青藏高原草地植物叶解剖特征

运用常规石蜡制片技术对我国青藏高原66种草地植物优势种的叶解剖特征进行研究,并分析了叶解剖特征与海拔、生长季降水及生长季均温之间的关系.结果表明:青藏高原草地植物叶片具有很多适应高寒环境的结构特征,如表皮层厚且表皮细胞大小差异显著,表皮毛等表皮附属物发达,异细胞丰富,通气组织普遍发达等;叶片各组成部分厚度的变异程度不同,其中海绵组织厚度变异最大,其次为上角质层、下表皮层、下角质层、上表皮层、栅栏组织,叶片厚度的变异最小;青藏高原草地植物叶片各组成部分的厚度存在协同进化,上下角质层厚度呈强烈正相关,海绵组织厚度与叶片厚度相关性最强;青藏高原草地植物叶片各组成部分的厚度与海拔、生长季降水、生长季均温3个重要环境变量呈较弱的相关性,总体表现为随海拔升高叶片各组成部分的厚度减小,而随生长季降水和生长季均温的增加叶片厚度增加.     

Anatomical considerations related to photosynthesis in cotton (Gossypium hirsutum L.) leaves, bracts, and the capsule wall

Light and electron microscopy was used to relate histologicaland ultrastructural differences of cotton (Gossypium hirsutumL.) leaves, bracts, and capsule walls to their different photosyntheticactivities. Light microscopy revealed that the leaf thicknesswas approximately 152µm, had a well-defined internal organizationwith elongated palisade mesophyll cells and loosely packed spongymesophyll cells. In contrast, the bract was thinner (111 µm),lacked a defined palisade layer, and was largely composed ofinternal air spaces. The capsule wall was very thick (1013µm)and composed of numerous tightly packed, paren-chymatous corticalcells with little or no intercellular air space. Chloroplastswith well-defined granal stacks and extensive stroma lamellaewere observed in each of these three tissues, however, theirdensity was always greater in the palisade cells of the leafcompared to spongy mesophyll cells of the bract and the parenchymatouscells of the capsule wall. The low rates of photosynthesis inthe bracts and the capsule wall were associated with the internalorganization of these tissues. Key words: Cotton, photosynthesis, anatomy, cuticle, tissues     

番荔枝科蚁花属和澄广花属叶的比较解剖学研究

利用扫描电镜技术,叶片离析方法和石蜡切片法对蚁花属1种和澄广花属9种植物叶的形态结构进行比较研究。结果表明,两属植物有许多相似之处,但又有以下一些显著不同;蚁花属植物叶表皮细胞均具一晶族,叶肉组织中具1-2层栅栏组织细胞,油细胞均匀分布在栅栏组织和海绵组织中,栅栏组织在主脉处不连续,而澄广花属植物叶的表皮细胞内具一单斜晶,叶肉组织中具1层栅栏组织细胞,油细胞仅分布在海绵组织中,栅栏组织在主脉处连续,结果为蚁花属和澄广花属的分类学处理提供了新证据。     

Comparative leaf anatomy of Salix species and hybrids

Epidermal features, mesophyll differentiation and calcium oxalate characteristics of 19 species and 12 hybrids of Salix are described. The species and hybrids can be distinguished by the presence or absence of the following epidermal features: striated cuticle; stomata; covering trichomes; beaded anticlinal walls, and diosmin-like njstals. In or near marginal teeth, glandular trichomes are present in all cases. The leaf veins of all specimens examined have calcium oxalate prism sheaths and, with the exception of S. herbacea , cluster crystals in some cells of the mesophyll. Most sprcies studied in the subgenus Salix show: both adaxial and abaxial stomata; striated cuticle metopllyll of palisade cells, with little or no spongy mesophyll, but with a well-defined hypodermis, and absence of thick-walled, sinuous trichomes. Characteristic features of the subgenus Caprisalix are: abaxial stomata only; epidermal crystals; smooth cuticle; mesophyll diflerentiated into palisade cells and spongy mesophyll and without a hypodermis, and trichomes more numerous and varied than those of the subgenus Salix . Leaves of the two species of the subgenus Chaemelia examined and those of S. lapponum , have predominantly anomocytic stomata, whereas all the other leaves studied have predominantly paracytic stomata. The anatomical features described, in conjunction with the morphologiral characters, enable the species and hybrids of Salix studied to be autheenticated.     

Characteristics of leaf structure and photosynthetic apparatus within the crown of systematically shadedQuercus petraea andNothofagus procera seedlings

Four-year-old seedlings ofQuercus petraea (Matt.) Liebl. andNothofagus procera (Poepp. et Endl.) Querst were grown outdoors in pots while subjected to full, medium and low irradiances. Shading and decrease in height of leaf attachment generally increased specific leaf area, the diameters of chloroplasts and of palisade and spongy mesophyll cells, but decreased leaf thickness, number of palisade cell layers, length of palisade and spongy mesophyll cells, number of chloroplasts per mesophyll cell and epidermal cell and cuticle thickness, stomata and hair densities per unit leaf area, hair length, maximum hair breath and cell wall thickness in the two species. However, inN. procera grown under full irradiance, leaves at the upper and middle positions had hairs on both upper and lower epidermes, whereas those in other treatments and all leaves in all treatments inQ. petraea, had theirs only on the upper epidermis.     

风毛菊属3种植物叶的解剖结构比较

采用石蜡切片法对分布于祁连山海拔5 000 m左右流石滩上菊科风毛菊属水母雪兔子（Saussurea medusa Maxim）、鼠曲雪兔子（Saussurea gnaphalodes (Royle) Sch.）、红叶雪兔子（Saussurea paxiana Diels.）3种植物叶片的解剖结构进行了比较研究,结果表明：叶片表皮细胞均为单层,上下表皮都有气孔分布,气孔不下陷;角质层较厚,叶表面均被单列细胞的表皮毛。3种植物均为异面叶;叶肉栅栏组织较发达,通常由2～3层细胞组成,但栅栏组织细胞排列较疏松;海绵组织存在大量的细胞间隙;叶肉中通气组织发达,且均有不规则裂生性气腔。叶脉维管束中韧皮部都具有异细胞存在。这些共同特征是3种植物对高山地区缺氧、低温、强辐射等自然条件长期适应的结果。但是,3种植物在叶片的外部形态特征、叶肉栅栏组织细胞的特点、维管束发育程度、内分泌结构、不规则裂生气腔等方面又存在明显的不同,表现出3种植物对环境的适应也是存在差异的。     

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.     

Estimating near-infrared leaf reflectance from leaf structural characteristics

The relationship between near-infrared reflectance at 800 nm (NIRR) from leaves and characteristics of leaf structure known to affect photosynthesis was investigated in 48 species of alpine angiosperms. This wavelength was selected to discriminate the effects of leaf structure vs. chemical or water content on leaf reflectance. A quantitative model was first constructed correlating NIRR with leaf structural characteristics for six species, and then validated using all 48 species. Among the structural characteristics tested in the reflectance model were leaf trichome density, the presence or absence of both leaf bicoloration and a thick leaf cuticle (>1 μm), leaf thickness, the ratio of palisade mesophyll to spongy mesophyll thickness (PM/SM), the proportion of the mesophyll occupied by intercellular air spaces (%IAS), and the ratio of mesophyll cell surface area exposed to IAS (A(mes)) per unit leaf surface area (A), or A(mes)/A. Multiple regression analysis showed that measured NIRR was highly correlated with A(mes)/A, leaf bicoloration, and the presence of a thick leaf cuticle (r = 0.93). In contrast, correlations between NIRR and leaf trichome density, leaf thickness, the PM/SM ratio, or %IAS were relatively weak (r < 0.25). A model incorporating A(mes)/A, leaf bicoloration, and cuticle thickness predicted NIRR accurately for 48 species (r = 0.43; P < 0.01) and may be useful for linking remotely sensed data to plant structure and function.     

白蜡虫7种寄主植物叶片解剖结构与寄主选择性的关系

用石蜡切片法在显微镜下观察白蜡虫[Ericerus pela(Chavannes)]7种寄主植物叶的解剖结构。结果表明,寄主植物的叶脉、表皮、栅栏组织、海绵组织、维管束解剖结构及数量性状特征在属、种间存在显著差异。7种寄主植物中,华南小蜡(Ligustrum calleryanum Decne.)和白蜡树(Fraxinus chinensis Roxb.)表皮被毛,华南小蜡表皮毛浓密,白蜡树表皮毛稀疏,其它寄主植物表皮无毛;女贞树(Ligustrum lucidum Ait.)栅栏组织、海绵组织和叶脉的厚度最厚、维管束直径最大,其它寄主植物相对较小。因此,叶片表面光滑、叶脉发达、叶片肥厚是白蜡虫优良寄主植物的重要解剖学特征。7种寄主植物中脉和侧脉发达,近轴面凹陷,远轴面突起,肉脉包埋在叶肉中,推测叶脉突起和凹槽可能是白蜡虫固定位点选择的关键线索。     

Compared Anatomy of Young Leaves of Prunus persica (L.) Batsch with Different Degrees of Susceptibility to Taphrina deformans (Berk.) Tul

Anatomical observations of leaves infected by Taphrina deformans were studied in tolerant peach trees (TPT) and in very susceptible (VSPT) ones. Leaves from the first sampling (2nd April) showed hyphae penetrating through the stomata or into the cuticle of the host tissue; anatomical structures of leaf sections were similar for both TPT and VSPT. The ultrastructure of the leaves of TPT showed seemingly normal mesophyll cells. In contrast, mesophyll cells of the VSPT showed important signs of degradation. Cells were organelle‐free and the middle lamella was expanded and invaded by hyphae of T. deformans. In some samples, the leaves of TPT showed deformed epidermal cells, loss of some spongy cells and increase of the intercellular spaces and division of the palisade cells. The pathogen proliferation in the leaves of the VSPT was considerably superior. In this case, stimulation of cell division occurred in the abaxial epidermis. Cells showed periclinal and oblique divisions, with an increased number of plasmodesmata; palisade or spongy cells were not differentiable. Leaves from TPT collected on 26th April showed hyphae with a non‐cylindrical section and with a squashed aspect. The hyphae were very evident in the intercellular spaces, showing abundant endoplasmic reticulum of rough type (RER) in the cytoplasm. On the other hand, epidermis of the leaves of the VSPT had numerous hyphae under the cuticle, which were growing in a thick pectin matrix. Leaves from TPT and VSPT collected on 6th May showed relevant differences. The leaves of TPT had a palisade mesophyll with fewer cells but with active chloroplasts. In contrast, the leaves from VSPT showed empty mesophyll cells, the cytoplasm was collapsed and the adaxial epidermis was covered with the fungus fructification. The observed anatomical and ultrastructural differences of leaves from TPT and VSPT confirm a different behaviour in plant‐host reaction at early stages of infection.     

Structural Adaptation of the Leaf Mesophyll to Shading

Structural characteristics of the mesophyll were studied in five boreal grass species experiencing a wide range of light and water supply conditions. Quantitative indices of the palisade and spongy mesophyll tissues (cell and chloroplast sizes, the number of chloroplasts per cell, the total cell and chloroplast surface area per unit leaf surface area) were determined in leaves of each of the species. The cell surface area and the cell volume in spongy mesophyll were determined with a novel method based on stereological analysis of cell projections. An important role of spongy parenchyma in the photosynthetic apparatus was demonstrated. In leaves of the species studied, the spongy parenchyma constituted about 50% of the total volume and 40% of the total surface area of mesophyll cells. The proportion of the palisade to spongy mesophyll tissues varied with plant species and growth conditions. In a xerophyte Genista tinctoria, the total cell volume, cell abundance, and the total surface area of cells and chloroplasts were 30–40% larger in the palisade than in the spongy mesophyll. In contrast, in a shade-loving species Veronica chamaedris, the spongy mesophyll was 1.5–2 times more developed than the palisade mesophyll. In mesophyte species grown under high light conditions, the cell abundance and the total cell surface area were 10–20% greater in the palisade mesophyll than in the spongy parenchyma. In shaded habitats, these indices were similar in the palisade and spongy mesophyll or were 10–20% lower in the palisade mesophyll. In mesophytes, CO₂ conductance of the spongy mesophyll accounted for about 50% of the total mesophyll conductance, as calculated from the structural characteristics, with the mesophyll CO₂ conductance increasing with leaf shading.     

Dark Leaf Respiration in Light and Darkness of an Evergreen and a Deciduous Plant Species

Dark respiration in light as well as in dark was estimated for attached leaves of an evergreen (Heteromeles arbutifolia Ait.) and a deciduous (Lepechinia fragans Greene) shrub species using an open gas-exchange system. Dark respiration in light was estimated by the Laisk method. Respiration rates in the dark were always higher than in the light, indicating that light inhibited respiration in both species. The rates of respiration in the dark were higher in the leaves of the deciduous species than in the evergreen species. However, there were no significant differences in respiration rates in light between the species. Thus, the degree of inhibition of respiration by light was greater in the deciduous species (62%) than in the evergreen species (51%). Respiration in both the light and darkness decreased with increasing leaf age. However, because respiration in the light decreased faster with leaf age than respiration in darkness, the degree of inhibition of respiration by light increased with leaf age (from 36% in the youngest leaves to 81% in the mature leaves). This suggests that the rate of dark respiration in the light is related to the rate of biosynthetic processes. Dark respiration in the light decreased with increasing light intensity. Respiration both in the light and in the dark was dependent on leaf temperature. We concluded that respiration in light and respiration in darkness are tightly coupled, with variation in respiration in darkness accounting for more than 60% of the variation in respiration in light. Care must be taken when the relation between respiration in light and respiration in darkness is studied, because the relation varies with species, leaf age, and light intensity.     

EVOLUTION OF LEAF ARCHITECTURE IN THE CHAPARRAL SPECIES FREMONTODENDRON CALIFORNICUM SSP. CALIFORNICUM (STERCULIACEAE)

The chaparral species Fremontodendron californicum ssp. californicum and the cloud forest species Cheirostemon platanoides arose from a common mesophytic stock. The leaf of C. platanoides is proposed as a model for the ancestral leaf and provides an architectural baseline allowing identification of the types and relative magnitudes of morphological and anatomical modifications which have occurred in the leaf of F. californicum. The leaf of F. californicum reflects intense selection for reduced surface area; however, both deletion and addition of lobes has occurred. Vein density has increased due to a greater number of more highly branched terminal veinlets. Mechanical structures, i.e., sclerenchyma, cuticle, show a quantitative reduction; whereas, water storage tissue, i.e., mucilage cells, has been augmented at the expense of spongy mesophyll. The leaf has become weakly isolateral and the number of palisade strata has increased. No increase in the volume of palisade tissue per unit volume of mesophyll is apparent due to a reduction in palisade cell length and palisade packing density. Total leaf thickness has not increased. The indumentum shows selection for non-living, pedestalled stellate trichomes which form a transpiration-limiting canopy above the stomata. Stomatal density has decreased while guard cell dimensions have become larger. Some structural modifications in F. californicum appear to have evolved directly in response to long-term water stress, others seem more directly related to leaf diminution. Xeroplastic changes in foliar structure are in some cases unreliable indicators of ultimate xeromorphic modifications arising in an evolutionary context.     

中国假鹰爪属和皂帽花属植物叶的形态结构及其分类学意义

利用扫描电镜技术、叶片离析法和石蜡切片法研究了假鹰爪属Desmos 4种植物和皂帽花属Dasy-maschalon 3种植物叶片的形态结构。结果表明：假鹰爪属植物叶片近轴面表皮具大型球状含晶簇细胞和不含晶簇的表皮细胞两种类型,远轴面表皮细胞均具一较小的晶簇;叶肉组织明显分化为栅栏组织细胞和海绵组织细胞,油细胞分布于第2层的栅栏组织和海绵组织内,单位毫米叶宽油细胞数为4～6个;主脉维管组织被薄壁细胞分隔成束状。皂帽花属植物叶片近轴面表皮细胞形状相同,均具一晶簇,远轴面表皮细胞的晶簇和近轴面表皮细胞的晶簇相似;靠近上、下表皮的叶肉组织均分化为栅栏组织细胞,在两层栅栏组织细胞之间分化为一至几层海绵组织细胞,油细胞分布于海绵组织内,单位毫米叶宽油细胞数为2～3个;主脉维管组织形成连续的环状。由此可见两属叶的结构具有明显的差异,因而支持假鹰爪属和皂帽花属为两个独立属的观点。     

Changes of Leaf Morphological, Anatomical Structure and Carbon Isotope Ratio with the Height of the Wangtian Tree （Parashorea chinensis） in Xishuangbanna, China

Leaf morphological and anatomical structure and carbon isotope ratio （δ^13C） change with increasing tree height. To determine how tree height affects leaf characteristics, we measured the leaf area, specific leaf mass （ratio of leaf mass to leaf area [LMA]）, thickness of the total leaf, cuticle, epidermis, palisade and sponge mesophyll, stomata traits and δ^13C at different heights of Parashorea chinensis with methods of light and scanning electron microscopy （SEM） and isotope-ratio mass spectrometry. The correlation and stepwise regression between tree height and leaf structure traits were carried out with SPSS software. The results showed that leaf structures and δ^13C differed significantly along the tree height gradient. The leaf area, thickness of sponge mesophyll and size of stomata decreased with increasing height, whereas the thickness of lamina, palisade mesophyll, epidermis, and cuticle, ratios of palisade to spongy thickness, density of stomata and vascular bundles, LMA and δ^13C increased with tree height. Tree height showed a significant relationship with all leaf indices and the most significant relationship was with epidermis thickness, leaf area, cuticle thickness, δ^13C. The δ^13C value showed a significantly positive relationship with LMA （R = 0.934）. Our results supported the hypothesis that the leaf structures exhibited more xeromorphic characteristics with the increasing gradient of tree height.     

Leaf anatomy of Desmos and Dasymaschalon (Annonaceae) from China in relation to taxonomic significance

Leaf morphology in four species of Desmos and three species of Dasymaschalon was comparatively studied using scanning electron microscopy (SEM) together with epidermal maceration and paraffin methods. The results showed that there were some remarkable foliar anatomical differences between Desmos and Dasymaschalon. In leaves of Desmos, some of the adaxial epidermal cells were enlarged into globose cells each containing one large cluster crystal, while other epidermal cells were normal without any crystal, and in abaxial epidermis each cell contained one smaller cluster crystal. The leaf structure was typically bifacial, and the mesophyll cells were differentiated into palisade tissue and spongy tissue. Oil cells were distributed in the second layer of palisade and the whole spongy tissue, and the number of oil cells per mm leaf width ranged from 4 to 6. The vascular tissue in the midrib was separated into bundles by parenchyma cells. In leaves of Dasymaschalon, all the adaxial epidermal cells contained one cluster crystal, and the crystal size was similar to that of thecrystals in abaxial epidermal cells. The leaf structure was more or less isobilateral. Oil cells were distributed only in the spongy tissue between the two layers of the palisade, and the number of oil cells per mm leaf width ranged from 2 to 3. The vascular tissue in the midrib formed a continuous circle. It is clear that the anatomical differences between Desmos and Dasymaschalon are remarkable, supporting the treatment of Desmos and Dasymaschalon as two independent genera.     

构树雌雄株叶片解剖结构特征的比较研究

为了研究雌雄异株植物构树（Broussonetia papyrifera（L.） Vent.）的性别差异,以其叶片为材料,采用石蜡切片法,对其主要解剖结构特征进行观察和比较。结果显示：（1）构树雌、雄株叶片解剖结构组成一致,均由表皮、叶肉组织和叶脉3部分组成。其上、下表皮均由一层细胞构成,具有较厚的角质层及丰富的表皮毛,叶肉中栅栏组织高度发达,此外,维管系统在叶中所占比例很大;（2）构树雌、雄株叶片细胞大小及厚度在各类型组织间存在一定差异,雄株叶片上表皮厚度、栅栏组织厚度、主脉维管束木质部厚度及维管束厚度均显著大于雌株叶片,且在栅海比、组织结构紧密度、组织结构疏松度和主脉维管束木质部面积占维管束的比例等方面也与雌株有极显著差异。研究结果表明构树叶片的解剖结构不仅具有旱生植物叶片的典型特征,而且还表现出明显的性别差异,这可能与构树雌、雄株的生殖分配有关。     

沙棘雌雄株叶片解剖结构比较研究

为了研究沙棘雌、雄株叶片的第二性征,本文采用石蜡切片法观察了沙棘雌、雄株叶片结构的差异。结果表明：（1）沙棘雌、雄株叶片均由表皮、叶肉和叶脉3部分组成,表皮均由1层细胞构成,表皮毛发达,上表皮有拟泡状细胞;叶肉栅栏组织与海绵组织分化明显。（2）雌株上表皮具更多的拟泡状细胞,其主脉韧皮部薄壁细胞及其下方的一些薄壁细胞含较多的后含物,下表皮的表皮毛更浓密;而雄株的叶片厚度、叶片上表皮厚度、栅栏组织厚度、栅栏组织厚度/海绵组织厚度均显著大于雌株,且其主脉维管束更发达。结果表明,沙棘雌雄株叶片解剖结构存在明显差异,这些差异是第二性征的表现,也是沙棘长期进化中形成的稳健的适应策略,可能有利于该物种的繁衍。     

LEAF ANATOMY OF TISSUE-CULTURED LIQUIDAMBAR STYRACIFLUA (HAMAMELIDACEAE) DURING ACCLIMATIZATION

Structural changes accompanying the acclimation process were observed in leaves of sweetgum, Liquidambar styraciflua, using light and transmission electron microscopy (TEM). Comparisons were made of leaves obtained from tissue culture, plantlets acclimated after transfer from the in vitro environment to soil, and field grown trees. Leaves of cultured plantlets lacked a differentiated palisade parenchyma and had spongy parenchyma interspersed with large air spaces. Field grown leaves showed distinct palisade and spongy tissues and a high cell density. New leaves from acclimated plantlets showed an elongation of the upper mesophyll with fewer intercellular spaces than cultured plants. Cells from leaves from in vitro plantlets had large vacuoles, limited cytoplasmic content and flattened chloroplast with an irregularly arranged internal membrane system. Acclimated and field leaf cells had a greater cytoplasmic content than cultured leaves, with the former having more dominate vacuoles. Chloroplasts had evident grana. Acclimated and field leaves had a well developed cuticle unlike leaves from culture.     

Probable mechanical transmission of a virus-like agent from rose rosette disease-infected multiflora rose to Nicotiana species

As part of efforts to identify the causal agent of the rose rosette disease (RRD) of multiflora rose (Rosa multiflora Thunb.), root tip extracts from both symptomatic and nonsymptomatic roses were used to mechanically inoculate leaves of Nicotiana glutinosa. Pale green spots were observed along the margins of the major leaf veins only on leaves inoculated with extracts prepared from symptomatic rose plants. Light microscopy revealed abnormal development of the palisade and spongy mesophyll cells in the symptomatic tissue, although no virus‐like particles (VLPs) were observed by electron microscopy. However, VLPs were observed in cells from tissue adjacent to the leaf veins and bordered by the pale green spots. Inoculation of N. benthamiana with extracts from symptomatic N. glutinosa initially did not result in visible symptoms on N. benthamiana inoculated leaves. However, approximately 4 wk post inoculation, splitting of leaf tissue across and along major leaf veins in expanding leaves occurred. In later stages of leaf expansion some leaves split in regions not associated with veins. Light microscopy of thick sections revealed separation between palisade cells and groups of small dead cells in the mesophyll tissue of expanding systemically infected leaf blades. Electron microscopy revealed crystalline arrays in the cytoplasm of mesophyll cells. No abnormal cellular changes were observed in plants inoculated with extracts prepared from nonsymptomatic rose plants.