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  • Author or Editor: Roman M. Mirecki x
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Cellulose diacetate has been widely used in UV-B enhancement studies under field and controlled-environment conditions since the early 1970s to remove wavelengths below ≈290 nm, without any evidence of toxicity effects. However, while conducting UV-B exclusion studies in window boxes covered with cellulose diacetate (CA) or in Plexiglas chambers lined with CA, there was marginal chlorosis and cotyledon epinasty in `Ashley' cucumber, which is normally resistant to elevated UV-B, while seedlings exposed to open sunlight and those grown under polyester (PE) film to exclude UV-B were free of visible injury. These findings suggested that the CA filter itself may be causing toxicity. To test this hypothesis, a UV exclusion study was conducted in which CA or Teflon (T), both UV-B and UV-A transmitting films, were used to cover window boxes in the following four combinations (top/bottom): CA/CA, CA/T,T/CA, and T/T. When CA was used as the bottom filter (CA/CA and T/CA), the plants showed significantly greater leaf injury and a 2- to 3-fold reduction in growth than when T was used as the bottom filter (CA/T and T/T). These findings suggest that toxicity is caused by CA itself rather than by solar UV-B radiation, possibly as a result of outgassing of phthalates known to be used as plasticizers in the manufacture of CA. Further evidence that CA was responsible for leaf injury was provided by a companion study in which T was replaced by PE and damage was still observed, although no significant growth effects of CA position were observed.

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A controlled-environment study was conducted in separate growth chambers with the wall surface covered either with white enamel paint (WEP) or polished aluminum (PA). `Williams' soybean were grown under 1500 mA cool white fluorescent lamps and internodes measured at 7, 14, and 21 days. Photosynthetic photon flux (PPF) levels in the center of each chamber were set at 320 μmol m-2 s-1 with a quantum sensor. Means ± SD for PPF levels in the WEP and PA chambers were 286 ± 28 and 307 ± 11 μmol m-2 s-1, respectively. This increase in mean PPF and decrease in variance of PPF in the PA chamber was reflected in: a) a decrease in hypocotyl, first internode, and total shoot elongation: and b) an increase in enlargement of the primary and the first trifoliolate leaves. These findings demonstrate that plants can detect small differences in irradiance within a growth chamber and suggest the advantages of using a highly polished wall surface to improve uniformity of irradiance and reduce variability in growth.

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UV-B (UV) induced changes in PAL activity and UV-absorbing compounds were followed in cotton after 1 to 9 days and in cucumber after 1 to 14 days. UV increased PAL activity in the lower hypocotyl (LH) of cotton but had no effect on the upper portion. In general, PAL decreased with time, but UV treatment slowed that decline in the LH portion. Anthocyanin concentration declined with time in both portions. In cucumber cotyledons, UV had no effect on PAL. In cucumber leaves, there was no overall effect of UV; but there were significant interactions with time. In both cotyledons and in leaves, PAL decreased with time. As in LH cotton tissue, UV slowed the rate of decline of PAL in cucumber leaves. In leaves, UV absorbing compounds (at 330 nm) were increased by UV; in cotyledons, the increase in absorption was greater in controls than in UV-B irradiated seedlings. In cotton, changes in anthocyanins mirrored those in PAL, this was not the case for UV absorbing compounds in either species.

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The influence of ambient UV radiation on growth and flavonoid concentration of Lactuca sativa L. (`New Red Fire' lettuce) was examined. Plants were grown outdoors for 31 days from seed in window boxes covered with one of three different UV filters—UV transparent tefzel (10%T, 245 nm), UV-B-absorbing polyester (10%T, 319 nm), or UV-Aand UV-B-absorbing Llumar (10%T, 399 nm). Plants were grown in plastic pots filled with vermiculite and subirrigated with nutrient solution. Lettuce plants grown in the absence of solar UV-A and UV-B radiation showed a significant increase in leaf number and biomass of tops and roots as compared to those grown under ambient UV-A and UV-B. They also had a lower concentration of flavonoids and other UV-absorbing substances at 270, 300, and 330 nm (on both an area and on a dry-weight basis). These findings should be of interest to researchers involved in protected cultivation because the transmission of UV-B radiation is greatly attenuated by standard greenhouse glass. Our results also have implications for human nutrition, since bioflavonoids are important as antioxidants.

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Abstract

Soil moisture stress (SMS) and abscisic acid (ABA) pretreatment had a marked effect in modifying SO2 sensitivity in 2 cultivars of poinsettia (Euphorbia pulcherrima Willd. ex Klotzch.) ‘Ruff and Reddy’ and ‘Rudolph’. Plants grown in 10-cm plastic pots in the greenhouse and exposed to SMS by withholding water for 2.5 days prior to SO2 fumigation in the growth chamber (4 hr at 3 μ1·liter−1) showed greatly reduced SO2 injury; both cultivars were protected similarly. SMS treatment also greatly decreased stomatal conductance and transpiration rate of the leaves. ‘Ruff and Reddy’ plants pretreated with ABA (200 mg·liter−1 of the racemic mixture) 4 hr prior to SO2 fumigation were injured less by SO2 than ‘Rudolph’ and had correspondingly lower stomatal conductance and transpiration rate. ‘Rudolph’ plants pretreated with ABA did not show significantly less SO2 injury, even though stomatal conductance and transpiration rate were lower than controls after ABA pretreatment. These findings demonstrate the importance of moisture stress preconditioning in modifying sensitivity of poinsettia plants to SO2 and suggest a protective role for ABA in certain cultivars.

Open Access

Abstract

‘Better Bush’ tomato (Lycopersicon esculentum Mill.) plants were grown in small- (450-cm3) or large-(13,500-cm3) volume plastic containers and harvested every 2 weeks from time of planting until 12 weeks, at which time ripe fruits had developed. Plants were fertilized three to six times daily to prevent drought and nutrient stress. After only 2 weeks, there were significant reductions in total height, node number, leaf area, and dry weight of leaves. By 4 weeks, dry weights of stems and roots were also significantly less in small pots than in large pots. These differences were maintained for the next 10 weeks. Root restriction also generally caused an increase in root : shoot ratio. Roots in small-volume containers formed a highly branched mat, whereas those in large-volume containers had long taproots and showed little branching. Root restriction also significantly reduced the total number and fresh and dry weight of mature fruits. Despite these differences, both groups of plants had nearly 41% of the total photosynthate in the reproductive portion of the plant after 12 weeks of treatment. During weeks 6–8, the mean relative growth rate of plants in small pots was twice that in large pots but thereafter was only half as much. Restricting root volume had little or no effect on net assimilation rate. These data suggest that, for a given growing area, a culture system using small containers would be more efficient in producing fruit for a given weight and size of plant than one using large containers. These findings have important implications for growers and researchers involved in growing plants in confined spaces such as in a phytotron or controlled ecological life support system (CELSS).

Open Access

Isotopic labeling of plants provides a unique opportunity for understanding metabolic processes. A significant challenge of isotopic labeling during plant growth is that isotopes must be administered without disrupting plant development and at sufficient levels for mass spectral analysis. We describe a system for isotopic labeling of leafy vegetables with 13C and demonstrate successful incorporation of 13C into anthocyanins of preheading red cabbage (Brassica oleracea L. var. capitata L.). ‘Super Red’ red cabbage seedlings were grown for 34 days in an airtight acrylic labeling chamber supplied with 13CO2 to maintain 400 μL·L−1. Nutrient solution was delivered hydroponically without allowing infusion of natural CO2 into the labeling chamber. Plants were initially grown at 22 °C ± 1 °C in constant light of 228 μmol·m−2·s−1. Upon canopy closure, anthocyanin development was promoted by reducing the nutrient solution concentration and reducing the temperature to 10.5 °C ± 1.5 °C. Total shoot fresh weight (FW) was 1556 g and root FW was 491 g at harvest. Analysis of red cabbage shoot tissue by high-performance liquid chromatography/tandem mass spectrometry indicated the presence of 37 anthocyanins, of which 14 are reported here for the first time. Mass shifts representing 13C incorporation into anthocyanins were evident in mass spectra of anthocyanins from labeled tissue and demonstrate successful isotopic labeling.

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Abstract

Intact plants of a green-leafed strain of Coleus blumei Benth. (PI 354190) were exposed to 5°C for 48 or 72 hr after pretreatment for 48 hr at two levels of photosynthetic photon flux (PPF) (8 or 320 μmol·s−1·m‒2) at two temperatures (13° or 20°). Plants were sprayed with two abscisic acid (ABA) levels (0 or 200 g·m‒3) either 0 or 48 hr before chilling. Postchilling condition of the plants was assessed by comparing the time courses of refreshed (cyclically excited and measured) delayed light emission (RDLE) and fluorescence (FLU) from dark-equilibrated leaves. Greater suppression of RDLE and FLU indicates greater injury. Plants pretreated at 8 μmol·s−1·m‒2 PPF showed less suppression of RDLE and FLU, contained more chlorophyll, and showed less injury than did plants pretreated at 320 μmol·s−1·m‒2 PPF. Increasing the duration of chilling from 48 to 72 hr reduced the maximum RDLE and FLU slightly. Pretreatment temperatures and ABA concentration had negligible effects on RDLE and FLU levels. The maximum RDLE, the RDLE level at 7.5 sec, the maximum FLU, the FLU at 1.5 sec, and variable FLU were the measurement variables most responsive to individual and combined treatment effects. Maximum RDLE from upper leaf surfaces was the measurement most responsive to the combined effects of all treatments. Chemical name used: [S-(Z,E)]-5-(1-hydroxy-2,6,6-trimethyl-4-oxo-2-cyclohexen-1-yl)-3-methyl-2,4-pentadienoic acid [abscisic acid (ABA)].

Open Access

Cucumis sativus L. (cvs. Poinsett and Ashley) plants were grown from seed in a growth chamber at a +10C (28/18) or a -10C (18/28) difference (DIF) between day temperature (DT) and night temperature (NT) on a 12-hour photoperiod for 24 days prior to ozone (O3) fumigation (3 hours at 0.5 umol·mol-1). Negative DIF, compared to +DIF, reduced plant height, node count, fresh weight, dry weight, and leaf area in both cultivars. Photosynthetic rate (Pn), chlorophyll concentration, and variable chlorophyll fluorescence (Fv) were lower and O3 injury and polyamine concentrations were higher at -DIF than at +DIF. Ozone fumigation generally increased leaf concentration of polyamines and reduced Pn, stomatal conductance, and chlorophyll fluorescence. `Poinsett' generally had a higher specific leaf mass and higher concentrations of chlorophyll a and polyamines than did `Ashley', but there was no cultivar difference in O3 injury, growth response, Pn, or stomatal conductance.

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