Corrado Tani

Structural and functional traits of Quercus ilex in response to water availability

Abstract Water potential and morpho-anatomical parameters were measured, during the course of 1 year, on leaves of Quercus ilex trees growing in two coastal stands in Tuscany (Central Italy) with different conditions of water availability: Colognole (CL, mesic site) and Cala Violina (CV, xeric site). Morpho-anatomical measurements included: general leaf features and sclerophylly indices (surface area, thickness, mass per area and density), leaf moisture indices (water content, relative water content, succulence) and histochemical analysis (detection and localization of cutine and tannins in the leaves and starch reserves in the twigs). During the warmest and driest period (August) pre-dawn water potential ( ψ pd ) in Holm-oak leaves reached −2.7 MPa at CV and −0.6 MPa at CL. Leaf surface was lower (−34%) and total leaf thickness (+10%), as well as spongy-palisade parenchyma ratio (+20%) were higher at CV. The sclerophylly parameters (leaf mass per area and leaf tissue density) were higher at CV than at CL (+24% leaf mass per area and +19% leaf tissue density). Among the moisture parameters, water content was higher at CL (+8%) and succulence was higher at CV (+13%). No differences in relative water content were observed between the two sites. All the parameters considered were substantially stable during the study period, with the exception of relative water content at CL, that fluctuated within the year. Histochemical analysis revealed a greater thickness of the upper cuticular layer at CV, whereas there were no differences in tannin distribution and content between the two sites. Differences in starch storage were detected in branchlets: it was abundant in CV but very scarce at CL. The strategies of Quercus ilex to cope with water stress were discussed at morpho-structural level.

Morpho-anatomical alterations in leaves collected from beech trees (Fagus sylvatica L.) in conditions of natural water stress

Abstract Morpho-anatomical observations were made of leaves of beech trees growing in conditions of natural stress, described in Central Italy as manifestations of forest decline. The study examined trees with normal (green) leaves and with altered leaves (curled and yellow); the observations consisted of determinations of weights and areas, and assessment using light, scanning and transmission electron microscopy. The following changes were observed in altered relative to normal leaves: increased thickness resulting primarily from the thickening of the mesophyll and the cuticle; as the season progressed, an increase in dry matter concentration levels per surface and unit volume. These alterations correlate with loss of moisture and are the result of water stress. Advanced stages of chloroplast degeneration were also observed. The findings indicate that these alterations were induced by long-term stress (reduction of mean rainfall and poor water retention in the stand) rather than the weather conditions recorded during that particular season.

Morpho-anatomical aterations in leaves of Gagus vatica L. and Quercus ilex L. in different environmental stress condition

Abstract By means of anatomical and folier structure observations, this paper examines the ecological behavior of two different species of boardleaf (a mesophile one, beech, and a xerophile one, holm-oak), under different conditions of water supply. The purpose ob this study was to evaluate their response in relation to possible climate changes. The results highlight certain similarities of behaviour (reduction of leaf surface, increased leaf thickness, increase of mechanical structure in xeric stands). The main difference between the two species lies in the tannins content, which increase in the epidermal cells (vacuoles and walls) only in beech trees in xeric conditions.

Anatomical and ultrastructural study of the secretory cavity development ofCitrus sinensis and Citrus limon: evaluation of schizolysigenous ontogeny

Summary The ontogeny and ultrastructure of secretory oil glands in the fruits of Citrus sinensis and Citrus limon were studied with light and electron microscopy (TEM). Oil glands were initiated by cell division in globular/oval clusters of young meristematic cells under or including also the epidermis. Successively, the central oil cells increased greatly in size by growth and coalescence of one or more vacuoles. Starting from these cells the oil cavity formation and enlargment occurred by schizogenous and lysigenous precesses which overlap one another. The separation of the cell walls, in both Citrus species, was accompanied by strong structural disorganization of the cytoplasm, loss of nuclei, plasmolysis, and followed by autolysis processes. Prior these changes a great quantity of oil droplets filled the cells. In Citrus sinensis this material was formed in the plastids; on the contrary, in Citrus limon oil droplets appeared only in the cytoplasm, and no connection with the plastids was observed. The processes of schizogeny and lysigeny occurred in a centrifugal direction. The peripheral oil chamber cells were so pushed outward and flattened with the progressive expansion of the gland cavity. Also these cells became vacuolated, showed schizogenous processes together with cytoplasm and nuclei breakdown. These cell modifications were preceded by an abundant essential oil synthesis. Electron dense material appeared in the cavity near the boundary cells. Among the cell layers surrounding the cavity, the outer peripheral cells showed very thick walls. These cells, probably, had a protective function, while the inner cells continued, at least in part, to produce and secrete oil compounds. In the two Citrus species the pattern of oil gland development was practically the same, except the different plastid behaviour.

Oak (Quercus robur L.) seedling responses to a realistic increase in UV-B radiation under open space conditions

Plants show different levels of sensitivity to ultraviolet-B (UV-B) radiation and acclimation to high UV-B irradiances had been developed in many species. A field experiment was performed during 1995 to study the adaptative responses of oak plants (Quercus robur L.) to artificial UV-B supplementation The most important effect of UV treatment was the increase in leaf thickness and the accumulation of phenolic compounds in the secondary wall of the adaxial epidennis of leaves in UV treated plants; the secondary wall of cells in the abaxial epidermis, that is not directly exposed to supplemental UV-B. did not present any alterations. No effects were observed on photosynthesis while plant morphology was sensible to UV treatment.

Ultrastructural effects of salinity in Nicotiana bigelovii var. bigelovii callus cells and Allium cepa roots

Abstract Salinity stress has been studied in two different plant systems such as Nicotiana bigelovii callus and Allium cepa roots in regard to its toxic effect on cells at ultrastructural level. Various types of cell damages have been observed either in N. bigelovii callus or in A. cepa root apices. However, differences in cell response have been found between these two plant tests. Callus cells appeared more tolerant to salt in comparison with root meristematic cells. In the first plant system the more relevant effect was seen in the chloroplasts which lost the capacity to synthesize starch contrarily to control and, especially, exhibited strong alterations in the thylakoidal structure. Changes at nuclear and cytoplasmic levels were also observed. In A. cepa root meristem cells more severe damages were induced by the salt. In this case, very strong alterations such as plasmolysis processes, disorganization of nuclei and cytoplasm content were observed. Moreover, in both plant systems a considerable growth decrease occurred. The results are discussed in regard to the underlying mechanism of salt stress.

Structural and ultrastructural characterization of Selaginella lepidophylla, a desiccation-tolerant plant, during the rehydration process

Summary Selaginella lepidophylla is a pteridophyte resurrection plant from Central America deserts that has been studied hitherto only for microphyll ultrastructure and photosynthetic activity during rehydration. With the present work the anatomy and cell ultrastructures have been examined during progressive rehydration. Light microscope observations clearly showed the maintenance in the dry condition of chloroplasts although in a crushed form, of chlorophyll content, and the restoration of the normal anatomical structures in stem and microphylls after the complete rehydration process. Electron microscope analyses permitted us to observe a gradual reorganization in the different cells of stem and microphylls of all the cytoplasmic components including the membrane systems present either in the protoplasm or in the organelles. In particular, the chloroplasts appeared to be able to newly accumulate starch, and then to recover the normal photosynthetic capacity. Therefore, it is possible to say that S. lepidophylla retains in the dry condition the cell structures in a well conserved state or, at least, in a functional state by protective mechanisms that permit a total reorganization of the cells after rehydration. This statement is further supported by the absence of any structural disruption effects in the rehydrated cells of S. lepidophylla .

Response of Quercus pubescens leaves exposed to geothermal pollutant input in southern Tuscany (Italy).

The paper reports a case of evident and widespread leaf damage on trees in southern Tuscany (Central Italy) attributed to the input of pollutants produced in a geothermal area. The main potentially phytotoxic substances are boron and hydrogen sulphide. Trees affected are conifers as well as both evergreen and deciduous broadleaves. In the present study the possible impact of geothermal pollutants on Quercus pubescens leaves has been considered. Leaf samples coming from three sampling locations (S1 inside the geothermal area; S2 on the margins; S3 outside) and three consecutive dates (June, July and August) were analyzed for the following parameters: sulphur and boron concentration; leaf area; leaf mass per area; chlorophyll fluorescence (Fv/Fm); chlorophyll a, chlorophyll b and carotenoid concentrations. Anatomical and ultrastructural observations were also performed. In all sampling location sulphur and boron concentrations are greater than the background values recorded in southern Tuscany in a previous survey. The sulphur concentration in leaves was higher in S1 than S2 and S3, but did not increase throughout the survey period. Boron reached the greatest concentrations in S2 and showed a continuous increase over the study period. Leaves subjected to a higher load of pollutants were smaller in size (in terms of leaf area), but were more sclerophyllous. Damaged chloroplasts and reduced Fv/Fm values were observed at S1 and S2, but chlorophyll concentration values were higher at S1. Such an apparent anomaly can possibly be explained by the onset of compensation and recovery mechanisms. Foliar injuries appeared to be related to boron concentration.

Crown status of holm oak (Quercus ilex L.) trees as related to phenology and environmental stress

In order to study the possible interactions between air pollution and climate conditions in Mediterranean evergreen broadleaf species, since 1987 we have been monitoring the annual and infra-annual variations in crown density of Quercus ilex L. (holm oak) in a permanent sample plot. The behaviour of crown density has been compared with litterfall pattern and aging processes in leaves. The results of this study confirm the important impact of climate on crown condition in Mediterranean broadleaves, so that even the role of nonacute pollution can be disguised. Xeromorph adaptations in holm oak leaves are also a mechanism providing a greater protection against pollutants.

Cytological and ultrastructural response of Nicotiana tabacum L. roots to manganese stress

ABSTRACT The effects of manganese on the morphology and ultrastructure of root cells were studied in in vitro selected plantlets tolerant to high concentrations (5 mM) of Mn which, in a previous investigation, had shown a significant reduction in root growth when compared to the control (0.1 mM Mn). A decrease in the length of the root cap and meristematic region was observed. The most serious effects of Mn toxicity occurred in the outer root cap and outer meristematic cells where extensive cytoplasmic disorganisation was observed. The plasma membrane, in particular, displayed ruptures associated with the formation of vesicular and multi-lamellar bodies. Mitochondria also revealed strong structural alterations. However, the cells in the inner regions of the meristem showed better preserved subcellular components and exhibited normal mitotic activity. These last conditions suggest a possible resistance strategy which permits root development to continue. The primary root structure was not affected by the m...