GRAVITY-INDUCED EFFECTS ON MATERIAL PROPERTIES AND SIZE OF LEAVES ON HORIZONTAL SHOOTS OF ACER SACCHARUM (ACERACEAE)

The influence of gravity on the size and mechanical properties of mature leaves on horizontal shoots and etiolated seedlings of Acer saccharum Marsh. (Aceraceae) was examined. Leaves were grouped into three categories regarding their location on shoots (dorsal or “top” T, lateral or “left/right” L/R, and ventral or “bottom” B). Young's modulus E, petiole length L, lamina surface area A and weight P, and the cross-sectional areas of different tissues within petioles were measured for each leaf and were found to be correlated with leaf location (T, L/R, and B): T leaves were smaller and had lower E than their B counterparts; the size and material properties of L/R leaves were intermediate between those of T and B leaves. In general, A, P, and E decreased from the base to the tip of shoots. In addition to anisophylly, the influence of gravity induced petiole bending and torsion and resulted in the horizontal planation of laminae. This was observed for field-grown mature plants and etiolated seedlings. Petiole bending and torsion were interpreted as gravimorphogenetic phenomena. Anatomically, L, E, and petiole deflection angle Fv measured from the vertical were highly correlated with the combined cross-sectional areas of phloem fibers and xylem in petioles of B leaves and when data from all leaves were pooled. It is tentatively advanced that the correlation of E with the transverse areas of phloem fibers and xylem is evidence that either the pattern or the extent of lignification of petiole tissues is influenced by petiole position with respect to gravity.     

Influence of leaf size on tree architecture: first branch height and crown dimensions in tropical rain forest trees

 First branch height is an important attribute of sapling architecture, as it defines the height at which prolonged lateral growth is possible. First branch height, measured on saplings of 70 species in tropical rain forests of Australia, Costa Rica, Panama, and Sabah, Malaysia, was highly correlated with leaf blade and petiole length. The observed relationship, first branch height ∝ blade length × (petiole length)^0.5, implies that the ratio of first branch height to blade length increases somewhat with increasing leaf size, among species with a given ratio of petiole to blade length. Orthotropic species, with more or less radially symmetric arrangements of leaves on ascending axes, had a mean first branch height of 7x that observed for plagiotropic species, with planar leaf arrangements. The greater first branch height of orthotropic species was associated with their larger leaves and longer petioles. Plagiotropic species had wider crowns than orthotropic species in the sapling stage, as assessed at the Costa Rican site. Thus, leaf dimensions influence the dynamics of crown construction (or visa versa), as well as affecting leaf energy balance and gas exchange. Received: 5 September 1997 / Accepted: 3 March 1998     

Structural and mechanical peculiarities of the petioles of giant leaves of Amorphophallus (Araceae)

Petioles (up to 4 m tall) of huge solitary leaves of mature plants of Amorphophallus titanum and A. gigas resemble tree trunks supporting an umbrella-like crown. In a mechanical sense, the petiole is a shell, composed of compact parenchyma with embedded collenchyma strands. The core of the shell is filled with aerenchyma. Mechanical stability of the petiole strongly depends upon the turgor pressure in the parenchyma of the shell and the core. The petiole collapses upon senescence when the turgor pressure decreases as a result of increasing osmolality of the solution permeating cell walls. The present study supports the postulate that aerenchyma serves a mechanical function. The petiole can be easily broken by animals during a collision. This risk is proposed to be lowered by the mimicry of the color pattern of the petiole's surface, which resembles a stiff tree trunk covered with lichen thalli (in both species) and with bark in the case of A. gigas. The cellular basis of these color patterns is described.     

THE ELASTIC MODULI AND MECHANICS OF POPULUS TREMULOIDES (SALICACEAE) PETIOLES IN BENDING AND TORSION

Changes attending leaf development in the mechanical behavior and elastic moduli of the petioles of Populus tremuloides Michx. were examined in terms of total leaf weight (Wt), lamina and petiole weight (Wl and Wp), petiolar length (L), and lamina surface area (A). A primary concern was the extent to which two elastic moduli (Young's modulus E and the shear modulus G) of petioles changed over time and were correlated with one another. E and G were measured by means of multiple resonance frequency spectra, and together with the dimensions of cross sections through petioles, these two elastic moduli were used to estimate the stiffness of petioles in simple bending and torsion. Petiolar bending was predicted by means of a model incorporating expressions for both the bending stiffness (El) and torsional rigidity (GJ), where I is the second moment of area and J is the torsional constant. The predictions from these models were compared to observed petiolar bendings due to Wl. Additionally, the frequency of the oscillatory motion of leaves (placed in a wind tunnel with a 1 m sec^-1 ambient wind speed, directed normal to the blade of the leaf) was determined. Results indicate that L, A, Wl, Wp, and Wt were positively correlated with the age of leaves (crudely estimated as a function of leaf plastochron index, LPI); these morphometric parameters were also correlated with the magnitudes of E and G. Also, G was positively and linearly correlated with E, and was, on the average, an order of magnitude less than E. EI and GJ were positively correlated with LPI. The relationships among E, G, EI, C and Wl, Wp, Wt are discussed in terms of leaf allometries.     

Diurnal oscillatory movements of growing leaves of tobacco

The analysis of diurnal oscillatory movements of tobacco leaves was used in the diagnosis of viral infection of plants. The oscillatory helices circumscribed by a growing leaf of a healthy plant were regular, but some deviations, particularly in the transition points, were recorded. In order to make clear the cause of these irregularities of trajectory, the course of elongation of leaf petiole and blade in relation to localization and shift of zones of elongation during ontogenesis was analysed. The present analysis is similar to that described by the author's earlier experiments with pea roots. Oscillatory curves circumscribed by petiole, projected on a horizontal plane, were compared with curves circumscribed by the blade tip. The analysis of the leaves of different ages enabled us to study this process in dependence on growth rate. It was confirmed that oscillations are a result of elongation; the extent of oscillations is quantitatively dependent on the growth rate. An analysis of the zones of growth showed that in petiole the active meristems are localized near to its base while in the leaf lamina they move gradually during the ontogenesis from the apical to the basal part of the leaf blade. Active meristems of young rapidly growing leaves are localized approximately in the middle of the blade while those of old leaves were found in close proximity to the base of the lamina. The growth rate of petiole can be expressed in hundreds of mm per hour (4.8×10^?2 mm h^?1); half of this value was recorded for its apical part. The growth rate of leaf blade was found approximately ten times higher (3.2×10^?1 mm h^?1). The oscillatory movements of growing leaf consists of two integrate components: of oscillations originating in the base of the petiole and of oscillations of leaf blade the centrum of which is localized in the basal third of the blade. The arrangement of the experiments did not enable us to determine to what extent the phototropic response of leaf blade participates in leaf movements. The movements of leaves of an intact plant are evidently affected by rhythmic stem oscillations. Stem is an integral part of a system which participates in the transfer of information in plants.     

Ontogenic change in leaf shape and crown form of a tropical tree,Scaphium macropodum (Sterculiaceae) in Borneo

Crown architecture was analyzed forScaphium macropodum (Sterculiaceae), a common shade-tolerant emergent tree of a tropical rain forest in West Kalimantan, Indonesia. Saplings and poles shorter than 12 m in height had no branches, and gathered their leaves at the ends of the stem. The leaves changed from entire to palmately-parted with increasing tree size. The parted leaves increased the light penetration through the clustered foliage. The size of leaves including the blade and petiole ranged from 22 cm to 147 cm. Because the weight of petiole per blade increased with leaf size, the leaf could not be enlarged infinitely. Taller trees with lateral branches bore small (about 40 cm in length) entire leaves. The light intensity in the forest increased from the ground to about 12 m tall and was nearly constant from 12 m to 18 m. Crown architecture ofS. macropodum adapted to this light environment. The monoaxial trees lower than 12 m could thus increase the amount of light with vertical elongation, and the branched trees higher than 12 m could increase it by means of lateral extension of crown area.     

Testing of corner’s rules across woody plants in Tiantong region,Zhejiang Province: effects of micro-topography

Aims The size and quantity relationships between twigs and leaves can be used to describe the hydraulic properties of plants in response to environmental stresses. The objective of this study was to examine how twig-leaf relationship would vary with changes in micro-habitat conditions.
Methods The study site is located in the Tiantong National Forest Park (29.87° N, 121.65° E), Zhejiang Province. We measured twig cross-sectional area (twig size), sub-twig cross-sectional area (sub-twig size), individual leaf area, total leaf area (leaf size per twig), the number of twigs at a given twig size (twig intensity), and the number of leaves at a given twig size (leafing intensity) across individual woody plants on 10 plots in each of the convex and concave habitats within an evergreen broad-leaved forest. The standardized major axis (SMA) analysis was conducted to determine the scaling relationships between twig size and leaf size, between sub-twig size and twig intensity, and between leaf size and leafing intensity.
Important findings Significant, positive allometric relationships between twig cross-sectional area and total leaf area were found in plants in both types of micro-habitats (p < 0.001). There was no significant difference between the two micro-habitats in the slope of the regression between twig cross-sectional area and total leaf area, and the common slope of the regressions was significantly greater than 1 (p < 0.001). The intercept was significantlygreater in plants of the concave habitat than in plants of the convex habitat (p < 0.001), indicating that plants in a concave habitat support greater total leaf area at a given twig size than in a convex habitat. Significant, negative allometric scaling relationships were found between twig size and twig intensity in plants in both micro-habitats. There was also no significant difference between the two habitats in the slope of the regression between twig size and twig intensity, and the common slope of the regressions was significantly less than –1 (p < 0.001). The similar intercept in the regression relationship of twig area and twig intensity between the two habitats suggests that plants deploy similar amount of sub-twigs per twig size in both types of habitat. In addition, significant, negative allometric scaling relationships between leaf size and leafing intensity were found to be consistently conserved across micro-habitat types, with the common slope being smaller than –1. A higher value of y-intercept in the scaling relationships of leaf area vs. leafing intensity for plants in the concave habitat indicates that at a given leaf area, more leaves were supported by plants in a concave habitat than in a convex habitat. Overall, plants in a concave habitat tend to deploy more large leaves per twig size than those in a convex habitat. This study demonstrated that both the Corner’s rules and the leaf size-number trade-offs could be generalized to apply at the small local spatial scales. The magnitude and quantitative adjustment of twig-leaf deployment manifests a selection preference of hydraulic properties of plants in coping with changes in water availability between concave and convex habitats.     

LeafJ: An ImageJ Plugin for Semi-automated Leaf Shape Measurement

High throughput phenotyping (phenomics) is a powerful tool for linking genes to their functions (see review¹ and recent examples^2-4). Leaves are the primary photosynthetic organ, and their size and shape vary developmentally and environmentally within a plant. For these reasons studies on leaf morphology require measurement of multiple parameters from numerous leaves, which is best done by semi-automated phenomics tools^5,6. Canopy shade is an important environmental cue that affects plant architecture and life history; the suite of responses is collectively called the shade avoidance syndrome (SAS)⁷. Among SAS responses, shade induced leaf petiole elongation and changes in blade area are particularly useful as indices⁸. To date, leaf shape programs (e.g. SHAPE⁹, LAMINA¹⁰, LeafAnalyzer¹¹, LEAFPROCESSOR¹²) can measure leaf outlines and categorize leaf shapes, but can not output petiole length. Lack of large-scale measurement systems of leaf petioles has inhibited phenomics approaches to SAS research. In this paper, we describe a newly developed ImageJ plugin, called LeafJ, which can rapidly measure petiole length and leaf blade parameters of the model plant Arabidopsis thaliana. For the occasional leaf that required manual correction of the petiole/leaf blade boundary we used a touch-screen tablet. Further, leaf cell shape and leaf cell numbers are important determinants of leaf size¹³. Separate from LeafJ we also present a protocol for using a touch-screen tablet for measuring cell shape, area, and size. Our leaf trait measurement system is not limited to shade-avoidance research and will accelerate leaf phenotyping of many mutants and screening plants by leaf phenotyping.     

The functional morphology of light capture and carbon gain in the Redwood forest understorey plant Adenocaulon bicolor Hook

1. A three-dimensional geometric simulation model of crown architecture was utilized to investigate the efficiency of light capture and its relationship to whole-plant CO₂ assimilation of Adenocaulon bicolor .
2. Positioning of the leaves by the combined effects of ontogenetic variations in petiole length and angle and leaf size, and the leaf divergence angles were shown to be effective in minimizing self shading. The efficiency of light absorption varied from 0·64 to 0·70 among individual plants that were sampled.
3. Plant to plant variation in simulated daily carbon gain was strongly influenced by variations in the direct and diffuse PFD received by the individual plants. When simulations were run for all plants under a single common light environment, the carbon gain was strongly dependent on the efficiencies of light absorption of the different plants.
4. Simulations in which petiole length was varied showed a non-linear dependence of light absorption efficiency on petiole length. When both petiole length and leaf size were varied in a way that maintained a constant biomass then an optimal petiole length that corresponded to the observed petiole length was apparent. The observed divergence angle between successive leaves also maximized light absorption efficiency as compared to greater or lesser angles, but increases in internode length had no significant effect.
5. The results of this study provide evidence for selection for an 'optimal design' of crown architecture in Adenocaulon bicolor that maximizes light capture.     

Translocation pathways in the petioles and stem between source and sink leaves of Populus deltoides Bartr. ex Marsh.

Microautoradiography was used to follow the translocation pathways of ¹⁴C-labeled photosynthate from mature source leaves, through the stem, to immature sink leaves three nodes above. Translocation occurred in specific bundles of the midveins and petioles of both the source and sink leaves and in the interjacent internodes. When each of six major veins in the lamina of an exporting leaf was independently spot-fed ¹⁴CO₂, label was exported through specific bundles in the petiole associated with that vein. When the whole lamina of a mature source leaf was fed ¹⁴CO₂, export occurred through all bundles of the lamina, but acropetal export in the stem was confined to bundles serving certain immature sink leaves. Cross-transfer occurred within the stem via phloem bridges. Leaves approaching maturity translocated photosynthate bidirectionally in adjacent subsidiary bundles of the petiole. That is, petiolar bundles serving the lamina apex were exporting unlabeled photosynthate while those serving the lamina base were simultaneously importing labeled photosynthate. The petioles and midveins of maturing leaves were strong sinks for photosynthate, which was diverted from the export front to differentiating structural tissues. The data support the idea of bidirectional transport in adjacent bundles of the petiole and possibly in adjacent sieve tubes within an individual bundle.Abbreviations C central leaf trace - L left leaf trace - LPI leaf plastochron index - R right leaf trace     

Gravity can induce epinastic bending of isolated leaves

Abstract Isolated leaves of Plectranthus fruticosus were grown in cubic plastic cuvettes, and were supplied via their cut petioles with nutrient solution and indole-3-acetic acid (10^?6m ). Holes bored in the cuvette walls allowed the petioles to be oriented at approximately 60°, 90° or 120° to the vertical. Growth of the leaves initially oriented at angles of 60° and 90°, which simulated the situation in the intact plant, did not result in epinastic bending of the petiole. Inversion of the leaves (adaxial surface of the petiole downwards) and orientation of the adaxial/abaxial surfaces of the horizontal petiole parallel to the gravity vector, however, yielded strong epinastic bending of the petioles. In the latter case, this bending was not in the direction of the gravity vector (evidence for point (iii), below). Furthermore, epinastic bending occurred, when the isolated leaves were rotated on a clinostat (petioles parallel to the rotation axis or inclined to the rotation axis at an angle of 30°; 3 r.p.m.). Since a possible influence of the shoot was excluded, it is concluded that (i) perception and response are restricted to the leaf, (ii) gravity alone is sufficient to induce epinasty, (iii) a gravitropic component of the response can probably be excluded. The clinostat induced epinasty may not have been caused by nullifying the effect of gravity but due to continuous gravistimulation of the leaf.     

亚热带常绿阔叶林植物叶小枝的异速生长

 植物生态学研究的重要内容之一是识别和定量刻画种间生态变异的主要维数,叶大小小枝大小维（谱）是其中之一,目前的研究相对比较薄弱,两者之间是异速还是等速生长关系仍存在着争论。亚热带常绿阔叶林植物叶大小-枝大小维的研究报道很少。该文以我国东部亚热带典型区域福建梅花山常绿阔叶林的68种常绿乔灌木植物为对象,进行了叶-小枝关系及其生态意义的研究。结果表明：1）小枝茎截面积与叶干重、总叶面积和单叶面积之间的SMA斜率分别为1.29、1.23和1.18,呈现异速生长关系,支持叶大小 小枝大小为异速生长的相关研究结论,但SMA斜率低于预期值,其原因及生态意义有待进一步研究;2）小枝总叶面积与单叶面积呈显著正相关,而与叶片数量不相关,反映了小枝总叶面积的增加主要是由单叶面积大小决定的,可能与这一地区湿润气候有关;而单叶面积与枝条长度呈正相关则可能反映了植物对常绿阔叶林内较弱光照环境的适应;3）叶干重同小枝干重、叶面积为等速生长关系,可能反映了植物与动物之间代谢方式的差异。     

The functional morphology of the petioles of the banana, Musa textilis

Bananas are among the largest herbs in the world and their lightweight petioles hold up huge leaves. This study examined how the petioles manage to achieve adequate rigidity to do this, while allowing extensive and reversible reconfiguration in high winds. Morphological and anatomical examination of the petioles and leaves of Musa textilis suggested how these two apparently incompatible abilities are achieved. The hollow U-shaped section of the petiole and the longitudinal strengthening elements in its outer skin give it adequate rigidity, while its ventral curvature help support the leaf without the need for thick lateral veins. These features, however, also allow the petiole to reconfigure by twisting away from the wind, while the leaf can fold away. In addition, two sets of internal structures, longitudinal partitions and transverse stellate parenchyma plates, help prevent dorsoventral flattening, allowing the petiole to flex further away from the wind without buckling. These ideas were tested and verified by a range of mechanical tests. Simple four-point-bending and torsion tests showed that the petioles are indeed far more compliant in torsion than in bending. Axial bending tests and crushing tests showed that petioles could be flexed twice as far and were four times as resistant to dorsoventral flattening when intact than when the internal tissue is removed. The banana petiole, therefore, seems to be an excellent example of natural integrated mechanical design.     

发育阶段和海拔对岷江源区陇蜀杜鹃小枝功能性状及生物量分配的影响

本研究分析了岷江源区卡卡山典型高山灌丛植物陇蜀杜鹃不同发育阶段(花芽期和开花期)及不同海拔(3600 m低海拔和3800 m高海拔)下功能小枝和叶片性状的差异,以及空间异质性对花芽期和开花期小枝功能性状相关性及其权衡作用的影响。结果表明: 低海拔同一生长期陇蜀杜鹃小枝长度显著大于高海拔,高海拔开花期小枝的花数量和花质量显著高于低海拔。同一海拔花芽期的小枝质量、叶片数量、总叶质量、总叶面积和总叶柄质量均显著大于开花期,单叶质量和单叶柄质量均显著小于开花期。与花芽期相比,开花期叶生物量占比减少了13%,而小枝质量占比显著增加。小枝的生物量权衡表明,花芽期性状倾向于小枝质量,开花期倾向于总叶质量;花芽期的叶偏好分配于单叶质量,低海拔和高海拔开花期叶片分别偏好分配到单叶柄质量和单叶质量。低海拔开花期小枝质量与总叶面积、总叶质量均为异速生长,单叶柄质量和单叶面积为异速生长。海拔和发育阶段共同影响了陇蜀杜鹃功能小枝和叶片的性状。     

银杏叶片形态研究

通过对银杏不同枝类、不同叶序的叶片形态进行调查,结果表明:银杏不同枝类的叶片形态差异较大,叶宽、叶柄长、叶基角:多年生鳞枝＞一年生鳞枝＞一年生长枝;叶长、叶形指数:一年生长枝＞一年生鳞枝＞多年生鳞枝;叶面积:一年生和多年生鳞枝＞一年生长枝;有缺刻叶比例:一年生长枝＞多年生鳞枝＞一年生鳞枝.一年生长枝叶片的叶宽、叶长、叶面积、叶柄长、叶基角均随叶序的增加逐渐减小,叶形指数和有缺刻叶的比例则增加.一年生和多年生鳞枝1～5叶的叶长、叶宽和叶面积随叶序增加而逐渐增加,第5～6叶达最大,以后随叶序增加而逐渐减小,叶形指数和叶柄长度随叶序增加而增加,叶基角随叶序增加而减小.一年生长枝的第2叶、一年和多年生鳞枝的第4叶可作为品种描述的标准叶.     

Studies on leaflet abscission of blue lupin leaves

Summary In blue lupin leaves, each leaflet abscises at an abscission zone situated in the pulvinus at its base. The time to abscission of leaflets of detached leaves is proportional to leaf age. Light accelerates abscission; within certain limits the acceleration is the greater the younger the leaf. At a given concentration, kinetin applied to a single leaflet accelerates leaflet abscission in young leaves kept in darkness, delays it in older ones. There is an interaction between kinetin and light which is dependent also on leaf age and kinetin concentration. The leaf can be considered as consisting of three regions, the petiole, the pulvinar region and the leaflets. The effects of kinetin and of light as well as their interactions depent on the regions of the leaf treated with these agents. Kinetin applied to a leaflet of a young leaf kept in darkness accelerates abscission, but kinetin applied to the pulvinar region of a similar leaf kept in darkness delays abscission. When any part of a leaf is illuminated, abscission is accelerated. The most light-sensitive region of the leaf is the pulvinar region, despite its relatively small area. Acceleration of abscission by light is greatest when illumination of the pulvinar region is combined with illumination of either the leaflets or the petiole. The interaction of light with kinetin is complex. Where the illuminated area includes the pulvinar region, kinetin delays abscission. This effect is most marked in the case where the pulvinar region alone is illuminated and kinetin is applied to a leaflet.Intrafoliar abscission as found in lupin leaves permits study of complex interactions of both distal and proximal stimuli involved in abscission.     

PHOTOSYNTHETIC RATE AND MESOPHYLL SURFACE AREA IN EXPANDING LEAVES OF ALTERNANTHERA PHILOXEROIDES GROWN AT TWO LIGHT LEVELS

Leaves of Alternanthera philoxeroides, alligator weed, developed at a photosynthetic photon flux density (PPFD, light energy at wavelengths of 400 to 700 nm) of 790 μmol sec⁻¹ m⁻² (High Light) had less surface area, were thicker, had a higher maximum P_n (net rate of CO₂ uptake), and required a higher PPFD for saturation of P_n, than leaves developed at 160 μmol sec⁻¹ m⁻² (Low Light). Mesophyll thickness at Low Light was within 19% of maximum 2 days after emergence but at High Light, thickness increased 79% between 2 and 16 days after leaf emergence. The ratio of mesophyll surface area to leaf surface area decreased during development in both light treatments; the ratio, however, was over 70% greater in fully expanded High Light leaves than in Low Light leaves. Maximum P_n expressed on a leaf surface area basis was 158% greater in High Light leaves than in Low Light leaves, but P_n was only 58% greater when expressed on a mesophyll surface area basis. It was estimated that fully expanded High Light leaves fixed 72% more CO₂ per leaf (P_n expressed per unit surface area times the total surface area per leaf) than fully expanded Low Light leaves when P_n was measured at the PPFD leaves expanded under. Both High and Low Light leaves would fix about the same amount of CO₂ per leaf when P_n was measured at 160 μmol sec⁻¹ m⁻² because the larger surface area of the Low Light leaves offset small differences in P_n.     

The leaf development process and its significance for reducing self-shading of a tropical pioneer tree species

On a monoaxial erect stem of trees with continuous leafing, the older leaves would be quickly shaded by newer (upper) leaves if the trees did not have any compensating mechanisms to avoid self-shading. We hypothesized that the dynamic adjustment of leaf deployment, by regulating the patterns of leaf growth and by changing leaf orientation as leaves age, is a compensating mechanism. To verify this hypothesis, we analyzed leaf development and crown structure of a Far Eastern tropical pioneer tree species, Macaranga gigantea (Rub. f. et Toll.) M.A., which unfolds huge leaves directly on a monoaxial stem with a short leafing interval. Petioles required more than 90 days for full elongation and the petiole angle (the angle between the petiole axis and the vertical) increased over time. Thus, a series of leaves on a stem progressively increased in petiole length and petiole angle from the youngest to the oldest leaves. This is beneficial because it decreases the degree of self-shading within a crown. A simulation suggested that an average crown for the M. gigantea seedlings, which was constructed using empirically determined morphometric data cannot entirely eliminate self-shading within the crown. But an average crown had a lower degree of self-shading, with less dry mass allocation to the petiole than simulated crowns that were identical to the average crown in all but one respect: they had constant petiole lengths or petiole angles. We conclude that M. gigantea seedlings reduce self-shading by regulating elongation of the petiole and changes in the petiole angle with increasing leaf age.     

Effect of salinity on tissue architecture in expanding wheat leaves

Salinity greatly reduces the leaf cross-sectional area of wheat (Triticum aestivum L.) during its development, which may lead to variation in the architectural properties of growing leaves that would result in a change in leaf physiological functions. Our objective was to characterize the effect of salinity on the spatial distribution of the cross-sectional area and the anatomy of large and small veins of a growing wheat leaf. Spring wheat was grown in a growth chamber in soils with or without 120 mM NaCl. Leaf 4 in both treatments was harvested 2–3 days after its emergence and then cut into five transverse segments. Examination of the transverse sections revealed that salinity significantly reduced the cross-sectional area, width, and radii of both epidermal and mesophyll cells along the leaf axis. Reduction in the cross-sectional area and width occurred mainly at the leaf base, indicating that these reductions occur during the period of leaf initiation. The reduction in cross-sectional area was attributed to a decrease in the size of the vein segments and a reduced number of medium and small veins. The thickness of the leaf was also reduced under the 120 mM NaCl treatment. A greater intercellular air space in the large vein segments under saline conditions was also found. The approximately 35% reduction observed in the number of veins under saline conditions (mainly in the number of small veins) may suggest that salinity reduces the capacity for re-translocation of mineral nutrients and assimilates. The reduced area of protoxylem and metaxylem in midrib and large vein segments in growing tissues may be responsible for lower water deposition into the growth zone under saline conditions.     

Petiole mechanics, leaf inclination, morphology, and investment in support in relation to light availability in the canopy of Liriodendron tulipifera

To determine the role of leaf mechanical properties in altering foliar inclination angles, and the nutrient and carbon costs of specific foliar angle variation patterns along the canopy, leaf structural and biomechanical characteristics, biomass partitioning into support, and foliar nitrogen and carbon concentrations were studied in the temperate deciduous species Liriodendron tulipifera L., which possesses large leaves on long petioles. We used beam theory to model leaf lamina as a uniform load, and estimated both the lamina and petiole flexural stiffness, which characterizes the resistance to bending of foliar elements at a common load and length. Petiole and lamina vertical inclination angles with respect to horizontal increased with increasing average daily integrated photon flux density (Q_int). Yet, the light effects on lamina inclination angle were primary determined by the petiole inclination angle. Although the petioles and laminas became longer, and the lamina loads increased with increasing Q_int, the flexural stiffness of both lamina and petiole increased to compensate for this, such that the lamina vertical displacement was only weakly related to Q_int. In addition, increases and decreases in the petiole inclination angle with respect to the horizontal effectively reduced the distance of lamina load from the axis of rotation, thereby reducing the bending moments and lamina inclination due to gravity. We demonstrate that large investments, up to 30% of total leaf biomass, in petiole and large veins are necessary to maintain the lamina at a specific position, but also that light has no direct effect on the fractional biomass investment in support. However, we provide evidence that apart from light availability, structural and chemical characteristics of the foliage may also be affected by water stress, magnitude of which scales positively with Q_int.