Exclusion Of UV Research Articles

Intraspecific variation in photosynthetic efficiency in soybean (Glycine max L.) varieties towards solar ultraviolet radiations

In the current study, we used four soybean varieties PK-1029, PK-472, NRC-7, and Hardee to examine the effect of exclusion of solar UV radiation on photosynthetic efficiency and to test possible variety-dependent sensitivity to ambient UV (280-400 nm). Plants that were grown under UV exclusion filters had higher chlorophyll a and b, efficiencies of PSII and more active reaction centers indicated that PSII were substantially affected by solar UV radiation. The significant increase in net photosynthesis was linked to increased stomatal conductance and lower intercellular concentration of CO2 in UV-excluded plants. The exclusion of solar UV increased seed mass per plant in all soybean varieties as compared to the control; this indicates that ambient UV exclusions boost photosynthetic efficiency and improve soybean yield. The overall cumulative stress response index of four varieties implies that Hardee and PK-472 were more sensitive whereas NRC-7 and PK-1029 were resistant to ambient UV radiations.

The transgenerational effects of solar short-UV radiation differed in two accessions of Vicia faba L. from contrasting UV environments

Background and aimsUVB radiation can rapidly induce gene regulation leading to cumulative changes for plant physiology and morphology. We hypothesized that a transgenerational effect of chronic exposure to solar short UV modulates the offspring’s responses to UVB and blue light, and that the transgenerational effect is genotype dependent. MethodsWe established a factorial experiment combining two Vicia faba L. accessions, two parental UV treatments (full sunlight and exclusion of short UV, 290−350 nm), and four offspring light treatments from the factorial combination of UVB and blue light. The accessions were Aurora from southern Sweden, and ILB938 from Andean region of Colombia and Ecuador. Key resultsThe transgenerational effect influenced morphological responses to blue light differently in the two accessions. In Aurora, when UVB was absent, blue light increased shoot dry mass only in plants whose parents were protected from short UV. In ILB938, blue light increased leaf area and shoot dry mass more in plants whose parents were exposed to short UV than those that were not. Moreover, when the offspring was exposed to UVB, the transgenerational effect decreased in ILB938 and disappeared in Aurora. For flavonoids, the transgenerational effect was detected only in Aurora: parental exposure to short UV was associated with a greater induction of total quercetin in response to UVB. Transcript abundance was higher in Aurora than in ILB938 for both CHALCONE SYNTHASE (99-fold) and DON-GLUCOSYLTRANSFERASE 1 (19-fold). ConclusionsThe results supported both hypotheses. Solar short UV had transgenerational effects on progeny responses to blue and UVB radiation, and they differed between the accessions. These transgenerational effects could be adaptive by acclimation of slow and cumulative morphological change, and by early build-up of UV protection through flavonoid accumulation on UVB exposure. The differences between the two accessions aligned with their adaptation to contrasting UV environments.

Alleviation of Adverse Effects of Ambient UV Stress on Growth and Some Potential Physiological Attributes in Soybean (Glycine max) by Seed Pre-treatment with Static Magnetic Field

The effect of seed pre-treatment with a static magnetic field (SMF) of 200 mT for 1 h on the impact of ambient UV (280–400 nm) stress was tested using soybean var. JS-335 seeds. The SMF-pre-treated and untreated seeds were sown in plastic nursery bags placed in iron mesh cages covered with polyester filters that cutoff UV-B (<315 nm) and UV-A/B (<400 nm) radiations, transmitted all the ambient UV or without filters. The results of solar UV exclusion suggested that ambient UV caused reduction in growth, nitrogen, and carbon metabolism which ultimately reduced the yield of soybean seedlings, whereas SMF-pre-treatment increased plant height, leaf area, biomass accumulation with higher Lb, and hemechrome content in the root nodules, and improved the PS II efficiency and rate of photosynthesis both in the presence of solar UV components as well as under exclusion of solar UV as compared to untreated seeds. The amount of ROS like hydrogen peroxide (H2O2) and the activity of antioxidant enzymes like superoxide dismutase (SOD), glutathione reductase (GR), and guaiacol peroxidase (POD) assayed in the leaves of soybean were higher in the plants grown under ambient UV as compared to the exclusion of solar UV. Whereas under ambient UV stress, the plants that emerged from SMF-treated seeds showed lower amount of H2O2 and lesser activities of antioxidant enzymes SOD, GR, and POD as compared to untreated seeds. Thus, reduction in the H2O2 content and antioxidant enzyme activities after SMF-pre-treatment and UV exclusion indicated that solar UV components exert a significant stress on soybean plants. The levels of UAS were also decreased by both exclusion of UV and SMF-treatment. Reduction in the production of UAS indicated a changed pattern of metabolism leading to improved primary metabolism. The results indicate that exclusion of solar UV components and SMF-pre-treatment eliminates the need for defense against the ambient UV stress. Comparing SMF-treated groups with their respective untreated group, the remedial effects of SMF were found to be more striking on overall growth, nitrogen metabolism, and photosynthetic performance even in the presence of ambient UV stress. Consequently, SMF-pre-treatment ameliorated the ambient UV stress, so that the plants do not have to divert their metabolic energy for detoxification of ROS produced under UV stress. Thus, SMF-pre-treatment can be effectively used for alleviation of adverse effect of ambient UV stress and improve the yield of crop plants.

CO&amp;lt;sub&amp;gt;2 &amp;lt;/sub&amp;gt;and Chamber Effects on Epidermal Development in Field-Grown Peanut (&amp;lt;i&amp;gt;Arachis hypogaea&amp;lt;/i&amp;gt; L.)

Peanut, (Arachis hypogaea L.) cvar. C76-16, was grown either in the field, or in open gas exchange chambers under elevated or ambient CO2 concentrations. Stomatal density and other selected epidermal parameters associated with leaf development and gas exchange were measured on recently fully expanded canopy leaves. It was hypothesized that exclusion of solar UV by chambers would affect stomatal density, but no clear statistically significant chamber effect on stomatal density was found. However, elevated [CO2] did lead to a reduction in both adaxial and abaxial stomatal developmental initiation and in stomatal density. Since each stomate was bounded by companion cells resulting from developmental events, non-random stomatal spacing as the “one cell spacing rule” appears to result from ontogeny rather than a long hypothesized chemical signal inhibiting adjacent meristemoid differentiation into guard cells. A method of visualizing epidermal patterns is also described.

Synchrotron X-ray phase contrast imaging of leaf venation in soybean (Glycine max) after exclusion of solar UV (280-400 nm) radiation.

The hydraulic efficiency of a leaf depends on its vascular structure as this is responsible for transport activities. To investigate the effect of exclusion of UVAB and UVB radiation from the solar spectrum on the micro-structure of leaves of soybean (Glycine max, variety JS-335), a field experiment was conducted using synchrotron-based phase contrast imaging (PCI). Plants were grown in specially designed UV exclusion chambers, and wrapped with filters that excluded UVB (280-315 nm) or UVAB (280-400 nm), or transmitted all the ambient solar UV (280-400 nm) radiation (filter control). Qualitative observation of high-resolution X-ray PCI images obtained at 10 keV has shown the differences in major and minor vein structures of the leaves. The mid-rib width of the middle leaflet of third trifoliate leaves, for all treatments, were obtained using quantitative image analysis. The width of the mid-rib of the middle leaflet of third trifoliate leaves of UVB excluded plants was found to be more compared to leaves of filter control plants, which are exposed to ambient UV. The mid-rib or the main conducting vein transports water and sugars to the whole plant; therefore, mid-rib enhancement by the exclusion of solar UV radiation possibly implies enhancement in the leaf area which in turn causes an increased rate of photosynthesis.

Exclusion of solar UV radiation improves photosynthetic performance and yield of wheat varieties

Field studies were conducted to determine the potential for alterations in photosynthetic performance and grain yield of four wheat (Triticum aestivum) varieties of India- Vidisha, Purna, Swarna and Naveen Chandausi by ambient ultraviolet radiation (UV). The plants were grown in specially designed UV exclusion chambers, wrapped with filters that excluded UV-B (<315 nm), UV-A/B (<400 nm) or transmitted ambient UV or lacked filters. The results indicated that solar UV exclusion increased the leaf mass per area ratio, leaf weight ratio and chlorophylls per unit area of flag leaves in all the four varieties of wheat. Polyphasic chlorophyll a fluorescence transients from the flag leaves of UV excluded wheat plants gave a higher fluorescence yield. Exclusion of solar UV significantly enhanced photosynthetic performance as a consequence of increased efficiency of PS II, performance index (PIABS) and rate of photosynthesis in the flag leaves of wheat varieties along with a remarkable increase in carbonic anhydrase, Rubisco and nitrate reductase activities. This additional fixation of carbon and nitrogen by exclusion of UV was channelized towards the improvement in grain yield of wheat varieties as there was a decrease in the UV-B absorbing substances and an increase in soluble protein content in flag leaves of all the four varieties of wheat. The magnitude of response for UV exclusion for all the measured parameters was higher in two varieties of wheat Vidisha and Purna as compared to Swarna and Naveen Chandausi. Cumulative stress response index (CSRI) for each variety was developed from the cumulative sum of physiological and yield parameters such as leaf mass area ratio of flag leaf, total chlorophyll content, performance index at absorption basis, rate of photosynthesis and grain yield. All the varieties had a negative CSRI, demonstrating a negative impact of ambient UV radiation. Naveen Chandausi and Swarna are less sensitive to ambient UV radiation; Vidisha is more sensitive to both UV-A and UV-B and Purna is more sensitive to ambient UV-B radiation.

Regulation of growth and development in phytochrome mutants of Arabidopsis thaliana by solar UV

Phytochrome mutants (phyA, phyB and phyAB) of Arabidopsis thaliana were grown under ambient and UV-excluded sunlight to understand their influence on growth and development by mutual exclusion. Phytochrome A and B played a complementary role in the regulation of germination. Suppression of hypocotyl length was predominantly under the control of phytochrome B; UV photoreceptors were active in suppression of hypocotyl growth only in phyB and phyAB mutants. Exclusion of UV promoted the number and the area of rosette leaves only in presence of phytochrome A and B. Phytochrome mutation reduced petiole length, whereas UV exclusion led to an increase. Requirement of long-day period for flowering was removed in the mutants. Under short-day conditions, flowering was predominantly under the control of phytochrome B, since phyB mutants flowered earlier than phyA mutants. Solar UV regulates the number of boltings and number of siliques per plant. Overall biomass of the plants is enhanced by the exclusion of UV only in the wild type. The interaction of phytochromes with UV photoreceptors is discussed in the paper.

Growth, photosynthesis and nitrogen metabolism in soybean varieties after exclusion of the UV-B and UV-A/B components of solar radiation

A field experiment was conducted to study the impact of the exclusion of the solar UV components on growth, photosynthesis and nitrogen metabolism in soybean (Glycine max) varieties PK-472, Pusa-24, JS 71-05, JS-335, NRC-7 and Kalitur. The plants were grown in specially designed UV exclusion chambers wrapped with filters to exclude UV-B or UV-A/B and transmitted all UV. Exclusion of UV significantly enhanced the growth of the aerial parts as well as the growth of the below ground parts in all of the six soybean varieties. Nitrate reductase activity (NRA) was significantly reduced, whereas leghemoglobin (Lb) content, total soluble protein, net photosynthesis (Pn) and α-tocopherol content were enhanced after UV exclusion. The exclusion of solar UV-A/B enhanced all parameters to a larger extent than the exclusion of solar UV-B in four of the six varieties of soybean except for NRC-7 and Kalitur. These two varieties responded more to UV-B exclusion compared to UV-A/B exclusion. A significant inverse correlation between the NRA and the number of nodules per plant was observed. The extent of response in all parameters was greater in PK-472 and JS71-05 than that in Kalitur and JS-335 after UV exclusion. The exclusion of UV augmented the growth of nodules, Lb content and α-tocopherol levels and conferred higher rates of Pn to support better growth of nodules. Control plants (+UV-A/B) seemed to fulfill their N demand through the assimilation of NO3− resulting in lower symbiotic nitrogen fixation and higher NR activity.

Exclusion of solar UV components improves growth and performance of Amaranthus tricolor varieties

A field experiment was conducted to study the influence of exclusion of solar UV components on the growth responses, gas exchange rates, chlorophyll fluorescence, pigmentation, carboxylation enzymes and foliage yield of four Amaranthus tricolor varieties; Arka arunima, Arka suguna, Pusa lalchaulai and Pusa kiran. The plants were grown in specially designed UV exclusion chambers, wrapped with filters that excluded UV-B (<315nm), UV-A/B (<400nm) or transmitted ambient UV or lacked filters. Plants grown under ambient UV radiation (280–400nm) were compared with those grown without UV-B or UV-A/B. The results indicated increased plant height, leaf weight ratio, specific leaf weight and foliage yield in all the four varieties of A. tricolor grown without UV-B and UV-A/B compared with those grown under ambient UV. Exclusion of UV significantly increased the total chlorophyll while Chl a/b ratio decreased. The efficiency of PS II (Fv/Fm), rate of photosynthesis and stomatal conductance significantly enhanced along with a remarkable increase in Carbonic anhydrase, PEP carboxylase and total soluble proteins. Thus UV excluded plants have higher reducing power and increased CO2 fixation and decreased UV-B absorbing compounds, channelling the additional fixation of carbon towards the improvement of yield in A. tricolor varieties. The response for UV exclusion was higher in variety Arka arunima and Arka suguna compared with Pusa kiran and Pusa lalchaulai. UV sensitivity of the A. tricolor varieties was in the following sequence – Pusa lalchaulai>Pusa kiran>Arka suguna>Arka arunima. Thus Arka arunima and Arka suguna were most sensitive and Pusa lalchaulai and Pusa kiran the least sensitive varieties to ambient level of UV. The least sensitive varieties may be used in the development of UV-B tolerance mechanisms and also developing new varieties tolerant to higher levels of UV-B in future attempts in plant breeding programmes.

Enhancement of growth, photosynthetic performance and yield by exclusion of ambient UV components in C3 and C4 plants

A field experiment was conducted under tropical climate for assessing the effect of ambient UV-B and UV-A by exclusion of UV components on the growth, photosynthetic performance and yield of C3 (cotton, wheat) and C4 (amaranthus, sorghum) plants. The plants were grown in specially designed UV exclusion chambers, wrapped with filters that excluded UV-B (<315nm), UV-A+B (<400nm), transmitted all the UV (280–400nm) or without filters. All the four plant species responded to UV exclusion by a significant increase in plant height, leaf area, leaf biomass, total biomass accumulation and yield. Measurements of the chlorophyll, chlorophyll fluorescence parameters, gas exchange parameters and the activity of Ribulose-1,5-bisphosphate carboxylase (Rubisco) by fixation of 14CO2 indicated a direct relationship between enhanced rate of photosynthesis and yield of the plants. Quantum yield of electron transport was enhanced by the exclusion of UV indicating better utilization of PAR assimilation and enhancement in reducing power in all the four plant species. Exclusion of UV-B in particular significantly enhanced the net photosynthetic rate, stomatal conductance and activity of Rubisco. Additional fixation of carbon due to exclusion of ambient UV-B was channeled towards yield as there was a decrease in the level of UV-B absorbing substances and an increase in soluble proteins in all the four plant species. The magnitude of the promotion in all the parameters studied was higher in dicots (cotton, amaranthus) compared to monocots (wheat, sorghum) after UV exclusion. The results indicated a suppressive action of ambient UV-B on growth and photosynthesis; dicots were more sensitive than monocots in this suppression while no great difference in sensitivity was found between C3 and C4 plants. Experiments indicated the suppressive action of ambient UV on carbon fixation and yield of C3 and C4 plants. Exclusion of solar UV-B will have agricultural benefits in both C3 and C4 plants under tropical climate.

Control of aphids and whiteflies on Brussels sprouts by means of UV-absorbing plastic films

Use of UV-absorbing films has recently developed into a promising tool to control insect pests under greenhouse conditions. UV-absorbing films that significantly reduce transmission of UV-A and UV-B natural solar radiation can interfere with vision of herbivorous insects. The exclusion of UV from natural sunlight hampers flight initiation, dispersal, host finding and establishment, hence affects the population build-up. To study the effects of UV-absorbing films on population dynamics of Aleyrodes proletella and Brevicoryne bras-sicae, eight “walk-in” tunnels covered either with UV-absorb-ing or UV-transmitting films were constructed. In each tunnel, 49 Brussels sprouts seedlings were planted. Densities of the pest insects and their parasitation rates were determined on ten randomly chosen plants per tunnel two times per week. UV-absorbing materials significantly reduced the population densities of A. proletella and B. brassicae. Parasita-tion rates of the pests were not reduced under UV-deficient conditions. The results indicate that UV-absorbing films can be a very powerful tool to control pests in Brassica crops.

Enhancement of root growth and nitrogen fixation in Trigonella by UV-exclusion from solar radiation

A field experiment was conducted to study the impact of solar UV on root growth and nitrogen fixation in Trigonella foenum-graecum. Plants were grown in iron mesh cages covered with polyester filters that could specifically cut off UV-B (280-315 nm) or UV-A + B (280-400 nm) part of the solar spectrum. The control plants were grown under a polythene filter transmissible to UV. Root biomass, number of nodules and nodule fresh weight were enhanced after exclusion of solar UV. Nitrogenase activity was significantly enhanced by 120% and 80% in the UV-B and UV-A + B excluded plants respectively. Along with nitrogenase there was concomitant increase in leghemoglobin and hemechrome content in the nodules after exclusion of solar UV. These components of sunlight limits nitrogen fixation and their elimination can enhance nitrogen fixation with agricultural advantages like reduction in the use of fertilizers.

Intraspecific variations in growth, yield and photosynthesis of sorghum varieties to ambient UV (280–400 nm) radiation

A field study was conducted to investigate the impact of ambient solar UV on the various growth, physiological and yield parameters of four sorghum (Sorghum bicolor L.) varieties—Indore-12, Indore-26, CSV-23 and Indore-27 by excluding either UV-B (<315nm) or UV-A/B (<400nm) components of solar spectrum. Exclusion of UV significantly enhanced plant height, area and specific leaf weight of flag leaf, biomass accumulation, yield parameters and harvest index in all the sorghum varieties. Chlorophyll b was significantly enhanced and chlorophyll a increased to a lesser extent, UV-B absorbing substances and chlorophyll a/b ratio were significantly decreased by the exclusion of solar UV. The enhancement in the vegetative growth and yield by UV exclusion might be linked to the remarkable increase in rate of photosynthesis in sorghum varieties. The magnitude of the response was high in I-26 and I-27 as compared to CSV-23 and I-12 after exclusion of solar UV. All the varieties of sorghum had a negative cumulative stress response index (CSRI), the sensitivity of the sorghum varieties was in the following sequence I-12>CSV-23>I-26>I-27. Thus I-27 was the most sensitive and I-12 the least sensitive variety to present level of solar UV radiation. The differences in UV sensitivity identified among sorghum varieties might be useful in breeding programs for increased tolerance to UV-B radiation.

Effect of Exclusion of Ambient Solar Uv-A/B Components on Growth and Antioxidant Response of Cotton (Gossypium Hirsutum L.)

The influence of ambient solar UV-A or UV-B radiation on growth responses was investigated in three varieties of cotton (Gossypium hirsutum L.) after exclusion of solar UV-A/B radiation: JK-35, IH-63 and Khandwa-2. Cotton plants were grown from seeds in UV-exclusion chambers lined with selective UV filters to exclude either UV-B (280–315 nm) or UV-A/B (280–400 nm) from the solar spectrum under field conditions. Excluding UV-B and UV-A/B significantly increased plant height, leaf area and dry weight accumulation in all three varieties of cotton. The varieties differed considerably in their sensitivity to ambient UV-A/B. Khandwa-2 was most sensitive and JK-35 least sensitive to ambient solar UV. We monitored the activity of the antioxidant enzymes superoxide dismutase (SOD), ascorbic acid peroxidase (APX), glutathione reductase (GR) and guaiacol peroxidase (GPX), as well as the level of the antioxidant ascorbic acid (ASA), in primary leaves of the most UV-sensitive variety (Khandwa-2). The level of UV-B-absorbing substances was significantly decreased by exclusion of solar UV-B and UV-A/B. Exclusion of solar UV decreased the activity of all the antioxidant enzymes monitored and the level of ascorbic acid versus control plants (+UV-A/B) grown under filters transparent to solar UV. Reduction of the antioxidant defense after UV exclusion indicates that ambient solar UV exerts significant stress and induces some reactive oxygen species to accumulate, which in turn retards the growth and development of cotton plants. Ambient solar UV stresses cotton plants, shifting their metabolism towards defense against solar UV. Exclusion of solar UV eliminates the need for that defense and leads to enhancement of primary metabolism.

Photosynthesis and yield in cotton (Gossypium hirsutum L.) Var. Vikram after exclusion of ambient solar UV-B/A

The impact of ambient solar UV was studied on the photosynthesis and yield of cotton (Gossypium hirsutum) var. Vikram in a field experiment by excluding either UV-B (<315 nm) or UV-B/A (<400 nm) components of solar spectrum. Cotton plants were grown in cages covered with polyester filters that could specifically cut off UV-B or UV-B/A part of the solar spectrum. The control plants were grown under a filter transmissible to UV. Exclusion of UV enhanced plant height, leaf area, total biomass, and the yield parameters (number and weight of bolls, length of fiber and number of seeds) of cotton. Enhancement in the vegetative growth and yield of the plants could be related to enhanced rate of photosynthesis in the leaves. Polyphasic chlorophyll a fluorescence (OJIP) transients from UV excluded plants gave a higher fluorescence yield at I–P phase. Fluorescence measurements indicated enhanced F v/F m ratio and reduction capacity after exclusion of solar UV. Exclusion also enhanced stomatal conductance and intercellular CO2 concentration and reduced the stomatal resistance. Total soluble proteins were higher after UV exclusion, and in SDS–PAGE analysis, bands corresponding to smaller subunits (14 kDa) of Rubisco were more intensely stained. Experiments indicated suppressive action of ambient UV on carbon fixation and yield of cotton plants. Exclusion of solar UV proved to be beneficial in enhancing the yield of cotton plants.

Solar UV-B and UV-A/B exclusion effects on intraspecific variations in crop growth and yield of wheat varieties

UV exclusion studies would help in the assessment of the sensitivity of varieties to ambient level of UV radiation. A field study was conducted to determine the intraspecific responses in relative to sensitivity of Indian wheat ( Triticum aestivum L.) varieties to ambient solar ultraviolet (290–400 nm) radiation. Specifically, the influence of ambient UV radiation on crop growth and yield parameters was investigated by the exclusion of UV radiation form solar spectrum using four Indian wheat varieties; Naveen Chandausi, Swarna, Vidisha and Purna. The plants were grown in specially designed UV exclusion chambers, wrapped with filters that excluded both UV-A/B (<400 nm), UV-B (<315 nm), transmitted all the UV (280–400 nm) or lacked filters. Exclusion of UV significantly enhanced plant height, tiller number, flag-leaf area, dry matter accumulation and yield parameters like number of grains and grain yield in all the four wheat varieties tested. Purna and Vidisha showed more enhancements compared to Swarna and Naveen Chandausi. Sensitivity index showed that all four varieties were UV-sensitive; SI was higher for N. Chandausi and lowest for Purna and it was in the following sequence; Naveen Chandausi > Swarna > Vidisha > Purna. Thus Purna was the most sensitive and Naveen Chandausi the least sensitive to current level of solar UV radiation. The intraspecific differences in sensitivity identified among the wheat varieties imply the options for selecting varieties with increased tolerance to UV-B/UV-A radiations to future attempts in plant breeding.

Assessment of impact of solar UV components on growth and antioxidant enzyme activity in cotton plant.

A field experiment was conducted to study the impact of solar UV-B (280-315nm) and UV-A (315-400nm) components on the growth and antioxidant enzyme activity in cotton plant (Gossypium hirsutum var. Vikram). Solar UV components were excluded by filtering the sunlight through selective UV-B (<315nm) and UV-B/A (<400nm) absorbing polyester films. Plants grown under filters that transmitted solar UV served as controls. Exclusion of UV-B and UV-B/A enhanced plant height, leaf area and total biomass of plants. The activity of antioxidant enzymes superoxide dismutase (SOD), ascorbic acid peroxidase (APX), glutathione reductase (GR) and guaiacol peroxidase (GPx) assayed in the leaves were lesser in the UV excluded plants. The level of ascorbic acid and UV absorbing substances were also decreased by the exclusion of UV. Solar UV components exerted a limitation on the potential growth of cotton plants. Reduction in the antioxidant enzyme activity and ascorbic acid after UV exclusion indicated that ambient UV components exert a significant stress on cotton plants. Reduction in the production of UAS indicated a changed pattern of metabolism leading to improved primary metabolism. Exclusion of UV components is advantageous from the agricultural point to enhance the growth of cotton plants.

Growth enhancement of soybean (Glycine max) upon exclusion of UV-B and UV-B/A components of solar radiation: characterization of photosynthetic parameters in leaves

Exclusion of UV (280-380 nm) radiation from the solar spectrum can be an important tool to assess the impact of ambient UV radiation on plant growth and performance of crop plants. The effect of exclusion of UV-B and UV-A from solar radiation on the growth and photosynthetic components in soybean (Glycine max) leaves were investigated. Exclusion of solar UV-B and UV-B/A radiation, enhanced the fresh weight, dry weight, leaf area as well as induced a dramatic increase in plant height, which reflected a net increase in biomass. Dry weight increase per unit leaf area was quite significant upon both UV-B and UV-B/A exclusion from the solar spectrum. However, no changes in chlorophyll a and b contents were observed by exclusion of solar UV radiation but the content of carotenoids was significantly (34-46%) lowered. Analysis of chlorophyll (Chl) fluorescence transient parameters of leaf segments suggested no change in the F v/F m value due to UV-B or UV-B/A exclusion. Only a small reduction in photo-oxidized signal I (P700+)/unit Chl was noted. Interestingly the total soluble protein content per unit leaf area increased by 18% in UV-B/A and 40% in UV-B excluded samples, suggesting a unique upregulation of biosynthesis and accumulation of biomass. Solar UV radiation thus seems to primarily affect the photomorphogenic regulatory system that leads to an enhanced growth of leaves and an enhanced rate of net photosynthesis in soybean, a crop plant of economic importance. The presence of ultra-violet components in sunlight seems to arrest carbon sequestration in plants.

Effect of Light Upon Wool

In Berkeley, California, it was found that sunlight bleached wool during exposures of 1 to 150 sun-hr. However, when the visible light was excluded, wool was yellowed by the solar ultraviolet. Bleaching was increased by progressive exclusion of solar UV with various cut-off filters and was greatest with only visible light, the visible violet being the most effective. Solar UV below 311 mμ was the most yellowing. Thus, the net effect of sunlight upon wool varies with its spectral composition, and its variability in place and time probably explains the variable results, yellowing or bleaching, reported by others around the world. Full sunlight also bleached wet wool that, after a long induction period, turned yellow, apparently, in a dark-follow reaction.