Resistance of Anhydrobiotic Aphelenchus avenae to Methyl Bromide Fumigation

The effect of methyl bromide (MB) was tested on active and anhydrobiotic Aphelenchus avenae. A. avenae was induced into anhydrobiosis by three different techniques. Both active and anhydrobiotic nematodes were subjected to 3,000 μ1 MB/liter air for 14 periods from 0 to 82 h. Anhydrobiotic nematodes were more resistant to fumigation than active nematodes, regardless of the technique used to induce anhydrobiosis. The percent survival decreased with increasing MB exposures (μ1 MB × h). For an LD₉₅ of 45,000-54,000 μ1/1 × h were required for active nematodes and >279,000 μ1/1 × h for anhydrobiotic nematodes.     

The effects of ultraviolet-B radiation on loblolly pine. I. Growth, photosynthesis and pigment production in greenhouse-grown seedlings

One-year old loblolly pine ( Pinus taeda L.) seedlings were grown in an unshaded greenhouse for 7 months under 4 levels of ultraviolet-B (UV-B) radiation simulating stratospheric ozone reductions of 16, 25 and 40% and included a control with no UV-B radiation. Periodic measurements were made of growth and gas exchange characteristics and needle chlorophyll and UV-B-absorbing-compound concentrations. The effectiveness of UV-B radiation on seedling growth and physiology varied with the UV-B irradiance level. Seedlings receiving the lowest supplemental UV-B irradiance showed reductions in growth and photosynthetic capacity after only 1 month of irradiation. These reductions persisted and resulted in lower biomass production, while no increases in UV-B-absorbing compounds in needles were observed. Seedlings receiving UV-B radiation which simulated a 25% stratospheric ozone reduction showed an increase in UV-B-absorbing-compound concentrations after 6 months, which paralleled a recovery in photosynthesis and growth after an initial decrease in these characteristics. The seedlings grown at the highest UV-B irradiance (40% stratospheric ozone reduction) showed a more rapid increase in the concentration of UV-B-absorbing compounds and no effects of UV-B radiation on growth or photosynthetic capacity until after 4 months at this irradiance. Changes in photosynthetic capacity were probably the result of direct effects on light-dependent processes, since no effects were observed on either needle chlorophyll concentrations or stomatal conductance. Further studies are necessary to determine whether these responses persist and accumulate over subsequent years.     

Effect of UV-B (290–320 nm) irradiation on growth and metabolism of cucumber cotyledons

Cucumber ( Cucumis sativus L. cv. Natsusairaku 3) seedlings were grown in a growth cabinet under UV-B (290–320 nm) irradiation (equivalent to the UV-B radiation normally incident at Tokyo, 36°N latitude, during clear sky conditions in mid-april on a weighted daily fluence basis) and a UV-B-free control condition. UV-B irradiation inhibited the growth of the cotyledons, i.e. the increase in area, and increase in fresh and dry weights of the cotyledons. The greatest inhibition rate was observed in the increase in area, causing a significant increase in specific leaf weight (the ratio of weight to area). UV-B irradiation had no significant effect on DNA and RNA contents in the cotyledons, but decreased protein content slightly. In contrast, the irradiation reduced the amounts of organic acids and soluble sugars, indicating that primary carbon metabolism was very sensitive to UV-B radiation. UV-B irradiation lowered the photosynthetic activity in the cotyledons without any effect on chlorophyll content and respiratory activity. These results indicate that UV-B radiation at the ambient level may act as a physiological stress in some UV-sensitive plants.     

Seasonal changes in the pigments, carbohydrates and growth of red spruce as affected by ozone

Two-year-old red spruce seedlings were exposed to various levels ot ozone, from 0.4 to 3 times ambient levels, in open-top chambers in Ithaca, NY, USA. Exposures, which varied with changes in day length, commenced on May 30, 1987 and continued until December 14, 1987. Seedling biomass, carbohydrate contents, pigment contents, and rate of electron transport were assessed twice monthly during the fumigation period. Orthogonal quadratic or cubic polynomials were used to model the response through time each variable measured. A one-way analysis of variance model was fitted to every regression coefficient in each polynomial model to test for ozone effects on seasonal physiological patterns. Ozone did not influence growth, foliar pigment content, foliar starch content, root carbohydrate content, or rate of electron transport. The seasonal change of needle raffinose content differed between exposed to low (0.4 ×, 1×) and high (2×, 3×) ozone levels. There was also a trend towards reduced total soluble sugar content foliage during late autumn in higher ozone treatments.     

Effects of ultraviolet-B radiation on plants during mild water stress. IV. The insensitivity of soybean internal water relations to ultraviolet-B radiation

The combined effects of ultraviolet-B (UV-B, 280–320 nm) radiation and water stress were investigated on the water relations of greenhouse grown soybean [ Glycine max (L.) Merr. cv. Essex]. On a weighted (Caldwell 1971), total daily dose basis, plants received either 0 or 3 000 effective J m² UV-B_BE supplied by filtered FS-40 sunlamps. The latter dose simulated the solar UV-B radiation anticipated at College Park, Maryland, U.S.A. (39°N latitude) in the event that the global stratospheric ozone column is reduced by 25%. Plants were either well-watered or preconditioned by drought stress cycles. Diurnal measurements of water potential and stomatal conductance were made on the youngest fully expanded leaf. Various internal water relations parameters were determined for detached leaves. Plants were monitored before, during and after water stress. There were no significant differences in leaf water potential or stomatal conductance between treatments before plants were preconditioned to water stress. However, drought stress resulted in significantly lower midday and afternoon leaf water potentials and lower leaf conductances as compared to well-watered plants. UV-B radiation had no additional effect on leaf water potential; however, UV did result in lower leaf conductances in plants preconditioned to water stress. Turgid weight:dry weight ratio, elastic modulus, bound water and relative water content were unaffected by UV-B radiation. Osmotic potentials at full and zero turgor were significantly lower in the drought stressed treatments as compared to well-watered plants.     

Effects of ultraviolet-B radiation on plants during mild water stress. III. Effects on photosynthetic recovery and growth in soybean

Soybean { Glycine max (L.) Merr. ev. Essex} was grown from seed in a greenhouse under ultraviolet-B (UV-B, 280–320 nm) radiation supplied by filtered FS-40 sunlamps. On a weighted, total daily dose basis these plants received either 0 (control) or 2875 effective J m⁻² day⁻¹ UV-B_BE. When weighted with the generalized plant action spectrum (Caldwell 1971), this simulated the solar ultraviolet-B irradiance expected to occur at College Park, Maryland, USA (39°N) in the event the global stratospheric ozone column is reduced by 23%. The effects of ultraviolet radiation on the photosynthetic recovery from water stress were measured with an infrared gas analyzer. These effects were examined in plants which were either well-watered or previously preconditioned to water stress, during two distinct phenological stages of development. During the early stages of soybean growth, enhanced levels of UV-B reduced net photosynthesis by 25%, and water stress also reduced photosynthesis to nearly the same extent (by 20%). The combination of these two stresses resulted in smaller biomass than that produced by plants exposed to either stress independently. Photosynthesis in older, larger plants was much more sensitive to water stress and was reduced by as much as 50–60% in non-preconditioned plants. Although non-irradiated, non-preconditioned (control) plants recovered to only within 60% of their prestressed value, preconditioned plants recovered to within 70–80% during the 3 day recovery period. Both water stress and UV-B radiation affected non-stomatal conductance, while stomatal conductance was primarily affected by water stress.     

接触二氧化硫后小麦叶片中逆境乙烯的生物合成

AVG和AOA强烈抑制二氧化硫处理小麦叶片中乙烯产生和ACC合成,对MACC的形成也有一定的抑制作用。CoGl_2明显抑制乙烯产生,而ACC大量积累,MACC含量则未因ACC增加而相应增加。DNP和CCCP也抑制乙烯产生,但前者引起ACC大量积累,后者引起ACC含量下降。CHI对乙烯产生和ACC形成均显示强烈的抑制作用,同时也明显抑制MACC形成。这表明小麦叶片接触SO_2引起的逆境乙烯也是循蛋氨酸→SAM→ACC→乙烯途径。