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R K Dela Fuente

Publications and source records attributed to R K Dela Fuente.

11 recordsLinked to original sources
PubMed1986

Polar Calcium Flux in Sunflower Hypocotyl Segments : II. The Effect of Segment Orientation, Growth, and Respiration.

Calcium flux in sunflower (Helianthus annuus L. cv Russian mammoth) hypocotyl was measured with a Ca(2+) electrode as the increase or decrease in Ca(2+) in an aqueous solution (10 micromolar CaCl(2)) in contact with either the basal or apical end of 20 millimeter segments. Ca(2+) efflux was significantly higher at the apical end compared with the basal end; this apparent polarity was maintained even when the segments were inverted. No significant difference was observed in the cation exchange capacity of apical and basal cell walls that could explain the difference in Ca(2+) efflux at opposite ends of the hypocotyl segment. The presence of exogenous indoleacetic acid (IAA) in the segment medium resulted in the promotion of both Ca(2+) efflux and segment elongation. However, osmotic inhibition of the IAA-induced elongation did not result in inhibiting the IAA-induced Ca(2+) efflux. Ca(2+) efflux was inhibited by cyanide. Lowering the temperature from 25 degrees C also caused the gradual reduction of Ca(2+) efflux; at 5 degrees C the hypocotyl segments showed a net absorption of Ca(2+) from the segment medium. These findings support the suggestion that: (a) the observed Ca(2+) efflux in hypocotyl segments is probably the manifestation of the system which maintains the transmembrane Ca(2+) gradient at the cellular level. (b) The acropetal polarity of Ca(2+) efflux may be the result of the involvement of Ca(2+) in the basipetal transport of IAA.

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PubMed1986

The transport of indole-3-acetic Acid in boron- and calcium-deficient sunflower hypocotyl segments.

Transfer of sunflower (Helianthus annuus L. cv Russian Mammoth) seedlings from complete nutrient solution to solutions deficient in either boron or calcium resulted in a steady decline in the rate of auxin transport, compared to seedlings that remained in the complete solution. In seedlings transferred to solutions deficient in both B and Ca, the decline in auxin transport was greater than seedlings deficient in only one element. The transfer of B- or Ca-deficient seedlings back to the complete solution prevented further decline in auxin transport, but auxin transport did not increase to the same level as seedlings maintained in complete solution. The significant reduction in auxin transport during the early stages of B or Ca deficiency was not related to (a) reduced growth rate of the hypocotyl, (b) increased acropetal movement of auxin, or (c) lack of respiratory substrates in the hypocotyl. In addition, no difference was found in the water-extractable total and ionic Ca in B-deficient and control nondeficient hypocotyls, indicating a direct effect of B on auxin transport, rather than indirectly by affecting Ca absorption. The rate of auxin transport in hypocotyls deficient in either B or Ca, was inversely correlated with K(+) leakage and rate of respiration. The data presented strongly support the view that there are separate sites for B and Ca in the basipetal transport of the plant hormone indoleacetic acid.

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PubMed1986

Boron and calcium sites involved in indole-3-acetic Acid transport in sunflower hypocotyl segments.

Sunflower (Helianthus annuus L. cv Russian Mammoth) hypocotyl segments deficient in either B or Ca exhibited a higher rate of potassium leakage, compared to nondeficient segments. Potassium leakage, used here as an indication of membrane integrity, was completely reversed by the addition of H(3)BO(3) or Ca(NO(3))(2) to the incubation medium of the B-deficient or Ca-deficient hypocotyl segments, respectively. This role of B and Ca in membrane integrity, which may be important in the entry and exit of auxin in cells, is identified as the first site of action for each of these two essential elements in the basipetal secretion of auxin. A second site for B is postulated because auxin transport was not restored, even when K(+) leakage has been completely reversed to the nondeficient level, when B-deficient hypocotyls were incubated in B solution. This lack of reversibility of auxin transport implied that the incubation for 2 h in B solution was not enough to restore the auxin transport process. However, since the transfer of B-deficient seedlings to B solutions prevented further deterioration of auxin transport, these observations suggest that: (a) either an intact seedling, or a longer period of incubation of the hypocotyl in B solution, is required for the synthesis or maintenance of the functional second site for B; (b) B is probably essential in the synthesis of a ligand, which may or may not be needed to bind B, but which is essential in the basipetal transport of auxin. The second site for Ca in auxin transport, is indicated by the complete reversal of its inhibition in Ca-deficient hypocotyl, when incubated in Ca solution. The second site for Ca is thought to be directly involved in the secretion of auxin, in which Ca probably plays the role of a second messenger, as in stimulus-response coupling. The two sites for Ca can be distinguished from each other by their cation specificity. The requirement for Ca in the first site can be substituted by other divalent cations, while the second site is highly specific for Ca.

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PubMed1984

Role of calcium in the polar secretion of indoleacetic Acid.

The rate of auxin transport in sunflower hypocotyls (Helianthus annuus L. cv ;Russian mammoth') or corn coleoptiles (Zea mays L. cv ;WF9 x 38') was less in seedlings grown in Ca-deficient medium than in controls. The rate of IAA transport depended on the concentration of Ca in the root medium up to 1 millimolar. Further increases in auxin transport were observed when the isolated segments were incubated in medium containing up to 30 millimolar Ca. We suggest that the rate of auxin transport in plant tissue is dependent on the pool of ionic Ca in the extracellular space.Segments from Ca-deficient seedlings exhibited a high specific requirement for Ca(2+) in auxin transport. Magnesium, strontium, and several other divalent cations tested for their ability to replace Ca(2+) in restoring auxin transport showed no effect; partial replacement by lanthanum was observed.Auxin transport, or auxin flux through the segment, which is the result of IAA secretion by individual cells, was reduced in the low Ca(2+) segments due both to lowered velocity and to reduced capacity of transport. The requirement for Ca(2+) in the secretion of auxin is believed to be equivalent to the phenomenon observed in animal cell secretion, where the influx of Ca(2+) serves as a link between an external stimulus and the secretion response.

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PubMed1984

Polar calcium flux in sunflower hypocotyl segments : I. The effect of auxin.

The flux of Ca(2+) at the apical or basal ends of short sunflower (Helianthus annuus L.) hypocotyl segments was monitored using a Ca(2+)-specific electrode. A higher Ca(2+) efflux was observed at the apical end relative to the basal end, indicating a net polar flux of Ca(2+). The extreme low mobility of Ca(2+) in the isolated segment makes it likely that the observed Ca(2+) fluxes are of localized origin, that is, from the parenchyma cells close to the exposed cut ends and may represent acropetal transport of Ca(2+) at the cellular level. The rate of Ca(2+) efflux depended on the concentration of Ca in the seedling medium. Incubation of hypocotyl segments in 10 mm CaCl(2) for 24 h did not eliminate the net acropetal flux of Ca(2+) at the apical end.IAA, as well as the synthetic auxin alpha-naphthaleneacetic acid, significantly enhanced Ca(2+) efflux; the non-auxin analog, beta-naphthaleneacetic acid, was ineffective. The transport of auxin, not merely its presence in the medium, was found to be a requisite for the enhancement of Ca(2+) efflux since the presence of the auxin transport inhibitor 2,3,5-triiodobenzoic acid eliminated the auxin-promoted Ca(2+) efflux. A model for how auxin promotion of Ca(2+) efflux could play a role in promoting subsequent auxin secretion is proposed. Calcium probably serves as a ;second messenger', as it does in the secretion of various substances by animal cells.

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PubMed1973

A role for calcium in auxin transport.

The basipetal transport of the auxin, indoleacetic acid, in sunflower stem sections is markedly suppressed by washing the tissue in ethylenediaminetetraacetate, and transport is restored by subsequent application of calcium solutions. The ethylenediaminetetraacetate treatment is shown to result in the removal of substantial amounts of calcium from the tissue, and the restoration of transport is distinctive for calcium solutions, lesser effects being observed for magnesium and lanthanum, and little effect for monovalent cations. The calcium effects are interpreted as indicating that the auxin transport system depends upon structural or functional features of cellular membranes which involve calcium in a manner analogous to the transport of inorganic ions.

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PubMed1970

Time course of auxin stimulations of growth.

Measurements of the time course of growth responses of corn coleoptile sections to pulses of auxin (10(-5)m indoleacetic acid) establish that the growth rate changes in a regular pattern around the auxin pulse: a latent phase of 12 to 15 minutes is followed by an acceleration of growth rate lasting 15 to 20 minutes, after which a fairly steady rate is maintained. When the auxin source is withdrawn, there is an after-effect of about 15 minutes followed by a decay of growth rate, which reaches 50% decay after a further 15 to 40 minutes. The decay phase appears to be a function of the transport of auxin out of the sections. The 50% decay of growth for single cells is estimated at 30 minutes from the time of withdrawal of an exogenous supply of auxin. The regulation of growth by auxin is rapidly imposed or dissipated as auxin enters and exits, respectively, suggesting a facile association and disassociation of auxin with a growth-limiting site in the cell. It is proposed that the growth-stimulated state is dissipated at once when the transportable auxin has passed out of the cell.

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PubMed1969

Kinetics of abscission in the bean petiole explant.

The progress of bean petiole abscission has been followed using quantitative measurements of the mechanical force required to break explants at the separation zone. It is found that the shortest time for a measurable effect of ethylene (1 ppm) in stimulating the development of frangibility is about 1 hr. Removal of the ethylene is followed by a return to the endogenous rate of weakening, the slower rate being established in 1 hr. Application of the inhibitor cycloheximide leads to a cessation of abscission development within one-half hr. As in the stimulations of certain plant processes with auxins, gibberellins, and cytokinins. ethylene stimulation of abscission requires the continuous presence of the regulator.

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PubMed1968

Lateral movement of auxin in phototropism.

Lateral movement of indoleacetic acid-1-(14)C in corn coleoptiles was measured as radioactivity moving laterally following unilateral application of the auxin. The data suggest that there is an endogenous lateral movement of auxin, and that phototropic stimulation of the coleoptile depresses lateral movement towards the light and enhances lateral movement away from the light. The lateral movement was found to be principally as indoleacetic acid. In experiments using sunflower hypocotyl sections, evidence is also presented to support the suggestion that lateral redistribution of auxin may be effected by a deflection of auxin around a barrier to basipetal transport.

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PubMed1968

Senescence processes in leaf abscission.

There is a large body of evidence which correlates the development of some phases of senescence with the ability of petioles to experience abscission. We have suggested that the change-over from stage 1 to stage 2 in the aging of bean petiole explants may be a reflection of initial stages of senescence in the pulvinar tissue. The abscission-inhibiting effect of auxin in interpretable as a retardation of pulvinar senescence. Senescence of cells in the separation layer has not been unequivocally established, and it seems unlikely that separation is itself a consequence of cellular senescence in the separation zone. More probably, senescence plays a role in the preparatory phases of abscission, that is, in the development of a condition of responsiveness to ethylene. In bean explants, ethylene responsiveness for abscission is associated with an ethylene-stimulated production of ethylene in the pulvinar tissues.

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