Full Turgor Research Articles

Effects of Pseudomonas fluorescens on the Water Parameters of Mycorrhizal and Non-Mycorrhizal Seedlings of Pinus halepensis

Inoculation of forest seedlings with mycorrhizal fungi and rhizobacteria can improve the morphological and physiological qualities of plants, especially those used for regeneration of arid areas. In this paper, under standard nursery conditions, Aleppo pine seedlings were inoculated with Pseudomonas fluorescens CECT 5281 rhizobacteria. Some of these seedlings were also inoculated with the ectomycorrhizal fungus Pisolithus tinctorius. Five months after the inoculations, we examined the growth, water parameters (osmotic potential at full turgor [Ψπfull], osmotic potential at zero turgor [Ψπ0], and the tissue modulus of elasticity near full turgor [Emax]), mycorrhizal colonisation, and concentration of macronutrients (N, P, K, Ca and Mg) in the seedlings. Subsequently, a trial was conducted to assess the root growth potential. P. fluorescens CECT 5281 decreased the cellular osmotic potential of P. halepensis seedlings but increased its elasticity. P. tinctorius + P. fluorescens caused osmotic adjustment at zero turgor and increased tissue elasticity, which improved tolerance to water stress. All inoculations improved the growth and nutrition of the seedlings but caused non-significant effects on root growth potential. The co-inoculation Pisolithus tinctorius + Pseudomonas fluorescens at the nursery may be a suitable technique for producing improved seedling material for restoration purposes.

Regulatory effects of exogenous gibberellic acid (GA3) on water relations and CO2 assimilation among grapevine (Vitis vinifera L.) cultivars

Different impacts of exogenous gibberellic acid (GA3) on water relation and CO2 gas exchange in grapevine leaves were studied on four varieties belong to various ecogeographical groups. GA3 treatment resulted in increasing cell wall rigidity in some cultivars and affected the linear correlation between elasticity modulus (‘ɛ’) and relative water content at the turgor loss point (RWCTLC). The response of cultivar ‘Riesling’ agreed with the hypothesis; GA treatment resulted in increasing ‘ɛ’ values (‘ɛ’>12MPa), indicating decreased cell wall elasticity. According to pressure–volume analysis, osmotic potential at full turgor (Π100) in treated ‘Sauvignon Blanc’ vines was higher compared to the controls. Results of analysis demonstrated that the four varieties showed a negative linear correlation between apoplastic water content (AWSD%) and leaf water potential at the turgor loss point (ΨTLP) and a positive linear correlation between AWSD% and RWCTLP. Values of Ci and PN showed a positive exponential correlation; Ci values increased parallel with increasing net CO2 assimilation in a range between 10 and 24Pa of Ci both in control and treated vines. In each cultivar, intrinsic water use efficiency (WUEi) increased at reduced stomatal conductance. GA3 treatment resulted in favourable values of WUEi as expected for cultivar ‘Kadarka’ (group of convarietas pontica). WUEi was significantly (P<0.05) lower in the GA3 treated vines compared to the controls in most of the varieties irrespective of different ecogeographical groups.

Differences in membrane selectivity drive phloem transport to the apoplast from which maize florets develop.

Floral development depends on photosynthetic products delivered by the phloem. Previous work suggested the path to the flower involved either the apoplast or the symplast. The objective of the present work was to determine the path and its mechanism of operation. Maize (Zea mays) plants were grown until pollination. For simplicity, florets were harvested before fertilization to ensure that all tissues were of maternal origin. Because sucrose from phloem is hydrolysed to glucose on its way to the floret, the tissues were imaged and analysed for glucose using an enzyme-based assay. Also, carboxyfluorescein diacetate was fed to the stems and similarly imaged and analysed. The images of live sections revealed that phloem contents were released to the pedicel apoplast below the nucellus of the florets. Glucose or carboxyfluorescein were detected and could be washed out. For carboxyfluorescein, the plasma membranes of the phloem parenchyma appeared to control the release. After release, the nucellus absorbed apoplast glucose selectively, rejecting carboxyfluorescein. Despite the absence of an embryo, the apoplast below the nucellus was a depot for phloem contents, and the strictly symplast path is rejected. Because glucose and carboxyfluorescein were released non-selectively, the path to the floret resembled the one later when an embryo is present. The non-selective release indicates that turgor at phloem termini cannot balance the full osmotic potential of the phloem contents and would create a downward pressure gradient driving bulk flow toward the sink. Such a gradient was previously measured by Fisher and Cash-Clark in wheat. At the same time, selective absorption from the apoplast by the nucellar membranes would support full turgor in this tissue, isolating the embryo sac from the maternal plant. The isolation should continue later when an embryo develops.

Influence of water stress and abscisic acid on free proline accumulation in barley leaves

Rapid accumulation of free proline was found in barley leaves under conditions of osmotic stress at the level of -8.3 bars, but not before 9 days of its duration. The threshold value of osmotic stress for the start of a rapid accumulation of proline was about -6 bars. The excised leaves of barley subjected to water stress by wilting accumulated free proline more rapidly. In the course of 24 hours free proline content increased about 30-fold, while the water content in the leaves decreased 3-fold only. We found also that excised barley leaves with full turgor treated with abscisic acid (10&lt;sup&gt;-4&lt;/sup&gt; M) accumulated free proline as early as after 3 hours and subsequently after 24 hours free proline content increased 10-fold.

Effects of Increasing Salinity Stress and Decreasing Water Availability on Ecophysiological Traits of Quinoa (Chenopodium quinoa Willd.) Grown in a Mediterranean‐Type Agroecosystem

AbstractQuinoa is a native Andean crop for domestic consumption and market sale, widely investigated due to its nutritional composition and gluten‐free seeds. Leaf water potential (Ψleaf) and its components and stomatal conductance (gs) of quinoa, cultivar Titicaca, were investigated in Southern Italy, in field trials (2009 and 2010). This alternative crop was subjected to irrigation treatments, with the restitution of 100 %, 50 % and 25 % of the water necessary to replenish field capacity, with well water (100 W, 50 W, 25 W) and saline water (100 WS, 50 WS, 25 WS) with an electrical conductivity (ECw) of 22 dS m−1. As water and salt stress developed and Ψleaf decreased, the leaf osmotic potential (Ψπ) declined (below −2.05 MPa) to maintain turgor. Stomatal conductance decreased with the reduction in Ψleaf (with a steep drop at Ψleaf between −0.8 and 1.2 MPa) and Ψπ (with a steep drop at Ψπ between −1.2 and −1.4 MPa). Salt and drought stress, in both years, did not affect markedly the relationship between water potential components, RWC and gs. Leaf water potentials and gs were inversely related to water limitation and soil salinity experimentally imposed, showing exponential (Ψleaf and turgor pressure, Ψp, vs. gs) or linear (Ψleaf and Ψp vs. SWC) functions. At the end of the experiment, salt‐irrigated plants showed a severe drop in Ψleaf (below −2 MPa), resulting in stomatal closure through interactive effects of soil water availability and salt excess to control the loss of turgor in leaves. The effects of salinity and drought resulted in strict dependencies between RWC and water potential components, showing that regulating cellular water deficit and volume is a powerful mechanism for conserving cellular hydration under stress, resulting in osmotic adjustment at turgor loss. The extent of osmotic adjustment associated with drought was not reflected in Ψπ at full turgor. As soil was drying, the association between Ψleaf and SWC reflected the ability of quinoa to explore soil volume to continue extracting available water from the soil. However, leaf ABA content did not vary under concomitant salinity and drought stress conditions in 2009, while differing between 100 W and 100 WS in 2010. Quinoa showed good resistance to water and salt stress through stomatal responses and osmotic adjustments that played a role in the maintenance of a leaf turgor favourable to plant growth and preserved crop yield in cropping systems similar to those of Southern Italy.

Effects of inoculation with Azospirillum brasilense on the quality of Prosopis juliflora seedlings

Inoculation of mycorrhizal fungi and rhizobacteria in plants can improve their growth and physiological status, which could be particularly important for agricultural and forestry plants used for the revegetation of arid areas. Prosopis juliflora is a forest pioneer species that is drought resistant and has multiple uses (fodder, shade and shelter for livestock; timber and firewood, live fences and windbreaks in agroforestry systems). Azospirillum brasilense is a rhizobacterium that improves the growth of many agricultural crops. The hypothesis of this study was that P. juliflora seedlings produced in the nursery can respond positively to inoculation with A. brasilense CECT 590. Five months after inoculation, we examined the growth, water relations (osmotic potential at full turgor, osmotic potential at zero turgor, and the modulus of elasticity at full turgor), and concentration and content of macronutrients (N, P, K, Ca and Mg) in the seedlings. Subsequently, a trial was conducted to analyse root growth potential. A. brasilense CECT 590 inoculation caused an osmotic adjustment in P. juliflora seedlings but decreased the elasticity of the cell walls. Inoculation with A. brasilense CECT 590 significantly improved plant growth due in part to an increase of N concentration in the seedlings. A. brasilense CECT 590 inoculation also caused an increase in the root growth potential. The increased growth of P. juliflora seedlings inoculated with A. brasilense was probably caused by more than one mechanism. Inoculation with A. brasilense at the nursery may be a suitable technique for producing improved seedling material for restoration purposes.

Applications of xerophytophysiology in plant production—LED blue light as a stimulus improved the tomato crop

Recent research using Arabidopsis has shown that blue light stimulates the plant through the receptor protein and induces regulations physiologically and morphologically. It is important to know whether the theory can be used in food crop production. In the present study blue light emitted from light-emitting diodes (LED) was used as a stimulus to tomato crop canopy after sunset for 2h to induce xerophytophysiological regulations. Blue (450nm), white and red (660nm) LED lamps, all with a properties of 0.48W, 24V, and 45μmolm2s−1 at 10cm over the lamp, were compared with non-illumination control. A 2×4 two factor experiment was conducted in a randomized split block design with the two cultivars as the main block. Results showed that the osmotic potential in the symplasm at full turgor was lower and the leaf turgor potential at full turgor was higher in tomato leaves in blue light treatment. The water fraction in the symplasm in the leaf was larger or the apoplastic water fraction was smaller in leaf of blue light irradiated plants. Both osmotic potential and relative water content at the point of incipient plasmolysis were lower in tomato leaves in blue light treatment. More leaf water was lost by stomatal transpiration and less leaf water was lost by cuticular transpiration in leaves of blue light treated tomato plants. Fruit color was improved and redder in blue light treatment. Fruit yield was increased by all light illumination treatments. The damage of fruit caused by Helicoverpa armigera worms was more severely in red light treatment and less severely in blue and white light treatments compared with the control. The leaf blight index was lower in blue and white light illumination treatments than the red light treatment and the control. Both cultivars showed LED illumination responses similar to each other although fruit yield was lower and leaf blight was severer in ‘Baiju’ than in ‘Myoko’. In conclusion, illumination treatment with blue light from LED as a stimulus was effective in fruit yield increase and quality improvement as well as improvement in disease resistance of the tomato crop.

A comparison of pressure–volume curves with and without rehydration pretreatment in eight woody species of the semiarid Loess Plateau

Pressure–volume (P–V) curves are frequently used to analyze water relation properties of woody plants in response to transpiration-induced tissue water loss. In this study, P–V analyses were conducted on eight woody species growing in the semiarid Loess Plateau region of China during a relatively dry summer season using both the recently recommended instantaneous measurement and the traditional method with rehydration pretreatment. Generally, P–V-derived parameters in this study reflected conditions in a dry growth environment. Species-specific differences were also found among P–V parameters, suggesting each species uses different mechanisms to respond to drought. Based on the results from instantaneous measurements, a descending sequence for drought tolerance ranked by water potentials at the turgor loss point (Ψtlp) was Rosa hugonis > Syringa oblata = Armeniaca sibirica > Caragana microphylla > Pyrus betulaefolia > Acer stenolobum > Quercus liaotungensis > Robinia pseudoacacia. The first five species also showed lower levels of osmotic potential at full turgor (Ψ π sat ) and higher symplastic osmotic solute content per dry weight, suggesting they possess advantages in osmotic adjustment. Also, this study supports previous reports noting rehydration pretreatment resulted in shifts in P–V parameters. The magnitude of the shifts varied with species and water conditions. The effect of rehydration was stronger for species with higher drought tolerance or subjected to the influence of drought. Differences in the parameters among species were mitigated as a result of rehydration. Those with a lower Ψtlp or midday water potential were more deeply affected by rehydration. Application of instantaneous measurements was strongly recommended for proper analysis of P–V curves particularly in arid and semiarid areas.

Estimating contribution of anthocyanin pigments to osmotic adjustment during winter leaf reddening

The association between plant water stress and synthesis of red, anthocyanin pigments in leaves has led some plant biologists to propose an osmotic function of leaf reddening. According to this hypothesis, anthocyanins function as a solute in osmotic adjustment (OA), contributing to depression of osmotic potential (Ψπ) and maintenance of turgor pressure during drought-stressed conditions. Here we calculate the percent contribution of anthocyanin to leaf Ψπ during OA in two angiosperm evergreen species, Galax urceolata and Gaultheria procumbens. Both species exhibit dramatic leaf reddening under high light during winter, concomitant with declines in leaf water potential and accumulation of solutes. Data previously published by the authors on osmotic potential at full turgor (Ψπ,100) of G. urceolata and G. procumbens leaves before and after leaf reddening were used to estimate OA. In vivo molar concentrations of anthocyanin, glucose, fructose, and sucrose measured from the same individuals were converted to pressure equivalents using the Ideal Gas Law, and percent contribution to OA was estimated. Estimated mean OA during winter was −0.7MPa for G. urceolata and −0.8MPa for G. procumbens. In vivo concentrations of anthocyanin (3–10mM) were estimated to account for ∼2% of OA during winter, and comprised <0.7% of Ψπ,100 in both species. Glucose, fructose, and sucrose combined accounted for roughly 50 and 80% of OA for G. urceolata and G. procumbens, respectively, and comprised ∼20% of Ψπ,100. We observed that a co-occurring, acyanic species (Vinca minor) achieved similar OA without synthesizing anthocyanin. We conclude that anthocyanins represent a measurable, albeit meager, component of OA in red-leafed evergreen species during winter. However, due to their low concentrations, metabolic costliness relative to other osmolytes, and striking red color (unnecessary for an osmotic function), it is unlikely that they are synthesized solely for an osmoprotectant role.

The determinants of leaf turgor loss point and prediction of drought tolerance of species and biomes: a global meta‐analysis

Increasing drought is one of the most critical challenges facing species and ecosystems worldwide, and improved theory and practices are needed for quantification of species tolerances. Leaf water potential at turgor loss, or wilting (π(tlp) ), is classically recognised as a major physiological determinant of plant water stress response. However, the cellular basis of π(tlp) and its importance for predicting ecological drought tolerance have been controversial. A meta-analysis of 317 species from 72 studies showed that π(tlp) was strongly correlated with water availability within and across biomes, indicating power for anticipating drought responses. We derived new equations giving both π(tlp) and relative water content at turgor loss point (RWC(tlp) ) as explicit functions of osmotic potential at full turgor (π(o) ) and bulk modulus of elasticity (ε). Sensitivity analyses and meta-analyses showed that π(o) is the major driver of π(tlp) . In contrast, ε plays no direct role in driving drought tolerance within or across species, but sclerophylly and elastic adjustments act to maintain RWC(tlp,) preventing cell dehydration, and additionally protect against nutrient, mechanical and herbivory stresses independent of drought tolerance. These findings clarify biogeographic trends and the underlying basis of drought tolerance parameters with applications in comparative assessments of species and ecosystems worldwide.

Dew, where and when? ‘There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy …’

Dew, where and when? ‘There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy …’

Morphological and physiological differences between bareroot and container Juniperus excelsa seedlings

The effects of stock type on morphological and physiological characteristics were compared in 1 + 0 Crimean juniper (Juniperus excelsa Bieb.) seedlings. In October 2010, the morphological characteristics of both stock types were determined. The physiological condition of both stock types was evaluated by measuring water relation, root growth potential (RGP), and root electrolyte leakage (REL) parameters in seedlings at periodic intervals from October 2010 to April 2011. Container seedlings had greater root collar diameter, higher height, and greater shoot dry weight than bareroot seedlings, but these differences were not significant. However, the shoot-to-root ratios of the container seedlings were significantly lower than those of the bareroot seedlings, but their root dry weights were higher. In both stock types, osmotic potential at turgor loss point, osmotic potential at full turgor, relative water at turgor loss point, apoplastic water fraction, symplastic water at saturated point per dry weight, dry weight fraction, RGP, and REL showed a seasonal variation. The differences between stock types in terms of the water relation parameters were not generally significant. The RGP values of the bareroot seedlings were higher than those of the container seedlings in January, February, and March, but their REL values were generally lower than those of the container seedlings on most lifting dates. For each type of stock, seedlings lifted in January and February had greater stress resistance than seedlings lifted in the autumn or spring. If the weather conditions are suitable, the safe period for lifting and planting is mid-January to mid-March.

Understanding Differential Responses of Grapevine (Vitis vinifera L.) Leaf and Fruit to Water Stress and Recovery Following Re-Watering

Among all fruit crops of horticultural importance, grapevines (Vitis vinifera L.) stand out as the most drought tolerant crop species whose tolerance is credited to their proficiency to recover from water stress in both the natural and vineyard growing conditions. However, information on the recovery responses is relatively scant. Studies were conducted to address this issue using potted vines of the grapevine cultivar, Cabernet Sauvignon, which was subjected to water stress and along with anatomical and ultrastructural characterizations, physiological status was assessed in healthy and water stressed vines, and following recovery via rewatering from the water stressed vines. Water stress induced wilting of leaves, drooping of tendrils, and desiccation followed by abscission of shoot tip leaving behind a brown scar at the shoot apex. The wilted leaves accumulated ABA, which correspondingly reduced stomatal conductance and leaf water potential. Upon re-watering, both these parameters made a recovery with values similar to healthy leaves. Likewise, leaf anatomical features following rewatering resembled to that of healthy leaves. In clusters, water stress caused shriveling of preveraison (unripened) berries, which regained full turgor following water resupply, whereas the postveraison (ripening) berries in the same cluster remained unaffected as evidenced by the presence of viable mesocarp cells and epicuticular wax in the form of platelets. The study revealed that shoot tip with leaf primordia was most sensitive to water stress followed by fully expanded leaves and preveraison berries, whereas the postveraison berries remained unaffected. This information could be valuable to implementing irrigation strategies towards sustaining grape production in existing vineyards experiencing episodic droughts and targeted areas prone to drought.

Durum wheat salt tolerance in relation to physiological, yield and quality characters

Durum wheat (Triticum turgidum L. Desf.) is a species well adapted to the Mediterranean environments where salt stress due to seawater intrusion is an increasing problem. The purpose of this study was to deep insight into the relationships among physiological, productive and qualitative aspects under salinity, being these aspects still poorly investigated in durum wheat. In 2004–2005 crop season 10 durum wheat genotypes of different origin and breeding time were grown in a naturally-lit polycarbonate greenhouse under three irrigation water salinity levels (0.9, 6.0 and 12.0 dS m−1). A complete randomized block design with three replications was adopted. The osmotic damage was evaluated by estimating relative water content (RWC), leaf water potential (Φw) and osmotic potential at full turgor (Φπ100). The toxic damage to the plants was evaluated by measuring Na+ accumulation and Na+/K+ ratio in the leaves. Differences in yield performance were evaluated by assessing the main yield components and some qualitative traits, carotenoid pigment and protein content and Sedimentation test in sodium dodecyl sulphate. A significant effect of genotype, salt stress and of their interaction on all the characters was observed. Durum wheat genotypes generally showed a moderate tolerance to salt stress. The genotype performance was dependent on stress level and RWC maintenance. Osmotic adjustment and low sodium accumulation were found to play a key role in salt tolerance. An improvement in the grain quality characters on increasing salinity level, consistently with a yield decrease, was observed.

Adaptability of &lt;i&gt;Cornus Alba&lt;/i&gt; Seedling under Drought Stress in Highway Greening

The drought resistance adaptation mechanism of highway greening plants was always the focal point which the researcher payed attention. This experiment took Cornus alba as the study object and examines its resistance to drought stress by using the potting and water control method. The researcher measured bond water content, water saturation deficit, relevant water content, relevant content of osmotic water, and osmotic potential when full turgor and turgor were both zero. Other water condition indexes also were analyzed systematically. Finally, a comprehensive evaluation on the drought resistance of Cornus alba by fuzzy mathematics’ anti-membership function was conducted. According to the experiment result, Cornus alba had the highest drought resistance at B-level treatment (soil water content: 53.60%), followed by D-level (soil water content: 29.90%) treatment. Cornus alba had strong endurance and resistance to drought stress. This study could provide a scientific basis for the future introduction of other urban greenbelt plants and the choice of excellent traits.

Water stress, shoot growth and storage of non‐structural carbohydrates along a tree height gradient in a tall conifer

We analysed concentrations of starch, sucrose, glucose and fructose in upper branch wood, foliage and trunk sapwood of Douglas-fir trees in height classes ranging from ~2 to ~57 m. Mean concentrations of non-structural carbohydrates (NSC) for all tissues were highest in the tallest height class and lowest in the lowest height class, and height-related trends in NSC were most pronounced in branches. Throughout a 17-month sampling period, mean values of branch NSC from the 57 m trees ranged between 30 and 377% greater than the 2 m trees. Branch NSC was inversely correlated with midday shoot water potential (Ψ(l)), shoot osmotic potential at full turgor (Ψ) and shoot extension. Temporal fluctuation in branch NSC was inversely correlated with height, and positively correlated with midday Ψ(l) , Ψ and shoot extension. The positive correlation between height and storage of NSC, and the negative correlation between NSC storage and shoot extension provide evidence that size-related growth decline in trees is not strongly associated with constraints on photosynthesis. The negative correlation between height and fluctuation in NSC suggests that mobilization of photosynthate in taller trees is constrained by some factor such as reductions in turgor-driven cell expansion or constraints on phloem transport.

The impact of long‐term water stress on relative growth rate and morphology of needles and shoots of Metasequoia glyptostroboides seedlings: research toward identifying mechanistic models

Leaf morphology in the upper canopy of trees tends to be different from that lower down. The effect of long-term water stress on leaf growth and morphology was studied in seedlings of Metasequoia glyptostroboides to understand how tree height might affect leaf morphology in larger trees. Tree height increases water stress on growing leaves through increased hydraulic resistance to water flow and increased gravitational potential, hence we assume that water stress imposed by soil dehydration will have an effect equivalent to stress induced by height. Seedlings were subjected to well-watered and two constant levels of long-term water stress treatments. Drought treatment significantly reduced final needle count, area and mass per area (leaf mass area, LMA) and increased needle density. Needles from water-stressed plants had lower maximum volumetric elastic modulus (ε(max)), osmotic potential at full turgor (Ψ¹⁰⁰(π)) (and at zero turgor (Ψ⁰(π)) (than those from well-watered plants. Palisade and spongy mesophyll cell size and upper epidermal cell size decreased significantly in drought treatments. Needle relative growth rate, needle length and cell sizes were linear functions of the daily average water potential at the time of leaf growth (r² 0.88-0.999). We conclude that water stress alone does mimic the direction and magnitude of changes in leaf morphology observed in tall trees. The results are discussed in terms of various models for leaf growth rate.

Seasonal changes in the physiological characteristics of Anatolian black pine and the effect on seedling quality

Seasonal changes in water relations parameters, dry weight fraction (DWF), and root growth potential (RGP) were examined for Anatolian black pine [Pinus nigra Arn. subsp. pallasiana (Lamb.) Holmboe] seedlings. In addition, phenological conditions were monitored. Water relations parameters were estimated using the pressure-volume technique, including osmotic potential at full turgor (\psi_{\pi100}), osmotic potential at turgor loss point (\psi_{\piTLP}), free water content at turgor loss point (FWC_{TLP}), relative water content at turgor loss point (RWC_{TLP}), and symplastic water/dry weight (Vo/DW). \psi_{\piTLP}, \psi_{\pi100}, DWF, and RGP showed seasonal changes, but FWC_{TLP}, RWC_{TLP}, and Vo/DW did not show a clear seasonal change. The osmotic potentials (\psi_{\piTLP} and \psi_{\pi100}) increased rapidly during rapid shoot elongation, then decreased gradually until autumn, and the minimum values were reached in midwinter. DWF and RGP were highest at the end of January and in mid-February, respectively. The results of the study were discussed based on nursery practices (e.g. lifting and planting time, quality of seedlings) for the species, and as a synthesis of these results, mid-November through mid-March was suggested as the lifting and planting period for bare root Anatolian black pine seedlings.

Restoration of photosystem II photochemistry and carbon assimilation and related changes in chlorophyll and protein contents during the rehydration of desiccated Xerophyta scabrida leaves.

Recovery of photosynthesis in rehydrating desiccated leaves of the poikilochlorophyllous desiccation-tolerant plant Xerophyta scabrida was investigated. Detached leaves were remoistened under 12 h light/dark cycles for 96 h. Water, chlorophyll (Chl), and protein contents, Chl fluorescence, photosynthesis–CO2 concentration response, and the amount and activity of Rubisco were measured at intervals during the rehydration period. Leaf relative water contents reached 87% in 12 h and full turgor in 96 h. Chl synthesis was slower before than after 24 h, and Chla:Chlb ratios changed from 0.13 to 2.6 in 48 h. The maximum quantum efficiency recovered faster during rehydration than the photosystem II operating efficiency and the efficiency factor, which is known to depend mainly on the use of the electron transport chain products. From 24 h to 96 h of rehydration, net carbon fixation was Rubisco limited, rather than electron transport limited. Total Rubisco activity increased during rehydration more than the Rubisco protein content. Desiccated leaves contained, in a close to functional state, more than half the amount of the Rubisco protein present in rehydrated leaves. The results suggest that in X. scabrida leaves Rubisco adopts a special, protective conformation and recovers its activity during rehydration through modifications in redox status.

Leaf–water relations and ion concentrations of the halophyte Atriplex hortensis in response to salinity and water stress

The impact of salinity and water stress was analyzed in the xero-halophyte Atriplex hortensis using two varieties: green orach (A. hortensis var. purpurea) and red orach (A. hortensis var. rubra). A. hortensis L. is a C3 species well adapted to salt and drought conditions. To collect information on the physiological impact of different salt and water deficit levels on their water stress resistance, plants were exposed for 3 months to solution containing four levels of NaCl or to water stress regimes including four levels of field capacity. Osmotic potential at zero turgor Ψ s 0 , osmotic potential at full turgor (Ψ s 100 ), relative water content (RWC), ion concentration (Na+, K+, Ca2+, Mg2+, and Cl−), and malondialdehyde (MDA) were determined at the end of the treatment. The salinity and water stress induced a decrease in Ψ s 100 , Ψ s 0 , and RWC in both varieties, recorded changes being higher in plants of red variety than those of green variety. Both varieties specifically accumulated Na+ in response to drought and salt stress, suggesting that this element could play a physiological role in the stress response of this xero-halophyte species. In contrast, the presence of NaCl and water stress induced a decrease in K+, Ca2+, and Mg2+ concentration in both varieties. Salinity clearly induced an increase in Cl– concentration in all tissues, but water stress had no impact on this parameter. MDA concentration increased in response to water stress and exogenous NaCl. Based on these findings the more drought-tolerant red orach may be grown in water-limiting soils.