Effect of Exclusion of Solar UV radiation on Plants

UV exclusion studies can provide the realistic assessments of sensitivity of plant to current level of UV radiation. Perusal of relevant literature reveals that UV exclusion causes enormous increase in the growth of aerial parts along with below ground parts of the plants. Exclusion of UV-B (280-315 nm) and UV-A+B (280-400 nm) enhanced the photosynthetic pigments, net photosynthetic rate and stomatal conductance along with remarkable increase in the activity of Carbonic anhydrase, Rubisco and PEPCase. UV excluded plants have higher PS II efficiency, reducing power, CO2 fixation and decreased UV-B absorbing compounds, channeling the additional fixation of carbon to improvement of yield. UV exclusion studies indicate that dicot plants are more sensitive than the monocot plants to current level of UV-B.


Introduction
UV radiation (200-400 nm) is harmful to all organisms mainly due to DNA damage and production of reactive oxygen species (Mazza et al., 1999, p. 61).The environmental implication of increasing solar UV-B radiation on agricultural production has heightened concern due to decrease in stratospheric ozone as a result of the chlorofluorocarbons in the atmosphere (McKenzie et al., 2011).In global agriculture, now effect of UV-B radiation on plants is of major concern to plant biologists due to the threat to productivity.An elevation in the flux of UV-B (280-315 nm) is an important atmospheric stress and is detrimental to plant growth and photosynthesis (Reddy et al., 2013).At the metabolism level, UV-B severely inhibits photosynthesis (Reddy, Kakani, Zhao, Koti, & Gao, 2004, p.416;Kataria, Guruprasad, Ahuja, & Singh, 2013) and hampers nodulation and nitrogen fixation (Rajendiran, & Ramanujam, 2006, p.50), changes in the carbon partitioning from growth pools to secondary metabolic pathways (Bassman, 2004) and thus changes in crop morphology, crop reproductive organ abortion and yield reduction (Mohammed, & Tarpley, 2010) in sensitive plants.On the other hand, UV-A (315-400 nm) is considered less harmful than UV-B radiation.The enhanced levels of pigments such as chlorophyll, carotenoids, and UV-absorbing compounds, including antioxidants, and has been reported to stimulate growth in general by supplementation of UV-A with photosynthetically active radiation (PAR, 400-700nm) (Shiozaki, Hattor, Gojo, Tezuka, 1999;Helspar et al., 2003, p.117).UV-A irradiation is moreover reported to alleviate the damaging effect of UV-B (Flint & Caldwell, 1996).
Most of the previous research dealing with the effects of UV-B and UV-A radiation on plant metabolism has been conducted in greenhouse, growth chamber or laboratory conditions.These types of indoor experiments are important for understanding the physiology of the UV response.The two most widely used approaches in outdoor studies are the attenuation approach (UV exclusion studies with filters) and the enhancement/supplementation approach (high UV-B provided).
While the field studies with supplemental/enhanced UV-B provide information on mechanisms and processes of UV-B action.The enhancement studies supplement solar UV-B with fluorescent lamps to mimic future UV-B enhancements due to ozone depletion but the UV exclusion studies can Sunita Kataria , Sanjay S. Baroniya, Lokesh Baghel and Mansi Kanungo Effect of Exclusion of Solar UV radiation on Plants 225 provide the realistic assessments of sensitivity of plant species or varieties to current level of UV-A and UV-B radiation (Rousseaux, Flint, Searles, & Caldwell, 2004).The reduction of UV-B from ambient level may lead to increase in biomass production in various land plants (Mazza et al., 1999, p. 61;Xiong, & Day, 2001;Kataria et al., 2013, p.140).Sensitivity to ambient UV-B radiation varies considerably within and between plants species, a high intraspecific variation in plant response to ambient UV-B radiation has been observed after the exclusion of solar UV components as demonstrated in many crops (Kataria, & Guruprasad, 2012 a, b;Kataria et al., 2013, p.140;Kataria, & Guruprasad, 2014).
The intensity of UV-B radiation reaching the biosphere is dependent on solar zenith angle, thickness of the ozone layer clouds and aerosols.In tropics due to small solar zenith angle and thin stratospheric ozone layer, terrestrial plants encounter much higher levels of UV-B radiation than at higher latitudes.Thus to evaluate the possible consequences of increased UV-B radiation for tropical plants, it is important to elucidate the effects of present ambient UV level.The effect of ambient UV-B and UV-A can be best assessed by the exclusion of UV components, with specific type of filters that exclude UV-B (< 315 nm), UV-A+B (< 400 nm), transmits all the UV (280 -400 nm).This review provides an overview of existing literature on the effects of the exclusion of solar ultraviolet radiation on growth and subsequently on yield of crop plants.

Plant Growth and Biomass Accumulation
Reduction in growth is one of the most common responses to enhanced and ambient UV-B.Exclusion of UV-B alone and UV-A/B both from solar radiation caused a significant increase in the growth (plant height, leaf area, specific leaf weight, leaf weight ratio) and biomass production in many plant species like barley, cotton, mung bean and pea, pumpkin, soybean, Cyamopsis, wheat, sorghum and amaranthus (Pal, Sharma, Abrol, & Sengupta, 1997, Pal, Zaidi, Voleti, & Raj, 2006;Mazza et al., 1999, p. 61;Amudha, Jayakumar, & Kulandaivelu, 2005;Guruprasad et al., 2007;Kataria, & Guruprasad, 2014).Exclusion of ambient UV-B produced more branches in dicots or tillers in monocots with a larger leaf area in barley, cotton and sorghum (Mazza et al., 1999, p. 61;Coleman, & Day, 2004).Root biomass, number of nodules and nodule fresh weight were also enhanced after exclusion of solar UV (Sharma, & Guruprasad, 2012).Rinnan et al., (2005, p.11) showed that below ground biomass of Vaccinium uliginosum is reduced under ambient UV-B when compared to UV-B exclusion.UV exclusion studies reveals that dicots like mung bean, pea, cotton, soybean and amaranthus are more sensitive to solar UV-B than monocots like maize, sorghum and wheat (Pal et al., 1997, p. 29, Pal et al., 2006, p.19;Kataria et al., 2013, p.140) while it does not differ between C3 and C4 plants.Thus the UV components present in the solar spectrum seemed to inhibit the growth and biomass accumulation whereas exclusion of solar UV-B and UV-A/B from the solar radiation causes significant enhancement in morphological changes in the crop plants.

Non Photosynthetic Pigments
Generally, accumulation of UV-B absorbing substances, mainly flavonoids, in leaf epidermis was suggested to be a protective measure against UV-B effects.The two main groups of phenolics that provide protection from UV radiation are the flavonoids and hydroxycinnamic acids, these compounds have absorption bands in the ranges 240-545nm and 227-332 nm, respectively (Cerovic et al., 2002).Both groups of phenolics protecting the inner cells from the harmful radiation (Bassman, 2004) and act as sunscreens in the leaf epidermis while transmitting photosynthetically active radiation (PAR) to the mesophyll cells.Flavonols strongly absorb UV and have high antioxidant activity (Jenkins, 2008, p.240), and thus they are very important for UV-B tolerance in plants (Hofmann et al., 2000,p.527;Balouchi, Sanavy, Emam, & Dolatabadian, 2009, p. 443).
Epidermal flavonoids in vivo decreased, when UV-B was excluded and the concentrations of six flavonoids (myricetin-3-galactoside, quercetin-3-galactoside, quercetin-3-glucuronide, quercetin-3-arabinopyranoside, quercetin-3-rhamnoside and kaempferol-3-rhamnoside) determined by high-performance liquid chromatography-mass spectrometry were also decreased with the exclusion of UV-B (Morales et al., 2010).Thus previous studies demonstrated that the increases in flavonoids and other phenolic compounds in plants could protect mesophyll cell from UV-B radiation damage and exclusion of solar UV decreases these compounds due to elimination of defense against UV-B damage.Since UV-B induces the synthesis of flavonoids (Jenkins, 2009), it is not unexpected that concentrations of certain flavonoids are lower in environments with reduced UV-B.Some other field experiments have also confirm that leaf flavonoid contents can decrease with UV-B exclusion, for example in Pinus sylvestris (Turunen et al., 1999) and Nothofagus antarctica (Rousseaux et al., 2004, p.224) and Amaranthus tricolor (Kataria, & Guruprasad, 2014).

Photosynthetic Pigments
The pronounced decrease in the amount of photosynthetic pigments by ambient and enhanced UV-B may possibly affect photosynthesis and reduce both biomass accumulation and economic yield (Yao et al., 2006).The chlorophyll components, thylakoids and grana were sensitive to the incoming solar radiation (He, Huang, Whitcross, 1994).An increase in UV-B radiation resulted in rupture of the thylakoids and grana due to the Plant Science Today (2014) 1( 4 226 disintegration of the membranes (He et al., 1994, p.771).The significant increase of total chlorophyll occurred under reduced UV-B and UV-A+B radiation, and this implied that the UV radiation has a negative impact on the parameters related to photosynthesis.The exclusion of solar UV-B and UV-A+B caused enhancement in photosynthetic pigments like-Chlorophyll a (Chl a), Chl b, total Chl and carotenoid content per unit fresh weight.The increase in total Chl level by the exclusion of solar UV was due to the enhanced synthesis of Chl a and Chl b.Though the extent of promotion was greater in Chl b rather than Chl a, which cause the decrease in the ratio of Chl a/b after exclusion UV-B and UV-A+B (Amudha et al., 2005, p.284;Kataria et al., 2013, p.140).Chl a/b could reflect the relative ratio of stacked regions to unstacked regions, which were inversely proportional to the stacking degree of thylakoids (Ibanez et al., 2008).
Carotenoids are also significantly increased by exclusion of solar UV (Amudha et al., 2005 p. 284;Kataria et al., 2013, p.140).They play an important role against UV-B damage in higher plants.Carotenoids, the scavengers of singlet oxygen species formed during intense light, are involved in the light harvesting and protection of chlorophylls from photoxidative destruction (Middleton & Teramura, 1993).The reduction in carotenoids in presence of solar UV-B and UV-A could have serious consequences for UV-B radiation effects on chlorophyll pigments, its role in the photoprotection of the photosynthetic system by dissipating excess excitation energy through the xanthophylls cycle (Demmig-Adams, & Adams, 1992, p.599).On the other hand, on removal of the stress, the inhibition is overcome or degradation processes might have been 'stopped, resulting in an accumulation of these pigments.

Chlorophyll Fluorescence
Chlorophyll fluorescence analysis is a powerful technique to conveniently assess the condition of PSII and vitality in intact plants.He et al. (1993) observed that decrease in the ratios of variable to maximum chlorophyll fluorescence yield and in the quantum yield of photosynthetic oxygen evolution by supplemental UV-B in pea and rice leaves.In contrast to UV-B, UV-A is not usually regarded as a potentially damaging stress factor, although Turcsanyi and Vass (2000) reported the UV-A induced impairment of photosystem II and concluded that UV-A radiation is highly damaging for PSII, and affected the electron transport at both the water oxidizing complex, and the binding site of the QB quinone electron acceptor in a similar way to that caused by UV-B radiation.Hakala-Yatkin, Mäntysaari, Mattila, & Tyystjärvi (2010) studied the contribution of the UV part of sunlight in photoinhibition of PSII in leaves and also suggested that especially the UV-A part, are potentially highly important in photoinhibition of PSII by the means a UV-permeable or UV-blocking filters.
On the other hand reduction of the UV-B and UV-B+A both caused a rise in many of the Chlorophyll fluorescence parameters in several crops.The UV-exclusion experiments showed that a reduction of the ambient UV-B level resulted in decreased content of UV-B absorbing compounds and lower stress level indicated by increased maximal quantum yield (FV/FM) and Performance Indexes (PI) (Bredahl, Ro-Poulsen, Mikkelsen, 2004;Albert et al., 2005Albert et al., , 2008Albert et al., , 2010;;Kataria et al., 2013, p.140).Bredahl et al. (2004, p.363) reported higher maximal photochemical efficiency (measured as the chlorophyll fluorescence parameter Fv/Fm) under UV-B reduction.Quantum efficiencies, specific and phenomenological fluxes were all enhanced by UV exclusion indicating a negative impact of ambient UV on all of these parameters in the plant species (Albert, Mikkelsen, & Ro-Poulsen, 2005, Albert, Mikkelsen, & Ro-Poulsen, 2008, Albert et al., 2010, p.1542;Kataria et al., 2013, p.140).The increases in the efficiency that an absorbed photon will be trapped by the PSII reaction centre with the resultant reduction of QA to QA -(ET0/ABS = FV/FM) and the efficiency that an electron residing on QA-will enter the intersystem electron transport chain (ET0/TR0) were observed in reduced UV-B.Moreover, estimated per cross-section of leaf sample, the number of active PSII reaction centres (RC/CSM) and electron transport rate (ETM/CSM) and all performance indexes (PIABS, PICSo and PICSm) were increased in reduced UV-B (Albert et al., 2005, p.208, Albert et al., 2008, p.199;Kataria et al., 2013, p.140).
Among the constellation of JIP (a test applied to analyze fast fluorescence kinetics O-J-I-P) expressions, one of the most sensitive parameters are the performance index (PIABS).Moreover, PIABS allows broader analysis of photosynthetic performance such as the relationship between photon absorption efficiency and capture of excited energy in PS II, as well as analysis of density of active RC and the probability that excited energy moves an electron further than QA _ (Goncavles, & Junior, 2005), all of these parameters were significantly increased after exclusion of UV-B and UV-A+B (Kataria et al., 2013, p.140).Their enhancement clearly indicates an improved overall processing of light energy per leaf sample CS in UV excluded plants (Albert et al., 2005, p.208, Albert et al., 2008, p.199;Albert et al., 2010Albert et al., , p.1542;;Kataria et al., 2013, p.140).The leaves of UV excluded plants species had higher reducing power with higher efficiency of electron transport and more active reaction centers, which may lead to the increase in carbon uptake in these plants (Albert et al., 2005, p.208, Albert et al., 2008, p.199;Albert et al., 2010Albert et al., , p.1542;;Shine, & Guruprasad, 2012;Kataria et al., 2013, p.140;Kataria, & Guruprasad, 2014).

Photosynthesis (Pn)
The process of photosynthesis is considered to be sensitive to UV-B radiation.The reductions in rate of photosynthesis have been attributed to changes in photophosphorylation, electron transport and carbon assimilatory processes (Teramura, 1983).Current ambient levels of UV radiation have been shown to modify leaf morphology and gas exchange in Populus, and increased net photosynthesis was observed under sub-ambient (-UV-B) radiation (Schumaker, Bassman, Robberecht, & Radamaker, 1997).Similarly, Krause et al. (2003) have reported a reduction in net CO2 uptake and photosystem I efficiency in tree seedlings when exposed to solar UV-B radiation.Reduction in biomass has been linked with reduced rate of photosynthesis in many crop species after supplemental UV-B and ambient UV-B (Kataria et al., 2013, p.140;Pal et al., 1997, p.29;Ambasht & Agrawal, 1998).Moussa & Khodary (2008) found a higher photosynthetic capacity in UV-B-free grown common bean plants (up to 33%) against only a marginal increase (12%) in barley plants grown under similar conditions.A similar observation of enhancement in the net rate of photosynthesis and concomitant increase in stomatal conductance after exclusion of UV-B has been made in Populus (Schumaker et al., 1997, p.617), maize and mung bean (Pal et al., 1997, p.29), wheat and pea (Pal et al., 2006, p.19), sorghum (Kataria, & Guruprasad, 2012b), Amaranthus tricolor (Kataria, & Guruprasad, 2014) and Vaccinium uliginosum (Albert et al., 2008, p.199).The primary effect of ambient UV is thus on the photosynthetic performance that reduces rate of photosynthesis and fixation of CO2.Variation in photosynthesis is also dependent on the ability of a leaf to draw down CO2 within the leaf.Lower stomatal conductance suggests a direct impact of UV-B on stomatal closure (Day, & Vogelmann, 1995) and stomatal limitation accounting for the decline in photosynthesis.UV-B radiation has the potential to affect the stomatal density in pea (Nogués, Allen, Morison, & Baker, 1998).

Enzymes related to carbon metabolism
Enhanced and ambient UV-B significantly inhibits net photosynthetic rate as the consequences of decrease in the light saturated rate of CO2 assimilation, accompanied by decreases in carboxylation velocity and Rubisco content and activity (Allen, Mckee, Farage & Baker, 1997).Limited CO2 assimilation due to UV-B leads to excessive production of ROS which, in turn, cause oxidative damage in plants (Strid, Chow & Anderson, 1994).Rao, Palijyath, & Ormrod, (1996) suggested that UV-B exposure generates activated oxygen species by increasing NADPH-oxidase activity.The productions of hydroxyl radicals, singlet oxygen, superoxide radicals and hydrogen peroxide have been detected in response to UV-B exposure.It has been suggested that exposure to UV-B results in generation of ROS within the chloroplast, as thylakoid membranes are very rapidly perturbed on exposure to UV-B radiation (Chow, Strid, & Anderson, 1992).
Hence the decrease in Pn by ambient UV might be associated with changes in the activities of enzymes involved in carbon assimilation along with damage to PSII.Ribulose-1,5 biphosphate carboxylase/oxygenase (Rubisco) is the primary catalyst for the assimilation of atmospheric CO2 in to the biosphere.It is a key enzyme in C3 cycle of photosynthetic fixation of CO2 and a remarkably abundant protein (upto 65% of total soluble leaf proteins) (Furbank, & Taylor, 1995).In C4 photosynthetic carbon metabolism, the initial carboxylation reaction is catalyzed by phosphoenolpyruvate carboxylase (PEPC).PEPC utilizes bicarbonate rather than CO2 as the inorganic substrate (O'Leary, 1982).To sustain this process, atmospheric CO2 entering the mesophyll cells must be rapidly converted to HCO3 -and this reaction is the critical first step of C4 photosynthesis (Hatch & Burnell, 1990).Carbonic anhydrase (CA) plays an important role in the acceleration of carbon assimilation, by catalyzing the reversible interconversion of CO2 and HCO3 -.In leaves CA represents 1-20% of total soluble protein and abundant next only to Rubisco in chloroplast.In C3 plants, CA activities largely restricted in stroma of mesophyll chloroplasts, where it is believed to facilitate the diffusion of CO2 across the chloroplast envelope.In C4 plants, however most of the CA activity is found in mesophyll cells, where PEP carboxylase is also located (Hatch & Burnell, 1990).Co-existence and feeding of Rubisco in C3 plants and PEPC in C4 plants with carbon source by CA assumes the special significance of CA as an efficient biochemical marker for carbon sequestration and environmental amelioration in the current global warming scenario linked with elevated CO2 concentration.
The recent reports in lower and higher plants, suggests that ambient level of UV-B and UV-A radiations affect the activity of carbonic anhydrase, Rubisco and PEPCase.Exclusion of UV-B and UV-A+B from solar spectrum resulted in an elevated overall activity of carbonic anhydrase, RuBisco and PEPcase and increase in its concentration (Bischof, Hanelt, & Wiencke, 2000; Plant Science Today (2014) 1(4): 224-232 Bischof, Krabs, Wiencke, & Hanelt, 2002;Kataria et al., 2013, p. 140;Kataria, & Guruprasad, 2014).The increase in CA activity by exclusion of UV radiations may enhance the fixation of CO2 via PEP carboxylase as well as via Rubisco.UV-B exposure has been shown to lead to a reduction in the expression and level of key photosynthetic proteins including Rubisco (Allen, Nougúes, & Baker, 1998).Bischof et al. (2002, p.502) observed an increase in the concentration and the activity of Rubisco in Ulva lactuca after exclusion of solar UV.The enhancement in the activity of Rubisco by the fixation 14 CO2 was found in C3 and C4 monocot/dicot crop species by the exclusion of solar UV components (Kataria et al., 2013, p.140).The enhanced activity of CA, Rubisco and PEP carboxylase in the absence of solar UV radiation could be due to degradation of protein subunits upon exposure to UV-B as shown for higher plants and macroalgae (Bischof et al., 2000, p.555;Bischof et al., 2002, p.502;Xu, Natarajan, & Sullivan, 2008).Damage to enzyme proteins such as Rubisco could also results from the active oxygen species formed under UV-B radiation (Shine, & Guruprasad, 2012).With regard to the degradation of Rubisco, Ishida et al. (1998Ishida et al. ( , 1999) ) demonstrated that under illumination the large subunit (LSU) of Rubisco could be directly fragmented into two polypeptides by reactive oxygen species in chloroplast.In addition, Desimone et al. (1996Desimone et al. ( , 1998) ) reported that light stress induced reactive oxygen-mediated denaturation of Rubisco followed by proteolytic degradation of LSU in chloroplasts.Elevated UV-B induced injury might be associated with active oxygen species in rice (Dai et al., 1997, p.301); this has also been found in other species (Mackermess, Surplus, Jordan, & Thomas, 1998).However, it should be noted that the fast rate of degradation of Rubisco occurred after the leaf had developed to maturity, around that time active growth of the leaf drew near the end and senescence began.Thus, it can be speculated that the formation of proteases may be increased at this point, resulting in enhanced Rubisco degradation (Callis, 1995).However, the future studies needed for the molecular mechanisms behind the Rubisco degradation

Crop yield
In the natural environment plants are usually subjected to combined stresses and the stress factors cause several changes in plant metabolism and morphology.The main concern for producers and agricultural scientists is whether or not enhanced UV-B radiation due to stratospheric O3 depletion reduces economic yields and product quality of field crops.The UV components present in the solar spectrum seemed to inhibit the photomorphogenetic pattern.Exclusion of ambient UV has a potential for producing higher biomass/yield which gets limited under ambient UV.Removal of UV from solar radiation caused a significant increase in yield attributes like number of pods and seeds, weight of seeds in cymopsis (Amudha et al., 2005, p.284) and soybean varieties (Baroniya, Kataria, Pandey, & Guruprasad, 2011).Germ et al. (2005) found that exclusion of UV-B from the solar radiation led to more than double the yield of pumpkin fruits.The reason for yield reduction may be due to alterations in plant vegetative and reproductive growth, e.g., plant stunting, flower suppression and/or delay of flowering and lower pod set (Saile-Mark, & Tevini, 1997;Amudha et al., 2005, p.284).High level of UV-B radiation delays flowering and thereby reducing the yield.In the case of Cyamopsis, a delay in the onset of flowering was observed in the ambient light grown plants.The cause for the delay is maybe due to the impact of solar UV radiation on the biosynthesis of gibberellins as explained by Saile-Mark (1993) in Hyoscyamas niger.Exclusion of UV-A along with UV-B enhanced the yield parameters in terms of weight of total bolls and fibers in cotton; number of leaves and foliage yield (fresh weight of leaves) in amaranthus; number of ears/panicles, grains and grain yield per plant in wheat and sorghum, the extent of promotion in yield parameters was more by exclusion of UV-B alone than the exclusion of UV-A+UV-B (Kataria et al., 2013, p.140).
Reduction in photosynthesis by ambient UV (280-400 nm) radiations is a basis of reduced dry matter production and lower yield.Enhanced production of UAS by ambient UV-B, suggests that the reduced photosynthesis may be due to, diversion of primary metabolites towards the protective sunscreens and in results in reduced secondary metabolism.While in the absence of ambient UV-B; the reduction in the synthesis of these secondary products (UAS) can save the carbon that can be channelized to primary metabolism.Since secondary and primary metabolic pathways compete for the common pool of carbon, reduction in secondary metabolism by the exclusion of solar UV-B and UV-A+UV-B can channelize the carbon to improved biomass accumulation and increased rate of Pn which ultimately results in improvement of crop yield (Fig. 1).The exclusion of UV components from the solar radiation brings about a larger increase in the vegetative growth, pigments as well as in crop yield in certain crops, however, these changes are species specific.

Conclusions
Exclusion studies will have significance under tropical environment where the plants receive higher amount of ambient UV-B.Exclusion studies would help in the assessment of the adaptability of a variety to ambient UV-B received.Exclusion of UV components from solar radiation under field condition stimulates plant growth and enhanced biomass.This increased growth and biomass appear to be due to the better harvesting of light and lower level of free radicals in plants grown under UV-B and UV-A+B exclusion filters.The economics feasibility of using this technique is currently being marked out.Instead of Plant Science Today (2014) 1(4): 224-232 ISSN: 2348ISSN: -1900 Horizon e-Publishing Group 229 using UV exclusion filters there is a possibility of developing chemicals that can selecting absorb UV light part of the solar spectrum without interfering in the transmission of PAR part of the solar spectrum.Exclusion of UV radiations increases overall processing of light energy per leaf sample and as a consequence higher amounts of ATP and NADPH are produced and thus, increase the capacity for ribulose-1,5-bisphosphate/ phosphoenol pyruvate regeneration.Thus suggesting that the exclusion of UV components from the solar spectrum triggered carbon sequestration in biomass, which seems directly linked to enhancement in photosystem components in field grown plants.Solar UV exclusion could be advantageous from agricultural point to enhance growth and yield of crops.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.

Fig. 1 .
Fig. 1.A model to summarize the growth, photosynthetic and yield responses to ambient UV radiation by exclusion of solar UV