Seedlings of sweet corn (Zea mays L. cv. Iochief) were grown in sand with 3 rates of N at a moderate and severe water-stress rate produced by adding polyethylene glycol (PEG 6000) to the nutrient solution. As water stress increased, dry-matter production decreased. Increasing N rate compensated in part for the loss in dry-matter production that resulted from the water stress. Leaf chlorophyll levels and stomatal density on the abaxial leaf surface increased with an increase in N, and a faster recovery of the relative water content of leaf tissue following waterstress treatment occurred. All 3 responses could have contributed to the N response in dry-matter production observed at the 2 water-stress levels. A low N rate may aid young sweet corn seedlings under severe water stress to resist drought, as indicated by a stabilization in dry-matter production in plants receiving only 8 mm N in the nutrient solution when moving from moderate to severe water stress. These plants had a higher relative water content and leaf water potential under severe water stress than plants receiving higher rates of N, which may have contributed to the ability of plants receiving a low-N rate to cope with the severe water stress.
High-density, annual, strawberry production systems (“plasti-culture”) have shown high productivity under New Jersey conditions; however, cultural practice and variety research is needed to increase profitability. The system includes raised beds, plastic mulch, trickle irrigation, and double-row 12 × 12-inch plant spacing. Polypropylene floating rowcovers were applied in December and removed in early April when flowers were visible under the cover. Treatments included comparisons of plugs and dormant crowns of the cultivars Chandler and Allstar, planted at multiple planting dates, on white or plastic mulch, in “matted-row” (single row at 18-inch spacing; peg runners through plastic) or high-density production systems. The plug plants were superior to dormant crowns. Black plastic was best all planting dates with plugs; `Allstar' performed best on black on the early planting dates, while `Chandler' preferred the white for the early planting dates. Both `Allstar' and `Chandler' had commercially profitable yield, fruit weight, and quality. “Matted-row” system on plastic is high-yielding but labor-intensive. Late-summer plugs on black plastic is best overall.
Triploid watermelon seed does not germinate in cold, wet soils as well as diploids; germination is slower due to reduced embryo size and thicker seed coat; fissures on the seed coat provide safe harbour for fungal spores; and triploid fruit set is later than most diploid cultivars. Because of these problems producers often transplant rather than direct-seed seedless watermelons. Seed priming has been shown to improve germination in other crops and would be an attractive method allowing for direct seeding of seedless watermelons. Seed from open-pollinated 4n × 2n crosses were primed in solutions of H2O, polyethylene glycol 8000, KNO3, or left untreated. Treatment times were 1, 3, or 6 days, and treated seed were subsequently dried for either 1 or 7 d. Seed were scored for germination in the laboratory and emergence under field conditions. Germination was better using H2O than KNO3 and PEG but not always better than the untreated control. Treatment time of 1 day was superior to 3 or 6 days, but length of drying time was insignificant. In the field trial, treatments did not differ in emergence.
Developing an efficient gene transfer system for apple (Malus ×domestica L.) remains a major objective in genetic engineering efforts of this fruit crop. Transient expression of the uidA gene coding for β-glucuronidase (GUS) and driven by the cauliflower mosaic virus 35S promoter (CaMV35S) has been induced in apple cotyledonary explants of mature seeds by tungsten particle bombardment using the Particle Inflow Gun (PIG). Several factors that affect transient expression of the GUS gene in apple cotyledons were investigated. The gene transfer efficiency was monitored by recording the number of blue spots observed on explants two days following bombardment. Precultivation of cotyledons for 18 hours before bombardment significantly increased the number of blue foci. Of the three different precipitation methods tested including water, 25% PEG, and 60% glycerol, the latter was the most effective for coating DNA onto tungsten particles. Washing DNA-coated tungsten particles with 70% ethanol and resuspending in 100% ethanol significantly enhanced gene delivery to cotyledons. The amount of particles used for each bombardment also influenced GUS expression. About 0.5 mg of particles per shot resulted in the highest number of blue foci. Using larger quantity of particles (i.e., 2 mg) drastically decreased GUS expression probably due to the toxicity of tungsten particles.
to simulate drought stress in vitro ( Pandey and Agarwal, 1998 ). Polyethylene glycol molecules (PEG 6000) are osmotically active, inert, nonionic, and virtually impermeable to plant cells and are frequently used to induce water stress and maintain
was placed in either H 2 O 2 or polyethylene glycol (PEG) (5%; 1, 3, or 5 h). Proteins were extracted as previously described ( Ahn et al., 2004 ) using an extraction buffer [0.3% sodium dodecyl sulfate (SDS), 200 m m dithiothreitol, 28 m m Tris
The effects of chemical or physical factors during pregermination imbibition phase, or on dry seeds, on embryo growth potential (EGP) was studied in lettuce (Grand Rapids and Mesa 659) and tomato (H-9889) seeds in relation to dormancy, invigoration, and vigor loss. Embryos were excised from treated seeds (washed if imbibed in chemical solutions) and their growth rate (a measure of EGP) followed at 25°C at high magnification (X55). Treated seeds were also germinated at 25°C. In lettuce seeds, dormancy inducing treatments, i.e., a 2-day dark soak at 25°C with 50–100 μM tetcyclacis (TCY) or a 2-day dark soak in water at 35°C, reduced the subsequent embryo growth and germination rate at 25°C. The reduction was prevented by 1 mM GA4+7 or irradiation applied during dormancy induction. A -d osmoconditioning (OC) at 15C with -1.2 MPa PEG-8000 solution in light or in dark with added GA4+7 enhanced the EGP; addition of TCY reduced the EGP and the TCY inhibition reversed by GA4+7. A progressive reduction in EGP occurred with increase in vigor loss. In tomato seeds, a soak with 100 μM TCY in light or dark for 2 days at 30°C induced a dormancy, but had little effect on EGP. Application of GA4+7 plus TCY prevented dormancy induction without affecting EGP. A 4-day matriconditioning (MC) at 25°C in light or dark with moist Micro-Cel E enhanced the EGP; TCY and/or GA added during MC, had little effect on EGP. EGP progressively decreased as the aging period increased. Thus, in lettuce, the EGP is coupled with the reversible –GA/+GA or phytochrome-controlled dormancy induction/release process, enabling germination, its inhibition, or its enhancement. In tomato, the EGP is not subject to light or GA control. Reduction in EGP, accompanying vigor loss in both seeds, is independent of light or GA action.
Using an aqueous polymer two-phase [polyethylene glycol (PEG) 3400/dextran T500, 6.2%: 6.2%, w/w] partitioning procedure combined with isopycnic fractionation, plasma membranes derived from muskmelon (Cucumis melo L. var. reticulates Naud.) leaf blades have been isolated and examined for marker enzyme activity, density, and molecular composition. After aqueous polymer partitioning, plasma membranes were centrifuged on a linear sucrose density gradient, and a single band was found at the 31% (w/w) sucrose (1.13 g-cm-3). Identification of plasma membranes was performed by the combination of K+-stimulated ATPase, pH 6.5, vanadate inhibition of ATPase and KNO3-insensitive ATPase activity. Plasma membranes from seedling leaves grown for 5 days at 15C had the highest concentration of total phospholipids, the lowest concentration of proteins, and a total sterol concentration not significantly different from leaves grown at 30C. The total sterol to total phospholipid ratio of the plasma membrane from leaves grown for 5 days at 15C was ≈1:1; from leaves grown for 10 days at 15C or 5 days at 30C the ratio was ≈2:1; and from leaves grown for 10 days at 30C the ratio was ≈3:1. The plasma membrane phospholipid saturated to unsaturated fatty acid ratio from leaves grown for 5 days at 15C was ≈0.8:1.0; from leaves grown for 10 days at 15C or 5 days at 30C the ratio was ≈1.0:1.0; and from leaves grown for 10 days at 30C it was 1.4:1.0.
Among the factors affecting germinability of a seed lot are the environmental conditions under which the seeds are produced. The objective of this study was to determine the effects of temperature during seed development on seed quality of two Asteraceae species. Seeds of lettuce cv. Tango and Helianthus debilis cv. Vanilla Ice and sp. cucumerifolius were produced in a greenhouse under one of two treatments: i) hot (27, 40, and 20 °C temperatures average, max, and min, respectively), and ii) cool (23, 33, and 18 °C temperatures average, max, and min, respectively). In both species, heavier seeds were produced under the cool conditions and no differences were observed in standard germination. In lettuce, germination percentage and rate were both affected by increased levels of exogenous ABA concentrations and reduced water potential (PEG solutions), and, in both cases, seeds from cool treatments were more affected. Germination at 30 °C and constant light was higher for seeds from the hot treatment. Lettuce seed showed a strong light requirement for germination. However, seeds from the hot treatment gave better dark germination at 13 and 19 °C. Seeds of H. debilis did not required light for germination, and the germination percentage and rates were evaluated at 13, 21, and 29 °C. For both lines, seeds from each treatment behave similarly; however, the germination of H. debilis cv. Vanilla Ice at 29 °C was higher when seeds were produced in the hot conditions. The results showed that temperature during seed development affected aspects of seed quality that are not detectable by the standard germination, but by germination at suboptimal conditions. Within the Asteraceae family, differences varied among and within species.
Aleppo Pine (Pinus halepensis Mill.) is known to be the most drought-resistant Mediterranean Pine. This species is widely distributed throughout the Mediterranean region and displays a high intraspecific variability, with respect to its physiological and morphological response to environmental conditions. In this experiment we evaluated the response of Pinus halepensis seedlings to drought. Sixty germinated seeds (accession A6, Shaharia, Israel) were grown in soil for 8 weeks and then transferred to black plexiglass tanks containing half-strength air-sparged Hoagland solution. After 6 weeks of acclimation to hydroponics, the osmotic potential of the solution was lowered by adding polyethylene-glycol (PEG) 8000. Water potential was lowered in 0.2 MPa increments every 4 days, until a final value of –0.8 was reached. The seedlings were then maintained at –0.8 MPa for a further 8 days. Ultrasonic acoustic emissions, pressure–volume (P–V) curves, shoot and root growth, leaf area, xylem diameter, root apex mitotic index and cell length were measured on control and stressed seedlings. Seedlings were then transferred to normal Hoagland solution for 24 hours to simulate rewatering, and P–V curves and ultrasonic emissions measurements were repeated. Results showed that the final root growth is maintained in the stressed seedlings at the same rate as controls, whereas shoot growth was significantly reduced. The leaf area was reduced by stress to 36%, but the xylem diameter only to 10%, leading to a lower leaf area:xylem section ratio in the stressed plants. Ultrasonic emissions in the stressed plants were 365% of the control, and 182%, after rewatering. Specific details of the growth and physiology data are presented.