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  • Author or Editor: Dariusz Swietlik x
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Abstract

Studies were conducted to compare responses of pressure- and transpiration-induced water fluxes (Jv) through root systems of sour orange (Citrus aurantium L.) (SO) seedlings and to quantify the apoplastic component of fluxes in the both systems. Roots excised from water-cultured SO seedlings were sealed in a nutrient solution-filled pressure chamber and pressurized at 0.5 MPa with air, N2, or CO2. Changing the pressurizing gas from air to N2 or CO2 reduced Jv, but the response to CO2 was more pronounced than to N2. The fluxes recovered when N2 and CO2 were in turn replaced by air. Transpiration of water-culture-grown intact SO seedlings responded similarly to changes in gasses bubbled through the nutrient solution. The Jv in excised root systems was decreased at elevated salt concentration in the root medium, a phenomenon commonly observed in intact plants. Root conductance taken from the slopes of the linear portion of pressure/flux curves was lower at low than high salt levels. The apoplastic water fluxes through pressurized roots and intact SO seedlings was quantified using trisodium 3-hydroxy-5,8,10-pyrenetrisulfonate. The increased proportion of the apoplastic component in pressure-, compared to transpiration-induced, fluxes indicates that root pressurization opens one or more new avenues for water transport that are not operative in a transpiring seedling. Steady-state flow rates through the roots pressurized at 0.5 MPa were attained within ≈3 hr.

Open Access

Chelator-buffered nutrient solutions were used to study the effect of different levels of Zn activity in the rhizosphere on growth and nutritive responses of various tissues of sour orange seedlings. The seedlings were grown for 3 months in a growth chamber in a hydroponic culture containing from 5 to 69 μm and 5 to 101 μm total Zn in Expts. 1 and 2, respectively. Zn+2 activities were calculated with a computerized chemical equilibrium model (Geochem-PC), and buffered by inclusion of a chelator, diethylenetriamine pentaacetate (DTPA), at 74 and 44 μm in excess of the sum of Fe, Mn, Zn, Cu, Ni, and Co in Expts. 1 and 2, respectively. The use of DTPA-buffered solutions proved successful in imposing varying degrees of Zn deficiency. The deficiency was confirmed by leaf symptomatology, leaf chemical analyses, i.e., <16 mg·kg-1 Zn, and responses to foliar sprays and application of Zn to the roots. Growth parameters varied in their sensitivity to Zn deficiency, i.e., root dry weight < leaf number and white root growth < stem dry weight < leaf dry weight < shoot elongation and leaf area. The critical activities, expressed as pZn = -log(Zn+2), were ≈10.2±0.2 for root dry weight, 10.1±0.2 for leaf number and white root growth, 10.0±0.2 for stem dry weight, 9.9±0.2 for leaf dry weight, and 9.8±0.2 for shoot growth and leaf area. Increases in growth were observed in response to Zn applications even in the absence of visible Zn-deficiency symptoms. Seedlings containing >23 mg·kg-1 Zn in leaves did not respond to further additions of Zn to the nutrient solution. Zinc foliar sprays were less effective than Zn applications to the roots in alleviating severe Zn deficiency because foliar-absorbed Zn was not translocated from the top to the roots and thus could not correct Zn deficiency in the roots.

Free access

Abstract

Foliar application of CaCl2 at concentrations of 60 to 100 meq·liter-1 to in vitro-propagated ‘Jonathan’ apple (Malus domestica Borkh.) trees reduced stomatal conductance (gs). Responses in gs were not associated with visible leaf injuries. No reduction in gs was observed when Ca at 100 meq·liter-1 was applied to the leaves in conjunction with nonabsorbable anions (IDA or DMDADS), indicating that Ca2 alone was not responsible for stomatal closure after CaCl2 application. Foliar-applied Cl- at 100 meq·liter-1 with the organic cation 2-amino-2-hydroxymethyl-1,3-propanediol (Tris), induced stomatal closure. However, no changes in gs were observed after Tris application alone or when Cl- was applied with K- as an accompanying cation. These results indicate that CaCl2-induced reductions of gs derive from the interaction between Ca2 and Cl- rather than the effect of Ca2- or Cl- alone. CaCl2 sprays lowered transpiration for 2 days and increased stem water potential of water-stressed and unstressed trees. Transpiration was reduced less in stressed than unstressed trees. Chemical names used: iminodiacetate (IDA); 4,4-dimethyl-4,7-diazadecane-1,10 disulfate (DMDADS).

Open Access

Water extracts of cocklebur,CBX (Xanthium spinosa L.) and velvetleaf,VLX (Abutilon theophrasti Medic.) shoots and Mexican ash,AshX (Fraxinus Berlandieriana A.DC.) roots were added to 9 month-old sour orange Citrus aurantium L.) seedlings(SOs) in water culture. Final extract concentrations represented either 50 or 12.5 g. of plant material liter-1 of culture solution, i.e. 1/20 or 1/80 dilutions. Leaf water potential(ψ); stomatal conductance(gs);transpiration(T) and growth responses were measured for 13 days. After 1 day, SOs in AshX and CBX had lower ψ than controls. After 11 days SOs in CBX had higher ψ than the others. ψ responded similarly to both extract concs.. Thru day 5, AshX decreased gs vs. the controls and VLX. By day 11, gs of SOs in AshX was less than for VLX but not the others. On days 1 and 5, gs for VLX at 1/20 was lower than controls but at 1/80, gs's were the highest of all treatments. These results supported by the T rates, growth responses and others findings suggest AshX and VLX induce water stress by reducing water absorption and/or transport in addition to possibly disrupting normal root/shoot communications

Free access

Abstract

The addition of (2RS, 3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-1,2,4-triazoI-1-yl-) pentan-3-ol) (paclobutrazol, PP333) at 0.05 or 0.20 ppm to a nutrient solution in which 4-month-old apple (Malus domestica, Borkh.) seedlings were growing, reduced terminal growth and increased root to leaf ratio. Plants pretreated with 0.20 ppm PP333 did not show a reduction in transpiration due to subsequent applied water stress induced by polyethylene glycol (PEG), whereas untreated plants decreased their transpiration in response to PEG stress at −0.5 and −0.75 MPa. The PP333 pretreatment at 0.20 ppm improved water balance of the seedlings since they had a higher water potential than untreated seedlings at equal or higher transpiration rates. Leaf osmotic adjustment to lower water potentials was shown to be leaf age-dependent irrespective of PP333 pretreatment.

Open Access

Abstract

Solution cultures altered with polyethylene glycol to induce a water stress of− 1.0 bar decreased net photosynthesis (Pn) and stomatal conductance (Cs) in the leaves of ‘York Imperial’ apple seedlings (Malm domestica Borkh.). Sprays with a complete nutrient solution produced similar responses and further decreased Pn and Cs in water-stressed plants. It appeared from the mesophyll conductance (Cm) calculation that reduction in Pn rate in water-stressed, as well as sprayed trees, was not caused solely by a stomatal factor. It is not known, however, whether nonstomatal limitation of Pn reflects a decreased capacity for CO2 fixation or increased light respiration, since mesophyll conductance was calculated assuming constant (zero) sink CO2 concentration in the leaf. In another experiment, decreasing to − 1.0 bar water potential of nutrient solution reduced daily water consumption and fresh weight of ‘York Imperial’ apple seedlings. Sprays with complete nutrient solution also tended to decrease daily water consumption of plants. Water stress decreased leaf Ca and root K and Mg concentrations, indicating that water stress may lower the absorptive capacity of the roots. However, water-stressed plants contained more Ca in the roots than unstressed plants, suggesting that lower leaf Ca concentration in stressed plants was caused by suppressed transport. Leaf sprays with complete nutrient solution increased Mg concentration in the leaves and stems and Ca concentration in the leaves.

Open Access

Abstract

‘York Imperial’ apple seedlings (Malus domestica Borkh.) grown in nutrient solution cultures with decreased water potential to− 1.0 bar by polyethylene glycol (PEG) increased water consumption, photosynthesis rate (Pn), and stomatal conductance (Cs). High light preconditioning of the plants used in this experiment was probably the reason why− 1.0 bar water potential in the nutrient solution was not low enough to induce apple seedling responses typical of water-stressed plants. However, application of PEG stress (−1.0 bar), to K-sprayed (K2SO4, −0.5%) trees lowered seedling water consumption Pn, and Cs. Potassium sprays alone did not significantly affect water consumption, Pn or Cs. When the water potential of the nutrient solution of PEG stressed plants was further decreased to −2.5 bars, unsprayed trees started to wilt within 2 days while sprayed trees did not. It is proposed that earlier stomatal closure of K-sprayed trees when stressed, already at low level of water stress (−1.0 bar), prevented plant water depletion when stress level was increased. This in turn delayed commencement of plant wilting. Potassium sprays also increased root:shoot ratio and root K concentration in PEG-stressed plants. These responses of K-sprayed trees could also contribute to greater tolerance to higher levels of water stress.

Open Access

Abstract

Low- and high-K pretreated ‘York Imperial’ apple seedlings (Malus domestica Borkh.) were grown in nutrient solution cultures. Addition of polyethylene glycol (PEG) to the nutrient solution to reduce water potential to −1.0 bar reduced water consumption, fresh weight, specific leaf weight (SLW), and leaf water potential and increased the amount of water consumed per unit of fresh weight gain. High-K pretreatment increased water consumption of unstressed seedlings but decreased water consumption of PEG-stressed plants. Daily sprays with 0.5% KCl applied in early afternoon had no effect on water consumption rate in apple seedlings. However, sprays probably induced wider stomatal opening, since K-sprayed trees had lower leaf water potential when measured at noon than unsprayed trees. This effect was not observed when water potential was measured in the morning (0800 hr). High-K plants had higher leaf water potential than low-K plants in the morning. Potassium pretreatment and PEG stress as well as K-sprays had numerous effects on plant mineral composition. The K-pretreatment or K-sprays did not alleviate the detrimental effects of PEG-induced water stress despite the effects of K-pretreatment and K-sprays on mineral composition and leaf water potential.

Open Access

Abstract

Application of a complete nutrient solution (CNS) on apple seedling leaves reduced stomatal conductance (gs). Tween 20 and CaCl2 were components of the CNS which induced gs reduction. Tween 20 alone, however, did not cause stomatal closure, but CaCl2 (24.8 mm) had a consistent, negative effect on gs when applied alone. Application of CaCl2 in combination with one of the other macrocomponents of the CNS (MgSO4, urea, or K2SO4 + KH2PO4) produced less consistent gs reductions indicating that the CaCl2 effect on gs can be modified by the presence of these compounds. Urea, MgSO4, or K2SO4 + KH2PO4 had little effect on gs when applied separately. Application of MgCl2 or KCl, which were not the CNS components, decreased and had no effect on gs, respectively. In addition to gs reduction, CaCl2 sprays reduced net photosynthesis (Pn). The equivalence of intercellular CO2 concentration in sprayed and unsprayed seedlings implied that the Pn drop following CaCl2 sprays resulted from decreased capacity of mesophyll for CO2 fixation and not from reduction in the stomatal aperture. Two possible explanations for stomata closure are discussed: a direct effect of CaCl2 on stomata and an indirect effect of CaCl2 spray through changes in mesophyll CO2 fixation capacity. Reductions in gs and Pn following treatments with different salts were not associated with visible leaf injury.

Open Access

Abstract

The effect of polyethylene glycol (PEG)-induced water stress on stomatal and nonstomatal inhibition of photosynthesis of apple seedlings (Malus domestica Borkh.) grown in solution culture was investigated. Water stress was applied gradually by modifying the nutrient solution water potential daily to a minimum of -8.0 bar. Nutrient solution of less than or equal to water potentials -6 bar decreased net and gross photosynthesis rates. Stomatal and nonstomatal factors were responsible for photosynthetic inhibition. Nonstomatal inhibition of photosynthesis appears to be due to decreased capacity for CO2 fixation and not increased photorespiration. The ratio of gross to net photosynthesis was not affected. A higher level of water stress was required to affect mesophyll resistance than stomatal resistance and/or there was a lag time for mesophyll resistance to respond to stress.

Open Access