Xylem Vessel Area Research Articles

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.

Effects of high salinity on physiological and anatomical indices in the early stages of Populus euphratica growth

The effects of salinity stress on stomatal aperture and density, xylem vessels, the activities of antioxidant enzymes, such as superoxide dismutase (SOD) and peroxidase (POD), and xylem embolism (PLC values) in Populus euphratica in the arid ecosystem of China. Pot experiment was conducted at different concentrations of salt (50, 100, 150, and 200 mM NaCl) contained in the irrigation water used for 3 months The POD activity increased with the increase in the severity of NaCl stress, but SOD activity was varied at different levels of salt. Results indicated that salt treatment reduced stomatal aperture and leaf photosynthetic capacity. However, the significant reduction in the stomatal area, in the length of stomata openings and an increase in stomata density were noticed. Salinity stress affected water transport, which reduced native PLC value, whereas xylem vessel area was also decreased. Presented results open the possibility of genetic improvement for selecting the high salt-tolerant of Populus spp.to reclaim salinized lands.

INTERACTIVE EFFECTS OF KINETIN AND SPERMINE ON ANATOMICAL ADAPTATIONS AND PRODUCTIVITY TO SEAWATER SALINITY IN WHEAT

A pot experiment was conducted to evaluate the beneficial effect of grain presoaking in kinetin (0.1mM), spermine (0.3mM) or their interaction on wheat plants (Triticum aestivum L.) variety Sakha 93 on some anatomical features in flag leaf as and pedicle of main shoot as well as grain yield at ear emergence (after 65 days from sowing) by measuring leaf thickness, ground tissue thickness, number of hairs, meta-xylem vessel area, xylem vessel area, phloem tissue area, vascular bundle tissues area, number of motor cells as well as number of opened and closed stomata on both upper and lower epidermis and some anatomical features of peduncle (peduncle diameter, tracheids area, meta-xylem vessel area, xylem area, phloem area, vascular area, number of vascular bundle as well as opened and closed stomata) of wheat plants. Wheat plants respond to seawater salinity with characteristic modifications in their anatomy to counter the ill effect of seawater stress. Therefore, Irrigation of wheat plants with seawater caused significant increase in leaf and ground tissue thickness in flag leaves as well as meta-xylem vessel area, xylem vessel area, vascular bundle area in flag leaf and peduncle of main shoot of wheat plants. However, irrigation of wheat plants with seawater decreased phloem area in flag leaves and peduncle of the main shoot of wheat plants. The application of kinetin, spermine or their interaction induced some modifications in the anatomical features of the flag leaf and peduncle of the main shoot which appeared to be an adaptive response to salinity stress caused by seawater. Furthermore, grain priming with kinetin, spermine or their interaction increased phloem thickness in both leaf and peduncle of main shoot and consequently induced rapid rate of translocation of photo-assimilates from flag leaf to developing grains in spikes and consequently increase productivity of wheat plants irrigated by seawater.

Azospirillum brasilense mitigates water stress imposed by a vascular disease by increasing xylem vessel area and stem hydraulic conductivity in tomato

Water stress, with its negative consequences on plant growth and survival, can be mitigated by Azospirillum brasilense inoculation. In tomato, A. brasilense delays wilting caused by a vascular pathogen, Clavibacter michiganensis subsp. michiganensis, by yet unknown mechanisms. We studied morphological, anatomical and physiological changes induced by A. brasilense in tomato that relate to water stress tolerance, which could explain the deferral in symptom expression. For this purpose, tomato seeds were treated or not with A. brasilense BNM65, and 5 weeks later plants were challenged with C. michiganensis subsp. michiganensis or mock inoculated with water. There was a large growth promotion associated to Azospirillum: treated plants had higher total biomass and leaf area. In relation to water stress tolerance, Azospirillum treated plants had larger xylem vessel area, higher stem specific hydraulic conductivity, thicker stems, and lower shoot/root dry matter and specific leaf area. These changes were opposite to those induced by C. michiganensis subsp. michiganensis. We conclude that A. brasilense favoured a better adjustment of plant-water relations by several mechanisms, and thus, transitorily alleviated symptoms expression of a vascular disease.

Heterosis for water uptake by maize (Zea mays L.) roots under water deficit: responses at cellular, single-root and whole-root system levels

To examine the potential heterosis for water uptake by maize roots, the hydraulic properties of roots in the F1 hybrid (Hudan 4) were compared with those of its inbred parents (♂ 478 and ♀ Tian 4) at cellular, single-root and whole-root system levels under well-watered and water-deficit conditions. The cell hydraulic conductivity (Lp c) decreased under water deficit, but the Lp c of the F1 was higher than that of its inbred parents with or without stress from water deficit. Marked reductions in Lp c were observed following Hg2+ treatment. The hydrostatic hydraulic conductivity of single roots (hydrostatic Lp sr) varied among genotypes under the two water treatments, with the highest in the F1 and the lowest in ♂ 478. Radial hydraulic conductivity (radial Lp sr) and axial hydraulic conductance (L ax) of the three genotypes varied similarly as Lp sr . The variations in hydraulic parameters were related to root anatomy. Radial Lp sr was negatively correlated with the ratio of cortex width to root diameter (R 2=−0.77, P<0.01), whereas L ax was positively correlated with the diameter of the central xylem vessel (R 2=0.75, P<0.01) and the cross-sectional area of xylem vessels (R 2=0.93, P<0.01). Hydraulic conductivity (Lp wr) and conductance (L wr) of the whole-root system followed the same trend under the two water treatments, with the highest values in the F1. The results demonstrated that heterosis for water uptake by roots of the F1 occurred at cellular, single-root and whole-root system levels under well-watered and water-deficit conditions.

Photosynthetic and wood anatomical responses of Tamarixafricana Poiret to water level reduction after short‐term fresh‐ and saline‐water flooding

AbstractIn the Mediterranean basin, Tamarix spp. constitute important populations along rivers and sea coasts, and might be primarily subjected to water level fluctuations and salinization, as a consequence of global climate change. Here, we analyze leaf gas exchange and xylem anatomy during a water level decrease below the soil surface after short‐term flooding with fresh‐ and saline‐water (200 mM) in order to predict Tamarixafricana Poiret responses under future environmental conditions. Fresh‐water level reduction negatively affected stomatal conductance (−56.3 %), but only when water decreased to the lowest level (15 cm below the soil surface). No effects on assimilation rates and xylem vessel dimensions occurred. Under saline conditions, the rate of the water level decrease was lower compared to the non‐saline treatment, as stomatal conductance was negatively affected by salinity (−59.5 %) and significantly declined over time. Moreover, decreases in mean xylem vessel area (−51.3 %), assimilation rates (−52.2 %) and stomatal conductance (−76.0 %) were also observed compared to the control, indicating both an osmotic stress and a toxic effect of NaCl on leaf gas exchange. These leaf responses were probably induced by greater belowground‐root salt absorption and transport compared to previous flooding conditions, as confirmed by the increase in salt excretion (+473.2 %). The results emphasize the survival risk of Tamarix spp. to water level variation under both saline and non‐saline conditions, and the need of management practices focused on the conservation of these populations.

Developmental Reaction Norms for Water Stressed Seedlings of Succulent Cacti

Succulent cacti are remarkable plants with capabilities to withstand long periods of drought. However, their adult success is contingent on the early seedling stages, when plants are highly susceptible to the environment. To better understand their early coping strategies in a challenging environment, two developmental aspects (anatomy and morphology) in Polaskia chichipe and Echinocactus platyacanthus were studied in the context of developmental reaction norms under drought conditions. The morphology was evaluated using landmark based morphometrics and Principal Component Analysis, which gave three main trends of the variation in each species. The anatomy was quantified as number and area of xylem vessels. The quantitative relationship between morphology and anatomy in early stages of development, as a response to drought was revealed in these two species. Qualitatively, collapsible cells and collapsible parenchyma tissue were observed in seedlings of both species, more often in those subjected to water stress. These tissues were located inside the epidermis, resembling a web of collapsible-cell groups surrounding turgid cells, vascular bundles, and spanned across the pith. Occasionally the groups formed a continuum stretching from the epidermis towards the vasculature. Integrating the morphology and the anatomy in a developmental context as a response to environmental conditions provides a better understanding of the organism's dynamics, adaptation, and plasticity.

Sap flow in ‘Hass’ avocado trees on two clonal rootstocks in relation to xylem anatomy

The rates of sap flow and xylem vessel features were studied in two-year-old nongrafted and grafted avocado ( Persea americana Mill.) trees. Daily sap flow rates were measured with heat and balance stem gauges in clonal Duke 7 (D7) and Toro Canyon (TC) trees and ‘Hass’ clonal scions grafted onto clonal D7 (H/D7) and TC (H/TC) rootstocks. Vessel features as size, number and total vessel area were determined histologically in the stem of the scion and rootstock and the roots of the grafted trees. Significant differences in the sap flow rate were found among the rootstocks, where D7 had a 29% higher sap flow rate than did TC (grafted and nongrafted trees). There were no differences among xylem vessel features in the stems of any of the varieties. However in the roots, D7 had wider and fewer vessels then TC do. Also, D7 had a 19% higher total vessel area than TC. These results suggest that the differences in water consumption of ‘Hass’ on different rootstocks may be associated with differences in the efficiency of the roots to absorb water across conductive tissue which may be linked to differences in the area of xylem vessels in the root.

Temperature effects on wood anatomy, wood density, photosynthesis and biomass partitioning of Eucalyptus grandis seedlings

Wood density, a gross measure of wood mass relative to wood volume, is important in our understanding of stem volume growth, carbon sequestration and leaf water supply. Disproportionate changes in the ratio of wood mass to volume may occur at the level of the whole stem or the individual cell. In general, there is a positive relationship between temperature and wood density of eucalypts, although this relationship has broken down in recent years with wood density decreasing as global temperatures have risen. To determine the anatomical causes of the effects of temperature on wood density, Eucalyptus grandis W. Hill ex Maiden seedlings were grown in controlled-environment cabinets at constant temperatures from 10 to 35 degrees C. The 20% increase in wood density of E. grandis seedlings grown at the higher temperatures was variously related to a 40% reduction in lumen area of xylem vessels, a 10% reduction in the lumen area of fiber cells and a 10% increase in fiber cell wall thickness. The changes in cell wall characteristics could be considered analogous to changes in carbon supply. Lumen area of fiber cells declined because of reduced fiber cell expansion and increased fiber cell wall thickening. Fiber cell wall thickness was positively related to canopy CO2 assimilation rate (Ac), which increased 26-fold because of a 24-fold increase in leaf area and a doubling in leaf CO2 assimilation rate from minima at 10 and 35 degrees C to maxima at 25 and 30 degrees C. Increased Ac increased seedling volume, biomass and wood density; but increased wood density was also related to a shift in partitioning of seedling biomass from roots to stems as temperature increased.

Canopy development and hydraulic function in Eucalyptus tereticornis grown in drought in CO2-enriched atmospheres.

We report on the relationship between growth, partitioning of shoot biomass and hydraulic development of Eucalyptus tereticornis Sm. grown in glasshouses for six months. Close coordination of stem vascular capacity and shoot architecture is vital for survival of eucalypts, especially as developing trees are increasingly subjected to spasmodic droughts and rising atmospheric CO2 levels. Trees were exposed to constant soil moisture deficits in 45 L pots (30-50% below field capacity), while atmospheric CO2 was raised to 700 μL CO2 L-1 in matched glasshouses using a hierarchical, multi-factorial design. Enrichment with CO2 stimulated shoot growth rates for 12-15 weeks in well-watered trees but after six months of CO2 enrichment, shoot biomasses were not significantly heavier (30% stimulation) in ambient conditions. By contrast, constant drought arrested shoot growth after 20 weeks under ambient conditions, whereas elevated CO2 sustained growth in drought and ultimately doubled the shoot biomass relative to ambient conditions. These growth responses were achieved through an enhancement of lateral branching up to 8-fold due to CO2 enrichment. In spite of larger transpiring canopies, CO2 enrichment also improved the daytime water status of leaves of droughted trees. Stem xylem development was highly regulated, with vessels per unit area and cross sectional area of xylem vessels in stems correlated inversely across all treatments. Furthermore, vessel numbers related to the numbers of leaves on lateral branches, broadly supporting predictions arising from Pipe Model Theory that the area of conducting tissue should correlate with leaf area. Diminished water use of trees in drought coincided with a population of narrower xylem vessels, constraining hydraulic capacity of stems. Commensurate with the positive effects of elevated CO2 on growth, development and leaf water relations of droughted trees, the capacity for long-distance water transport also increased.

Response of alfalfa to bidirectional selection for root bark area and xylem vessel diameter

Development of alfalfa [Medicago sativa L. ssp. sativa and M. sativa ssp. falcata (L.) Arcangeli] germplasm with contrasting root bark area and xylem vessel area could be useful to evaluate relationships between anatomical root characteristics and plant functions such as drought tolerance. This study was conducted to determine the response of alfalfa to bidirectional selection for root bark area and xylem vessel area of the largest vessels as viewed in cross section. Bidirectional selection for large and small root bark area and for large and small xylem vessel area was conducted for two cycles. Selection for high root bark area resulted in an increase in root bark area in cycle one (C1), but no further response occurred in cycle two (C2). Response to selection for low bark area resulted in no response in the C1, but a response occurred in the C2. Response to selection for large xylem vessel area increased xylem area in the C1 but no further response occurred in the C2. There was no response to selection for small vessel area in either of the two cycles of selection. Asymmetrical responses to bidirectional selection were found. Root size increased significantly over the two cycles of selection and was probably due to indirect selection for large root size. Key words: Medicago sativa L., ssp. sativa and M. sativa ssp. falcata (L.) Arcangeli, root bark area, xylem vessel diameter

Differences in the photosynthetic response to air humidity among rice varieties with special reference to the xylem-vessel size.

Photosynthetic response to air humidity and leaf characters were observed in fourteen rice varieties. In the indica type varieties the water-conduction system relative to their specific leaf weight and leaf nitrogen content was found to be more developed than in the japonica type varieties. The water-conduction system in the leaf was evaluated based on the ratio of the total cross-sectional area of xylem-vessels at the leaf blade, base to the leaf area (RVA). Higher positive correlations between the photosynthetic rates and the RVA, and specific leaf weight were detected under dry than humid air conditions. The present study suggests that RVA may be related to varietal differences in the photosynthetic rate, at least under low air humidity conditions, and that RVA can be used as an index for evaluating the development of the water supply system. The well-developed water conduction svstem of indica type varieties may have evolved as an adaptation to high temperature conditions.