the xylem. MATERIALS AND METHODSSpergularia marina (L.) Griseb. see...

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Section: Methodssupporting

confidence: 81%

Sodium and Potassium Compartmentation and Transport across the Roots of Intact Spergularia marina

Lazof

Cheeseman²

1988

Plant Physiol.

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“…The patterns of absorption and transport of nutrient elements were much altered by the medium of growth of the plants (9,10). Molybdate absorption by rice roots grown in Hoagland solution was greater than in those raised inCaSO4 (Fig.…”

Section: Discussionmentioning

confidence: 98%

“…2). It is possible that MoO42-absorption in seedlings grown in Hoagland solution relates to the entry into vacuole, on the basis of the argument that cytoplasmic sites get saturated during growth in nutrient medium (9). However, more precise experiments are needed to confirm this explanation.…”

Section: Discussionmentioning

confidence: 99%

Studies on Molybdenum Absorption and Transport in Bean and Rice

Kannan¹,

Ramani²

1978

Plant Physiol.

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The patterns of molybdenum (MoO42-) absorption and transport were investigated in intact bean ( Phaseolus vulgars L.) Several studies have been made in the past years relating to the mechanisms of absorption and transport of major nutrients and also some micronutrient elements (5, 12). However, information on the mechanisms of micronutrient absorption is still inadequate, and Moore (13) has rightly emphasized the need for a systematic investigation to understand the manner in which the micronutrients, especially boron and molybdenum, are absorbed by plant systems and also the factors which control their absorption and transport. Molybdate absorption and transport have been studied in intact plants and excised roots, and the results are reported here. MATERIALS AND METHODS

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“…If this is the case, then it is difficult to invoke cytoplasmic K ϩ as the K ϩ pool responsible for regulating HKT1 expression. Nevertheless, Hooymans (1974) observed that when exogenous K ϩ was withdrawn from barley roots, translocation of K ϩ to the shoot continued until root [K ϩ ] was reduced to the level of CaSO 4 -grown roots. This involved mobilization of vacuolar K ϩ for transport to the xylem via the cytoplasm.…”

Section: Regulation Of Hkt1 Expression By Root [K ؉ ]mentioning

confidence: 99%

“…By contrast, there is a rapid up-regulation of high-affinity K ϩ uptake when the exogenous K ϩ supply is interrupted (Glass, 1975;Kochian and Lucas, 1982;Fernando et al, 1990). Under these conditions, root K ϩ concentrations are rapidly depleted by K ϩ translocation to the shoot and by root growth (Hooymans, 1974;Glass, 1978;Walker et al, 1996a). Likewise, when K ϩ uptake is limited by pruning the root system (Claassen and Barber, 1977) or by restricting the K ϩ supply to certain regions of the root , high-affinity K ϩ uptake increases to compensate for the reduced absorptive surface.…”

mentioning

confidence: 99%

Rapid Up-Regulation of HKT1, a High-Affinity Potassium Transporter Gene, in Roots of Barley and Wheat following Withdrawal of Potassium

et al. 1998

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High-affinity K؉ uptake in plant roots is rapidly up-regulated when K ؉ is withheld and down-regulated when K ؉ is resupplied. These processes make important contributions to plant K ؉ homeostasis. A cDNA coding for a high-affinity K ؉ transporter, HKT1, was earlier cloned from wheat (Triticum aestivum L.) roots and functionally characterized. We demonstrate here that in both barley (Hordeum vulgare L.) and wheat roots, a rapid and large upregulation of HKT1 mRNA levels resulted when K ؉ was withdrawn from growth media. This effect was specific for K ؉ ; withholding N caused a modest reduction of HKT1 mRNA levels. Up-regulation of HKT1 transcript levels in barley roots occurred within 4 h of removing K ؉ , which corresponds to the documented increase of high-affinity K ؉ uptake in roots following removal of K ؉ . Increased expression of HKT1 mRNA was evident before a decline in total root K ؉ concentration could be detected. Resupply of 1 mM K ؉ was sufficient to strongly reduce HKT1 transcript levels. In wheat root cortical cells, both membrane depolarizations in response to 100 M K ؉ , Cs ؉ , and Rb ؉ , and high-affinity K ؉ uptake were enhanced by K ؉ deprivation. Thus, in both plant systems the observed physiological changes associated with manipulating external K ؉ supply were correlated with levels of HKT1 mRNA expression. Implications of these findings for K ؉ sensing and regulation of the HKT1 mRNA levels in plant roots are discussed.

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Role of cell compartments in the redistribution of K and Na ions absorbed by the roots of intact barley plants

Cited by 25 publications

References 8 publications

Sodium and Potassium Compartmentation and Transport across the Roots of Intact Spergularia marina

Sodium and Potassium Compartmentation and Transport across the Roots of Intact Spergularia marina

Studies on Molybdenum Absorption and Transport in Bean and Rice

Rapid Up-Regulation of HKT1, a High-Affinity Potassium Transporter Gene, in Roots of Barley and Wheat following Withdrawal of Potassium

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