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1

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Inhibitory effects of ambient levels of solar UV-A and UV-B radiation on growth of cv. New Red Fire lettuce (1998)

Krizek, Donald T. ; Britz, Steven J. ; Mirecki, Roman M.

Copenhagen : Munksgaard International Publishers

Physiologia plantarum 103 (1998), S. 0

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ISSN: 1399-3054

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: The influence of solar UV-A and UV-B radiation at Beltsville, MD, USA, on growth of Lactuca sativa L. (cv. New Red Fire lettuce) was examined during early summer of 1996 and 1997. Plants were grown from seed in plastic window boxes covered with Llumar to exclude UV-A and UV-B, polyester to exclude UV-B, or tefzel (1996) or teflon (1997) to transmit UV-A and UV-B radiation. After 31–34 days, plants grown in the absence of solar UV-B radiation (polyester) had 63 and 57% greater fresh weight and dry weight of tops, respectively, and 57, 72 and 47% greater dry weight of leaves, stems and roots, respectively, as compared to those grown under ambient UV-B (tefzel or teflon). Plants protected from UV-A radiation as well (Llumar) showed an additional 43 and 35% increase, respectively, in fresh and dry weight of tops and a 33 and 33% increase, respectively, in dry weight of leaves and stems, but no difference in root biomass over those grown under polyester. Excluding ambient UV-B (polyester) significantly reduced the UV absorbance of leaf extracts at 270, 300 and 330 nm (presumptive flavonoids) and the concentration of anthocyanins at 550 nm as compared to those of leaf extracts from plants grown under ambient UV-A and UV-B. Additional removal of ambient UV-A (Llumar) reduced the concentration of anthocyanins, but had no further effect on UV absorbance at 270, 300 or 330 nm. These findings provide evidence that UV-B radiation is more important than UV-A radiation for flavonoid induction in this red-pigmented lettuce cultivar. Although previous workers have obtained decreases in lettuce yield under enhanced UV-B, this is the first evidence for inhibitory effects of solar UV-A and UV-B radiation on lettuce growth.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1034/j.1399-3054.1998.1030101.x

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2

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Inhibitory effects of ambient levels of solar UV-A and UV-B radiation on growth of cucumber (1997)

Krizek, Donald T. ; Mirecki, Roman M. ; Britz, Steven J.

Oxford, UK : Blackwell Publishing Ltd

Physiologia plantarum 100 (1997), S. 0

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ISSN: 1399-3054

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: The influence of solar UV-A and UV-B radiation at Beltsville, Maryland, on growth and flavonoid content in four cultivars of Cucumis sativus L. (Ashley, Poinsett, Marketmore, and Salad Bush cucumber) was examined during the summers of 1994 and 1995. Plants were grown from seed in UV exclusion chambers consisting of UV-transmitting Plexiglas, lined with Llumar to exclude UV-A and UV-B, polyester to exclude UV-B, or cellulose acetate to transmit UV-A and UV-B. Despite previously determined differences in sensitivity to supplemental UV-B radiation, all four cultivars responded similarly to UV-B exclusion treatment. After 19–21 days, the four cultivars grown in the absence of solar UV-B (polyester) had an average of 34, 55, and 40% greater biomass of leaves, stems, and roots, respectively, 27% greater stem height, and 35% greater leaf area than those grown under ambient UV-B (cellulose acetate). Plants protected from UV-A radiation as well (Llumar) showed an additional 14 and 22% average increase, respectively, in biomass of leaves and stems, and a 22 and 19% average increase, respectively, in stem elongation and leaf area over those grown under polyester. These findings demonstrate the extreme sensitivity of cucumber not only to present levels of UV-B but also to UV-A and suggest that even small changes in ozone depletion may have important biological consequences for certain plant species.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1399-3054.1997.tb00014.x

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3

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Spectral quality during pod development affects omega-6 desaturase activity in soybean seed endoplasmic reticulum (1994)

Holden, Marcia J. ; Norman, Helen A. ; Britz, Steven J.

Oxford, UK : Blackwell Publishing Ltd

Physiologia plantarum 91 (1994), S. 0

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ISSN: 1399-3054

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: Polyunsaturated fatty acids (i.e. linoleic acid [18:2], linolenic acid [18:3]) in triacylglycerols (TAG) of soybean seeds increase more during reproductive development under simulated shadelight: i.e., light with reduced blue and/or increased far-red (Britz and Cavins 1993). Elevation of 18:2 and 18:3 is matched by corresponding reduction of oleic acid (18:1), consistent with observations that total seed oil remains constant. We therefore tested the hypothesis that spectral quality affects the activity of the omega-6 and/or omega-3 desaturases involved in TAG biosynthesis. Membranes were isolated from developing soybean cotyledons 24–31 days after flowering. Separate fractions, enriched for chloroplasts and endoplasmic reticulum (ER) respectively, were obtained by sucrose gradient centrifugation and incubated in an in vitro desaturase assay system containing 14C-18:1–CoA at room temperature. Omega-6 and omega-3 desaturase activity was calculated from the rate of formation of 14C-18:2 and 14C-18:3. Radioactive 18:2 and 18:3 were recovered only from phosphatidylcholine (PC) in both ER and chloroplast membranes, consistent with membrane-bound desaturases with specificity towards PC. The specific activity of omega-6 desaturase was high in ER membranes from seeds matured under light sources that promote a canopy shade response, but was reduced in membranes from seeds matured under lamps (high blue and low far-red emission) previously shown to reduce the level of 18:2 in seed oil by 50%. Chloroplast membranes possessed both omega-6 and omega-3 desaturases. Light appeared to have little or no effect on the activity of chloroplast desaturases.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1399-3054.1994.tb00443.x

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4

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The effect of daylength on photosynthate partitioning into leaf starch and soluble sugars in a gibberellin-deficient dwarf mutant of Zea mays (1988)

Britz, Steven J. ; Saftner, Robert A.

Oxford, UK : Blackwell Publishing Ltd

Physiologia plantarum 73 (1988), S. 0

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ISSN: 1399-3054

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: The possibility that gibberellins (GAs) mediate the photoperiodic regulation of photosynthate partitioning into stored leaf carbohydrates (starch and soluble sugars) was investigated with the dwarf-5 mutant of Zea mays L., a single-gene recessive mutant with greatly reduced endogenous GA content relative to tall maize. The mutant responded to daylength as did tall maize, with higher rates of carbohydrate accumulation observed under short daylength (8.5 h of light) than under long day-length (14 h of light). Neither inhibitors of GA biosynthesis (CCC, [(2-chloroethyl) trimethylammonium chloride], ancymidol[α-cyclopropyl-α-(p-methoxy-phenyl)-5-pyrimidine methyl alcohol], and tetcyclacis [5-(4-chlorophenyl)- 3,4,5,9, 10-penta-azatetracyclo-5,4,1,02.6,08.11-dodeca-3.9-diene]) nor treatment with GAs further modified the response of partitioning to daylength even though biologically active GAs stimulated plant growth. The results indicate that photoperiodic modulation of endogenous GA titre is unlikely to be responsible for the photoperiodic response of photosynthate partitioning in Z. mays.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1399-3054.1988.tb00593.x

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5

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Light-enhanced perception of gravity in stems of intact pea seedlings (1982)

Britz, Steven J. ; Galston, Arthur W.

Springer

Planta 154 (1982), S. 189-192

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ISSN: 1432-2048

Keywords: Graviperception ; Epicotyl (gravitropism) ; Light and graviperception ; Pisum

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Dark-grown, 6-d-old pea seedlings (Pisum sativum L. cv. Alaska) do not respond gravitropically to brief (approx. 3 min) horizontal presentations, but seedlings given a pulse of red light (R) 16–24 h earlier respond to such stimuli by vigorous curvature of the epicotyl. With continuous horizontal stimulation (approx. 100 min), the kinetics and extent of the gravitropic response are almost identical in irradiated and dark-control plants. Prior R thus increases graviperception without altering the rate-limiting steps underlying the generation of curvature. This effect of R on graviperception develops slowly; seedlings studied only a few hours after R show differences in the kinetics of the gravitropic response, but not in presentation time. Neither the kinetics nor the extent of gravitropic curvature should be used as criteria for establishing changes in primary processes in gravitropism.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00387915

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6

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Rhythms during extended dark periods determine rates of net photosynthesis and accumulation of starch and soluble sugars in subsequent light periods in leaves of Sorghum (1987)

Britz, Steven J. ; Hungerford, Wayne E. ; Lee, David R.

Springer

Planta 171 (1987), S. 339-345

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ISSN: 1432-2048

Keywords: Photosynthate partitioning ; Photosynthesis ; Circadian rhythm ; Photoassimilate export ; Carbohydrate

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Photosynthesis and photosynthate partitioning in leaves of Sorghum bicolor (L.) Moench exhibited a cyclic dependence on the duration (10–62 h) of dark periods inserted prior to bright light test periods (550 μmol·s-1·m-2, photosynthetic photon flux). Maximum rates of net photosynthesis and of accumulation of starch and soluble sugars were, in the order given, two-, three- and fourfold greater than minimum values. Between 14 and 53% of photosynthate was retained in leaves depending on the length of the dark period. These changes were sufficient to account for the previously described stimulatory effect of short daylengths (i.e., long nights) on carbohydrate accumulation in leaves (N.J. Chatterton and J.E. Silvius, 1980, Physiol. Plant. 49, 141–144). The freerunning periods for the rhythmic dependence on darkness, determined either directly or by curve fitting, were about 24 h for net photosynthesis, 23 h for starch accumulation, and 26 h for solublesugar cccumulation. The deviation from period lengths of 24 h for carbohydrate accumulation indicates that these rhythms are probably endogenous and circadian. Initial maxima were observed after 14 h of darkness for photosynthesis, after 18–22 h for starch, and after 26 h for soluble sugars. The differences in period length and phase indicate that at least three separate rhythms underlie the dependence of photosynthate partitioning in Sorghum on darkness. Periods of low leaf dry-matter accumulation coincided approximately with periods of high net photosynthesis. As a result, maximum photoassimination and maximum export were synchronized and, furthermore, occurred at about the same time as expected light periods.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00398679

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7

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Tolerance of a field grown soybean cultivar to elevated ozone level is concurrent with higher leaflet ascorbic acid level, higher ascorbate-dehydroascorbate redox status, and long term photosynthetic productivity (2000)

Michael Robinson, J. ; Britz, Steven J.

Springer

Photosynthesis research 64 (2000), S. 77-87

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ISSN: 1573-5079

Keywords: ascorbic acid ; ascorbate-glutathione cycle ; bean yield ; dehydroascorbate ; ozone ; photosynthesis ; soybean ; vegetative yield

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract We examined the characteristics of ascorbic acid (ASC) level, dehydroascorbate (DHA) level, and the ASC–DHA redox status in the leaflets of two soybean cultivars grown in a field environment and exposed to elevated ozone (O3) levels. These two cultivars, one that preliminary evidence indicated to be O3-tolerant (cv Essex), and one that was indicated to be O3-sensitive (cv Forrest), were grown in open-top chambers during the summer of 1997. The plants were exposed daily to a controlled, moderately high O3 level (≈58 nl l−1 air) in the light, beginning at the seedling stage and continuing to bean maturity. Concurrently, control plants were exposed to carbon-filtered, ambient air containing a relatively low O3 level (≈24 nl l−1 air) during the same period. Elevated O3 did not affect biomass per plant, mature leaf area accretion, or bean yield per plant of cv Essex. In contrast, elevated O3 level decreased the biomass and bean yield per plant of cv Forrest by approximately 20%. Daily leaflet photosynthesis rate and stomatal conductance per unit area did not decrease in either cultivar as a result of prolonged O3 exposure. A 10% lower mature leaflet area in O3-treated cv Forrest plants contributed to an ultimate limitation in long-term photosynthetic productivity (vegetative and bean yield). Possible factors causing cv Essex to be more O3 tolerant than cv Forrest were: 1) mature leaflets of control and O3-treated cv Essex plants consistently maintained a higher daily ASC level than leaflets of cv Forrest plants, and 2) mature leaflets of cv Essex plants maintained a higher daily ASC–DHA redox status than leaflets of cv Forrest plants.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1026508227189

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