Artemios M. Bosabalidis

Comparative effects of drought stress on leaf anatomy of two olive cultivars

Abstract The leaf anatomical features of two olive cultivars (‘Mastoidis’ and ‘Koroneiki’) were comparatively studied in irrigated and drought stressed plants. Drought stress in both cultivars resulted in a decrease of the size of the epidermal and mesophyll cells with a parallel increase of the cell density. These changes were more characteristic in cv. ‘Mastoidis’. Stomata became more numerous and smaller, while non-glandular hairs (scales) greatly increased in number, particularly in cv. ‘Koroneiki’. The implication of the drought stress-induced leaf anatomical alterations in physiological processes, like transpiration and photosynthesis, is discussed.

Water stress affects leaf anatomy, gas exchange, water relations and growth of two avocado cultivars

Two cultivars of avocado (Persea americana Mill., ‘Fuerte’ and ‘Hass’) plants, grown in 50 l containers, were studied under two irrigation regimes for 6 months in order to evaluate the growth response and leaf physiological and anatomical changes induced by moderate water stress. Irrigation was applied when soil water potential reached at � 0.03 and � 0.5 MPa for the wet and dry treatments, respectively. Leaf anatomy changed in water-stressed leaves, which could have accounted for the decreased stomatal conductance. Photosynthesis is inhibited by reducing the diffusion of CO2 to the chloroplast, both by stomatal closure and changes in mesophyll structure, which decreases the conductance to CO2 diffusion within the leaf. Predawn leaf water potential (C) declined by 0.9 MPa for ‘Fuerte’ and 1.2 MPa for ‘Hass’ after 12 days of withholding water, whereas the turgor potential (Cp) remained positive due to a decrease in the osmotic potential (Cp) in both cultivars. The reduction in osmotic potential was mainly due to dehydration and only partly related to active accumulation of solutes. Tissue elasticity seems to be the predominant physiological mechanism of drought adaptation of avocado. Growth data suggests that ‘Hass’ seems to be more affected by moderate water stress. # 2002 Elsevier Science B.V. All rights reserved.

Changes in water relations, photosynthesis and leaf anatomy induced by intermittent drought in two olive cultivars

Abstract Photosynthetic rate, water relations parameters as well as leaf anatomical characteristics were studied in two olive cultivars ( Olea europea, cv ‘Koroneiki’ and cv ‘Mastoidis’) grown under water stress conditions. No significant differences were obtained between the two cultivars concerning their ability for turgor maintenance under water stress conditions. ‘Koroneiki’ seems to maintain higher photosynthetic rates with lower values of stomatal conductance than ‘Mastoidis’, a fact that could be attributed to differentiation in leaf anatomy induced by water stress conditions. The fraction of mesophyll volume represented by intercellular air spaces as well as the surface area of mesophyll cell walls exposed to intercellular spaces was larger in ‘Koroneiki’ than in ‘Mastoidis’. The possibility of using leaf anatomical characteristics as selection factors for olive cultivars grown under drought conditions is discussed.

Anatomical and Ultrastructural Changes Associated with Sink-to-Source Transition in Developing Maize Leaves

We studied the anatomical and ultrastructural changes accompanying sink-to-source transition in developing maize (Zea mays L. cv. W273) leaves, in which sink, transition, and source regions had been identified by whole-leaf autoradiography. In the leaves examined, a complete structural gradient existed from nonimporting to importing regions of the blade. Although all components, except metaxylem elements. of the large (transport) bundles reach maturity before their counterparts in intermediate and small (loading) bundles, the final events in structural maturation are uniform for all bundle types across the blade. Among the very last structures to mature are the plasmodesmata at the interfaces between mesophyll cells and between mesophyll cells and bundle sheath cells. Maturation of the plasmodesmata coincides with maturation of the thick-walled sieve tubes, the last components of the vascular bundles to mature. Significantly, the vasculature reaches structural maturity in advance of cessation of import, and maturation of bundles involved with phloem loading is not closely correlated with initiation of export from the blade. Deposition of suberin lamellae in the walls of the bundle sheath cells coincides with the deposition of secondary walls in the metaxylem vessels. It is suggested that a primary role of the suberin lamellae may be to prevent leakage of sucrose from the bundles.

Glandular scale development and essential oil secretion in Origanum dictamnus L.

Glandular scales of Origanum dictamnus L. originate from a single protodermal cell. They are composed of a 12-celled head and an unicellular stalk and foot. During the early stages of gland differentiation, the head cells possess a small number of plastids which contain globular inclusions. Similar inclusions are also observed in the plastids of the stalk and the foot cell. The lateral walls of the stalk cell progressively undergo cutinization which does not extend to the upper and lower periclinal walls. At the onset of secretion the electron density of the plasmalemma region lining the apical walls of the head cells remarkably increases. These walls are impregnated with an osmiophilic substance identical in appearance to the content of the subcuticular space. In a following stage of the secretory process osmiophilic droplets of various size arise in the cytoplasm of the secretory cells which undergoes simultaneously a reduction of its initial density. After secretion has been concluded the protoplast of the head cells becomes gradually degenerated. The chlorenchyma cells of the mesophyll possess numerous microbodies closely associated with various organelles. In the cytoplasm of these cells crystalloids occasionally occur.

NUTRITIONAL STATUS, GROWTH, CO2 ASSIMILATION, AND LEAF ANATOMICAL RESPONSES IN TWO KIWIFRUIT SPECIES UNDER BORON TOXICITY

ABSTRACT Two Actinidia species [Actinidia deliciosa (A.Chev.) C.F. Liang et A.R. Ferguson var. deliciosa cv. Hayward] and (Actinidia arguta Planch.) were grown in a sand-perlite mixture (1 : 1) in a growth room and irrigated with Hoaglands nutrient solutions containing 20, 50, 100, 200, and 500 μM boron (B). Growth, leaf ion concentration, photosynthetic rate and B induced changes in leaf anatomy were investigated. The greatest shoot length of the two species was recorded with 50 μM B. Boron concentration was highest in the leaf margin, intermediate in the remaining leaf blade and minimum in petioles. Boron toxicity induced a decrease of photosynthetic rate (Pn), of the volume of mesophyll cells, an increase of the volume of intercellular spaces and cell damage. Inclusion of 500 μM of B in the nutrient solution decreased calcium (Ca) and manganese (Mn) concentrations in kiwifruit leaves but did not affect the concentration of other mineral nutrients. Finally, the two species did not differ significantly in leaf B accumulation and sensitivity to B.

Seasonal Variation of Essential Oils in a Linalool-Rich Chemotype of Mentha spicata Grown Wild in Greece

Abstract The seasonal variations of the essential oil content and composition of a Mentha spicata population grown wild in Greece were examined. The oil content ranged from 0.1–1.8%, with the maximum values in late summer/early autumn. The essential oil obtained from the leaves was characterized by a very high content in linalool, i.e. 85.0–93.9% of the total oil (highest percentage in mid-autumn). Other oil constituents occurring in much lower amounts were germacrene D (up to 4.2%), β-caryophyllene (up to 2.6%) and 1,8-cineole (up to 2.1%).

The relationships between CO2 transfer mesophyll resistance and photosynthetic efficiency in grapevine cultivars

Abstract Physiological and leaf anatomical characteristics were studied in the three grapevine (Vitis vinifera L.) cvs Athiri, Asyrtiko and Syrah grown under field conditions. Athiri and Asyrtiko exhibited higher values of photosynthetic rate and photosynthetic rate to intercellular CO2 ratio at high leaf water potential than Syrah, while there were no significant differences in stomatal conductance and chlorophyll content between the cultivars. Palisade and spongy parenchyma thickness and the fraction of the intercellular air spaces were significantly lower in Syrah. The surface of mesophyll cells exposed to the intercellular air spaces per unit leaf area was also lower in Shiraz, but there were no significant differences in the calculated value of the leaf internal CO2 gas phase resistance between the cultivars. The differences in the rate of photosynthesis might be attributed to differences in the CO2 liquid-phase resistance in the leaves.

Bacterial colonization of the phyllosphere of nineteen plant species and antimicrobial activity of their leaf secondary metabolites against leaf associated bacteria

Summary.The scope of this work was to examine whether leaf constitutive secondary metabolites play a role in determining bacterial colonization of the phyllosphere. To this aim, we surveyed nineteen native or cultivated plant species that share a common bacterial pool in a North Mediterranean area, and estimated the size of total and ice nucleation active (INA) bacterial populations on their leaves. Large differences in the colonization of their phyllosphere were found; the population size of epiphytic bacteria ranged from 7.5 × 102 to 1 × 106 CFU/g fresh weight, in eucalypt and celery, respectively. Species native in Mediterranean-type climate areas, particularly those belonging to the group of aromatic plants, are characterized by scarce presence of INA bacteria. The antibacterial activity of essential oils, surface phenolics and leaf tissue extracts was also estimated against the INA strains P. syringae and E. herbicola, isolated from two of these plant species. E. herbicola proved more sensitive than P. syringae. Of the species examined, oregano [Origanum vulgare L. subsp. hirtum (Link.) Ietswaart], an aromatic plant, had the highest antimicrobial activity, whereas six species showed no activity at all. Further experiments were performed with oregano and bean (Phaseolus vulgaris L.) that represent two extremes in their secondary metabolite content. Both plants were inoculated with P. syringae. By the end of incubation, the bacterial population on bean plants was about 100 times higher than that on oregano leaves. Scanning electron micrographs showed that bacterial growth on oregano leaves was confined to sites away from glandular hairs. Results from the bacterial colonization survey together with those from the toxicity tests showed that all species rich in antibacterial secondary metabolites harbored low leaf bacterial populations. These results provide substantial evidence that leaf secondary metabolites function as constitutive defense chemicals against microbial invasions. However, the fact that species with non- or moderately active leaf secondary metabolites are not always highly colonized suggests mediation of other unknown factors, the contribution of which requires further investigation.

Effects of light, magnesium and sucrose on leaf anatomy, photosynthesis, starch and total sugar accumulation, in kiwifruit cultured in vitro

Shootlets of kiwifruit plants (Actinidia deliciosa) were culturedin vitro. Combinations of light intensity, Mg and sucrose in the cultures showed that an increase of light intensity resulted in a corresponding increase of the relative size of the leaf mesophyll cells and in a decrease of the numbers of chloroplasts and contained starch grains. The addition of sucrose to the substrate media negatively affected the size of the mesophyll cells under normal Mg concentration (35 mg l−1), and positively under high Mg concentration (105 mg l−1 ). Sucrose further resulted in an increase in the numbers of chloroplasts and contained starch grains. The photosynthetic capacity of leaves greatly increased when Mg concentration was enhanced and sucrose was excluded from the nutrient substrate. Total sugar accumulation in all treatments was favoured by normal light intensity and addition of sucrose.