Unraveling Seasonal Allocation of Soluble Sugars, Starch and Proline in Sternbergia lutea

This study focuses on Sternbergia lutea (L.) Ker Gawl. ex Spreng., a bulbous, perennial, autumnal flowering geophyte mainly distributed around the Mediterranean Basin. The seasonal content of total sugars, starch and proline in above- and below-ground plant parts in this study, which has hitherto not been the subject of a published study. Geophytes possess underground storage organs that support sprouting, leaf growth and flowering. Furthermore, their buds remain protected below the soil surface during periods of dormancy. Understanding the fluctuation of these compounds in S. lutea contributes to our knowledge of its adaptation to the Mediterranean ecosystem. It seems likely that monthly fluctuations in proline accumulation, sugar and starch content in both above- and below-ground tissues of S. lutea correspond to the distinct seasonality of the Mediterranean ecosystem. Elevated starch content was investigated in the bulbs, while lower starch content was estimated in the leaves. Substantial values of soluble sugar content have been detected in bulbs and leaves. Additionally, elevated sugar content was detected in the yellow petals of S. lutea in October. Pronounced proline accumulation was detected in the leaves and bulbs of S. lutea during its active and dormant phase, respectively.

A holistic and sustainable approach linked to drought tolerance of Mediterranean crops

The rapid increase in average temperatures and the progressive reduction in rainfalls caused by climate change is reducing crop yields worldwide, particularly in regions with hot and semi-arid climates such as the Mediterranean area. In natural conditions, plants respond to environmental drought stress with diverse morphological, physiological, and biochemical adaptations in an attempt to escape, avoid, or tolerate drought stress. Among these adaptations to stress, the accumulation of abscisic acid (ABA) is of pivotal importance. Many biotechnological approaches to improve stress tolerance by increasing the exogenous or endogenous content of ABA have proved to be effective. In most cases the resultant drought tolerance is associated with low productivity incompatible with the requirements of modern agriculture. The on-going climate crisis has provoked the search for strategies to increase crop yield under warmer conditions. Several biotechnological strategies, such as the genetic improvement of crops or the generation of transgenic plants for genes involved in drought tolerance, have been attempted with unsatisfactory results suggesting the need for new approaches. Among these, the genetic modification of transcription factors or regulators of signaling cascades provide a promising alternative. To reconcile drought tolerance with crop yield, we propose mutagenesis of genes controlling key signaling components downstream of ABA accumulation in local landraces to modulate responses. We also discuss the advantages of tackling this challenge with a holistic approach involving different knowledge and perspectives, and the problem of distributing the selected lines at subsidized prices to guarantee their use by small family farms.

Structural and Physiological Traits of Compound Leaves of Ceratonia siliqua Trees Grown in Urban and Suburban Ambient Conditions

Ceratonia siliqua L. (carob tree) is an endemic plant to the eastern Mediterranean region. In the present study, anatomical and physiological traits of successively grown compound leaves (i.e., the first, third, fifth and seventh leaves) of C. siliqua were investigated in an attempt to evaluate their growth under urban and suburban environmental conditions. Chlorophyll and phenolic content, as well as the specific leaf area of the compound leaves were determined. Structural traits of leaflets (i.e., thickness of palisade and spongy parenchyma, abaxial and adaxial epidermis, as well as abaxial and adaxial periclinal wall) were also investigated in expanding and fully expanded leaflets. Fully expanded leaflets from urban sites exhibited increased thickness of the lamina and the palisade parenchyma, while the thickness of the spongy parenchyma was thicker in suburban specimens. The palisade tissue was less extended than the spongy tissue in expanding leaflets, while the opposite held true for the expanded leaflets. Moreover, the thickness of the adaxial and the abaxial epidermises, as well as the adaxial and abaxial periclinal wall were higher in suburban leaflets. The chlorophyll content increased concomitantly with the specific leaf area (SLA) of both expanding and expanded leaflets, and strong positive correlations were detected, while the phenolic content declined with the increased SLA of expanding and expanded leaflets. It is noteworthy that the SLA of expanding leaflets in the suburban site was comparable to the SLA of expanded leaflets experiencing air pollution in urban sites; the size and the mass of leaf blades of C. siliqua possess adaptive features to air pollution. These results, linked to the functional structure of expanding and expanded successive foliar tissues, provide valuable assessment information coordinated with an adaptive process and yield of carob trees exposed to the considered ambient conditions, which have not hitherto been published.

Stomata in Close Contact: The Case of Pancratium maritimum L. (Amaryllidaceae)

A special feature found in Amaryllidaceae is that some guard cells of the neighboring stomata form a "connection strand" between their dorsal cell walls. In the present work, this strand was studied in terms of both its composition and its effect on the morphology and function of the stomata in Pancratium maritimum L. leaves. The structure of stomata and their connection strand were studied by light and transmission electron microscopy. FM 4-64 and aniline blue staining and application of tannic acid were performed to detect cell membranes, callose, and pectins, respectively. A plasmolysis experiment was also performed. The composition of the connection strand was analyzed by fluorescence microscopy after immunostaining with several cell-wall-related antibodies, while pectinase treatment was applied to confirm the presence of pectins in the connection strand. To examine the effect of this connection on stomatal function, several morphological characteristics (width, length, size, pore aperture, stomatal distance, and cell size of the intermediate pavement cell) were studied. It is suggested that the connecting strand consists of cell wall material laid through the middle of the intermediate pavement cell adjoining the two stomata. These cell wall strands are mainly comprised of pectins, and crystalline cellulose and extensins were also present. Connected stomata do not open like the single stomata do, indicating that the connection strand could also affect stomatal function. This trait is common to other Amaryllidaceae representatives.

Comparison of Pericarp Functional Traits in Capparis spinosa from Coastal and Inland Mediterranean Habitats

The caper (Capparis spinosa L.) is a winter deciduous, perennial plant that grows and completes its life cycle entirely during the dry season in the Mediterranean region. Mature caper fruits and their pericarp, collected from the wild shrubs of the Capparis spinosa grown in the inland and coastal sites of Greece during summer, have been studied in order to improve and complete our knowledge of the successful establishment of the C. spinosa in Mediterranean ecosystems. Caper fruits possess substantial nutritional, medicinal and ecological properties that vary according to the developmental stage, agroclimatic and geographical parameters; however, the fruit pericarp and pedicel, unlike the other aboveground plant parts of the caper, have not hitherto been studied. The higher sugar and starch content in the pericarps and fruit pedicels harvested from wild caper plants grown in coastal habitats was investigated in comparison with those from inland habitats, while the higher proline and nitrogen content in pericarps and fruit pedicels harvested from wild caper plants grown in inland habitats was investigated in comparison with those from coastal habitats. The PCA, based on the considered functional traits underlying the constitutional aspects, reveals groupings of fruit pericarp specimens of the C. spinosa collected from coastal and inland habitats that are grounds for adaptive variation.

The Influence of the Partitioning of Sugars, Starch, and Free Proline in Various Organs of Cyclamen graecum on the Biology of the Species and Its Resistance to Abiotic Stressors

The geophyte Cyclamen graecum is native to the eastern Mediterranean. Its beautiful flowers with upswept pink petals appear during early autumn, after the summer drought period and before leaf expansion in late autumn. The floral and leaf development alternates with their cessation in early winter and late spring, respectively. Ecophysiological parameters and processes underlining the life-cycle of C. graecum have not previously been published. Seasonal fluctuations of sugars, starch, and free proline have been investigated in tubers, leaves, pedicels, and petals, as well as petal and leaf water status. At the whole plant level, the seasonal co-existence of leaves and flowers is marked by an elevated soluble sugar content, which was gradually reduced as the above-ground plant parts shed. The sugar content of petals and pedicels was lower than that of leaves and tubers. Leaf starch content increased from late autumn to spring and was comparable to that of tubers. The starch content in petals and pedicels was substantially lower than that of tubers and leaves. In tubers, monthly proline accumulation was sustained at relatively constant values. Although the partitioning of proline in various organs did not show a considerable seasonal variation, resulting in an unchanged profile of the trends between tubers, leaves, and flowers, the seasonal differences in proline accumulation were remarkable at the whole plant level. The pronounced petal proline content during the flowering period seems to be associated with the maintenance of floral turgor. Leaf proline content increased with the advance of the growth season. The values of leaf relative water content were sustained fairly constant before the senescence stage, but lower than the typical values of turgid and transpiring leaves. Relationships of the studied parameters with rainfall indicate the responsiveness of C. graecum to water availability in its habitat in the Mediterranean ecosystem.

Hydraulic Response of Deciduous and Evergreen Broadleaved Shrubs, Grown on Olympus Mountain in Greece, to Vapour Pressure Deficit

In this study, leaf hydraulic functionality of co-occurring evergreen and deciduous shrubs, grown on Olympus Mountain, has been compared. Four evergreen species (Arbutus andrachne, Arbutus unedo, Quercus ilex and Quercus coccifera) and four deciduous species (Carpinus betulus, Cercis siliquastrum, Coronilla emeroides and Pistacia terebinthus) were selected for this study. Predawn and midday leaf water potential, transpiration, stomatal conductance, leaf temperature and leaf hydraulic conductance were estimated during the summer period. The results demonstrate different hydraulic tactics between the deciduous and evergreen shrubs. Higher hydraulic conductance and lower stomatal conductance were obtained in deciduous plants compared to the evergreens. Additionally, positive correlations were detected between water potential and transpiration in the deciduous shrubs. The seasonal leaf hydraulic conductance declined in both deciduous and evergreens under conditions of elevated vapor pressure deficit during the summer; however, at midday, leaf water potential reached comparable low values, but the deciduous shrubs exhibited higher hydraulic conductance compared to the evergreens. It seems likely that hydraulic traits of the coexisting evergreen and deciduous plants indicate water spending and saving tactics, respectively; this may also represent a limit to drought tolerance of these species grown in a natural environment, which is expected to be affected by global warming.

Visual perception of colourful petals reminds us of classical fragments

Colour has attracted the interest and attention of many of the most gifted intellects of all time. Ideas of early thinkers were not -and could not have been- grasped on a scientific level without knowledge of a kind that lay far in the future. One character that is being considered is the colourful surfaces of living tissues, which could hardly have been visualized without a corresponding reference to the microscale parallel. Millions of years before man made manipulated synthetic structures, biological systems were using nanoscale architecture to produce striking optical effects. Here we show the microsculpture of the adaxial surface of flower petals from the asphodel, the Stork's-bill and the common poppy by using optical, scanning electron and atomic force microscopy. Microsculpture has been studied in leaves and pollen grains of higher plants. To the best of our knowledge imaging and nanoscale morphometry of petals has not been reported hitherto. Our findings on flower petals' microsculpture may be linked with aspects on colour revealed from ancient literature.

Symbolic plant(s) of the Olympic Games

The victors of the Olympic Games in ancient Greece were awarded crowns made of olive branches. In Antiquity, the symbolism of plants was related to myths, properties, aesthetic values, and civilization. Theophrastus first classifies and identifies plants, and gathers information about them, in his classic books (4th century BC). Symbolic plants are native to the Mediterranean region and they exhibit some convergent behaviour with respect to their functional characteristics. These plants were collected (among other species) by Professor J. Sibthorp and his partners in two botanical journeys in the Levant during the 18th century, and they have been illustrated for Flora Graeca Sibthorpiana.