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Anne K. Hurley and B. Greg Cobb

Cucumis sativus, L., `Poinsett' seedlings were grown under artificial light in 40% modified Hoagland's solution until an average plant plastochron index of 4.73 was reached. Plants were then placed in solutions of (1) 0 mM NaCl, (2) 80 mM NaCl (salt-shock), or (3) placed in a dropwise gradient solution of NaCl and Hoagland's until the final concentration of 80 mM NaCl was reached at 41 hours. Leaves of the 80 mM shock treatment wilted immediately, but recovered turgor within 6 hours. Leaves of 80 mM gradient did not wilt at anytime. The control and gradient treatments had relative growth rates which were similar to each other, but RGR decreased in the shock treatment. Invertase activity was measured in the roots at 24, 41, and 48 hours after initial treatment. Invertase activity of shock treatment increased significantly over the controls at 24 hours. The 80mM gradient was not significantly different than either treatment. Four isozymes of α– galactosidase were detected. The relative intensities of the bands varied with time and treatment. One invertase band was resolved in roots on 8% native acrylamide gels. SDS gels indicated increases in proteins in the gradient treatment compared to the control and the 80 mM shock treatment.

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Anne K. Hurley and B. Greg Cobb

Cucumis sativus, L., `Poinsett' seedlings were grown under artificial light in 40% modified Hoagland's solution until an average plant plastochron index of 4.73 was reached. Plants were then placed in solutions of (1) 0 mM NaCl, (2) 80 mM NaCl (salt-shock), or (3) placed in a dropwise gradient solution of NaCl and Hoagland's until the final concentration of 80 mM NaCl was reached at 41 hours. Leaves of the 80 mM shock treatment wilted immediately, but recovered turgor within 6 hours. Leaves of 80 mM gradient did not wilt at anytime. The control and gradient treatments had relative growth rates which were similar to each other, but RGR decreased in the shock treatment. Invertase activity was measured in the roots at 24, 41, and 48 hours after initial treatment. Invertase activity of shock treatment increased significantly over the controls at 24 hours. The 80mM gradient was not significantly different than either treatment. Four isozymes of α– galactosidase were detected. The relative intensities of the bands varied with time and treatment. One invertase band was resolved in roots on 8% native acrylamide gels. SDS gels indicated increases in proteins in the gradient treatment compared to the control and the 80 mM shock treatment.

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Patrick T. Smith and B. Greg Cobb

Sweet pepper (Capsicum annuum L. cv. Keystone Resistant Giant #3) seeds were imbibed (primed) in salt solutions to determine a) what concentrations would inhibit radicle emergence and b) the influence this delay in radicle emergence would have on subsequent germination. Seeds were primed for 17 days at 23C in petri dishes with KNO3, KCl, NaCl, K2SO4, Na2SO4, 1 NaCl: 1 CaCl2 (mol/mol), Ca(NO3)2, CaCl2, Na2HPO4, and K2HPO4 in 10, 25, 50, 100, 200, or 300 mm of the salts. Germination was not inhibited in the 10- to 100-mm salt range, although most 200- and all 300-mm solutions reduced radicle emergence to <5.0%. The time to 50% germination (T50) of these primed seeds in water significantly (P < 0.01) decreased, when compared to unprimed seeds, and a negative correlation (r = – 0.98) was observed between this reduction and the osmotic potential of the solutions. Solutions with the highest osmotic potentials most severely reduced T50 without reducing the final germination percentage. For seeds primed in K2SO4 or Na2SO4 (200 and 300 mm) through 18 days, the reduction in T50 and duration of priming were negatively correlated (r = - 0.99). Seeds soaked in double distilled water and then dried germinated faster than controls, but not as fast as seeds primed in salt solutions. Priming of pepper seeds in this study was dependent on the osmotic potential of the solution, rather than a specific salt, and the duration of treatment.

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Kil Sun Yoo, Leonard M. Pike, and B. Greg Cobb

Inner scales excised from dormant bulbs of the short-day `Texas Grano 1015Y' onion (Allium cepa L.) were cultured in vitro and leaf growth was examined. Light promoted leaf growth, but no differences in leaf growth were observed for media pH between 4 and 7. Leaf growth rate in darkness was highest at 24C, reduced at 15C, and greatly reduced at SC. Kinetin promoted leaf growth at 1, 10, and 100 μm. IAA was effective at 1 and 10 μM, but not at 0.1 and 100 μm. GA3 promoted growth at 0.1 μM. No inhibitory effects of ABA on leaf growth could be detected. Chemical names used: 1-H-indole-3-acetic acid (IAA), abscisic acid (ABA), gibberellic acid (GA3), 6-furfurylaminopurine (Kinetin).

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Dina Margaret Samfield, Jayne M. Zajicek, and B. Greg Cobb

Seeds of tickseed (Coreopsis lanceolata L.) and purple coneflower [Echinacea purpurea (L.) Moench] were primed in aerated solutions of distilled water or 50 or 100 mM salt (potassium phosphate, pH 7.0) at 16C for 3, 6, 9, or 12 days. Coreopsis seeds primed in the 50 mM buffer germinated the most rapidly and uniformly, and, under stress conditions in the greenhouse, resulted in a faster-growing, more-uniform crop than other treatments. Seeds primed in distilled water and the 50 mM buffer germinated faster and at higher rates at suboptimal temperatures in the laboratory than nonprimed seeds. Priming of Echinacea purpurea seeds for 6 or 9 days in distilled water or in the 50 mM buffer resulted in faster, more-uniform germination than other treatments. Seedling emergence under stress conditions was improved by all priming regimes, with best emergence occurring in treatments that lasted > 3 days. Priming also increased germination rates of E. purpurea at suboptimal temperatures in the laboratory.

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Beyoung-han Yoon, Harvey J. Lane, and B. Greg Cobb

Pansy (Viola × wiffrockiana cv. Majestic Giant Blue Shades and Crystal Bowl Sky Blue) seeds were primed in various salt sololions at -1.0 MPa for 3, 6 or 9 days at 23C to determine if priming could overcome thermoinhihition at high temperatures (30C and above). Salt solutions tested were KNO3, KCl, NaCl, MgCl2, Na2SO4, Na2HPO4, K2HPO4 and CaCl2, with polyethylene glycol (PEG) serving as a comparison non-salt solution. Total percent germination (G) of non-primed seeds decreased significantly for both cultivars as germination temperature increased from 25C to 35C. Total seed germination and time to 50% germination (TS,) varied widely among the different priming solutions, with all solutions decreasing Tso as compared to non-primed seeds. Seeds primed with PEG for 6 and 9 days, however, germinated during the priming process and were not further examined. Priming did not significantly improve total percent germination versus non-primed seed at 25C. Seeds that had the best G and T50 at temperatures at or above 30C were those primed for 3 days with CaCl2 (for `Crystal Bowl' there was a 40% increase in G at 35C), and MgCl2 (for `Majestic Giant' there was a 15% increase in G at 35C).

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BeYoung-Han Yoon, Harvey J. Lang, and B. Greg Cobb

Priming regimes were evaluated on pansy seeds (Viola ×wittrockiana Gam. `Crystal Bowl Sky Blue') in high-temperature germination tests. Priming regimes evaluated included CaCl2, MgCl2, K2HPO4, Na2HPO4, NaCl, KCl, KNO3, Na2SO4, and polyethylene glycol 15,000 (PEG15,000) at –1.0 and –2.0 MPa, for 3, 6, or 9 d at 23 °C. Primed and nonprimed control seeds were then germinated at 25, 30, or 35 °C. Total percent germination of nonprimed control seeds was significantly less at 35 °C than at 25 °C. Seeds primed with CaCl2 at –1.0 MPa for 3 d at 23 °C had significantly higher germination at 35 °C than all other priming regimes tested, including aerated PEG8000 at –1.0 MPa for 7 d at 15 °C. Seed respiration, measured by O2 uptake, during germination of seeds primed with CaCl2 was higher than for control seeds or those primed with PEG8000. Priming pansy seed with CaCl2 at –1.0 MPa for 3 d at 23 °C was effective in increasing seedling emergence and for reducing the time of emergence in summer greenhouse studies.

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Peng Hwang, J. Creighton Miller Jr., and B. Greg Cobb

Field studies were conducted at two Texas locations: Lubbock, near the major production area for Texas potatoes, and College Station which is hotter and more humid. Early and late plantings were established at each location to compare cool and hot growing conditions. Nine genetically diverse cultivars, including those previously reported to be heat resistant or susceptible, were used in this study. Results indicated that the distribution of soluble carbohydrate and starch differed significantly among plant parts. In leaves and stems, glucose and fructose were the major soluble carbohydrates, while sucrose was the major soluble carbohydrate in tubers. Total soluble carbohydrate and starch content in leaves, stems and roots from the early plantings were significantly higher than those from the late plantings. Inositol increased significantly in the College Station late stress environment.

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Dina Margaret Samfield, Jayne M. Zajicek, and B. Greg Cobb

Seeds of tickseed (Coreopsis lanceolata L.) and purple coneflower [Echinacea purpureo (L.) Moench] were primed in aerated solutions of a 50 mm potassium phosphate buffer at 16C. C. lanceolata seeds were primed for 3 or 6 days; E. purpurea seeds were primed for 6 or 9 days. Seeds were vacuum-stored for 2 months immediately after priming. Identical treatments were imposed on open-stored seeds just before the termination of the storage duration, thus producing four treatments: a vacuum-stored control, an open-stored control, primed vacuum-stored seed, and seed primed after open storage. Although priming significantly improved the performance of C. lanceolata seed, vacuum storage alone also significantly increased the speed of germination and final germination. The advantage of priming was diminished during 2 months of vacuum storage of E. purpurea, but priming enhanced germination as compared with the open-stored nonprimed control. There was little difference between the performance of E. purpurea seeds both primed and vacuum-stored. and the vacuum-stored control.

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B. Greg Cobb, Malcolm C. Drew, David L. Andrews, James Johnson, David M. MacAlpine, Tricia L. Danielson, Meredith A. Turnbough, and Ronald Davis