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The surface of peach (Prunus persica 'Calrico') is covered by a dense indumentum, which may serve various protective purposes. With the aim of relating structure to function, the chemical composition, morphology, and hydrophobicity of the peach skin was assessed as a model for a pubescent plant surface. Distinct physicochemical features were observed for trichomes versus isolated cuticles. Peach cuticles were composed of 53% cutan, 27% waxes, 23%, cutin, and 1% hydroxycinnamic acid derivatives (mainly ferulic and p-coumaric acids). Trichomes were covered by a thin cuticular layer containing 15% waxes and 19% cutin and were filled by polysaccharide material (63%) containing hydroxycinnamic acid derivatives and flavonoids. The surface free energy, polarity, and work of adhesion of intact and shaved peach surfaces were calculated from contact angle measurements of water, glycerol, and diiodomethane. The removal of the trichomes from the surface increased polarity from 3.8% (intact surface) to 23.6% and decreased the total surface free energy chiefly due to a decrease on its nonpolar component. The extraction of waxes and the removal of trichomes led to higher fruit dehydration rates. However, trichomes were found to have a higher water sorption capacity as compared with isolated cuticles. The results show that the peach surface is composed of two different materials that establish a polarity gradient: the trichome network, which has a higher surface free energy and a higher dispersive component, and the cuticle underneath, which has a lower surface free energy and higher surface polarity. The significance of the data concerning water-plant surface interactions is discussed within a physiological context. [ABSTRACT FROM AUTHOR]

Functional and structural characteristics of corticular photosynthesis of sun-exposed bark of olive tree (Olea europaea L.) were examined. Stomata are only sporadically present during stem primary growth. Light transmission through the phellem was age dependent, decreasing rapidly in stems older than five years of age. Light transmission was also low in pubescent 1-year-old stems. Light transmission was about 50% higher in wet phellem than in dry phellem. Photosynthetic capacity on a unit area basis (measured with an oxygen disc electrode at 27 °C and about 5% CO2 on chlorophyllous tissue discs isolated from the stem) was higher in 1-, 20- and 30-year-old stems compared with 2-10-year-old stems. Low chlorophyll a/b ratio and light compensation points were recorded in olive stems with low phellem light transmission, in accordance with the shade acclimation hypothesis. The intrinsic photochemical efficiency of photosystem II of all stems, especially young stems,was less than that of the leaves. Our results show that olive tree bark possesses an efficient photosynthetic mechanism that may significantly contribute not only to the reduction in concentrations of CO2 in the inner bark, but also to whole-tree carbon balance. [ABSTRACT FROM AUTHOR]

The UV‐absorbing capacity (measured as A310 cm−2 and A365 cm−2 or AUVR cm−2) of the shade leaves of four representative evergreen sclerophylls of the Mediterranean region (Quercus coccifera, Q. ilex, Arbutus andrachne and A. unedo) was considerably lower than the corresponding one of sun leaves of the same species. However, fibre optic microprobe measurements showed that adaxial as well as abaxial epidermis of shade leaves of all examined plants, except abaxial epidermis of A. andrachne, were almost as effective as the corresponding ones of the sun leaves in screening out most of the incident UV‐B radiation. There is probably a threshold, under which the concentration of the UV‐B absorbing compounds in the protective tissues is not furthermore reduced, in spite of the low levels of the stress factor (UV‐B radiation) in the environment. On the other hand, the ability of both abaxial and adaxial epidermis to attenuate UV‐A radiation, except of adaxial leaf epidermis of Quercus species, depended on the UV absorbing capacity of the whole‐leaf extracts, with different correlation patterns between the two Quercus species and the two Arbutus species. This could be explained by the fact that shade leaves showed not only quantitative, but also qualitative differences (higher A310/A365 ratio) in the absorbance of their methanolic extracts compared to these of sun leaves. The results of the present study showed that we should not always correlate the depth of penetration of UV radiation into sun and shade leaves according to the corresponding UV absorbing capacity of the whole leaf methanolic extracts, without taking into account all the anatomical, developmental and biochemical (such as different composition and distribution of the UV‐absorbing compounds among the different protective tissues) peculiarities of the leaves of each species. [ABSTRACT FROM AUTHOR]

We compared growth, morphology, anatomy and physiology of field-grown Olea europaea L. plants after one year with or without supplemental UV-B radiation equivalent to the increase at ground level resulting from a 15% depletion in stratospheric ozone concentration over Patras, Greece (38.3° N, 29.1° E). In a parallel greenhouse experiment, plants were exposed for four months to either zero UV-B radiation or UV-B radiation equivalent to that of the supplemented outdoor treatment. In the field, the only significant changes in response to supplemental UV-B radiation were an increase in adaxial epidermal thickness and a decrease in total protein concentration. In the greenhouse-grown plants, UV-B radiation caused significant increases in abaxial cuticle thickness and trichome UV-B absorbing compounds. We conclude that Olea europaea exhibits high UV-B tolerance and will not be affected by the predicted increases in UV-B radiation. [ABSTRACT FROM PUBLISHER]

Abstract: Leaf flavonoid compounds from six olive (Olea europaea L.) cultivars were analysed by HPLC. The composition of the soluble fractions of the dehaired lamina and the isolated trichome layers of the abaxial leaf surface were analysed in separate, as to study the distribution of flavonoids between the two leaf parts. Quercetin and quercetin 3-O-rhamnoside that have been reported to occur in the leaves seem to be located exclusively in the trichome layer. A greater variety of flavonoids was found in the lamina but the trichome layer was richer in terms of total flavonoids per unit mass. Trichome layer demonstrated an independent chemical character since its flavonoid concentration and composition was not coordinated with that of the lamina. The occurrence of flavonoid compounds in trichomes is related to the UV-filtering capacity of these cells. The results of the present study showed that apart from the soluble fraction, the cuticular waxes and cell walls of the trichomes also showed significant UV-absorbing capacity, indicating the occurrence of UV-absorbing compounds in these fractions as well. Moreover, the cuticular waxes of the trichome layer exhibited not only a higher investment of mass per unit of leaf area, but also a higher UV-absorbing capacity expressed per unit mass as compared to the cuticular waxes of the lamina surface. The importance for the separate chemical investigation of the phenolic composition of the leaf lamina and the trichome layers as well as the ecological significance of the findings is discussed. [Copyright &y& Elsevier]

The surface of peach (Prunus persica 'Calrico') is covered by a dense indumentum, which may serve various protective purposes. With the aim of relating structure to function, the chemical composition, morphology, and hydrophobicity of the peach skin was assessed as a model for a pubescent plant surface. Distinct physicochemical features were observed for trichomes versus isolated cuticles. Peach cuticles were composed of 53% cutan, 27% waxes, 23%, cutin, and 1% hydroxycinnamic acid derivatives (mainly ferulic and p-coumaric acids). Trichomes were covered by a thin cuticular layer containing 15% waxes and 19% cutin and were filled by polysaccharide material (63%) containing hydroxycinnamic acid derivatives and flavonoids. The surface free energy, polarity, and work of adhesion of intact and shaved peach surfaces were calculated from contact angle measurements of water, glycerol, and diiodomethane. The removal of the trichomes from the surface increased polarity from 3.8% (intact surface) to 23.6% and decreased the total surface free energy chiefly due to a decrease on its nonpolar component. The extraction of waxes and the removal of trichomes led to higher fruit dehydration rates. However, trichomes were found to have a higher water sorption capacity as compared with isolated cuticles. The results show that the peach surface is composed of two different materials that establish a polarity gradient: the trichome network, which has a higher surface free energy and a higher dispersive component, and the cuticle underneath, which has a lower surface free energy and higher surface polarity. The significance of the data concerning water-plant surface interactions is discussed within a physiological context. [ABSTRACT FROM AUTHOR]

Water deprivation affects photosynthesis, leaf anatomy, and cell wall composition. Although the former effects have been widely studied, little is known regarding those changes in cell wall major (cellulose, hemicelluloses, pectin, and lignin) and minor (cell wall-bound phenolics) compounds in plants acclimated to short- and long-term water deprivation and during recovery. In particular, how these cell wall changes impact anatomy and/or photosynthesis, specifically mesophyll conductance to CO2 diffusion (gm), has been scarcely studied. To induce changes in photosynthesis, cell wall composition and anatomy, Helianthus annuus plants were studied under five conditions: (i) control (i.e. without stress) (CL); (ii) long-term water deficit stress (LT); (iii) long-term water deficit stress with recovery (LT-Rec); (iv) short-term water deficit stress (ST); and (v) short-term water deficit stress with recovery (ST-Rec), resulting in a wide photosynthetic range (from 3.80 ± 1.05 μmol CO2 m-2 s-1 to 24.53 ± 0.42 μmol CO2 m-2 s-1). Short- and long-term water deprivation and recovery induced distinctive responses of the examined traits, evidencing a cell wall dynamic turnover during plants acclimation to each condition. In particular, we demonstrated for the first time how gm correlated negatively with lignin and cell wall-bound phenolics and how the (cellulose+hemicelloses)/pectin ratio was linked to cell wall thickness (Tcw) variations., (© The Author(s) 2020. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Calcium oxalate (CaOx) crystals are widespread among plant species. Their functions are not yet completely understood; however, they can provide tolerance against multiple environmental stress factors. Recent evidence suggested that CaOx crystals function as carbon reservoirs since its decomposition provides CO 2 that may be used as carbon source for photosynthesis. This might be advantageous in plants with reduced mesophyll conductance, such as the Antarctic plant Colobanthus quitensis , which have shown CO 2 diffusion limitations. In this study, we evaluate the effect of two CO 2 concentrations in the CaOx crystals decomposition and chlorophyll fluorescence of C. quitensis . Plants were exposed to airflows with 400 ppm and 11.5 ppm CO 2 and the number and relative size of crystals, electron transport rate (ETR), and oxalate oxidase (OxO) activity were monitored along time (10 h). Here we showed that leaf crystal area decreases over time in plants with 11.5 ppm CO 2 , which was accompanied by increased OxO activity and only a slight decrease in the ETR. These results suggested a relation between CO 2 limiting conditions and the CaOx crystals decomposition in C. quitensis . Hence, crystal decomposition could be a complementary endogenous mechanism for CO 2 supply in plants facing the Antarctic stressful habitat.

The functional role(s) of plant calcium oxalate (CaOx) crystals are still poorly understood. Recently, it was shown that crystals function as dynamic carbon pools whose decomposition could provide CO 2 to photosynthesis when stomata are closed (e.g. under drought conditions) and CO 2 starvation conditions may be created within the mesophyll. This biochemical process, named as 'alarm photosynthesis', can become crucial for plant survival under adverse conditions. Here, we study crystal decomposition under controlled CO 2 starvation conditions (either in the shoot or in the root) to obtain a better insight into the process of crystal formation and function. Hydroponically grown pigweed plants were kept in CO 2 -free air and/or CO 2 -free nutrient medium for 9 days. Crystal volume was monitored daily, and carbon stable isotope composition (δ 13 C) and Fourier transformation Raman spectra were obtained at the end of the experiment. A considerable reduction in the leaf crystal volume was observed in shoot-CO 2 -starved plants at the end of the experiment. The smallest crystals were isolated from the plants in which carbon was excluded from both the shoot and the root and contained potassium nitrate. Crystal δ 13 C of CO 2 -starved plants was altered in a predicted way. Specifically, it depended on the average calculated isotope fractionation of all carbon fixation processes considered to be contributing in each experimental treatment. The results of the present study confirmed the correlation between CO 2 starvation conditions and the CaOx crystal decomposition. Inorganic carbon fixed in the root may represent a major carbon source for CaOx formation., (© 2018 Scandinavian Plant Physiology Society.)

Boron deficiency is the most frequent micronutrient disorder in olive (Olea spp.) orchards. We tested the hypothesis that plant boron status affects phenolic metabolism, which, in turn, influences several ecophysiological traits of olive (Olea europaea L.) trees, by studying the effects of boron deficiency on leaf phenolic compounds of olive in a growth chamber experiment (CE) and a field experiment (FE). In the CE, a semi-hydroponic system was used to control nutrient supply. Plants received complete nutrient solution containing either 23 (control) or 0 microM H3BO3 (boron-deficient treatment). In the FE, boron-deficient trees were chosen based on visible boron-deficiency symptoms and analysis of their leaf boron concentration. Boron deficiency caused significant accumulation of phenolic compounds in leaves of CE plants (1.7 to 5.8 times more, depending on leaf age), but not in leaves of FE plants. However, in both experiments, the concentration of an unidentified phenolic compound, with a UV-spectrum resembling that of caffeic acid, increased in response to boron deficiency (by a factor of 40 to 184 in the CE and by a factor of three in the FE). Regression analysis showed that the concentration of this compound was negatively correlated to leaf boron concentration, irrespective of growth conditions and treatment. We conclude that, under field conditions, boron deficiency may not be the only factor determining the concentration of total phenolics, but it may be responsible for the accumulation of a distinct phenolic metabolite in olive leaves.

For plant species in which a considerable portion of the photoassimilates are translocated in the phloem as sugar alcohols, boron is freely translocated from mature organs to growing tissues. However, the effects of decreased plant boron status on boron remobilization are poorly understood. We conducted a growth chamber experiment (CE) and a field experiment (FE) to study the effects of low boron supply on boron remobilization in olive (Olea europaea L.), a species that transports considerable amounts of mannitol in the phloem. For the CE, several physiological parameters were compared between control (B+) and boron-deficient olive plants (B-) during the expansion of new leaves. Boron remobilization was assessed by measuring boron content of selected leaves at the beginning and at the end of the CE. As expected, boron was remobilized from mature leaves to young leaves of B+ plants; however, considerable boron remobilization was also observed in B- plants, suggesting a mechanism whereby olive can sustain a minimum boron supply for growth of new tissues despite an insufficient external boron supply. Boron deficiency caused inhibition of new growth but had no effect on photosynthetic capacity per unit leaf surface area of young and mature leaves, thereby altering the carbon utilization pattern and resulting in carbon allocation to structures within the source leaves and accumulation of soluble carbohydrates. Specifically, in mature B- leaves in the CE and in B- leaves in the FE, mannitol concentration on a leaf water content basis increased by 48 and 27% respectively, compared with controls. Carbon export ability (assessed by both phloem anatomy and phloem exudate composition of FE leaves) was enhanced at low boron supply. We conclude that, at low boron supply, increased mannitol concentrations maintain boron remobilization from source leaves to boron-demanding sink leaves.