High germination seed lots of purple coneflower [Echinacea purpurea (L.) Moench] were evaluated for laboratory germination following osmotic priming or chilling stratification. Compared to nontreated seeds, osmotic priming at 25C in salts (KNO3 + K3PO4; 1:1, w/w) or polyethylene glycol 4000 (PEG) increased early (3-day) germination percentage at 27C of all seed lots, and improved total (10-day) germination percentage of low-germination seed lots. Total germination percentage was unaffected or increased by priming for 4 days compared to 8 days, and by priming at –1.0 MPa compared to –0.5 MPa (except for one low-germination seed lot). Chilling stratification in water at 5 or 10C increased early and total germination of all seed lots, except for that same lot, compared to nontreated seeds. Total germination percentage was unaffected or increased by stratification at 10C rather than at 5C. Neither extending stratification ≥20 days nor lowering osmotic potential with PEG during stratification improved total germination percentage.
Osmotic compounds, such as polyethylene glycol 8000 (PEG-8000), reduce plant elongation by imposing controlled drought. However, the effects of PEG-8000 on nutrient uptake are unknown. Impatiens `Dazzler Pink' (Impatiens walleriana Hook. F.) were grown hydroponically in modified Hoagland solutions containing 0, 10, 17.5, 25, 32.5, 40, 47.5, 55, or 62.5 g·L–1 PEG-8000. Impatiens were up to 68% shorter than control plants when grown with PEG-8000 in the nutrient solution. Plants treated with PEG-8000 rates above 25 g·L–1 were either damaged or similar in size to seedlings treated with 25 g·L–1 of PEG-8000. Impatiens leaf water potentials (Ψw) were positively correlated with plant height. PEG-8000 reduced the electrical conductivity of Hoagland solutions as much as 40% compared to nontreated Hoagland solutions, suggesting that PEG-8000 may bind some of the nutrient ions in solution. Foliar tissue of PEG-treated impatiens contained significantly less nitrogen, calcium, zinc, and copper, but significantly more phosphorus and nickel than tissue from nontreated impatiens. However, no nutrient deficiency symptoms were induced.
French marigold (Tagetes patula L. `Boy Orange') was grown in a peat-based growing medium containing different rates (0, 15, 20, 30, 42, or 50 g·L–1) of polyethylene glycol 8000 (PEG-8000) to determine if PEG-8000 would reduce seedling height. Only 28% to 55% of seedlings treated with 62, 72, or 83 g·L–1 of PEG-8000 survived, and these treatments would be commercially unacceptable. Marigolds treated with the remaining concentrations of PEG-8000 had shorter hypocotyls, and were up to 38% shorter than nontreated controls at harvest. Marigold cotyledon water (ψw), osmotic (ψs), and turgor (ψp) potentials were significantly reduced by PEG-8000, and ψp was close to zero for all PEG-treated seedlings 18 days after seeding. Whole-plant net photosynthesis, whole-plant dark respiration, and net photosynthesis/leaf area ratios were reduced by PEG-8000, while specific respiration of seedlings treated with PEG-8000 increased. Marigolds treated with concentrations greater than 30 g·L–1 of PEG-8000 had net photosynthesis rates that were close to zero. Fourteen days after transplanting, PEG-treated marigolds were still shorter than nontreated seedlings and they flowered up to 5 days later. Concentrations of PEG from 15 to 30 g·L–1 reduced elongation of marigold seedlings without negatively affecting germination, survival, or plant quality. It appears that marigold seedlings were shorter because of reduced leaf ψp and reductions in net photosynthesis.
We previously found that incorporation of PEG-8000 into the growing medium delayed germination and resulted in shorter seedlings. However, in that study, we were unable to determine whether the reduced height was merely the effect of delayed germination or of reduced elongation after germination. To answer this question, we studied whether postgermination drenches with PEG-8000 can reduce seedling height. Annual salvia (Salvia splendens F. Sellow. ex Roem. & Shult. `Bonfire') and French marigold (Tagetes patula L. `Boy Orange') seedlings were treated with drenches of PEG-8000: 0, 15, 20, 30, 42, 50, 62, 72, or 83 g·L–1. At least 20% of seedlings treated with 62 to 83 g·L–1 of PEG-8000 were dead 14 d after treatment. Salvia and marigolds treated with the remaining PEG-8000 concentrations were up to 34% and 14% shorter than untreated seedlings, respectively. Leaf water (Ψw) and turgor potential (Ψp) also decreased for salvia which were grown with greater concentrations of PEG-8000, one probable cause of the observed reduction in elongation. Since the PEG-8000 in this study was applied after germination, it is clear that PEG-8000 does not reduce elongation merely by delaying germination, but also by reducing the elongation rate. Thus, postgermination drenches with PEG-8000 can be used to produce shorter seedlings.
). This indicates that PHTs are involved not only in low P but also in drought resistance. Polyethylene glycol 6000 (PEG6000) is frequently used in experiments to simulate osmotic stress ( Bhargava and Paranjpe, 2004 ; Radhouane, 2007 ). With a
Polyethylene glycol (PEG-4000)-induced water stress (—0.5 to —7.5 bars) reduced shoot and root growth, water use, and stem 45Ca in seedlings of peach (Prunus persica (L.) Batsch). Sucrose feeding through a leaf did not affect stem 45Ca with or without osmotic stress. 45Calcium uptake per milligram water used was not different at different solution osmotic potentials. A split-root study, with half the root system receiving 45Ca and/or PEG, showed that if 45Ca was supplied only to the water-stressed root half, 45Ca uptake into stems was low regardless of whether the other root half was stressed or not. Results indicate that reduced stem Ca during water stress is probably not a direct result of decreased root energy needed for active uptake or reduced translocation out of the root. Calcium absorption appeared to be related to the amount of unsuberized root surface available for Ca uptake.
Micropropagated grapes (Vitis sp. `Valiant') were subjected to water stress while rooting with the addition of 2% (w/v) PEG 8000. PEG-treated plantlets exhibited reduced growth, as compared to control (in vitro, no PEG), but developed greater leaf epicuticular wax. PEG-treated plantlets had three times the wax level of control. Although treated plantlets showed changes in leaf anatomy, no effect on stomatal frequency or stomatal index was evident. Differences in epidermal cell configuration were also observed among leaves from different treatments. PEG-treated plantlets resembled those grown in the greenhouse, morphologically and anatomically, and exhibited a higher survival rate than control upon transfer to the greenhouse.
Cell suspension cultures of four date palm cultivars were established, namely, Niboat Saif, Madjhool, Sukarri, and Berhi. In this study, two factors were tested for their effect on embryo maturation and hyperhydration. The effect of sucrose concentration was assessed by inoculating 0.5 g of embryogenic callus into a liquid MS basal medium supplemented with 10 mg/L inositol, 3 mg/L glycine, 20 mg/L glutamine, and 0, 20, 30, 40, 50 g/L sucrose. Polyethylene glycol (PEG) concentration effect on embryo maturation and hyperhydration was tested. PEG (molecular weight 7000–9000) was added at concentrations of 0, 10, 30, and 60 g/L to the date palm suspension cultures. Cultures were examined and subcultured every 3 weeks for 2 months. Embryos formed were then transferred to a solid MS medium supplemented with 10 mg/L inositol, 3 mg/L glycine, 5 mg/L glutamine, and 30 g/L sucrose. The number of embryos germinated from each treatment was counted to compare cultivar differences. Preliminary data suggests that the medium containing 30 g/L sucrose is most effective for embryo maturation, and those embryos germinated when transferred to a solidified MS medium. The study found that incorporating PEG into the medium reduced the hyperhydration of date palm tissues. The various cultivars reacted differently to the treatments employed.
Ficus benjamina L. were subjected to 48 hr of polyethylene glycol (PEG)-induced water stress. Leaf abscission and concentrations of endogenous ethylene (C2H4) in the leaves were monitored. Leaf abscission began 24 to 48 hr after stress initiation, and most abscission occurred within the first 24 hr after water stress was relieved. PEG-stressed plants lost 35% to 47% of their leaves by 120 hr after the experiment was initiated. Older leaves abscised first and remained green throughout the abscission process. Endogenous C2H4 concentrations increased sharply and then declined during the first 6 hr of water stress. Endogenous C2H4 concentrations then increased gradually, and, by the time leaf abscission began, leaves contained 1.50 to 2.25 µl C2H4/liter.
Germination of tomato (Lycopersicon esculentum Mill.) seeds in petri dishes at various levels of water stress was comparable, except under conditions of severe stress when a PEG pretreatment improved final percentage germination and enhanced the onset and rate of germination. At intermediate or high watering levels, PEG-pretreated seeds germinated more rapidly than untreated seeds, but final germination was not altered by PEG. Germination of seeds in soil, under controlled laboratory conditions, was similar to that in petri dishes except under the driest conditions (5% ASM) when little emergence occurred whether the seeds were pretreated or not. A majority of the seeds which failed to germinate after 2 weeks under dry soil conditions were still viable, since subsequently they could be induced to germinate by moistening the soil to 100% ASM. Water requirement of tomato seeds for optimal rate of germination was cultivar dependent; PI-341988 seeds germinated well at 60% ASM or greater, whereas ST-24 required 100% ASM for best germination.