Effects of Flooding the Root System of Sunflower Plants on the Cytokin in Content in the Xylem Sap

Facultative plant hemiparasites exhibit optimal growth only when attached to a suitable host. After attachment, stomata of the parasite remain continuously open, thus, optimising the extraction of host xylem sap. When the host shoot was removed from the hemiparasitic Rhinanthus/barley association ~14 days after attachment, the resulting host-free attached Rhinanthus continued to grow and develop similarly well as the attached parasites. These plants, however, showed altered stomatal behaviour: their stomata were open at daytime and closed at night, whereas parasitising Rhinanthus has continuously open stomata all day and night and unattached single Rhinanthus has practically closed stomata throughout day and night. After removal of the host the root growth was strongly increased, thereby increasing the root-to-shoot ratio. Abscisic acid and cytokinin relationships became more ‘normal’ with the Rhinanthus roots becoming able to synthesise zeatin nucleotides and zeatin ribosides, thus, behaving much as non-parasitic plants in general. It is suggested that the degrading root system of the host plant produces signals that trigger this conversion. Two explanations for these changes are discussed, the supply of dissolved organic nitrogen by the degrading host root system and a possible strong growth of growth promoting soil microorganisms using the degrading host root system as a substrate.

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The pH gradients in the root system and the abscisic acid concentration in xylem and apoplastic saps

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.1993.0090 ◽

1993 ◽

Vol 341 (1295) ◽

pp. 49-56 ◽

Cited By ~ 17

Keyword(s):

Plasma Membrane ◽

Abscisic Acid ◽

Root System ◽

Free Acid ◽

Stomatal Closure ◽

Xylem Sap ◽

Cytosolic Ph ◽

Root Cells ◽

Ph Gradients ◽

Stress Signal

Abscisic acid (ABA) is a stress signal that is transported from the root system to leaves, and induces stomatal closure before water relations of the leaves are affected by soil drying. Xylem vessels are in direct contact with the leaf apoplasm, the only leaf compartment that is directly connected with the primary site of ABA action, the outer surface of the guard cell plasma membrane (Hartung 1983). ABA distributes among the leaf compartments according to the anion trap concept and the Henderson-Hasselbalch equation, with the free acid as the permeating and the anion as the nearly non-permeating molecular species. Applying this concept, a flattening of the intracellular pH gradients increases the apoplastic ABA concentration. Indeed, stress increases the apoplastic pH (Hartung et al. 1988) and decreases slightly the cytosolic pH . The validity of this concept has been shown repeatedly and was confirmed by a mathematical leaf model (Slovik et al. 1992). It is appropriate to ask whether these mechanisms also contribute to ABA compartmentation and redistribution in the root system. Therefore, we have incorporated compartmental pH values of unstressed and stressed root cells, the permeability coefficients of root membranes for ABA and anatomical data into a mathematical model, similar to that of Slovik et al. (1992). The simulation shows that ABA redistribution in roots caused by changing pH gradients can account for up to a 2 to 3-fold accumulation of ABA in the xylem sap of stressed plants. The model also predicts that the pH gradient across the cortical plasma membrane has the most distinct effects on redistribution of ABA into the xylem sap of stressed plants and, additionally, that the ABA concentration in the rhizospheric aqueous solution can play an im portant role in root-to-shoot signalling.

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Abscisic Acid and Cytokinins as Possible Root-to-Shoot Signals in Xylem Sap of Rice Plants in Drying Soil

Functional Plant Biology ◽

10.1071/pp9930109 ◽

1993 ◽

Vol 20 (1) ◽

pp. 109 ◽

Cited By ~ 64

Author(s):

A Bano ◽

K Dorffling ◽

D Bettin ◽

H Hahn

Keyword(s):

Abscisic Acid ◽

Stomatal Conductance ◽

Water Potential ◽

Root System ◽

Nutrient Solution ◽

Xylem Sap ◽

Zeatin Riboside ◽

Stem Water Potential ◽

Rice Plants ◽

Stem Water

Seedlings of rice cv. IR 36 were grown in soil in small pots with a horizontally divided root system: after 6-7 weeks, about 20% of the entire root system had protruded through the holes at the base of the pots and was kept in contact with nutrient solution. At this stage the plants were exposed to three different treatments: (a) the soil was kept watered and the protruding free roots were dried in air; (b) the free roots were kept moist and the soil left unwatered; (c) both soil and protruding roots were left unwatered for 30 h and then rewatered. During the first hours of treatment a and b, a decline in stomatal conductance was observed, whereas the stem water potential remained unchanged. The concentration of abscisic acid (ABA) in the xylem, however, increased. At later stages of treatment a and b, the stem water potential began to decrease with a parallel further increase of xylem ABA. Xylem sap contained considerable amounts of bound ABA, the level of which increased during total root drying and decreased again after rewatering. Level of cytokinins, zeatin (t-Z)+zeatin riboside (t-ZR) and isopentenyladenine (2iP) + isopentenyladenosine (2iPA), on the contrary, decreased during root drying and increased again after rewatering. The results are discussed with regard to a possible function of ABA and cytokinins as root-to-shoot signals.

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Low-temperature pretreatment of the root system of Brassica rapa L. plants: effects on the xylem sap exudation and on the nitrate absorption rate

Plant Cell & Environment ◽

10.1111/j.1365-3040.1994.tb00164.x ◽

1994 ◽

Vol 17 (6) ◽

pp. 721-729 ◽

Cited By ~ 8

Author(s):

J. BIGOT ◽

J. BOUCAUD

Keyword(s):

Low Temperature ◽

Root System ◽

Brassica Rapa ◽

Absorption Rate ◽

Xylem Sap ◽

Nitrate Absorption ◽

Temperature Pretreatment ◽

Sap Exudation

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Reciprocal Grafts of Standard and Dwarf Peach Alter Dry-matter Partitioning and Root Physiology

HortScience ◽

10.21273/hortsci.27.3.241 ◽

1992 ◽

Vol 27 (3) ◽

pp. 241-243 ◽

Cited By ~ 8

Author(s):

D.M. Glenn ◽

R. Scorza

Keyword(s):

Root System ◽

Water Flow ◽

Dry Matter ◽

Prunus Persica ◽

Xylem Sap ◽

Dry Weight ◽

Dry Matter Partitioning ◽

Root And Shoot Growth ◽

Root Resistance ◽

System Water

In reciprocal grafts of tall (`Elberta' and `Loring') and dwarf (`Empress' and `Juseito') peach (Prunus persica Batsch.) phenotypes, we measured dry-matter partitioning, resistance to root system water flow, and phytohormone content of xylem exudate. Scion characteristics determined the phenotype and growth characteristics of the tree irrespective of the rootstock. Tall phenotypes had higher dry weight and lower root resistance to water flow than dwarf phenotypes. Cytokinin-like activity and auxin levels in xylem sap were higher in dwarf than in tall phenotypes; whereas gibberellin-like activity was unaffected by either rootstock or scion. The scion of peach influenced phytohormone levels and resistance to water flow in the root system in addition to root and shoot growth.

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Influence of P-Ca on cytokinins in xylem sap and on stomatal resistance in apple

Ecosistemas y Recursos Agropecuarios ◽

10.19136/era.a8n1.2580 ◽

2021 ◽

Vol 8 (1) ◽

Author(s):

Homero Ramírez ◽

Aarón Isain Malendres-Álvarez ◽

Alejandro Zermeño-González ◽

Diana Jasso-Cantú ◽

José ´Ángel Villarreal-Quintanilla

Keyword(s):

Root System ◽

Xylem Sap ◽

Stomatal Resistance ◽

Full Bloom ◽

Control Range ◽

Golden Delicious ◽

Leaf Resistance ◽

And Control

With the purpose to search upon the cytokinins origin, a study was conducted on the effects of prohexadione-ca (P-Ca) on cytokinins in xylem sap and on stomatal resistance in apple. Golden Delicious seedlings were sprayed with 100 ppm P-Ca. Stomatal leaf resistance was measured at intervals between 1 and 4 hours of spraying and 15 days after the treatment. Golden Delicious trees were sprayed with 200 ppm P-Ca two weeks after full bloom. At intervals between 1 and two weeks after P-Ca treatment, the main de-shooted stem was removed from root system and xylem sap was collected for cytokinins analysis using the suction technique. Prohexadioneca significantly increased stomatal resistance (range 2.74-4.35 s/cm−1) when compared to control (range 2.12-3.44 s/cm−1); however, P-Ca did not modify the level of cytokinins in xylem sap since range values were between 0.10 to 0.20 μg kinetin equivalents/20 ml xylem sap for both, cytokinin and control.

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Root-derived trans-zeatin riboside and abscisic acid in drought-stressed and rewatered sunflower plants: interaction in the control of leaf diffusive resistance?

Functional Plant Biology ◽

10.1071/fp02223 ◽

2003 ◽

Vol 30 (4) ◽

pp. 365 ◽

Cited By ~ 35

Author(s):

Hauke Hansen ◽

Karl Dörffling

Keyword(s):

Water Potential ◽

Root System ◽

Xylem Sap ◽

Leaf Tissue ◽

Fold Increase ◽

Zeatin Riboside ◽

Significant Rise ◽

Gas Chromatography Mass Spectrometry ◽

Flux Rate ◽

Diffusive Resistance

Four-week-old potted sunflower plants (Helianthus annuus L.) were exposed to drought for up to two days by withholding irrigation. During the stress treatment and after rewatering, xylem sap was collected from decapitated hypocotyls by pressurising the root system. The water potential (Ψw) of the hypocotyl, the diffusive resistance of the second leaf pair, total transpiration and the concentration and flux rates of ABA and trans-zeatin riboside (ZR), identified by combined gas chromatography–mass spectrometry (GC–MS) as the dominant cytokinin in xylem sap, were determined. ABA contents were also analysed in root and leaf tissue. When Ψw of the hypocotyl decreased, the concentration and flux rate of ZR decreased drastically after a transient rise. A significant rise in ABA concentration and flux rate in xylem sap as well as a parallel rise in leaf diffusive resistance occurred as soon as Ψw reached values of –0.4 MPa and lower. Root ABA concentration began to rise at the same water potential parallel to the rise in xylem sap, whereas the ABA concentration in leaves began to rise only at Ψw values lower than –0.6�MPa. Treatment of the root system with norflurazon prior to drought stress suppressed the increase in the ABA concentration in xylem sap and caused higher transpiration rates. Watering the drought-stressed plants led to a rapid decrease in ABA content of the xylem sap within three hours, whereas the decrease in leaf diffusive resistance was somewhat slower. The ZR concentration in the xylem sap rose continuously after rewatering, reaching a 60-fold increase after five hours, and declined again afterwards. Studies in which ZR and ABA were applied to cut shoots in concentrations similar to those in xylem sap of well-watered plants (ZR) and drought-stressed plants (ABA) showed that ZR, even in very low concentrations, antagonised the effect of ABA on transpiration. The results are discussed with regard to a possible antagonistic interaction of ZR and ABA as non-hydraulic root-to-shoot signals, and with regard to their interplay with hydraulic signalling.

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