Xylem Vessel Size Research Articles

Effect of sucrose exposure on the xylem anatomy of three temperate species

ABSTRACTThis study is a continuation of research on the role of sucrose in figured wood formation in temperate trees. Different concentrations of sucrose solutions were administered for 7 weeks to trunk tissues ofBetula pendulaRoth, Alnus incana(L.) Moench andPopulus tremulaL. Then xylem anatomy was examined with particular emphasis to the number of vessels and the spatial orientation of xylem elements. InB. pendulaandA. incanaa high level of exogenous sucrose caused a reduction in the number and size of xylem vessels, even to the point of absence of vessels. Sucrose concentrations of 100 and 200 g l-1induced the formation of curly grain and anomalous club-shaped rays in xylem ofB. pendula.Populus tremulaxylem was not significantly altered by the experiment; the xylem anatomy was more seriously affected by wounding than by sucrose. InB. pendulaandA. incanathe wood formed during the experiment was similar to figured wood of these species. The decrease in the number and size of vessels in the xylem formed during the experiment possibly suggests that high concentrations of sucrose lead to a decline in the level of physiologically active auxin. Changes in the orientation of xylem elements points to a disruption of basipetal auxin transport. Further biochemical and physiological studies are needed to provide more comprehensive understanding of the relationship between sucrose and auxin during the development of figure in wood.

Changes in structure and physiological functioning due to experimentally enhanced precipitation seasonality in a widespread shrub species

Semi-arid shrub steppe occupies a vast geographic range that is characterized in part by distinct seasonal patterns in precipitation. Few studies have evaluated how variability in both the amount and timing of precipitation affect the structure and physiology of shrubs in these systems. We quantified changes in foliar crown parameters, xylem anatomy, gas exchange, and hydraulic transport capacity in deep-rooted Artemisia tridentata shrubs following 20 years of experimental manipulations in amount and seasonal timing of precipitation. We hypothesized that shrub growth (total leaf area per shrub and cover of shrub community), hydraulic transport efficiency, and gas exchange would increase in shrubs in irrigated plots compared to non-irrigated control plots, especially for irrigation applied in winter rather than summer. We also predicted similar changes in xylem anatomy (ring width, vessel size and frequency). Most treatment responses entailed changes in plant structure, and were generally consistent with our hypotheses: total-shrub leaf area, shrub basal area, canopy cover, and maximum sapwood-specific branch hydraulic conductivity were more than 2× greater in shrubs in winter-irrigated compared to control plots, while summer irrigation had few effects on these variables. Irrigation in either season did not affect xylem vessel size, but did increase xylem ring width by ~ 2 × and decreased xylem vessel frequency by about half. Anatomical, morphological, and stand-level abundance of A. tridentata appeared much more responsive to irrigation than state changes in gas exchange, particularly when the extra water is received during winter. Thus, it appears for sagebrush that seasonal timing is at least as important as the amount of precipitation, and that responses to changes in precipitation timing occur through changes in carbon allocation more so than changes in leaf-level carbon gain.

The tomato cytosolic fructokinase FRK1 is important for phloem fiber development

Tomato (Solanum lycopersicum) plants have four fructokinase genes, SlFRK1-4. The SlFRK4 is expressed only in pollen whereas the other three are expressed in all plant parts. While SlFRK2 and SlFRK3 are involved in vascular tissue development and affects the shape, size, and cell-wall width of xylem vessels and xylem fibers, the role of SlFRK1 has not been studied previously. The current work investigates the expression of SlFRK1 using transgenic tomato plants expressing the β-glucuronidase reporter gene under the SlFRK1 promoter, as well as the role of SlFRK1 using transgenic plants with antisense suppression of SlFRK1. The SlFRK1 promoter is expressed primarily in vascular tissues and specific suppression of SlFRK1 reduces water transport in stems, but has no other anatomical or phenotypic effects. Combined suppression of SlFRK1 and SlFRK2 severely inhibited plant growth and an anatomical analysis revealed a reduction in secondary xylem area and distorted phloem fibers characterized by thin cell walls and reduced lignification. The results suggest that SlFRK1 is involved in vascular tissue development and hydraulic conductivity in tomato plants and that SlFRK1 is important for normal phloem fiber development, together with SlFRK2.

Hydraulic and leaf reflectance alterations induced by Clavibacter michiganensis subsp. michiganensis on tomato plants

Clavibacter michiganensis subsp. michiganensis causes bacterial wilt and canker in tomato. A detailed account of pathogen effects on growth and water parameters of affected plants is lacking. Besides, the long latent period of the disease represents a limitation for its management. Our objectives were to determine the physiological and morphological changes induced by this pathogen in tomato, in relation to water stress, and to evaluate two well-known leaf spectral reflectance indices for the diagnosis of this vascular disease before symptoms expression. Experiments were conducted in a greenhouse with pot-grown plants inoculated with a bacterial suspension (107 CFU/ml); controls were treated with sterile distilled water. Five weeks later plants were harvested and several growth parameters, the number and size of xylem vessels and the hydraulic conductivity of the stems were determined. Inoculated plants were shorter, with smaller leaf area and lower biomass than those of mock-inoculated plants. While the number and hydraulic radius of xylem vessels were not affected, the stem-specific (Ks) and the leaf-specific (KL) conductivity were significantly reduced by inoculation. Wilting of leaves of diseased plants was associated to the reduction of KL. Inoculated plants showed leaf spectral reflectance changes 1 week after inoculation, and 2 weeks before symptom expression, as shown by the index NDWI, an indicator of the water content of the leaves. We conclude that C. michiganensis subsp. michiganensis reduced the growth and altered plant-water relations of tomato plants by reducing the stem hydraulic conductivity. The NDWI index could be used for the early, non- destructive, diagnosis of bacterial canker.

Root xylem characteristics and hydraulic strategies of species co-occurring in semi-arid Australia

Xylem traits such as xylem vessel size can influence the efficiency and safety of water transport and thus plant growth and survival. Root xylem traits are much less frequently examined than those of branches despite such studies being critical to our understanding of plant hydraulics. In this study, we investigated primary lateral and sinker roots of six co-occurring species of semi-arid Australia. Two species are restricted to a floodplain, two were sampled only from the adjacent sand plain, and two species co-occur in both habitats. We assessed root wood density, xylem traits (i.e., vessel diameter, fibre and vessel wall thickness), outer pit aperture diameter and calculated theoretical hydraulic conductivity and vessel implosion resistance. We hypothesized that (1) roots have larger xylem vessel diameters and lower wood density than branches of the same species and that (2) there is an inverse correlation between theoretical sapwood hydraulic conductivity and vessel implosion resistance for roots. Variation in root wood density was explained by variations in xylem vessel lumen area across the different species (r2 = 0.73, p = 0.03), as hypothesized. We rejected our second hypothesis, finding instead that the relationship between theoretical hydraulic conductivity and vessel implosion resistance was not maintained in roots of all of our studied species, in contrast to our previous study of branches from the same species. Xylem traits were found to depend upon habitat and eco-hydrological niche, with the groupings including (i) arid-adapted shrubs and trees with shallow lateral roots (Acacia aneura and Psydrax latifolia), (ii) trees restricted to the floodplain habitat, both evergreen (Eucalyptus camaldulensis) and deciduous (Erythrina vespertilio) and (iii) evergreen trees co-occurring in both floodplain and adjacent sand plain habitats (Corymbia opaca and Hakea sp.).

Effectiveness of peach (Prunus persica) rootstocks for vigor control of plum (P. salicina) scions in relation with xylem vessel size

Effectiveness of peach (<i>Prunus persica</i>) rootstocks for vigor control of plum (<i>P. salicina</i>) scions in relation with xylem vessel size

Three-dimensional Reconstruction of Maize Roots and Quantitative Analysis of Metaxylem Vessels based on X-ray Micro-Computed Tomography

Roots play an essential role in the acquisition of water and nutrients from soils in higher plants. Root anatomical traits have significant effects on root functions, including water transportation within the root system. Traits such as the size of xylem vessels influence axial water flow by controlling water conductance directly. Currently, two-dimensional microscopic images are often used to acquire root anatomical features; however, three-dimensional (3-D) anatomical analysis, which offers information of spatial distribution and connection relationships throughout root tissues, is hardly reported. We performed 3-D reconstruction and visualization of maize (Zea mays L.) root tissues based on X-ray micro-computed tomography and developed an image processing workflow for 3-D segmentation of metaxylem vessels. Three-dimensional quantitative analysis of metaxylem vessels from the first to the sixth whorl of maize crown roots was performed according to this procedure. The performance of this procedudure, bas...

Effectiveness of plant growth regulators on emission reduction of greenhouse gas (Nitrous oxide): An approach for cleaner environment

Global climate change is one of the most prominent and complex environmental problems caused by increasing concentrations of atmospheric greenhouse gases. Rice paddies are an important anthropogenic source of nitrous oxide (N2O), a greenhouse gas approximately 298 times stronger than carbon dioxide. Identifying a suitable mitigation method for N2O emissions from rice agriculture, while maintaining optimum crop productivity is strongly needed. A 2-year field study was conducted on rice to assess N2O emissions in response to the application of different plant growth regulators (PGRs). The PGRs abscisic acid (ABA) and cytozyme (20 mg L−1), kinetin (10 and 20 mg L−1) and wet tea extract (1:20 w/w) along with distilled water as control were sprayed at the tillering and panicle initiation stages of rice. Compared with control treatment, exogenously applied ABA and kinetin (10 and 20 mg L−1) significantly (p < 0.01) reduced N2O emission primarily through regulation of leaf growth, stomatal frequency, and xylem vessel size of rice plants. Cytozyme and kinetin improved the grain yield through efficient photosynthesis. Leaf area index, tiller number, leaf photosynthesis, and transpiration were found to be directly associated (p < 0.05) with N2O emission. The PGRs regulated N2O transport by manipulating anatomical and physiological processes. Kinetin (10 mg L−1) application can be suitable for N2O emission reduction coupled with an increase in economic productivity. Considering the effect of N2O on global climate change, such mitigation measures may be effective for sustaining a cleaner environment for global community.

Effect of foliar application of plant growth regulators on nitrous oxide (N2O) emission and grain yield in wheat

Agricultural soils are the major source of global nitrous oxide (N2O) emission, and more than two thirds of N2O emission originate from soil. Recent studies have identified that green plants contribute to transport of N2O to the atmosphere. We investigated the effects of foliar application of plant growth regulators (PGRs) and growth stimulating chemicals on N2O emission and wheat grain yield for 2years. The PGRs' abscisic acid (ABA) and cytozyme (20mgL-1), kinetin (10 and 20mg L-1) and wet tea extract (1:20 w/w) along with distilled water as control were sprayed on wheat canopy at the tillering and panicle initiation stages. Our results showed that cytozyme and tea extract enhanced the plant dry biomass over control. Kinetin (10 and 20mgL-1) and cytozyme increased the plant photosynthetic rate and photosynthate partitioning towards the developing grain. ABA (20mgL-1) and kinetin (10 and 20mgL-1) reduced the N2O emission over control primarily through regulation of leaf growth, stomatal density and xylem vessel size. Leaf area, stomatal density and xylem vessel size were found to be associated with N2O transport and emission. We concluded that use of ABA and kinetin can reduce N2O emissions without any impact on wheat grain yield.

The effect of preservatives on water balance in cut clematis flowers

ABSTRACTA positive water balance is crucial for longevity of cut shoots. When water loss by transpiration exceeds water uptake by cut flowers, wilting symptoms appear. Clematis is a very attractive plant which can be used as a cut flower provided that suitable cultivars are chosen. The vase life of four cultivars tested ranged between 6.7 days and 9.0 days and the standard preservative – 200 mg·dm−3 8-hydroxyquinoline citrate (8HQC) plus 2% sucrose – prolonged it significantly in two cultivars, while 8HQC alone was efficient in only one. The preservatives delayed reduction in fresh weight. An enhancement of water uptake by the preservatives resulted in prolonged vase life of flowers in two cultivars. However, the effect of preservatives on transpiration was not related to longevity. In addition, longevity did not depend on the xylem vessel size: the cultivar with the longest vase life had the lowest average xylem vessel diameter while the cultivar with the largest vessels had an intermediate vase life. Preservatives did not always affect the number of blockages in xylem appearing during vase life. Generally, the effects of preservatives on the elements of water balance in cut shoots of clematis were not directly related to the postharvest longevity.

Effects of foliar application of plant growth hormone on methane emission from tropical rice paddy

Methane (CH4), a major greenhouse gas, is an important agent of global warming and climate change. While rice agriculture is a major source of anthropogenic CH4 emissions, increased production of rice is essential for ensuring global food security. Mitigating CH4 emissions from rice cultivation with simultaneous increase in grain productivity is a challenging issue. A two-year field study was conducted to investigate the effects of foliar application of plant growth hormones on emission reduction of CH4 from rice paddies. CH4 emission measurement was done from rice plants treated with plant growth hormones – gibberellic acid (GA3), indole-3-acetic acid (IAA), indole-3-butyric acid (IBA) and kinetin (KIN) (in 20mgL−1 concentration) and compared with the emission from untreated/control (CONT) plants. IAA and KIN applications were found to bring about a reduction in the cumulative CH4 emission over control primarily through regulation of leaf growth, stomatal density and xylem vessel size. Foliar application of IAA and KIN enhanced the leaf photosynthetic rate and caused maximum partitioning of photosynthates to the grains as evident from the higher grain filling ability and grain yield. The IAA and KIN treatments improved the thousand grain weight and high density grain (%) in the rice plants resulting in higher grain productivity over untreated plants. It can be concluded that foliar application of indole acetic acid and kinetin can be an effective measure for regulating methane emission from rice paddies coupled with increase in economic yield of the most popular crop of this region.

Freezing resistance in Patagonian woody shrubs: the role of cell wall elasticity and stem vessel size.

Freezing resistance through avoidance or tolerance of extracellular ice nucleation is important for plant survival in habitats with frequent subzero temperatures. However, the role of cell walls in leaf freezing resistance and the coordination between leaf and stem physiological processes under subzero temperatures are not well understood. We studied leaf and stem responses to freezing temperatures, leaf and stem supercooling, leaf bulk elastic modulus and stem xylem vessel size of six Patagonian shrub species from two sites (plateau and low elevation sites) with different elevation and minimum temperatures. Ice seeding was initiated in the stem and quickly spread to leaves, but two species from the plateau site had barriers against rapid spread of ice. Shrubs with xylem vessels smaller in diameter had greater stem supercooling capacity, i.e., ice nucleated at lower subzero temperatures. Only one species with the lowest ice nucleation temperature among all species studied exhibited freezing avoidance by substantial supercooling, while the rest were able to tolerate extracellular freezing from -11.3 to -20 °C. Leaves of species with more rigid cell walls (higher bulk elastic modulus) could survive freezing to lower subzero temperatures, suggesting that rigid cell walls potentially reduce the degree of physical injury to cell membranes during the extracellular freezing and/or thaw processes. In conclusion, our results reveal the temporal-spatial ice spreading pattern (from stem to leaves) in Patagonian shrubs, and indicate the role of xylem vessel size in determining supercooling capacity and the role of cell wall elasticity in determining leaf tolerance of extracellular ice formation.

Xylem morphology determines the drought response of two Arundo donax ecotypes from contrasting habitats

AbstractArundo donax exhibits rapid growth and requires little nutrient input, making it an ideal perennial biomass crop species. However, this growth is accompanied by high rates of water use, potentially restricting the use of A. donax in rain‐fed marginal lands. Here, we investigated the physiological and morphological responses to drought in two ecotypes of A. donax from contrasting habitats: one from an arid environment in Morocco, and the second from a warm humid sub‐Mediterranean climate in central Italy. Prolonged drought resulted in identical reductions in leaf‐level photosynthesis (PN) and stomatal conductance (Gs) in the two ecotypes. However, water deficit induced an increase in xylem vessel diameter in the Moroccan plants, improving the movement of water along the stem, but also likely reducing the resistance to embolism. In contrast, the Italian ecotype reduced xylem vessel area, thus increasing resistance to water transport and xylem embolism. The increased xylem vessel size and associated vulnerability to embolism in the Moroccan plants may have contributed to an increase in the loss of leaf numbers, but also to higher relative water content (RWC) in the remaining leaves in comparison to the Italian ecotype, where a greater number of leaves persisted. Despite the Moroccan plants possessing stems with a lower basal area than their Italian counterparts, both ecotypes exhibited identical leaf to supporting stem area ratios under both control and water deficit conditions. This may account for the similarities observed in leaf area measures of PN and Gs in this and previous studies of different A. donax ecotypes. Selection of A. donax ecotypes on the basis of xylem responses to drought may facilitate the development of varieties suited to arid environments prone to severe drought and wetter habitats where prolonged droughts occur less frequently.

Xylem vessel traits predict the leaf phenology of native and non‐native understorey species of temperate deciduous forests

Summary Non‐native understorey woody species have been shown to extend leaf display and inhabit vacant phenological niches in early spring and late autumn when growing with native counterparts in temperate deciduous forests across the world. Despite the potential competitive advantages, extended leaf duration also subjects non‐native species to possible hydraulic risks associated with maintaining leaves during periods of increased frost probability. It remains unclear how non‐native species are able to maintain xylem function within this context. Leaf phenology in temperate deciduous trees has been shown to be a function of xylem anatomy, with earlier bud break associated with smaller xylem vessels due to the presumed resistance of smaller vessels to freezing‐induced cavitation. We examined relationships between leaf phenology and xylem vessel traits across 82 native and non‐native understorey deciduous woody species common to eastern U.S. deciduous forests. We hypothesized that non‐native species possess xylem vessel traits associated with maximum hydraulic safety during frost‐prone spring and autumn leaf display without compromising rapid growth rate. Larger metaxylem vessels in non‐native species were associated with both faster spring growth and delayed autumn leaf fall compared to native species. Non‐native species also had smaller latewood vessel diameter, latewood vessel area percentage and a higher proportion of solitary vessels in the entire secondary xylem cross section compared to natives, potentially increasing their resistance to freezing‐ and/or drought‐induced cavitation in autumn, thus allowing for delayed autumn leaf fall. Native and non‐native species exhibited similar dates of spring bud break and leaf emergence, consistent with similar xylem vessel size and vessel area percentage within metaxylem and earlywood. Within both groups, species with earlier bud and leaf emergence had a higher total percentage of vessel area within metaxylem and earlywood. This suggests understorey species need sufficient water to support their early spring growth at the risk of freezing‐induced cavitation. Our study suggests xylem vessel properties, along with cross‐sectional spatial xylem vessel distribution, reflect the capacity of non‐native plants to thrive in a new environment and deepen our understanding of the physiological mechanisms of successful invasions of non‐native understorey woody plant species.

Comparing morphological, chemical and anti-diabetic characteristics of Puerariae Lobatae Radix and Puerariae Thomsonii Radix

Ethnopharmacological relevancePuerariae Lobatae Radix (PLR) and Puerariae Thomsonii Radix (PTR) are traditional Chinese medicines used for the treatment of diabetes and cardiovascular diseases. These two herbs are used interchangeably in clinical practice, even though they possess significantly different chemical profiles. In the case of Pueraria species, the misidentification is related to the multiple Chinese common names in clinical practice and variable pharmaceutical Latin names in different versions of the Pharmacopoeia of the People׳s Republic of China. In addition, there is lack of evidence demonstrating how the differences in the chemical profile would impact on the pharmacological activity of the two herbs. Therefore, the aim of this study was to compare the microscopic, phytochemical profiles and anti-diabetic activity of PLR and PTR so that the two species can be differentiated. Materials and methodsThe microscopic characteristics of the PLR and PTR were observed and measured by an optical microscope. The major compounds were quantified by ultra-performance liquid chromatography (UPLC) and total flavonoid content (TFC) colorimetric assay. The free radical scavenging capacity was assessed by 2,2-diphenyl-2-picrylhydrazyl (DPPH) antioxidant assays. Anti-diabetic activity was determined by the inhibition of porcine pancreatic α-amylase and rat intestinal α-glucosidase activities. ResultsMicroscopic results illustrated that the size of xylem vessels (PLR: 0.1390±0.0184mm; PTR: 0.0471±0.0109mm), number of fibre per bundle (PLR: 32.6800±2.8780; PTR: 16.5900±0.9982) and the size of fibre (PLR: 0.0075±0.0003mm2; PTR: 0.0025±0.0002mm2) in PLR were significantly greater than that in PTR (p<0.01). PLR possessed a significantly lower total starch content (PLR: 0.5288±1.2559mg starch/g DM; PTR: 76.7954±2.9905mg starch/g DM) and total dietary fibre content (PLR: 4.2886±0.3466g/100g DM; PTR: 12.4148±0.4541g/100g DM) as compared to PTR. Isoflavonoids including puerarin, daidzin, genistin and daidzein were the major chemical constituents in both species. However, the average content of puerarin in PLR was found to be eleven times greater than that in PTR. Furthermore, the TFC, DPPH free radical scavenging capacity, anti-α-amylase and anti-α-glucosidase in the PLR extracts were 4.42, 4.91, 3.10 and 4.22 times greater than in the PTR extracts. ConclusionsThis study provides a comprehensive investigation on the two medicinal valuable Pueraria species and allows differences to be ascertained. This information can be used to update monographs which will help practitioners and dispensers differentiate the herbs. Further study on the interchangeable use of PLR and PTR in clinical practice is urgently warranted.

Root Morphology and Anatomy of Field-Grown Erianthus arundinaceus

Erianthus species are perennial C4 grasses with such high biomass productivity and high tolerance to environmental stresses that they can be grown in marginal land to supply raw material for cellulosic bioethanol. Because high biomass production and strong tolerance to environmental stresses might be based on their large and deep-root system, we closely examined the morphology and anatomy of roots in first-year seedlings of field-grown Erianthus arundinaceus. The deep-root system of E. arundinaceus consists of many nodal roots growing with steep growth angles. Diameter of nodal roots with large variations (0.5 - 5 mm) correlates with the size and number of large xylem vessels. The microscopic observation shows that the nodal roots with dense root hairs developed soil sheath, hypodermis with lignified sclerenchyma in the outer cortex, and aerenchyma in the mid-cortex. In addition, starch grains were densely accumulated in the stele of nodal roots in winter. In the first year, E. arundinaceus developed less lateral roots than other reported grass species. The lateral roots formed a large xylem vessel in the center of the stele and no hypodermis in the outer cortex. Morphology and anatomy of E. arundinaceus root were discussed with reference to strong tolerance to environmental stresses.

Adaptive components of tolerance to salinity in a saline desert grass Lasiurus scindicus Henrard

AbstractFive differently adapted natural populations of the native salt desert grass Lasiurus scindicus Henrard from Lesser Cholistan Desert (Pakistan) in South Punjab of east central Pakistan, were evaluated to examine their mechanism of adaptation to saline stress based on some key morpho–anatomical and physiological characteristics. Five ecotypes were collected from one saline site, two moderately saline sites, and two highly saline sites. Anatomical adaptations in each ecotype critically supported the physiological, but the adaptations were of specific nature depending on the type of each site's normal habitat conditions. Higher salinities resulted in increased Na+, Cl−, Mg2+, Ca2+ and K+ content in root and shoot. At root level, some specific structural modifications like increased sclerification in cortical and pith regions, endodermal thickness, and number and size of xylem vessels are vital for water conservation under osmotic stress. Several characteristics were promising for increasing the plants ability to deal with osmotic stress, including at the stem level, increased sclerification, stem area, cortical region thickness and vascular bundle area, and at the leaf level, significant structural modifications such as leaf thickness, epidermal thickness, sclerenchymatous area, cortical area, metaxylem area and bulliform cell area were promising. All these may contribute towards water conservation, which ultimately account for ecotype survival under saline–induced physiological droughts.

Functional water flow pathways and hydraulic regulation in the xylem network of Arabidopsis.

In vascular plants, the xylem network constitutes a complex microfluidic system. The relationship between vascular network architecture and functional hydraulic regulation during actual water flow remains unexplored. Here, we developed a method to visualize individual xylem vessels of the 3D xylem network of Arabidopsis thaliana, and to analyze the functional activities of these vessels using synchrotron X-ray computed tomography with hydrophilic gold nanoparticles as flow tracers. We show how the organization of the xylem network changes dynamically throughout the plant, and reveal how the elementary units of this transport system are organized to ensure both long-distance axial water transport and local lateral water transport. Xylem vessels form distinct clusters that operate as functional units, and the activity of these units, which determines water flow pathways, is modulated not only by varying the number and size of xylem vessels, but also by altering their interconnectivity and spatial arrangement. Based on these findings, we propose a regulatory model of water transport that ensures hydraulic efficiency and safety.

Root Anatomical Traits and Their Possible Contribution to Drought Tolerance in Grain Legumes

Legumes are mostly grown rainfed and are exposed to various types of drought ranging from terminal drought to intermittent drought. The objective of this study was to compare the root anatomy of six major legume crops in relation to their drought adaptation strategies. Plants of chickpea (Cicer arietinum L.), groundnut (Arachis hypogaea L.), pigeonpea (Cajanus cajan [L.] Millsp.), cowpea (Vigna unguiculata L. walp.), soybean (Glycine max [L.] Merr.) and common bean (Phaseolus vulgaris L.) were grown along with pearl millet (Pennisetum glaucum [L.] R. Br.) in a Vertisol field during the rainy season of 2010. Four root segments from 35-day-old plants of each crop species were collected, 10 cm from the root tip and used for making transverse sections. These root segments were thinner in both groundnut and pigeonpea than in other legumes but similar to those of pearl millet. Soybean and pigeonpea had a relatively thinner cortex than the other legumes. Xylem vessel size and the numbers were apparently the most discriminating traits of legumes. Pigeonpea is equipped to conduct small quantities of water per unit time with a few narrow xylem vessels and that explains the conservative early growth of pigeonpea. Chickpea and cowpea showed moderate xylem passage per root indicating that they are capable of absorbing water moderately and are well equipped for regular drought episodes. The development of cortical and stele tissue and their proportion is markedly influenced by moisture availability to the root system.

Variation in wood density and anatomy in a widespread mangrove species

Wood density is an important plant trait that influences a range of ecological processes, including resistance to damage and growth rates. Wood density is highly dependent on anatomical characteristics associated with the conductive tissue of trees (xylem and phloem) and the fibre matrix in which they occur. Here, we investigated variation in the wood density of the widespread mangrove species Avicennia marina in the Exmouth Gulf in Western Australia and in the Firth of Thames in New Zealand. We assessed how variation in xylem vessel size, fibre wall thickness and proportion of phloem within the wood contributed to variation in wood density and how these characteristics were linked to growth rates. We found the wood density of A. marina to be higher in Western Australia than in New Zealand and to be higher in taller seaward fringing trees than in scrub trees growing high in the intertidal. At the cellular level, high wood density was associated with large xylem vessels and thick fibre walls. Additionally, wood density increased with decreasing proportions of phloem per growth layer of wood. Tree growth rates were positively correlated with xylem vessel size and wood density. We conclude that A. marina can have large xylem vessel sizes and high growth rates while still maintaining high wood density because of the abundance and thickness of fibres in which vessels are found.