Seasonal allocation of defense investment in Ilex opaca Aiton and constraints on a specialist leafminer

Summary Phytomyza ilicicola (Diptera: Agromyzidae), a univoltine specialist leafminer, is one of the few insect herbivores of American holly. Adult emergence is closely synchronized with leaf flush in spring, and females make numerous feeding punctures on and oviposit in new leaves. Larvae hatch in late May and June, but their feeding period and development are prolonged so that more than 80% of the mine enlargement occurs from January until March of the following year. We propose that this unusual life cycle reflects adaptation to constraints imposed by seasonal and age-related changes in chemical and structural defenses, and in nutritional quality of holly foliage. As holly leaves age, there is a shift in allocation of defense investment away from allelochemicals, including phenolic compounds and saponins, toward leaf sclerophylly, spinose teeth, and low foliar nitrogen and water. Rapid increases in leaf toughness and decreases in nutritional quality limit availability of leaf tissues for adult feeding and oviposition to a two-to threeweek phenological window during leaf flush. Mature holly foliage is a nutritionally poor resource by nearly all criteria known to affect food quality for herbivores. This may be the main reason for the prolonged larval development of P. ilicicola. Alternatively, winter feeding and pupation in spring may be adaptations which help to ensure synchrony of adult emergence with leaf flush. Repeated puncturing by female P. ilicicola does not render leaves more suitable for larvae, nor is it a means by which females sample leaf exudate to assess leaf quality prior to oviposition. Rather, leaf puncturing occurs mostly on leaves that are relatively high in soluble nitrogen, and is apparently a means by which females obtain protein and sugars prior to and during oviposition.The investigation reported in this paper (No. 85-7-8-208) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with the approval of the Director     

Chlorophyll and light gradients in sun and shade leaves of Spinacia oleracea

Abstract. Light gradients were measured and correlated with chlorophyll concentration and anatomy of leaves in spinach (Spinacia oleracea L.). Light gradients were measured at 450, 550 and 680 nm within thin (455 μm) and thick (630 μm) leaves of spinach grown under sun and shade conditions. The light gradients were relatively steep in both types of leaves and 90% of the light at 450 and 680 nm was absorbed by the initial 140 μm of the palisade. In general, blue light was depleted faster than red light which, in turn was depleted faster than green light. Light penetrated further into the thicker palisade of sun leaves in comparison to the shade leaves. The distance that blue light at 450 nm travelled before it became 90% depleted was 120 μm in sun leaves versus 76 μm in shade leaves. Red light at 680 nm and green light at 550 nm travelled further but the trends were similar to that measured at 450nm. The steeper light gradients within the palisade-of shade leaves were caused by increased scattering of light within the intercellular air spaces and/or cells which were less compact than those in sun leaves. The decline in the amount of light within the leaf appeared to be balanced by a gradient in chlorophyll concentration measured in paradermal sections. Progressing from the adaxial epidermis, chlorophyll content increased through the palisade and then declined through the spongy mesophyll. Chlorophyll content was similar in the palisade of both sun and shade leaves. Chloroplast distribution within both sun and shade leaves was relatively uniform so that the chlorophyll gradient appeared to be caused by greater amounts of chlorophyll within chloroplasts located deeper within the leaf. These results indicate that the anatomy of the palisade may be of special importance for controlling the penetration of photo-synthetically active radiation into the leaf. Changing the structural characteristics of individual palisade cells or their arrangement may be an adaptation that maximizes the absorption of light in leaves with varying mesophyll thickness due to different ambient light regimes.     

Early spring defoliation,secondary leaf flush,and leafminer outbreaks on American holly

Summary Adults of Phytomyza ilicicola (Diptera: Agromyzidae), a univoltine specialist leafminer, emerge in close synchrony with leaf flush of American holly and feed on and oviposit in soft, partially expanded leaves. Early spring defoliation, such as commonly results from freezing injury to young shoots, is followed several weeks later by a second flush of young leaves from lateral buds. We simulated this phenomenon by manually defoliating whole small trees and individual shoots of large trees to test the hypothesis that freezing injury can encourage leafminer outbreaks by inducing an abundance of soft, protein rich young leaves late in the adult activity period, when availability of vulnerable leaves becomes limited. Defoliation of small trees one or two weeks after bud break resulted in six- to 13-fold increases in the incidence of feeding punctures and larval mines on second flush leaves as compared with densities on original young leaves of control trees. Similarly, we induced significant increases in feeding punctures and larval mines on second flush leaves of individual defoliated shoots, although leaves that did not open until after the flight period escaped this injury. These observations underscore the capability of adult female P. ilicicola to locate and exploit a small number of phenologically available leaves among many hundreds of older leaves on the same tree. By altering the phenology of leaf flush, certain kinds of environmental stress may predispose perennial plants to outbreaks of early season folivores that restrict their feeding or oviposition to very young leaves.     

Do holly leaf spines really deter herbivory?

Summary Although spinose teeth of holly leaves have been widely cited as an example of a physical defense against herbivores, this assumption is based largely on circumstantial evidence and on general misinterpretation of a single, earlier experiment. We studied the response of third and fifth instar larvae of the fall webworm, Hyphantria cunea Drury, a generalist, edge-feeding caterpillar, to intact American holly leaves and to leaves that had been modified by blunting the spines, by removing sections of leaf margin between the spines, or by removing the entire leaf margin. The results suggest that the thick glabrous cuticle and tough leaf margin of Ilex opaca are more important than the spinose teeth in deterring edge-feeding caterpillars. Microscopic examination of mature leaves revealed that the epidermis is thickened at the leaf margin, and that the leaf is cirucumscribed by a pair of fibrous veins. In simple choice tests neither domesticated rabbits nor captive whitetailed deer discriminated between spinescent holly foliage and foliage from which spines were removed. Nevertheless, we found little evidence of herbivory by mammals in the field, either on small experimental trees or in the forest understory. While it is possible that spinose teeth contribute to defense by reducing acceptibility of holly relative to other palatable plant species, we suggest that the high concentrations of saponins and poor nutritional quality of holly foliage may be more important than spines in deterring vertebrate herbivores. The degree of leaf spinescence and herbivory was compared at different heights with the tree canopy to test the prediction that lower leaves should be more spinescent as a deterrent to browsers. Leaves on lower branches of mature forest trees were slightly more spinescent than were upper leaves, and juvenile trees were slightly more spinescent than were mature trees. However, there was no relationship between degree of spinescence and feeding damage. The greater spinescence of holly leaves low in the canopy is probably an ontogenetic phenomenon rather than a facultative defense against browsers.The investigation reported in this paper (No. 87-7-8-77) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with the approval of the Dirctor     

The spatial distribution of chloroplast water in Acer platanoides sun and shade leaves

We evaluated a new, two-dimensional (2-D) nuclear magnetic resonance (NMR) imaging technique as a method for measuring the distribution of chloroplasts in leaves. NMR images that showed the distribution of chloroplast water and of total water as a function of depth into Acer platanoides sun and shade leaves were compared with the distribution of chlorophyll in the same leaf types (as measured by fluorescence microscopy), with the cellular structure (by scanning electron microscopy), and with published information. Results showed that the volume fraction of chloroplast water was much larger in shade than in sun leaves, and that it averaged about one-third larger in the palisade than in the spongy parenchyma region of both leaf types. Chlorophyll fluorescence was more intense in shade than in sun leaves. In sun leaves, fluorescence was maximal in the palisade region near the junction with the spongy parenchyma, while in shade leaves, fluorescence was maximal in the upper part of the spongy layer. We concluded that 2-D NMR imaging reliably indicates the location of chloroplast water.     

Light as a regulator of structural and chemical leaf defenses against insects in two Prunus species

Light is a key factor influencing competition between species, and the mechanisms by which trees overcome insect outbreaks can be associated with alternation of the leaves structure, which then prevent or promotes their susceptibility to herbivores. It was predicted that leaf tissue anatomy would likely be different in sun and shade leaves, with a gradual decline of leaves resistance coupled with reduction of accessible light. We quantified anatomical patterns and the distribution of defence compounds (phenols, total tannins, catechol tannins) within heavily grazed leaves of Prunus padus, native in Europe and Prunus serotina, an invasive to Central Europe. Both species were strongly attacked by folivorous insects when shrubs grew in the shade. In the sun, however only P. padus leaves were grazed, but P. serotina leaves were almost unaffected. We identified that anatomical characteristics are not linked to different P. padus and P. serotina leaf vulnerability to insects. Furthermore, the staining of defence compounds of P. serotina leaves grown in full sun revealed that the palisade mesophyll cells had a higher content of phenolic compounds and catechol tannins. Thus, our results indicate that a specific distribution of defence compounds, but not the anatomical relationships between palisade and spongy mesophyll, may be beneficial for P. serotina growth outside its natural range. The identified pattern of defence compounds distribution is linked to a lower susceptibility of P. serotina leaves to herbivores, and is associated with its invasiveness. This likely reflects that P. serotina is a stronger competitor than P. padus, especially at high sunlit sites i.e. gaps in the forest.     

Leaf architecture and direction of incident light influence mesophyll fluorescence profiles

Light propagation and distribution inside leaves have been recognized as important processes influencing photosynthesis. Monochromatic light absorption across the mesophyll was measured using chlorophyll fluorescence generated from illumination of the cut edge (epi-illumination), as well as the adaxial or abaxial surfaces of the leaf. Species were selected that had basic leaf types: laminar leaf with adaxial palisade layer (Rhododendron catawbiense), needle with palisade (Abies fraseri), and needle without palisade (Picea rubens). Fluorescence was more evenly distributed across the mesophyll for adaxially illuminated leaves with a palisade cell layer, as well as for the needles (cylindrical) without palisade, when compared to fluorescence generated by abaxial illumination. Moreover, fluorescence from green light illumination remained high across the mesophyll of adaxially illuminated R. catawbiense, indicating a possible influence of mesophyll structure on internal light distribution beyond that of chlorophyll levels. These data support the idea that light propagation within the mesophyll is associated with asymmetric mesophyll structure, in particular the presence of palisade cell layers. In addition, we propose that the evolution of a more cylindrical leaf form, such as found in conifer species, may be a structural solution to excessive sunlight that replaces the highly differentiated mesophyll found in most laminar-leaved species.     

Carbon Fixation Gradients across Spinach Leaves Do Not Follow Internal Light Gradients

In situ measurements of 14C-CO2 incorporation into 40-[mu]m paradermal leaf sections of sun- and shade-grown spinach leaves were determined. Chlorophyll, carotenoid, and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) content in similar 40-[mu]m paradermal leaf sections was also measured. The carbon fixation gradient did not follow the leaf internal light gradient, which decreases exponentially across the leaf. Instead, the 14C-CO2 fixation was higher in the middle of the leaf. Contrary to expectations, the distribution of carbon fixation across the leaf showed that the spongy mesophyll contributes significantly to the total carbon reduced. Approximately 60% of the carboxylation occurred in the palisade mesophyll and 40% occurred in the spongy mesophyll. Carbon reduction correlated well with Rubisco content, and no correlation between chlorophyll and carotenoid content and Rubisco was observed in sun plants. The correlation among chlorophyll, carotenoids, Rubisco, and carbon fixation was higher in shade leaves than in sun leaves. The results are discussed in relation to leaf photosynthetic and biochemical measurements that generally consider the leaf as a single homogeneous unit.     

Irradiance and phenotype: comparative eco-development of sun and shade leaves in relation to photosynthetic CO2 diffusion

The subject of this paper, sun leaves are thicker and show higher photosynthetic rates than the shade leaves, is approached in two ways. The first seeks to answer the question: why are sun leaves thicker than shade leaves? To do this, CO2 diffusion within a leaf is examined first. Because affinity of Rubisco for CO2 is low, the carboxylation of ribulose 1,5-bisphosphate is competitively inhibited by O2, and the oxygenation of ribulose 1,5-bisphosphate leads to energy-consuming photorespiration, it is essential for C3 plants to maintain the CO2 concentration in the chloroplast as high as possible. Since the internal conductance for CO2 diffusion from the intercellular space to the chloroplast stroma is finite and relatively small, C3 leaves should have sufficient mesophyll surfaces occupied by chloroplasts to secure the area for CO2 dissolution and transport. This explains why sun leaves are thicker. The second approach is mechanistic or 'how-oriented'. Mechanisms are discussed as to how sun leaves become thicker than shade leaves, in particular, the long-distance signal transduction from mature leaves to leaf primordia inducing the periclinal division of the palisade tissue cells. To increase the mesophyll surface area, the leaf can either be thicker or have smaller cells. Issues of cell size are discussed to understand plasticity in leaf thickness.     

Inhibition of herbivory on young holly leaves: evidence for the defensive role of saponins

Summary Response of the southern red mite, Oligonychus ilicis McGregor, to young and one year old leaves of Ilex opaca Aiton was studied on three dates during the period of leaf expansion in the spring. Young foliage, which is rich in nutrients but also contains high levels of saponins, was found to be unsuitable for colonization by this oligophagous herbivore until the leaves had matured and levels of saponins had declined. Mites preferentially colonized and had higher survival and reproduction on sclerophyllous, one-year old leaves than on young leaves in early spring. High levels of saponins in young, second-flush leaves of shoots that had earlier been damaged by frost were again correlated with low mite survival in June. Laboratory preference tests with the fall webworm, Hyphantria cunea Drury, and the eastern tent caterpillar, Malacosoma americanum (F.), indicated that young, saponin-rich holly foliage is especially unpalatable to these highly polyphagous caterpillars. Fifth instar fall webworms required significantly longer to complete their development, attained lower weights, and had greater mortality on artificial diet amended with low concentrations of purified holly saponins than on control diet. These results support the hypothesis that the high levels of saponins in young holly leaves provide protection from herbovores until the leaves have matured and their structural defenses are developed.The investigation reported in this paper (No. 88-7-8-196) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with the approval of the Director     

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.     

Photosynthetic and structural acclimation to light direction in vertical leaves of Silphium terebinthinaceum

The azimuth of vertical leaves of Silphium terebinthinaceum profoundly influenced total daily irradiance as well as the proportion of direct versus diffuse light incident on the adaxial and abaxial leaf surface. These differences caused structural and physiological adjustments in leaves that affected photosynthetic performance. Leaves with the adaxial surface facing East received equal daily integrated irradiance on each surface, and these leaves had similar photosynthetic rates when irradiated on either the adaxial or abaxial surface. The adaxial surface of East-facing leaves was also the only surface to receive more direct than diffuse irradiance and this was the only leaf side which had a clearly defined columnar palisade layer. A potential cost of constructing East-facing leaves with symmetrical photosynthetic capcity was a 25% higher specific leaf mass and increased leaf thickness in comparison to asymmetrical South-facing leaves. The adaxial surface of South-facing leaves received approximately three times more daily integrated irradiance than the abaxial surface. When measured at saturating CO₂ and irradiance, these leaves had 42% higher photosynthetic rates when irradiated on the adaxial surface than when irradiated on the abaxial surface. However, there was no difference in photosynthesis for these leaves when irradiated on either surface when measurements were made at ambient CO₂. Stomatal distribution (mean adaxial/abaxial stomatal density = 0.61) was unaffected by leaf orientation. Thus, the potential for high photosynthetic rates of adaxial palisade cells in South-facing leaves at ambient CO₂ concentrations may have been constrained by stomatal limitations to gas exchange. The distribution of soluble protein and chlorophyll within leaves suggests that palisade and spongy mesophyll cells acclimated to their local light environment. The protein/chlorophyll ratio was high in the palisade layers and decreased in the spongy mesophyll cells, presumably corresponding to the attentuation of light as it penetrates leaves. Unlike some species, the chlorophyll a/b ratio and the degree of thylakoid stacking was uniform throughout the thickness of the leaf. It appears that sun-shade acclimation among cell layers of Silphium terebinthinaceum leaves is accomplished without adjustment to the chlorophyll a/b ratio or to thylakoid membrane structure.     

The functional significance of palisade tissue: penetration of directional versus diffuse light

Light gradients were measured in leaves that had different types of anatomical development of the mesophyll but similar pigment content. Leaves of the legume, Thermopsis montana, had columnar palisade and spongy mesophyll whereas leaves of the monocot, Smilacina stellata, had spongy mesophyll only. Light gradients were measured at 550 nm in both types of leaves when they were irradiated with collimated or diffuse light. When irradiated with collimated light, light gradients were steeper in leaves with spongy mesophyll in comparison to those that had palisade tissue. On the other hand, light gradients were similar between both leaf types when they were irradiated with diffuse light. Thus, columnar palisade cells facilitated the penetration of collimated light over diffuse light. These results suggest that palisade tissue may help distribute light more uniformly to chloroplasts within the leaf. Moreover, the functional significance of palisade tissue may be related to the amount of collimated light within the natural environment.     

Leaf biomechanics, morphology, and anatomy of the deciduous mesophyte Prunus serrulata (Rosaceae) and the evergreen sclerophyllous shrub Heteromeles arbutifolia (Rosaceae)

Leaf tensile properties were compared between the mesic deciduous tree Prunus serrulata (var. "Kwanzan") and the xeric and sclerophyllous chaparral evergreen shrub Heteromeles arbutifolia (M. Roem). All values for biomechanical parameters for H. arbutifolia were significantly greater than those of P. serrulata. The fracture planes also differed between the two species with P. serrulata fracturing along the secondary veins, while H. arbutifolia most often fractured across the leaf irrespective of the vein or mesophyll position, thus yielding qualitative differences in the stress-strain curves of the two species. Anatomically, P. serrulata exhibits features typical for a deciduous mesophytic leaf such as a thin cuticle, a single layer of palisade mesophyll, isodiametric spongy mesophyll, and extensive reticulation of the laminar veins. Heteromeles arbutifolia leaves, however, are typically two- to three-fold thicker with a 35% higher dry mass/fresh mass ratio. The vascular tissue is restricted to the interface of the palisade and spongy mesophyll near the center of the leaf. Both epidermal layers have a thick cuticle. The palisade mesophyll is tightly packed and two to three layers thick. The spongy mesophyll cells are ameboid in shape and tightly interlinked both to other spongy cells as well as to the overlying palisade layer. We conclude that the qualitative and quantitative biomechanical differences between the leaves of these two species are likely due to a complex interaction of internal architectural arrangement and the physical/chemical differences in the properties of their respective cell walls. These studies illustrate the importance that morphological and anatomical correlates play with mechanical behavior in plant material and ultimately reflect adaptations present in the leaves of chaparral shrubs that are conducive to surviving in arid environments.     

Studies on Intercellular Pectic Strands of Leaf Palisade Parenchyma

Regular rows (‘scala’) of pectic strands of uniformthickness interconnect palisade cells of leaves of a wide rangeof plant species, the leaf lamina of which possesses a regularpalisade layer. As the strands can be viewed by scanning electronmicroscopy of fractured, uncoated, fresh frozen leaves, theyare not artefacts. The techniques of electron probe analysis have been used toexamine fresh frozen leaves of holly in which there are regularpectic scala. Evidence is presented to support the view alreadyput forward, to explain the origin of the strands, that theyare deficient in calcium. The strands are shown to be rich inpotassium which, like the potassium in leaf cells, can be readilyleached with water. The advantages of fresh frozen plant material for elementalelectron probe analyses as well as problems arising from surfaceirregularities and surface charging, are discussed. pectic strands, leaf palisade parenchyma, electron-probe micro analysis, calcium, potassium     

FEEDING HABITS OF THE LACE-BUG URENTIUS AEGYPTIACUS BERGEVIN (HEMIPTERA: TINGIDAE)

Adults and nymphs of the lace-bug Urentius aegyptiacus Bergevin (Tingidae) feed on leaves of the egg-plant ( Solanum melongena L.). The stylets of this insect are of typical hemipteran structure and are inserted into the leaf from either surface. Penetration of the epidermis is mainly intracellular, but may be intercellular or stomatal, while the course through the mesophyll and palisade tissues—frequently in a plane parallel to the leaf surfaces—is predominantly intracellular. The stylets terminate intracellularly, generally within a palisade cell, sometimes in a mesophyll cell, but only rarely in the vascular elements. The stylet sheath and track are absent and the saliva neither gels nor stains. Feeding damage, which results in externally visible chlorotic areas, is caused by the extraction of cell contents within feeding zones which are confined at first to the palisade but later extend to the mesophyll: it is accompanied by laceration of the cell walls and diffusion of an oral secretion of low phytotoxicity. Shrinkage of the leaf is due initially to collapse of the mesophyll and epithelial cells; the palisade and xylem cells retain their characteristic size and shape until destruction of the other tissues is complete.     

云南秋海棠属植物叶片横切面比较解剖研究

报道30种主产于云南的秋海棠属植物叶片的横切面解剖构造特征。采用常规石蜡切片法切片观察,结果表明:云南秋海棠属植物叶片薄、横切面均为异面叶、呈典型的阴叶结构,叶肉组织虽有栅栏组织和海绵组织的分化,但栅栏组织不发达,占叶肉组织的比例较小。表皮多为单表皮,极稀复表皮,表皮毛均由多细胞组成。气孔集中于下表皮,孔下室或下陷气孔特大、通气组织极发达;角质层形状多样,呈均匀增厚、瘤状和片状突起;叶绿体椭球形、数多、个体大,主要分布于叶肉组织,集中于栅栏组织。解剖构造特征在各分类组内呈现不完全一致性,而在相同茎的形态类型中有些较一致的特征,在不同种间解剖特征各有差别;根状茎和直立茎类型种类的横切面组织结构表现为表皮细胞壁外的角质层薄、栅栏组织与叶肉组织厚度比例较小等弱光照、湿生等适应性较弱的特征。球茎类型的种类表现为角质层较厚、栅栏叶肉组织厚度比例较大等适应略为干燥和较强光照的特征。     

Developmental process of sun and shade leaves in Chenopodium album L.

The authors’ previous study of Chenopodium album L. revealed that the light signal for anatomical differentiation of sun and shade leaves is sensed by mature leaves, not by developing leaves. They suggested that the two‐cell‐layered palisade tissue of the sun leaves would be formed without a change in the total palisade tissue cell number. To verify that suggestion, a detailed study was made of the developmental processes of the sun and shade leaves of C. album with respect to the division of palisade tissue cells (PCs) and the data was expressed against developmental time (leaf plastochron index, LPI). The total number of PCs per leaf did not differ between the sun and shade leaves throughout leaf development (from LPI ?1 to 10). In both sun and shade leaves, anticlinal cell division of PCs occurred most frequently from LPI ?1 to 2. In sun leaves, periclinal division of PCs occurred synchronously with anticlinal division. The constancy of the total number of PCs indicates that periclinal divisions occur at the expense of anticlinal divisions. These results support the above suggestion that two‐cell‐layered palisade tissue is formed by a change of cell division direction without a change in the total number of PCs. PCs would be able to recognize the polarity or axis that is perpendicular to the leaf plane and thereby change the direction of their cell divisions in response to the light signal from mature leaves.     

Functional consequences of stenophylly for leaf productivity: comparison of the anatomy and physiology of a rheophyte, Farfugium japonicum var. luchuence, and a related non-rheophyte, F. japonicum (Asteraceae)

We investigated the anatomical and physiological characteristics of stenophyllous leaves of a rheophyte, Farfugium japonicum var. luchuence, and sun and shade leaves of a non-rheophyte, F. japonicum, comparing three different populations from coastal, forest floor, and riparian habitats. Light adaptation resulted in smaller leaves, and riparian adaptation resulted in narrower leaves (stenophylly). The light-saturated rate of photosynthesis (P _max) per unit leaf area corresponded to the light availability of the habitat. Irrespective of leaf size, the P _max per unit leaf mass was similar for sun and shade leaves. However, the P _max per mass of stenophyllous leaves was significantly lower than that of sun and shade leaves. This was because the number and size of mesophyll cells were greater than that required for intercellular CO₂ diffusion, which resulted in a larger leaf mass per unit leaf area. Higher cell density increases contact between mesophyll cells and enhances leaf toughness. Stenophyllous leaves of the rheophyte are frequently exposed to a strong water flow when the water level rises, suggesting a mechanical constraint caused by physical stress.     

Feeding of pea leafminer larvae simultaneously activates jasmonic and salicylic acid pathways in plants to release a terpenoid for indirect defense

The pea leafminer, Liriomyza huidobrensis, is an important pest species affecting ornamental crops worldwide. Plant damage consists of oviposition and feeding punctures created by female adult flies as well as larva-bored mines in leaf mesophyll tissues. How plants indirectly defend themselves from these two types of leafminer damage has not been sufficiently investigated. In this study, we compared the indirect defense responses of bean plants infested by either female adults or larvae. Puncturing of leaves by adults released green leaf volatiles and terpenoids, while larval feeding caused plants to additionally emit methyl salicylate and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene (TMTT). Puncturing of plants by female adults induced increases in jasmonic acid (JA) and JA-related gene expressions but reduced the expressions of salicylic acid (SA)-related genes. In contrast, JA and SA and their-related gene expression levels were increased significantly by larval feeding. The exogenous application of JA+SA significantly triggered TMTT emission, thereby significantly inducing the orientation behavior of parasitoids. Our study has confirmed that larval feeding can trigger TMTT emission through the activation of both JA and SA pathways to attract parasitoids; however, TMTT alone is less attractive than the complete blend of volatiles released by infested plants.