Leaf plasticity in response to light of three evergreen species of the Mediterranean maquis

Morphological, anatomical, biochemical and physiological traits of sun and shade leaves of adult Quercus ilex, Phillyrea latifolia and Pistacia lentiscus shrub species co-occurring in the Mediterranean maquis at Castelporziano (Latium) were studied. Fully expanded sun leaves had 47% (mean of the three species) greater leaf mass area (LMA) and 31% lower specific leaf area (SLA) than shade leaves. Palisade parenchyma thickness contributed on an average 42% to the total leaf thickness, spongy layer 43%, upper epidermal cells 5%, and upper cuticle thickness 3%. Stomatal size was greater in sun (25.5 μm) than in shade leaves (23.6 μm). Total chlorophyll content per fresh mass was 71% greater in shade than in sun leaves, and nitrogen content was the highest in sun (13.7 mg g⁻¹) than in shade leaves (11.8 mg g⁻¹). Difference of net photosynthetic rates (P _N) between sun and shade leaves was 97% (mean of the three species). The plasticity index (sensu Valladares et al., New Phytol 148:79–91, 2000a) was the highest for physiological leaf traits (0.86) than for morphological, anatomical and biochemical ones. Q. ilex had the highest plasticity index of morphological, anatomical and physiological leaf traits (0.37, 0.28 and 0.71, respectively) that might explain its wider ecological distribution. The higher leaf plasticity of Q. ilex might be advantageous in response to varying environmental conditions, including global change.     

Relationships between vessel element anatomy and physiological as well as morphological traits of leaves in <Emphasis Type="Italic">Fagus crenata</Emphasis> seedlings originating from different provenances

We attempted to observe differences in vessel element anatomy, and physiological and morphological traits of leaves in Fagus crenata seedlings originated from seven different provenances grown under the uniform environmental conditions. We also investigated the relationships between the anatomical characteristics of the vessel elements and physiological plus morphological traits of leaves in Fagus crenata seedlings. To carry out the experiments, Fagus crenata samples were prepared from Chichibu Research Forest of Tokyo University. For anatomical studies of the vessel elements, vessel number per mm², average vessel area, and the percentage of vessel area from the pith to the bark side were measured. We also measured transpiration rate, stomatal conductance, leaf area, leaf thickness, leaf dry mass per unit leaf area and leaf density for foliar studies. The anatomical characteristics of the vessel elements as well as the physiological and morphological traits of leaves were noticeably different among provenances. In addition, we found significant correlations between the foliar characteristics not only with vessel number per mm², but also with vessel area percentage and sum of the (vessel area)², theoretical hydraulic conductivity, from the pith to the bark side. Therefore, we concluded that variations in physiological and morphological traits of leaves in response to provenance variation were in correspondence with vessel number per mm² as a parameter that determines the total vessel area and consequent water hydraulic conductance in Fagus crenata as a diffuse porous hardwood.     

Leaf dehydroascorbate reductase and catalase activity is associated with soil drought tolerance in bread wheat

A number of morphological, physiological and phenological traits have been suggested as significant markers of adaptation to drought in bread wheat (Triticum aestivum L.). This study was aimed at the identification of a relationship between dehydroascorbate reductase (DHAR, EC 1.8.5.1) and catalase (CAT, EC 1.11.1.6) activities in leaves of wheat plants and stability of yield components under water deficit. The single chromosome substitution lines of cv. Chinese Spring carrying separate chromosomes from the donor Synthetic 6x, an artificial hexaploid combining the genomes of the two wild species, Triticum dicoccoides (AABB) and Aegilops tauschii (DD), were the objects of the investigations. The activities of the DHAR and CAT were correlated with flag leaf relative water content and two indexes of stability of grain yield components under drought across the set substitution lines. The lines carrying a synthetic hexaploid homologous pair of chromosomes 1B, 1D, 2D, 3D or 4D all expressed a low constitutive level of DHAR and the lines carrying chromosomes 3B, 1D, 2D and 3D a low constitutive level of CAT. All were able to increase this level (by fourfold for DHAR and by 1.5-fold for CAT) in response to stress caused by water deficit. When challenged by drought stress, these lines tended to be the most effective in retaining the water status of the leaves and preventing the grain yield components from being compromised. The discovered genetic variability for enzymes activity in leaves of wheat might be a useful selection criterion for drought tolerance.     

Systemic regulation of leaf anatomical structure, photosynthetic performance, and high-light tolerance in sorghum

Leaf anatomy of C3 plants is mainly regulated by a systemic irradiance signal. Since the anatomical features of C4 plants are different from that of C3 plants, we investigated whether the systemic irradiance signal regulates leaf anatomical structure and photosynthetic performance in sorghum (Sorghum bicolor), a C4 plant. Compared with growth under ambient conditions (A), no significant changes in anatomical structure were observed in newly developed leaves by shading young leaves alone (YS). Shading mature leaves (MS) or whole plants (S), on the other hand, caused shade-leaf anatomy in newly developed leaves. By contrast, chloroplast ultrastructure in developing leaves depended only on their local light conditions. Functionally, shading young leaves alone had little effect on their net photosynthetic capacity and stomatal conductance, but shading mature leaves or whole plants significantly decreased these two parameters in newly developed leaves. Specifically, the net photosynthetic rate in newly developed leaves exhibited a positive linear correlation with that of mature leaves, as did stomatal conductance. In MS and S treatments, newly developed leaves exhibited severe photoinhibition under high light. By contrast, newly developed leaves in A and YS treatments were more resistant to high light relative to those in MS- and S-treated seedlings. We suggest that (1) leaf anatomical structure, photosynthetic capacity, and high-light tolerance in newly developed sorghum leaves were regulated by a systemic irradiance signal from mature leaves; and (2) chloroplast ultrastructure only weakly influenced the development of photosynthetic capacity and high-light tolerance. The potential significance of the regulation by a systemic irradiance signal is discussed.     

NaCl胁迫对宁夏枸杞叶和幼根显微及超微结构的影响

以宁夏枸杞为材料,采用超薄切片技术制备样品,应用光学显微镜和透射电镜分析了不同浓度NaCl胁迫条件下宁夏枸杞叶和幼根显微及超微结构的变化。结果表明：随着NaCl胁迫的加重,(1)叶片上表皮细胞增厚,栅栏组织细胞出现缩短现象,排列疏松且紊乱;幼根的初生结构无明显变化。(2)叶片栅栏组织中叶绿体不再紧靠在细胞膜上,叶绿体双层膜破坏,基粒片层松散排列,杂乱无章,出现膨胀和空泡现象,淀粉粒和嗜锇颗粒增多,叶肉细胞中线粒体发生轻微变化;幼根中皮层薄壁细胞线粒体形状发生改变,结构破坏,内膜和外膜模糊甚至破裂,大多数嵴模糊,出现空泡现象;细胞核解体,基质外溢。研究表明, 不同浓度的NaCl胁迫对宁夏枸杞叶片和幼根细胞的显微及超微结构影响不同,NaCl浓度大于200 mmol/L时,宁夏枸杞叶片和幼根细胞的显微及超微结构发生了明显变化,且叶肉细胞中线粒体的变化没有叶绿体的变化显著,推测叶肉细胞中线粒体的耐盐性比叶绿体强。     

Leaf morphology of 40 evergreen and deciduous broadleaved subtropical tree species and relationships to functional ecophysiological traits

We explored potential of morphological and anatomical leaf traits for predicting ecophysiological key functions in subtropical trees. We asked whether the ecophysiological parameters stomatal conductance and xylem cavitation vulnerability could be predicted from microscopy leaf traits. We investigated 21 deciduous and 19 evergreen subtropical tree species, using individuals of the same age and from the same environment in the Biodiversity‐Ecosystem Functioning experiment at Jiangxi (BEF‐China). Information‐theoretic linear model selection was used to identify the best combination of morphological and anatomical predictors for ecophysiological functions. Leaf anatomy and morphology strongly depended on leaf habit. Evergreen species tended to have thicker leaves, thicker spongy and palisade mesophyll, more palisade mesophyll layers and a thicker subepidermis. Over 50% of all evergreen species had leaves with multi‐layered palisade parenchyma, while only one deciduous species (Koelreuteria bipinnata) had this. Interactions with leaf habit were also included in best multi‐predictor models for stomatal conductance (g_s) and xylem cavitation vulnerability. In addition, maximum g_s was positively related to log ratio of palisade to spongy mesophyll thickness. Vapour pressure deficit (vpd) for maximum g_s increased with the log ratio of palisade to spongy mesophyll thickness in species having leaves with papillae. In contrast, maximum specific hydraulic conductivity and xylem pressure at which 50% loss of maximum specific xylem hydraulic conductivity occurred (Ψ₅₀) were best predicted by leaf habit and density of spongy parenchyma. Evergreen species had lower Ψ₅₀ values and lower maximum xylem hydraulic conductivities. As hydraulic leaf and wood characteristics were reflected in structural leaf traits, there is high potential for identifying further linkages between morphological and anatomical leaf traits and ecophysiological responses.     

Selection of hydroxyproline-resistant cell lines from Solanum Tuberosum L. Callus. II. Plant regeneration and frost tolerance of regenerated plants

The calluses of two hydroxyproline-resistant lines (D20-1 and D30-1) of Solanum tuberosum L. were transferred to a solidified MS medium containing 1.0 mg/I IAA, 2.0 mg/l zeatin, 40.0 mg/l adenine sulphate, 1 g/l casein hydrolysate, 20 g/l sucrose and 10 g/l agar for plant regeneration. The shoot regeneration was only achieved from the callus of line D20–1. Regenerated shoots exhibited morphological variability. The degrees of frost tolerance were higher in the leaves of the regenerated plants compared with the leaves of the non-selected control plants, but lower than that of the callus from which they were regenerated.     

Inhibition of Abscisic Acid 8′-Hydroxylase Affects Dehydration Tolerance and Root Formation in Cuttings of Grapes (Vitis labrusca L. × Vitis vinifera L. cv. Kyoho) Under Drought Stress Conditions

The effects of an inhibitor (Abz-E3M) of abscisic acid (ABA) 8′-hydroxylase, which is a primary enzyme of ABA catabolism, on dehydration tolerance and root formation in grape cuttings under drought conditions were investigated. Cuttings of ‘Kyoho’ grape (Vitis labrusca L. × Vitis vinifera L.) were sprayed with 100 μM of Abz-E3M and subjected to water deficit conditions at the stage when their first leaves fully expanded. The physiological and morphological changes in the leaves and basal portions of the cuttings were determined. In Abz-E3M-treated leaves, lower ABA metabolite and higher ABA and indole-3-acetic acid (IAA) concentrations were observed. Compared to the untreated control leaves, higher water potential was significantly maintained in Abz-E3M-treated leaves. Abz-E3M applications resulted in lower proline accumulation and 2,2-diphenyl-2-picrylhydrazyl radical scavenging activity in the leaves and led to enhanced dehydration tolerance. In addition, the percentage of rooted cuttings was significantly increased by Abz-E3M application. In the basal portion of Abz-E3M-treated cuttings, endogenous IAA concentrations and the gene expressions of VvARF6 and VvARF8, which are positive regulators of adventitious root formation, were significantly increased. Moreover, the expression levels of the negative regulator, VvARF17, were significantly lower. These results suggested that the inhibition of ABA 8′-hydroxylase enhanced dehydration tolerance and adventitious rooting and may be an effective strategy for achieving drought stress tolerance in grape cuttings.

     

Multivariate analysis of morphological and anatomical characters of Calophyllum (Calophyllaceae) in South America

Calophyllum (Calophyllaceae), previously placed in Clusiaceae, is easily recognizable by its opposite entire leaves with close parallel venation alternating with resin canals. However, distinction between species has been difficult, because of infraspecific variation in tepal and stamen number and resemblance among species that share similar habitats. Here, I report the results of multivariate analyses of morphological and anatomical characters for Calophyllum in South America, and provide a taxonomic treatment for the genus in South America, the first since that of Vesque in 1893. Thirteen preliminary morphogroups were identified. Thirty‐two morphological characters of the leaf, flower and fruit from 401 specimens, and 17 anatomical leaf characters from 45 specimens were measured and analysed using principal component analyses (PCAs) and discriminant analyses (DAs). PCAs were used to find groups and DAs were used to validate those PCAs that were potential groups. Two main subgroups were identified in the general analysis. Subgroup M1 has terete stems and smaller leaves and flowers than subgroup M2, which, instead, has quadrangular stems. Only subgroup M2 showed distinctive clusters in regional and local analyses. Distinctive clusters and morphological and anatomical characters helped us to recognize four species in South America, including a new species, Calophyllum pubescens sp. nov. . In addition, a new species, Calophyllum mesoamericanum sp. nov. , is described from Central America. © 2013 The Linnean Society of London,     

Morphological,structural and physiological differences in heteromorphic leaves of Euphrates poplar during development stages and at crown scales

• Euphrates poplar (Populus euphratica Oliv.) has heteromorphic leaves including strip, lanceolate, ovate, and broad‐ovate leaves from base to top in the mature canopy.
• To clarify how diameter at breast height (DBH) and tree height affect the functional characteristics of all kinds of heteromorphic leaves, we measured the morphological anatomical structure and physiological indices of five crown heteromorphic leaves of P. euphratica at 2, 4, 6, 8, 10, and 12 m from the same site. We also analysed the relationships between morphological structures and physiological characteristics of heteromorphic leaves and DBH and the height of heteromorphic leaves.
• The results showed that the number of abnormalities regarding blade width, leaf area, leaf thickness, leaf mass per area, cuticle layer thickness, palisade tissue thickness, and palisade tissue/sponge tissue ratio increased with size order and sampling height gradient. Net photosynthetic rate, transpiration rate, stomatal conductance, instantaneous water use efficiency, stable delta carbon isotope ratio, proline and malondialdehyde (MDA) content increased with DBH and sampling height. By contrast, blade length, leaf shape index, and intercellular CO2 concentration decreased with the increase in path order and sampling height gradient. Although MDA content and leaf sponge thickness were not correlated with DBH or sampling height, other morphological structure and physiological parameters were significantly correlated with these variables. In addition, correlations were found among leaf morphology, anatomical structure, and physiological index parameters indicating that they changed with path order and tree height gradient.
• The differences in the morphology, anatomic structure and physiological characteristics of the heteromorphic leaves ofP. euphratica are related to ontogenesis stage and coronal position.

     

Overexpression of the <Emphasis Type="Italic">Activated Disease Resistance 1-like1</Emphasis> (<Emphasis Type="Italic">ADR1-L1</Emphasis>) Gene Results in a Dwarf Phenotype and Activation of Defense-Related Gene Expression in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

The protein encoded by the activated disease resistance 1-like1 (ADR1-L1) gene (locus name, At4g33300) belongs to the activated disease resistance 1 (ADR1) family of coiled-coil nucleotide-binding site leucine-rich repeat-type disease resistance proteins. This family contains four proteins and they have specific features in their amino acid sequences. It has been reported that ADR1 protein belongs to the ADR1 family, which is related to not only defense response but also drought tolerance. We found that transgenic plants overexpressing the ADR1-L1 gene showed a dwarf phenotype and morphological change in leaves. The expression levels of defense-related genes and the resistance to Pseudomonas syringae pv. tomato DC3000 were increased in transgenic plants. However, enhancement of drought tolerance and activation of abiotic response genes were not observed. When the growth temperature was changed from 22°C to 28°C, the expression of defense-related genes and the enhancement of resistance to a bacterial pathogen were suppressed and the dwarf phenotype and morphological change of leaves recovered.     

砂藓RcPLD基因的抗旱功能分析

砂藓(Racomitrium canescens)是一种具有极强耐脱水性的苔藓植物,编码磷脂酶D的基因RcPLD能够在砂藓的脱水和复水过程中产生显著的表达响应,它可能参与了砂藓的强耐脱水性功能。该研究使用已克隆的RcPLD编码序列构建拟南芥(Arabidopsis thaliana)过量表达转基因株系rcpld-oe,初步考察过表达株系的干旱胁迫耐受能力及其相关的生理生化指标,分析RcPLD增强拟南芥抗旱性的机制。结果表明:(1)利用已克隆的RcPLD编码序列构建了植物中的过表达载体,成功构建了RcPLD的过表达转基因拟南芥株系rcpld-oe,并获得了多个T_3代rcpld-oe纯合体株系。(2)在正常生长条件下,rcpld-oe株系T_3代纯合体植株比野生型拟南芥植株体积小,但营养生长期较长,抽薹较晚,莲座叶衰老速率较慢;在干旱处理条件下,rcpld-oe株系表现出比野生型拟南芥更强的干旱耐受能力。(3)在干旱胁迫处理过程中,rcpld-oe株系莲座叶的水分散失速率降低,可能在一定程度上降低了干旱对膜完整性的损伤和光合作用的抑制,但其渗透调节物质含量的变化相对较小。研究发现,在干旱胁迫条件下,rcpld-oe植株莲座叶的水分散失速率和光合作用抑制程度显著降低,从而表现出明显强于野生型的干旱耐受能力,这为后续RcPLD功能的深入研究和更多砂藓抗旱功能基因的挖掘奠定了基础。     

Abnormal cell divisions in leaf primordia caused by the expression of the rice homeobox geneOSH1 lead to altered morphology of leaves in transgenic tobacco

Transgenic tobacco plants were generated carrying a rice homeobox gene,OSH1, controlled by the promoter of a gene encoding a tobacco pathogenesis-related protein (PR1a). These lines were morphologically abnormal, with wrinkled and/or lobed leaves. Histological analysis of shoot apex primordia indicated arrest of lateral leaf blade expansion, often resulting in asymmetric and anisotropic growth of leaf blades. Other notable abnormalities included abnormal or arrested development of leaf lateral veins. Interestingly,OSH1 expression was undetectable in mature leaves with the aberrant morphological features. Thus,OSH1 expression in mature leaves is not necessary for abnormal leaf development. Northern blot and in situ hybridization analyses indicate thatPR1a-OSH1 is expressed only in the shoot apical meristem and in very young leaf primordia. Therefore, the aberrant morphological features are an indirect consequence of ectopicOSH1 gene expression. The only abnormality observed in tissues expressing the transgene was periclinal (rather than anticlinal) division in mesophyll cells during leaf blade initiation. This generates thicker leaf blades and disrupts the mesophyll cell layers, from which vascular tissues differentiate. TheOSH1 product appears to affect the mechanism controlling the orientation of the plane of cell division, resulting in abnormal periclinal division of mesophyll cell, which in turn results in the gross morphological abnormalities observed in the transgenic lines.     

Physiological characterization of photosynthesis,chloroplast ultrastructure,and nutrient content in bracts and rosette leaves from <Emphasis Type="Italic">Glaucium flavum</Emphasis>

Glaucium flavum is a biennial plant that bears a rosette of leaves, producing a flower stalk, bracteate monochasium, in its second year. The aims of this work were both to investigate the contribution of bracts to gas-exchange activities in this species and to compare this contribution to that of rosette leaves. In addition, we investigated the extent to which its responses can be explained by chloroplast ultrastructure, as well as the possible role of nutrient concentrations in the physiological responses of both leaf types. Gas exchange and plant characteristics regarding chlorophyll fluorescence were examined in a field experiment; we also determined leaf relative water content, tissue concentrations of photosynthetic pigments, chloroplast ultrastructure and nutrient contents. Although bracts indeed contributed to gas-exchange activities of G. flavum, rosette leaves showed higher values of net photosynthetic rate and stomatal conductance to CO₂ for photosynthetic photon flux density above 200 μmol m⁻² s⁻¹. The incongruities in photosynthetic rates between bracts and leaves may be explained by the bigger chloroplasts of rosette leaves, which results in a larger membrane surface area. This agrees with the higher pigment concentrations and quantum efficiency of photosystem II values recorded as well for rosette leaves. On the other hand, bracts showed higher sodium concentrations, which could be a mechanism for salt tolerance of G. flavum.     

Increased glycine betaine synthesis and salinity tolerance in AhCMO transgenic cotton lines

Glycine betaine is an osmoprotectant that plays an important role and accumulates rapidly in many plants during salinity or drought stress. Choline monooxygenase (CMO) is a major catalyst in the synthesis of glycine betaine. In our previous study, a CMO gene (AhCMO) cloned from Atriplex hortensis was introduced into cotton (Gossypium hirsutum L.) via Agrobacterium mediation to enhance resistance to salinity stress. However, there is little or no knowledge of the salinity tolerance of the transgenic plants, particularly under saline-field conditions. In the present study, two transgenic AhCMO cotton lines of the T₃ generation were used to study the AhCMO gene expression, and to determine their salinity tolerance in both greenhouse and field under salinity stress. Molecular analysis confirmed that the transgenic plants expressed the AhCMO gene. Greenhouse study showed that on average, seedlings of the transgenic lines accumulated 26 and 131% more glycine betaine than those of non-transgenic plants (SM3) under normal and salt-stress (150 mmol l⁻¹ NaCl) conditions, respectively. The osmotic potential, electrolyte leakage and malondialdehyde (MDA) accumulation were significantly lower in leaves of the transgenic lines than in those of SM3 after salt stress. The net photosynthesis rate and Fv/Fm in transgenic cotton leaves were less affected by salinity than in non-transgenic cotton leaves. Therefore, transgenic cotton over-expressing AhCMO was more tolerant to salt stress due to elevated accumulation of glycine betaine, which provided greater protection of the cell membrane and photosynthetic capacity than in non-transgenic cotton. The seed cotton yield of the transgenic plants was lower under normal conditions, but was significantly higher than that of non-transgenic plants under salt-stressed field conditions. The results indicate that over-expression of AhCMO in cotton enhanced salt stress tolerance, which is of great value in cotton production in the saline fields.     

Overexpression of an Arabidopsis thaliana galactinol synthase gene improves drought tolerance in transgenic rice and increased grain yield in the field

Drought stress has often caused significant decreases in crop production which could be associated with global warming. Enhancing drought tolerance without a grain yield penalty has been a great challenge in crop improvement. Here, we report the Arabidopsis thaliana galactinol synthase 2 gene (AtGolS2) was able to confer drought tolerance and increase grain yield in two different rice (Oryza sativa) genotypes under dry field conditions. The developed transgenic lines expressing AtGolS2 under the control of the constitutive maize ubiquitin promoter (Ubi:AtGolS2) also had higher levels of galactinol than the non‐transgenic control. The increased grain yield of the transgenic rice under drought conditions was related to a higher number of panicles, grain fertility and biomass. Extensive confined field trials using Ubi:AtGolS2 transgenic lines in Curinga, tropical japonica and NERICA4, interspecific hybrid across two different seasons and environments revealed the verified lines have the proven field drought tolerance of the Ubi:AtGolS2 transgenic rice. The amended drought tolerance was associated with higher relative water content of leaves, higher photosynthesis activity, lesser reduction in plant growth and faster recovering ability. Collectively, our results provide strong evidence that AtGolS2 is a useful biotechnological tool to reduce grain yield losses in rice beyond genetic differences under field drought stress.     

Origin and evolution of C4 photosynthesis in the tribe Salsoleae (Chenopodiaceae) based on anatomical and biochemical types in leaves and cotyledons

 The Chenopodiaceae genus Salsola contains a large number of species with C₄ photosynthesis. Along with derivative genera they have a prominent position among the desert vegetation of Asia and Africa. About 130 species from Asia and Africa were investigated to determine the occurrence of C₃ versus C₄ syndrome in leaves and cotyledons, and to study specific anatomical and biochemical features of photosynthesis in both photosynthetic organs. The species studied belong to all six previously identified sections of the tribe Salsoleae based on morphological characters. Types of photosynthesis were identified using carbon ¹³C/¹²C isotope fractionation. The representatives of all systematic groups were investigated for mesophyll anatomy and biochemical subtypes by determination of enzyme activity (RUBPC, PEPC, NAD- and NADP-ME and AAT) and primary photosynthetic products. Two photosynthetic types (C₃ and C₄) and two biochemical subtypes (NAD- and NADP-ME) were identified in both leaves and cotyledons. Both Kranz and non-Kranz type anatomy were found in leaves and cotyledons, but cotyledons had more diversity in anatomical structure. Strong relationships between anatomical types and biochemical subtypes in leaves and cotyledons were shown. We found convincing evidence for a similar pattern of structural and biochemical features of photosynthesis in leaves and cotyledons within systematic groups, and evaluated their relevance at the evolutionary level. We identified six groups in tribe Salsoleae with respect to photosynthetic types and mesophyll structure in leaves and cotyledons. Two separate lineages of biochemical and anatomical evolution within Salsoleae were demonstrated based on studies of leaves and cotyledons. The sections Caroxylon, Malpighipila, Cardiandra and Belanthera have no C₃ species and only the NAD-ME C₄ subtype has been found in leaves. We suggest the C₄ species in the NADP-ME lineage evolved in Coccosalsola and Salsola sections, and originated in the subsection Arbuscula. Coccosalsola contains many species with C₃ and/or C₃-C₄ intermediate photosynthesis. Within these main evolutionary lineages, species of different taxonomic groups (sections and subsections) had differences in anatomical or/and biochemical features in leaves and cotyledons. We conclude that structural and biochemical changes in the photosynthetic apparatus in species of the tribe Salsoleae were a key factor in their evolution and broad distribution in extreme desert environments. Received January 25, 2001 Accepted July 17, 2001     

Anatomical changes induced by increasing NaCl salinity in three fodder shrubs, <Emphasis Type="Italic">Nitraria retusa</Emphasis>, <Emphasis Type="Italic">Atriplex halimus</Emphasis> and <Emphasis Type="Italic">Medicago arborea</Emphasis>

Nitraria retusa and Atriplex halimus (xero-halophytes) plants were grown in the range 0–800 mM NaCl while Medicago arborea (glycophyte) in 0–300 mM NaCl. Plants were harvested after 120 days of salt-treatment. The present study was designed to study the effect of salinity on root, stem and leaf anatomy, water relationship, and plant growth in greenhouse conditions. Salinity induced anatomical changes in the roots, stems and leaves. The cuticle and epidermis of N. retusa and A. halimus stems were unaffected by salinity. However, root anatomical parameters (root cross section area, cortex thickness and stele to root area ratio), and stem anatomical parameters (stem cross section area and cortex area) were promoted at 100–200 mM NaCl. Indicating that low to moderate salinity had a stimulating effect on root and stem growth of these xero-halophytic species. At higher salinities, root and stem structures were altered significantly, and their percentages of reduction were higher in A. halimus than in N. retusa whereas, in M. arborea, they were strongly altered as salinity rose. NaCl (100–300 mM) reduced leaf water content by 21.2–56.2% and specific leaf area by 51–88.1%, while increased leaf anatomical parameters in M. arborea (e.g. increased thickness of upper and lower epidermis, palisade and spongy mesophyll, entire lamina, and increased palisade to spongy mesophyll ratio). Similar results were evidenced in A. halimus leaves with salinity exceeding 100 mM NaCl. Leaves of N. retusa were thinner in salt-stressed plants while epidermis thickness and water content was unaffected by salinity. The size of xylem vessel was unchanged under salinity in the leaf’s main vein of the three species while we have increased number in M. arborea leaf main vein in the range of 200–300 mM NaCl. A longer distance between leaf vascular bundle, a reduced size and increased number of xylem vessel especially in stem than in root vascular system was evidenced in M. arborea treated plants and only at (400–800 mM) in the xero-halophytic species. The effects of NaCl toxicity on leaf, stem and root ultrastructure are discussed in relation to the degree of salt resistance of these three species. Our results suggest that both N. retusa and A. halimus show high tolerance to salinity while M. arborea was considered as a salt tolerant species.