Yiola Petropoulou
University of Patras, Biology, Faculty Member
The photosynthetic differences between adult and juvenile Mediterranean plants were previously studied under field conditions, yet the corresponding differentiation of their photoprotective efficiency has not been sufficiently... more
The photosynthetic differences between adult and juvenile Mediterranean plants were previously studied under field conditions, yet the corresponding differentiation of their photoprotective efficiency has not been sufficiently investigated. The present study aims to examine possible differences in the photoprotective potential between adults and juveniles of two native Mediterranean plants with distinct growth forms. Thus, the seasonal variations in individual carotenoids, electron transport rate (ETR), and non-photochemical quenching (NPQ) were monitored in fully exposed mature leaves from adults and juveniles of the winter deciduous tree Cercis siliquastrum L. and the evergreen sclerophyllous shrub Nerium oleander L. All plants were grown under apparently similar field conditions. In both species, juveniles displayed substantially lower ETR and increased NPQ values than adults in spring, with the differences intensifying during summer drought and diminishing in autumn. Concomitant...
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Research Interests: Functional Anatomy, Photosynthesis, Plant Biology, Biology, Plant Anatomy, and 15 moreFlora, Optical microscopy, Construction Cost, Cyclamen, Optical Properties, Electron Transport, Scanning Electron Microscope, Photosynthetic Rate, Dry Mass, Leaf Area, Chlorophyll a, Gas Exchange, Chlorenchima, Electron Transport Rate, and Arum italicum
Research Interests: Fluorescence Spectroscopy, Plant Biology, Biology, Chlorophyll Fluorescence, Fluorescence Imaging, and 12 moreQuercus Coccifera, Spectral Reflectance, Low Temperature, Low Light, Photoinhibition, Platanus orientalis, Nerium Oleander, PSII photochemistry, Eleagnus angustifolia, Chlorophyll Fluorescence Imaging, Tree Species, and high light
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... in order to minimise possible step effects and supplemental UV-B radiation was centred at solar noon. ... The seasonal variation of UV-BBE radiation dose under the control and UV-B frames, computed after Bjom ... of Patras weather... more
... in order to minimise possible step effects and supplemental UV-B radiation was centred at solar noon. ... The seasonal variation of UV-BBE radiation dose under the control and UV-B frames, computed after Bjom ... of Patras weather station, located 0,5 km from the experi-mental site ...
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The effects of enhanced UV-B radiation on Phlomis fruticosa L. were recorded during a 1- year field study. Plants received ambient or ambient plus supplemental UV-B radiation (simulating a 15% stratospheric ozone depletion over Patras,... more
The effects of enhanced UV-B radiation on Phlomis fruticosa L. were recorded during a 1- year field study. Plants received ambient or ambient plus supplemental UV-B radiation (simulating a 15% stratospheric ozone depletion over Patras, 38.3�N, 29.1�E) and only natural precipitation, i.e. they were simultaneously exposed to other natural stresses, particularly water stress during summer. Actual, biologically equivalent UV-B doses were 8.55 and 11.21 kJ m-2 day-1 during the summer maximum (14 July) and 0.85 and 1.12 kJ m-2 day-1 during the winter minimum (27 December) for control and W-B plants respectively, while intermediate values were received for the rest of the year. lho seasonally separated effects could be distinguished. The first was a growth response, observed at late spring, in the absence of any simultaneous stress and at the period most favourable for this shrub, during which it shows maximum photosynthetic performance. The effect was an inhibition of new leaf development...
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In olive (Olea europaea L.), hair removal had no effect on the photosynthetic rate and the apparent leaf resistance to water vapour diffusion in leaves illuminated with white light (900 μmol m-2 s-1 photosynthetically active radiation)... more
In olive (Olea europaea L.), hair removal had no effect on the photosynthetic rate and the apparent leaf resistance to water vapour diffusion in leaves illuminated with white light (900 μmol m-2 s-1 photosynthetically active radiation) devoid of ultraviolet-B radiation. In addition, intact and dehaired leaves showed no significant differences in absorptance in the visible spectral region, while leaf temper- ature was independent of hair removal. These results indicate that leaf hairs of O. europaea may play only a marginal role in leaf energy balance and transpiration. When the white light was supplemented with ultraviolet-B radiation (5.89 W m-2), however, there was a considerable decrease in the photo- synthetic rate, and a simultaneous increase in leaf resistance to water vapour in dehaired leaves. Photochemical efficiency of photosystem II, evaluated from chlorophyll fluorescence emitted from the illuminated side, was reduced in all cases, but the reduction in dehaired, ultravio...
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Seedlings of Nerium oleander L. were grown in the field under ambient or ambient plus supplemental UV-B radiation (simulating a 15% ozone depletion over Patras), and received natural precipitation or additional irrigation during the... more
Seedlings of Nerium oleander L. were grown in the field under ambient or ambient plus supplemental UV-B radiation (simulating a 15% ozone depletion over Patras), and received natural precipitation or additional irrigation during the summer dry period. Two experiments, in 1994 and 1995, were performed. Natural precipitation during summer in 1994 was near the mean for the area but summer 1995 was exceptionally wet. During 1994, supplemental UV-B radiation reduced by ca 25% the above-ground biomass under natural summer precipitation but had no effect on the plants receiving additional irrigation. During the wet 1995, UV-B radiation caused a 5%, non-significant reduction in biomass under natural summer precipitation, and a 16%, non-significant increase under ample water availability. No effects of UV-B radiation were observed on PSII photochemical efficiency (assessed from in vivo Chl fluorescence), photosynthetic pigments, UV-B absorbing compounds, leaf relative water content, leaf spe...
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Seedlings of Nerium oleander L. were grown in the field under ambient or ambient plus supplemental UV-B radiation (simulating a 15% ozone depletion over Patras), and received natural precipitation or additional irrigation during the... more
Seedlings of Nerium oleander L. were grown in the field under ambient or ambient plus supplemental UV-B radiation (simulating a 15% ozone depletion over Patras), and received natural precipitation or additional irrigation during the summer dry period. Two experiments, in 1994 and 1995, were performed. Natural precipitation during summer in 1994 was near the mean for the area but summer 1995 was exceptionally wet. During 1994, supplemental UV-B radiation reduced by ca 25% the above-ground biomass under natural summer precipitation but had no effect on the plants receiving additional irrigation. During the wet 1995, UV-B radiation caused a 5%, non-significant reduction in biomass under natural summer precipitation, and a 16%, non-significant increase under ample water availability. No effects of UV-B radiation were observed on PSII photochemical efficiency (assessed from in vivo Chl fluorescence), photosynthetic pigments, UV-B absorbing compounds, leaf relative water content, leaf specific mass or leaf thickness. However, cuticle thickness and cuticle mass (on a unit area basis) were increased by supplemental UV-B radiation, on both leaf surfaces, independent of water availability. We conclude that UV-B radiation effects on growth depend on the extent of summer precipitation. The increase in cuticle thickness may counteract UV-B radiation damage, through attenuation of UV-B radiation and/or reduction of cuticular transpiration during the dry summer.
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The winter annual species Anthemis arvensis L. (Asteraceae) was grown for 3.5 months in the field under ambient or ambient plus supplemental UV-B radiation, simulating a 15% ozone depletion over Patras (38.3° N, 29.1° E). Enhanced UV-B... more
The winter annual species Anthemis arvensis L. (Asteraceae) was grown for 3.5 months in the field under ambient or ambient plus supplemental UV-B radiation, simulating a 15% ozone depletion over Patras (38.3° N, 29.1° E). Enhanced UV-B radiation had no effect on the methanol extractable UV-B absorbing capacity of leaves, phenological and morphometric parameters of anthesis (flowering time, anthesis duration, head life
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The photosynthetic pigments of twigs in five tree and shrub species possessing chlorenchyma under a well developed, stomata-less, and highly photon absorptive periderm were analysed and compared to those of the corresponding canopy... more
The photosynthetic pigments of twigs in five tree and shrub species possessing chlorenchyma under a well developed, stomata-less, and highly photon absorptive periderm were analysed and compared to those of the corresponding canopy leaves. We asked whether the unavoidable shade acclimation of corticular chlorenchyma results in photosynthetic pigment complements typically found in shade leaves. As expected, chlorophyll (Chl) a/b ratios in twigs were consistently low. However, carotenoid (Car) analysis did not confirm the initial hypothesis, since twigs generally contained increased Chl-based pool sizes of the xanthophyll cycle components. The contents of photo-selective neoxanthin and lutein were high as well. Yet, -carotene content was extraordinarily low. In addition, twigs retained high pre-dawn ratios of the deepoxidized antheraxanthin and zeaxanthin, although environmental conditions were not pre-disposing for such a state. The unexpected Car composition allows the conclusion th...
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The aim of this investigation was to examine the reasons for the higher pollination success in Cistus creticus under enhanced UV-B radiation (Stephanou & Manetas 1998). Thus, a selected array of floral attributes as well as the frequency... more
The aim of this investigation was to examine the reasons for the higher pollination success in Cistus creticus under enhanced UV-B radiation (Stephanou & Manetas 1998). Thus, a selected array of floral attributes as well as the frequency and duration of insect visits were studied in the field under ambient or ambient plus supplemental UV-B radiation, simulating a 15% ozone depletion over Patras (38.3N, 29.1E). Video-recording revealed two categories of visitors, i.e. true pollinators (bees) and nectar thieves. The frequency of visits to both control and UV-B treated plants was the same and independent of whether the UV-B tubes were on or off during video recording. UV-B radiation had no effect on gross floral morphology (petal surface area, number of pollen grains, stamens and ovules, optical properties of petals and stamens), yet nectary size was almost doubled. In addition, the duration of insect visits was significantly longer on UV-B treated plants, provided that the UV-B tubes ...
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We checked the hypothesis that the transient presence of anthocyanins in young leaves serves a photoprotective function. For this purpose, Rosa sp. and Ricinus communis L., whose young leaves are red to become green upon maturation, were... more
We checked the hypothesis that the transient presence of anthocyanins in young leaves serves a photoprotective function. For this purpose, Rosa sp. and Ricinus communis L., whose young leaves are red to become green upon maturation, were used. Thus, young leaves with high and mature leaves with low anthocyanin contents were analysed concerning their carotenoid (Car) composition and susceptibility to photoinhibition. Cars, including the components of the xanthophyll cycle, had similar contents in young and mature leaves, when expressed on a chlorophyll basis. Yet, when expressed on a leaf area basis or on the assumed photon absorptive capacity of leaves, Cars contents were considerably lower in anthocyanic young leaves. Although this may indicate a low photodissipative potential, red young leaves were considerably less susceptible to photoinhibitory damage. The results are compatible with a photoprotective function of anthocyanins, indicating also that their presence may compensate f...
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Seedlings of Laurus nobilis L. and Ceratonia siliqua L., grown for 1 year in the field under ambient radiation conditions were subsequendy allowed to produce their new spring growth in a glasshouse in the absence or presence of UV-B... more
Seedlings of Laurus nobilis L. and Ceratonia siliqua L., grown for 1 year in the field under ambient radiation conditions were subsequendy allowed to produce their new spring growth in a glasshouse in the absence or presence of UV-B radiation. The UV-B radiation dose was biologically equivalent to that which would have being received by the plants in their natural environment. Plant height, number of leaves, total and mean leaf area, the biomass allocated to both above and below ground parts, photochemical efficiency of PS II and chlorophyll content were not affected. However, UV-B radiation resulted in slighdy thicker leaves in L. nobilis and considerably thicker cuticles in both plants. UV-B absorbing compounds were increased only in L. nobilis. In addition, the leaf nutritional quality of this plant was considerably reduced by UV-B radiation, since phenolics and tannins were increased but nitrogen was decreased. No such changes were observed in C. siliqua. We may conclude that L....
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Thirteen flavonoid aglycons, contained in the strongly allelopathic epicuticular exudates of Dittrichia viscosa, were investigated for their effects on lettuce seedling radicle growth. Concerning radicle length and mass, variable results... more
Thirteen flavonoid aglycons, contained in the strongly allelopathic epicuticular exudates of Dittrichia viscosa, were investigated for their effects on lettuce seedling radicle growth. Concerning radicle length and mass, variable results were obtained, with most of the substances having no effect, some being inhibitory and some even promotive. Shoot mass was slightly reduced in four cases. Seed germination rates, root hair and lateral root formation were not affected either. Three of the compounds (namely quercetin 3,3-dimethylether, naringenin and eriodictyol) induced a strong ageotropic response in radicle growth.
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... These involved a 200% increase in mean summer precipitation at Qaanaaq, 80% at Abisko, and up to 315% at Patras. ... Estimation of fluence rate from irradiance meas-urements with a cosine corrected sensor. ... Computer calculation of... more
... These involved a 200% increase in mean summer precipitation at Qaanaaq, 80% at Abisko, and up to 315% at Patras. ... Estimation of fluence rate from irradiance meas-urements with a cosine corrected sensor. ... Computer calculation of solar ultraviolet radiation at ground level. ...
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Research Interests: Plant Biology and Ecology
Research Interests: Plant Biology and Ecology
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ABSTRACT We have analyzed reflectance changes and carotenoid composition of young and mature leaves of Platanus orientalis L. in order to test the hypothesis that the transient occurrence of highly absorptive and reflective leaf hairs of... more
ABSTRACT We have analyzed reflectance changes and carotenoid composition of young and mature leaves of Platanus orientalis L. in order to test the hypothesis that the transient occurrence of highly absorptive and reflective leaf hairs of young leaves (M. Ntefidou and Y. Manetas 1996, Aust. J. Plant Physiol. 23: 535–538) may be correlated to a weakly developed photodissipative capacity in the chloroplast. Compared to mature leaves, young leaves showed negligible reflectance changes at 530 nm upon sudden illumination, possibly indicating a limited production of zeaxanthin. In addition, actual pigment analysis confirmed lower pools of xanthophyll cycle components and reduced capacity for violaxanthin photoconversion in young leaves. Accordingly, the epoxidation state at saturating photon fluence rates was particularly high. A notable feature of xanthophyll cycle interconversions in young leaves was the inability to drive the system to complete de-epoxidation, as antheraxanthin in the light was always higher than zeaxanthin. Among the rest of the carotenoids, the levels of β-carotene were particularly low. Moreover, most of the photosynthetic pigments were considerably bleached when young leaves were exposed to high light. The above results strongly suggest that young leaves possess a limited photodissipative capacity and therefore, the presence of leaf hairs affords protection against excess light. When the leaf has matured and presumably the concentrations of photoprotective compounds are adequate, the loss of hairs is not of consequence. In fact, their presence on mature leaves may reduce the photosynthetically active radiation to non-saturating levels for photosynthesis.
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ABSTRACT Isolated intact mesophyll protoplasts from Zea mays L. were used as an enzyme source for studying properties of phosphoenolpyruvate (PEP) carboxylase (EC 4.1 1 31) just after release from cells into the reaction medium. After the... more
ABSTRACT Isolated intact mesophyll protoplasts from Zea mays L. were used as an enzyme source for studying properties of phosphoenolpyruvate (PEP) carboxylase (EC 4.1 1 31) just after release from cells into the reaction medium. After the injection of protoplasts into the assay mixture, an initial lag of activity was observed, mainly due to the time necessary for complete disruption of protoplasts by the osmotic shock. The final specific activity obtained was ca 18 μmol mg-1 of liberated protein min-1, a value comparable to that usually achieved after arduous purification. Under the assay conditions employed, the chloroplasts were not disrupted and the retention of their proteins, together with the use of purified mesophyll protoplasts, were obviously the reasons for the high specific activity obtained. The activity and properties of phosphoenolpyruvate carboxylase stored in isolated protoplasts were stable for at least 24 h at 5°C. The main difference between the protoplast-derived and the routinely extracted enzyme was the sensitivity to malate inhibition, which was partially lost in the extracted phosphoenolpyruvate carboxylase; no difference was found in the Km(PEP). The stress imposed by the protoplast isolation procedure diminished the sensitivity of the enzyme to malate inhibition, so that it can be inferred that the real malate sensitivity of pbosphocnolpyruvale carboxylase is even greater and that it is grossly underestimated with routinely extracted enzyme.
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Recent reports have indicated a considerably inactivated PSII in twig cortices, in spite of the low light transmittance of overlying periderms. Corresponding information for more deeply located and less illuminated tissues like xylem rays... more
Recent reports have indicated a considerably inactivated PSII in twig cortices, in spite of the low light transmittance of
overlying periderms. Corresponding information for more deeply located and less illuminated tissues like xylem rays
and pith are lacking. In this investigation we aimed to characterize the efficiency of PSII and its light sensitivity along
twig depth, in conjunction with the prevailing light quantity and quality. To that aim, optical methods (spectral
reflectance and transmittance, chlorophyll fluorescence imaging, low temperature fluorescence spectra) and photoinhibitory
treatments were applied in cut twig sections of four tree species, while corresponding leaves served as
controls. Compared to leaves, twig tissues displayed lower chlorophyll (Chl) levels and dark-adapted PSII efficiency,
with strong decreasing gradients towards the twig center. The low PSII efficiencies in the inner stem were not an artifact
due to an actinic effect of measuring beam or to an enhanced contribution of PSI fluorescence. In fact, the PSII/PSI
ratios in cortices were higher and those in the xylem rays similar to that of leaves. Inner twig tissues were quite resistant
to photoinhibitory treatments, tolerating irradiation levels several-fold higher than those encountered in their
microenvironment. Moreover, the extent of high light tolerance was similar in naturally exposed and shaded twig sides.
The results indicate an increasing, inherent and light-independent inactivation of PSII along twig depth. The findings are
discussed on the basis of a recently proposed model for photosynthetic electron flow in twigs, taking into account the
specific atmospheric and light microenvironment as well as the possible metabolic needs of such bulky organs.
overlying periderms. Corresponding information for more deeply located and less illuminated tissues like xylem rays
and pith are lacking. In this investigation we aimed to characterize the efficiency of PSII and its light sensitivity along
twig depth, in conjunction with the prevailing light quantity and quality. To that aim, optical methods (spectral
reflectance and transmittance, chlorophyll fluorescence imaging, low temperature fluorescence spectra) and photoinhibitory
treatments were applied in cut twig sections of four tree species, while corresponding leaves served as
controls. Compared to leaves, twig tissues displayed lower chlorophyll (Chl) levels and dark-adapted PSII efficiency,
with strong decreasing gradients towards the twig center. The low PSII efficiencies in the inner stem were not an artifact
due to an actinic effect of measuring beam or to an enhanced contribution of PSI fluorescence. In fact, the PSII/PSI
ratios in cortices were higher and those in the xylem rays similar to that of leaves. Inner twig tissues were quite resistant
to photoinhibitory treatments, tolerating irradiation levels several-fold higher than those encountered in their
microenvironment. Moreover, the extent of high light tolerance was similar in naturally exposed and shaded twig sides.
The results indicate an increasing, inherent and light-independent inactivation of PSII along twig depth. The findings are
discussed on the basis of a recently proposed model for photosynthetic electron flow in twigs, taking into account the
specific atmospheric and light microenvironment as well as the possible metabolic needs of such bulky organs.
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ABSTRACT Total carotenoids assessed spectrophotometrically in crude extracts may be considerably overestimated when high contents of phenolic compounds are co-extracted. In this case, the absorbance tails of phenolics extend well into the... more
ABSTRACT Total carotenoids assessed spectrophotometrically in crude extracts may be considerably overestimated when high contents of phenolic compounds are co-extracted. In this case, the absorbance tails of phenolics extend well into the blue part of the spectrum, interfering with carotenoid estimation. Extracts of phenolic-rich organs, with a low ratio of photosynthetic to heterotrophic and/or supportive cells (for example, stems or twigs) are vulnerable to such pitfalls and may need chromatographic separation of carotenoids.
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... In this way, all plants were receiving the same levels of slightly subambient solar radiation and UV-B plants were receiving supplemental UV-B radiation simulating 15% ozone depletion overPatras (38°14′ N, 21°44′ E). This was... more
... In this way, all plants were receiving the same levels of slightly subambient solar radiation and UV-B plants were receiving supplemental UV-B radiation simulating 15% ozone depletion overPatras (38°14′ N, 21°44′ E). This was accomplished as follows: the absolute UV-B ...
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Research Interests: Photosynthesis, Plant Biology, Energy Conversion, Negative Affect, Chlorophyll, and 14 moreChlorophyll Fluorescence, Stress tolerance, Experimental Botany, Electron Transport, Anthocyanins, Light Acclimation, Experimental, Photosynthetic Pigment, Cistus, Seasons, Physiological Stress Markers, Plant Remains, Quantum Yield, and Plant Leaves
... to stabilize activity in order to detect differences between the 'day' and 'night' forms of the enzyme including addition of PEP (Shomer-Ilan et al ... tions of over 80 (Schnabl and Kottmeier, 1984), because the pH... more
... to stabilize activity in order to detect differences between the 'day' and 'night' forms of the enzyme including addition of PEP (Shomer-Ilan et al ... tions of over 80 (Schnabl and Kottmeier, 1984), because the pH of cytoplasm is about pH 7-0 (Roberts, Ray, Wade-Jardetzky, and Jardet ...
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... exposed to solar radiation and deeply shaded (under a canopy of evergreen sclerophylls) individuals of Urginea the mesophyll. In all cases a Shimadzu UV-160A recording spectrophotometer was used. maritima L. (Liliaceae), growing wild... more
... exposed to solar radiation and deeply shaded (under a canopy of evergreen sclerophylls) individuals of Urginea the mesophyll. In all cases a Shimadzu UV-160A recording spectrophotometer was used. maritima L. (Liliaceae), growing wild in the vicinity of the Patras ...
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... Yiannis ManetasA,B,Yiola PetropoulouA, George K. PsarasA and Antonia DriniaA ... stress, the unbalance principle between light absorption and utilisation can be applied in young leaves as well, since photosynthetic rates in these... more
... Yiannis ManetasA,B,Yiola PetropoulouA, George K. PsarasA and Antonia DriniaA ... stress, the unbalance principle between light absorption and utilisation can be applied in young leaves as well, since photosynthetic rates in these leaves are low (see Sestak 1985 inter alia) and ...
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... The computations were made for the Patras area (38.3N, 29.1E), cloudless conditions with aerosol level zero and relative humidity 50. ... Fig. 1. Spectral irradiance at plant apex with the UVB tubes on (), off (...) and under the... more
... The computations were made for the Patras area (38.3N, 29.1E), cloudless conditions with aerosol level zero and relative humidity 50. ... Fig. 1. Spectral irradiance at plant apex with the UVB tubes on (), off (...) and under the control frame (...) measured around solar noon on ...
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The leaves of some plants display an optical patchiness on their upper side, displaying light- and dark-green areas with high and low reflectance, respectively. In this investigation, we studied the fine structure of the corresponding... more
The leaves of some plants display an optical patchiness on their upper side, displaying light- and dark-green areas
with high and low reflectance, respectively. In this investigation, we studied the fine structure of the corresponding
sectors and we asked whether the lost reflected light entails a photosynthetic cost to these leaves. Four species, i.e.
Arum italicum, Ranunculus ficaria, Cyclamen hederifolium and Cyclamen persicum were investigated. Scanning electron
microscope examination revealed that epidermal cells of light-green sectors of all species are more bulgy than
corresponding cells of neighboring dark-green leaf sectors. The comparative anatomical study revealed that (i)
epidermis thickness of the light-green areas and the number of mesophyll cell layers does not differ from those of the
adjacent dark-green leaf sectors and (ii) palisade cells of light-green sectors are slightly larger and more loosely
arranged, allowing a much higher percentage of intercellular air spaces. The latter histological feature seems to provide
the structural basis for the different optical properties between the two leaf sectors. Contrary to expectations, net
photosynthetic rates (expressed on a leaf area basis) were similar in the light-green and the dark-green areas of the two
cyclamen species. Yet, in C. persicum net photosynthesis was higher in the light-green areas, if expressed on a dry mass
basis. The small size of the light-green spots in the rest of the test plants precluded CO2 assimilation measurements, yet
maximum linear photosynthetic electron transport rates displayed no differences between the two sectors in all plants.
Thus, the assumption of a photosynthetic cost in the light-green areas was not confirmed. On the contrary, a higher
construction cost was evident in the dark-green areas of three species, displaying a significantly higher specific leaf
mass, without any photosynthetic benefit. The results on net photosynthesis were compatible with leaf optical
properties and pigment levels. Thus, in spite of the considerably higher reflectance of the light-green areas and their
lower (yet normal for a green leaf) chlorophyll levels, corresponding differences in absorptance were slight. In addition,
dry mass-based pigment contents in dark-green areas were higher, while chlorophyll a/b (in two species) and
carotenoid/chlorophyll ratios (in three species) were lower, pointing to a shade adaptation in these sectors. We
conclude that in variegated leaves of this kind, dark-green areas are more costly to build and probably less
photosynthetically active. We argue that the high pigment contents of dark-green areas establish steep light gradients
in the corresponding mesophyll, rendering deeper chloroplast layers more shade adapted.
with high and low reflectance, respectively. In this investigation, we studied the fine structure of the corresponding
sectors and we asked whether the lost reflected light entails a photosynthetic cost to these leaves. Four species, i.e.
Arum italicum, Ranunculus ficaria, Cyclamen hederifolium and Cyclamen persicum were investigated. Scanning electron
microscope examination revealed that epidermal cells of light-green sectors of all species are more bulgy than
corresponding cells of neighboring dark-green leaf sectors. The comparative anatomical study revealed that (i)
epidermis thickness of the light-green areas and the number of mesophyll cell layers does not differ from those of the
adjacent dark-green leaf sectors and (ii) palisade cells of light-green sectors are slightly larger and more loosely
arranged, allowing a much higher percentage of intercellular air spaces. The latter histological feature seems to provide
the structural basis for the different optical properties between the two leaf sectors. Contrary to expectations, net
photosynthetic rates (expressed on a leaf area basis) were similar in the light-green and the dark-green areas of the two
cyclamen species. Yet, in C. persicum net photosynthesis was higher in the light-green areas, if expressed on a dry mass
basis. The small size of the light-green spots in the rest of the test plants precluded CO2 assimilation measurements, yet
maximum linear photosynthetic electron transport rates displayed no differences between the two sectors in all plants.
Thus, the assumption of a photosynthetic cost in the light-green areas was not confirmed. On the contrary, a higher
construction cost was evident in the dark-green areas of three species, displaying a significantly higher specific leaf
mass, without any photosynthetic benefit. The results on net photosynthesis were compatible with leaf optical
properties and pigment levels. Thus, in spite of the considerably higher reflectance of the light-green areas and their
lower (yet normal for a green leaf) chlorophyll levels, corresponding differences in absorptance were slight. In addition,
dry mass-based pigment contents in dark-green areas were higher, while chlorophyll a/b (in two species) and
carotenoid/chlorophyll ratios (in three species) were lower, pointing to a shade adaptation in these sectors. We
conclude that in variegated leaves of this kind, dark-green areas are more costly to build and probably less
photosynthetically active. We argue that the high pigment contents of dark-green areas establish steep light gradients
in the corresponding mesophyll, rendering deeper chloroplast layers more shade adapted.