Cytokinins play an important role in regulating plant growth and development. The cytokinin gene, isopentenyl transferase (ipt), was placed under the control of the ACC oxidase promoter from the LEACO1 gene from Lycopersicon esculentum and introduced into Nicotiana tabacum (cv. Havana) and chrysanthemum (Dendranthema × grandiflorum `Iridon'). Transformants were confirmed by PCR reaction and Southern blot and analyzed for phenotypical changes under both greenhouse and growth chamber conditions. With both species, LEACO1-ipt transgenic plants displayed a wide range of vegetative and generative phenotypes. With plants growing in the vegetative state, some LEACO1-ipt transgenic lines appeared similar to the non-transgenic wild-type cultivars while other lines showed excessive lateral branch development and short internodes. With plants grown under generative conditions, several LEACO1-ipt transgenic lines showed a 2 to 10-fold increase in the number of flower buds relative to the wild-type cultivars. With chrysanthemum, dramatic increases in bud count were observed on transgenic lines that otherwise displayed a morphology similar to the non-transgenic lines. Analysis of ipt expression indicated a marked change in gene expression between the most extreme phenotypes observed in this study. LEACO1-ipt lines that express normal vegetative development but increased flower bud counts appear to have great potential for ornamental crop improvement.
The bacterial isopentenyl transferase (ipt) gene involved in cytokinin biosynthesis was fused with a promoter from the serine proteinase inhibiter (win3.12) gene of Populus x generosa and introduced into Nicotiana tabacum (cv. Havana). Transformants were confirmed by PCR reaction and Southern blot analysis, and then analyzed for phenotypic characteristics. RT-PCR analysis detected transcripts of the ipt gene following the wounding of win3.12:ipt transgenic plants. In win3.12: ipt transgenic plants, lateral shoot number and the diameter of lateral branches that developed following apical shoot removal increased relative to wild-type plants. However, the increase in cytokinin production following wounding appeared to be short lived. The potential utility of this construct in enhancing lateral branching in ornamental crops will be discussed.
Poinsettias were grown in a closed hydroponic system with a modified Hoagland's solution concentration of either 1 or 3 mS·cm-1. Water use and whole plant fresh mass were measured gravimetrically at 2 to 3 day intervals over an eleven week period (initial break development through full bract development). At two week intervals, poinsettias were harvested and the fresh and dry mass of leaves, bracts stems, and roots were determined, and total laminar surface area was measured. Leaf temperature (LT), root-zone solution temperature (RZT), and at canopy level, air temperature (CAT), VPD, and photosynthetic photon flux (PPF) were monitored at 1 mm intervals and mean values recorded each 30 mm using a 21X micrologger (Campbell Scientific, Logan Utah). Water use (ml·dm-2·day-1) averaged 15% higher for poinsettias grown in the 1 mS·cm-1 solution than in the 3 mS·cm-1 nutrient solution. Simple linear regression of daily water use with PPF, or VPD, or CAT, while significant, accounted for less than half of the daily fluctuation in water use (r2; PPF= 0.47, VPD=0.21, CAT=0.30). However, multiple regression involving daily PPF, VPD, CAT, RZT and LT accounted for up to 82% of the variation in daily water use.
Chill injury and leaf senescence occur in plants held in prolonged cold, dark storage. To increase tolerance to these conditions, Nicotiana alata and N. tabacum were transformed with either the FAD7 or IPT genes under the control of a cold-inducible promoter (cor15a). FAD7 encodes for omega-3-fatty acid desaturase and was used to resist cold-stress. IPT encodes the cytokinin-pathway enzyme isopentenyl transferase and was used to delay senescence. Independent FAD7 and IPT lines were crossed to produce double transgenic seed. Seedlings from single transgenic (cor15a-IPT or cor15a-FAD7) lines, double transgenic lines, and the wild-type were exposed to prolonged cold, dark conditions. After 3 months in the dark at 2 °C, survival of independent double transgenic N. tabacum lines ranged up to 80% to 90%. However only 40% of FAD7 seedlings survived, 10% of IPT seedlings survived, and no wild-type plants survived. Double transgenic N. alata seedlings average 90% survival under similar conditions and RT-PCR revealed expression of both the IPT and FAD7 genes. Omega-3-FAD enzyme activity increases desaturation in chloroplast membrane fatty acids. When exposed to prolonged cold, the molecular fraction of polyunsaturated fatty acids (18:3 and 16:3) in leaves of wild-type N. alata decreased while monounsaturated (16:1 and 18:1) and saturated fatty acid species (16:0 and 18:0) increased dramatically. In double transgenic N. alata lines exposed to prolonged cold, the molecular fraction of 18:3 and 16:3 increased, while the 16:0 and 18:0 species decreased dramatically compared to nonchilled double transgenic plants.
The accuracy of a computer planning model for the management of a single-truss tomato (Lycopersicon esculentum Mill.) production system was tested in the greenhouse. The model was used to generate a production schedule for 24 successive crops during a 15-month study. The time, in days, required for an emerging seedling to reach anthesis and the total fresh weight fruit yield were predicted for each of the 24 crops by the planning model. Correlation analysis, used to compare the expected crop response (i.e., data generated by the planning model) to the actual crop response, indicated that both the number of days from emergence to anthesis and fresh weight fruit yield were accurately forecast, r2 = 0.76 and 0.83, respectively. More important, the cropping schedule that was generated by the planning model successfully produced a continuous harvest of tomatoes from sequential crops.
Can regulated deficit irrigation in an ebb and flow system alleviate the effects of salinity stress on poinsettia? Two cultivars of poinsettia (Euphorbia pulcherrima Willd ex Klotzsch) were grown under partial- or full-saturation irrigation using a standard fertilizer solution, with or without the addition of 0.5 g·L−1 NaCl. The volumetric water content of the medium averaged 0.25 and 0.33 L·L−1 before irrigation, and 0.5 and 0.67 L·L−1 following irrigation, for partial- or full-saturation regimes, respectively. Plants had lower fresh weight with partial than full saturation. Sodium concentrations in bract, leaf, and stem tissues were higher (P ≤ 0.05) in plants exposed to salinity, and these plants accumulated less K in stems and less P in bracts. Eight cultivars were grown in a second study with or without salinity of 1.2 g·L−1 NaCl under drip or ebb and flow watering. Cultivar and watering had effects on plant fresh weight, but salinity did not. Of the cultivars tested, ‘DaVinci’, ‘Premium Picasso’, and ‘Prestige Red’ had the highest sodium in bracts under salinity with drip irrigation, whereas ‘Snowcap’ had the least. ‘Ruby Frost’ had the most sodium in stems, whereas ‘Snowcap’ had the least. For all cultivars, added salinity resulted in lower K in leaves and stem. Snowcap was the cultivar with the least sodium in stems and bracts under saline irrigation, with either drip or ebb and flow. Our research demonstrates that regulated deficit irrigation resulting in partial saturation of the growing medium is an effective water management option, when control of plant height and overall crop growth are desirable, and it limits the accumulation of sodium when raw water contains elevated salinity.
A 920 bp fragment of the ACC oxidase gene promoter from tomato (LEACO1) was used to drive GUS gene expression. The LEACO10.92kb fragment contained two stress-responsive short motifs; a 10 bp TCA motif (5'-TCATCTTCTT-3') twice (allowing two substitutions) and an 8 bp element (5'-AA/TTTCAAA-3') once. The TCA motif is found in over 30 stress- and pathogen-inducible genes while the 8 bp element is necessary for ethylene-response in the carnation GST1 and the tomato E4 gene promoters. Previously in chrysanthemum, cytokinin regulation with LEACO10.92kb produced dramatic increases in lateral branching and bud initiation. Tobacco plants carrying LEACO10.92kb–GUS were used to examine the response of the LEACO10.92kb promoter to various hormones and hormone inhibitors. GUS activity in LEACO10.92kb–GUS plants was detected in leaves and stems, but not roots. High expression was detected in shoots with the apical bud intact, but GUS activity decreased with the apical bud removed. Applying IAA to the shoot apex after removing the apical bud, restored GUS activity. However, the IAA transport inhibitor TIBA reduced GUS activity in shoots with intact apical buds, and in IAA-treated shoots with excised buds. In shoots with excised apical buds, GUS activity increased when the ethylene precursor ACC was applied, but decreased in intact shoots when the ethylene biosynthesis inhibitor AOA was applied. These data suggest that auxins produced in the apical meristem are capable of regulating LEACO10.92kb activity, probably through auxin-induced ethylene biosynthetic pathway activity.
The rapid expansion of Asian populations in the United States presents significant opportunities and challenges for the eastern U.S. produce sector to take advantage of their close proximity to densely populated areas. Initial crop studies followed by ethnic consumer and crop surveys were conducted to examine vegetable, leafy green, and herb consumption and expenditures among Chinese, Asian Indians, and other Asian groups. Consumer choices were used to prioritize subsequent production trials. Family expenditures were determined for specific Asian produce types and total produce purchases. This market data were extrapolated to the east coast Asian populations to assess potential market size (90% confidence interval, error margin 5.6%). Chinese consumer values ranged from $245 to $296 million per annum and Asian Indians ranged from $190 to $230 million per annum. The average annual fresh fruit and vegetable expenditures by both Asian groups were 2 to 3.5 times respective national averages. Leading Chinese vegetables determined by average expenditures were baby bok choy, pak choy, oriental eggplant, snow pea, oriental spinach, and napa cabbage. Highest expenditure of leafy greens and herbs for Chinese consumers were chives and garland chrysanthemum. This market-driven survey reported consumption of over 100 Asian crops and 42 cultivars were ranked “feasible” to grow in the eastern section of the United States. Horticultural matrices of selection criteria narrowed the list to the most promising candidates for production. As a result, 28 cultivars were then grown in University research and demonstration plots at Massachusetts, New Jersey, and Florida in determining growth characteristics and yield to focus horticultural crop producers. Leading vegetable cultivars for Asian Indian consumers were bitter gourd, eggplant, fenugreek leaves, cluster beans, and bottle gourd. Leading leafy greens and herbs for Asian Indians were turmeric, fenugreek, sorrel spinach, and radish greens. Most of these Asian cultivars were demonstrated to grow well in the three main growing zones of 5, 7, and 9. Phytochemical attributes such as antioxidant activity, polyphenols, and mineral contents were analyzed for several of the leading crop candidates. This initial field and laboratory data shows that many of these ethnic crops can be grown in the eastern United States to direct production opportunities and are nutrient rich to help drive consumer demand.
Euonymus alatus (Thunb.) Sieb., commonly known as “burning bush,” is an extremely popular landscape plant in the United States as a result of its brilliant showy red leaves in fall. However, E. alatus is also seriously invasive because of its prolific seed production and effective seed dispersal by birds. Thus, development of sterile, non-invasive, seedless triploid E. alatus is in high demand. In this article, we report successful production of triploid E. alatus using endosperm tissues as explants. In our study, ≈50% of immature endosperm explants and 14% of mature endosperm explants formed compact, green calli after culture in the dark for 8 weeks and then under light for 4 weeks on Murashige and Skoog (MS) medium supplemented with 2.2 μM BA and 2.7 μM α-naphthaleneacetic acid (NAA). Approximately 5.6% of the immature endosperm-derived calli and 13.4% of mature endosperm-derived calli initiated shoots within 8 weeks after they were cultured on MS medium with 4.4 μM benzyladenine (BA) and 0.5 μM indole-3-butyric acid (IBA). Eighty-five percent of shoots rooted after culture on woody plant medium (WPM) containing 4.9 μM IBA for 2 weeks and then on hormone-free WPM medium containing 2.0 g·L−1 activated charcoal for 4 weeks. Eight independently regenerated triploid plants have been identified. Triploid plant regeneration rates observed were 0.42% from immature endosperm explants and 0.34% from mature endosperm explants, respectively, based on the number of endosperm explants cultured. Because triploid plants cannot produce viable seeds, and thus are sterile and non-invasive, some triploid E. alatus plant lines reported here can be used to replace the currently used invasive counterparts. Chemical names used: benzyladenine (BA), indole-3-butyric acid (IBA), and α-naphthaleneacetic acid (NAA).