Root metaxylem and architecture phenotypes integrate to regulate water use under drought stress

At the genus and species level, variation in root anatomy and architecture may interact to affect strategies of drought avoidance. To investigate this idea, root anatomy and architecture of the drought‐sensitive common bean (Phaseolus vulgaris) and drought‐adapted tepary bean (Phaseolus acutifolius) were analyzed in relation to water use under terminal drought. Intraspecific variation for metaxylem anatomy and axial conductance was found in the roots of both species. Genotypes with high‐conductance root metaxylem phenotypes acquired and transpired more water per unit leaf area, shoot mass, and root mass than genotypes with low‐conductance metaxylem phenotypes. Interspecific variation in root architecture and root depth was observed where P. acutifolius has a deeper distribution of root length than P. vulgaris. In the deeper‐rooted P. acutifolius, genotypes with high root conductance were better able to exploit deep soil water than genotypes with low root axial conductance. Contrastingly, in the shallower‐rooted P. vulgaris, genotypes with low root axial conductance had improved water status through conservation of soil moisture for sustained water capture later in the season. These results indicate that metaxylem morphology interacts with root system depth to determine a strategy of drought avoidance and illustrate synergism among architectural and anatomical phenotypes for root function.     

Temperature Effects on Mitochondrial Respiration in Phaseolus acutifolius A. Gray and Phaseolus vulgaris L

Electron transport, using succinate as a substrate, was measured polarographically in mitochondria isolated from Phaseolus vulgaris and P. acutifolius plants at 25°C and 32°C. Mitochondria isolated from P. vulgaris plants grown at 32°C had reduced electron transport and were substantially uncoupled. Growth at 32°C had no effect on electron transport or oxidative phosphorylation in P. acutifolius compared to 25°C grown plants. Mitochondria isolated from 25°C grown P. vulgaris plants measured at 42°C were completely uncoupled. Similarly treated P. acutifolius mitochondria remained coupled. The uncoupling of P. vulgaris was due to increased proton permeability of inner mitochondrial membrane. The alternative pathway was more sensitive to heat than the regular cytochrome pathway. At 42°C, no alternative pathway activity was detected. The substantially greater heat tolerance of P. acutifollus compared to P. vulgaris mitochondrial electron transport suggests that mitochondrial sensitivity to elevated temperatures is a major limitation to growth of P. vulgaris at high temperatures and is an important characteristic conveying tolerance in P. acutifolius.     

Effect of drought on phytyl wax esters in Phaseolus leaves

The small amount of phytol which is bound as wax ester in mature bean leaves is increased 10–20 fold by drought. Watering the plants before permanent wilt reverses this trend. Maximum amounts of phytyl wax esters in plants still viable are higher in the drought resistant tepary bean (Phaseolus acutifolius) than in the less resistant garden bean (P. vulgaris).     

Nodulation and Nitrogen Fixation Efficacy of Rhizobium fredii with Phaseolus vulgaris Genotypes

Phaseolus plant introduction (PI) genotypes (consisting of 684 P. vulgaris, 26 P. acutifolius, 39 P. lunatus, and 5 P. coccineus accessions) were evaluated for their ability to form effective symbioses with strains of six slow-growing (Bradyrhizobium) and four fast-growing (Rhizobium fredii) soybean rhizobia. Of the 684 P. vulgaris genotypes examined, three PIs were found to form effective nitrogen-fixing symbioses with the R. fredii strains. While none of the Bradyrhizobium strains nodulated any of the genotypes tested, some produced large numbers of undifferentiated root proliferations (hypertrophies). A symbiotic plasmid-cured R. fredii strain failed to nodulate the P. vulgaris PIs and cultivars, suggesting that P. vulgaris host range genes are Sym plasmid borne in the fast-growing soybean rhizobia.     

Relating foliar dehydration tolerance of mycorrhizal Phaseolus vulgaris to soil and root colonization by hyphae

Mycorrhizal symbiosis can modify plant response to drying soil, but little is known about the relative contribution of soil vs. root hyphal colonization to drought resistance of mycorrhizal plants. Foliar dehydration tolerance, characterized as leaf and soil water potential at the end of a lethal drying episode, was measured in bean plants (Phaseolus vulgaris) colonized by Glomus intraradices or by a mix of arbuscular mycorrhizal fungi collected from a semi-arid grassland. Path analysis modeling was used to evaluate how colonization rates and other variables affected these lethal values. Of several plant and soil characteristics tested, variation in dehydration tolerance was best explained by soil hyphal density. Soil hyphal colonization had larger direct and total effects on both lethal leaf water potential and soil water potential than did root hyphal colonization, root density, soil aggregation, soil glomalin concentration, leaf phosphorus concentration or leaf osmotic potential. Plants colonized by the semi-arid mix of mycorrhizal fungi had lower lethal leaf water potential and soil water potential than plants colonized by G. intraradices. Our findings support the assertion that external, soil hyphae may play an important role in mycorrhizal influence on the water relations of host plants.     

Stress responses in Salix gracilistyla cuttings subjected to repetitive alternate flooding and drought

To determine the tolerance of Salix gracilistyla to repetitive alternate flooding and drought, we measured leaf stomatal conductance, pre-dawn water potential, osmotic adjustment, and biomass production under greenhouse conditions. We used a control and nine crossed treatments (F1-D1–F3-D3) in which we combined 1-, 2-, or 3-week floodings (F) and droughts (D). Leaf stomatal conductance was lowest in 3 weeks of flooding or drought when the preceding event (flood or drought) was also of a 3-week duration. Leaf pre-dawn water potential was reduced in 3 weeks of drought when preceded by 2 or 3 weeks of flooding. Cuttings had slight osmotic adjustments in repetitions of long floodings and droughts. During longer durations of drought in crossed experiments, plants had low root and shoot mass, few hypertrophic lenticels, and reduced leaf mass; when flooding duration increased in crossed experiments, root mass was reduced, there were more hypertrophic lenticels, and the leaf area was reduced. Cuttings achieved stress tolerance by inhibition of transpiration, osmotic adjustment, reduction of transpiration area, and development of hypertrophic lenticels. Stress tolerance was weak when repetitive 2- or 3-week floodings were combined with 3-week droughts. The duration of flooding and drought periods under which S. gracilistyla achieves stress tolerance may be critical in determining distributions along riverbanks.     

Interspecific Grafts Demonstrate Root System Control of Leaf Water Status in Water-Stressed Phaseolus

We examined the importance and the mechanisms of the root systems'effect on leaf water status in two bean species: Phaseolus vulgarisL. cv. Redcloud (Pv) and P. acutifolius Gray MN cultivatedaccession 258/78 (Pa). Pa maintains a higher leaf water potential(₁) than Pv. We used reciprocal grafts between the two species.We grew four plants (one of each graft combination) in one potso they experienced the same soil water potential. Shoot genotypedetermined ₁ of well-watered plants. Root genotype determined₁ of the most stressed plants. Stressed Pa root systems increased₁ of Pv shoots by 0·1 MPa over Pv shoots on Pv roots.Pa roots did not maintain by affecting stomatal conductancenor by simply having more dry weight. Pa roots may have greaterhydraulic conductivity than Pv roots. Key words: Phaseolus acutifolius, Phaseolus vulgaris, leaf water potential, root-shoot communication     

The resistance of genotypes of two species of Phaseolus beans to the leafhopper Empoasca kraemeri

To determine whether two species of Phaseolus beans differ in their suitability for reproduction of the leafhopper Empoasca kraemeri, resistant and susceptible genotypes of the two species were exposed to egg laying leafhoppers and the resultant numbers of nymphs on each were compared. Resistant genotypes of P. acutifolius bore fewer nymphs than any genotype of P. vulgaris. Even susceptible P. acutifolius genotypes bore no more nymphs/leaf than resistant P. vulgaris genotypes though they did bear more nymphs/cm² of leaf area. These results indicate that P. acutifolius may be a useful donor of oviposition non-preference, increased egg mortality, or possibly nymphal non-preference, and confirm that counts of nymphs provide a useful screening technique in the selection of parental genotypes for an improvement programme.     

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 (Ψ^tlp) 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 Ψ^tlp 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.     

荒漠植物蒙古扁桃水分生理特征

蒙古扁桃(Prunus mongolica)是荒漠区和荒漠草原的水土保持植物和景观植物,是蒙古高原古老残遗植物,对其深入研究对于了解蒙古高原植被演替以及对当地生态环境的稳定和恢复有着重要意义。该实验采用PV技术和自然脱水法探讨了蒙古扁桃的水分生理特性。结果表明:在自然状态下,蒙古扁桃幼苗叶片的相对含水量为69%,饱和含水量为117%,临界饱和亏为48%,水势为-0.85 MPa。经 5% PEG-Hoagland (-0.46 MPa)干旱胁迫处理3 d后,其相对含水量、临界含水量和水势分别下降到48%、39%和 -1.97 MPa,而饱和含水量和束缚水与自由水比值分别增加到187%和11.94。对失水率分析的结果表明:在正常水分状态下,蒙古扁桃幼苗经102 h自然脱水后失水达到平衡,而经过干旱胁迫处理3 d后,其失水率曲线斜率变小,失水过程明显减缓,失水最终达到平衡的时间延长到152 h,其保水能力显著提高。将旱生植物蒙古扁桃的失水率曲线与中旱生植物长柄扁桃(P. pedunculata)的失水率曲线相比较发现,蒙古扁桃的耐脱水能力明显强于中旱生植物长柄扁桃。PV曲线(Pressure-volume curve)分析结果表明: 蒙古扁桃饱和含水量渗透势(Ψπ¹⁰⁰)和零膨压渗透势 (Ψπ⁰)很低,分别为-2.49 MPa和-3.11 MPa,而Ψπ¹⁰⁰和Ψπ⁰差值较大(0.62 MPa),表明其维持膨压的能力很强。其细胞壁弹性模量值低(4.18 MPa)进一步表明,蒙古扁桃具有很强的膨压调节能力。蒙古扁桃幼苗失去膨压时的渗透含水量(ROWC^tlp)为80%,这是其细胞壁特性所决定的渗透调节能力的基础。蒙古扁桃质外体含水量(AWC, %)较高(79%),因而具有较高的束缚水与自由水比值(7.76),这是其耐脱水性的生理基础。总之,蒙古扁桃叶水势、渗透势低有利于其根部对深层土壤水分的吸收,而较高的束缚水与自由水比值及较低的细胞壁弹性模量是其耐脱水的生理基础。     

Nitric oxide increases tolerance responses to moderate water deficit in leaves of Phaseolus vulgaris and Vigna unguiculata bean species

Drought stress is one of the most intensively studied and widespread constraints, and nitric oxide (NO) is a key signaling molecule involved in the mediation of abiotic stresses in plants. We demonstrated that a sprayed solution of NO from donor sodium nitroprusside increased drought stress tolerance responses in both sensitive (Phaseolus vulgaris) and tolerant (Vigna unguiculata) beans. In intact plants subjected to halting irrigation, NO increased the leaf relative water content and stomatal conductance in both species. After cutting leaf discs and washing them, NO induced increased electrolyte leakage, which was more evident in the tolerant species. These leaf discs were then subjected to different water deficits, simulating moderate and severe drought stress conditions through polyethylene glycol solutions. NO supplied at moderate drought stress revealed a reduced membrane injury index in sensitive species. In hydrated discs and at this level of water deficit, NO increased the electron transport rate in both species, and a reduction of these rates was observed at severe stress levels. Taken together, it can be shown that NO has an effective role in ameliorating drought stress effects, activating tolerance responses at moderate water deficit levels and in both bean species which present differential drought tolerance.     

Plant regeneration from embryo-derived callus in Phaseolus vulgaris L. (common bean) and P. acutifolius A. Gray (tepary bean)

Regeneration-competent callus of Phaseolus vulgaris and P. acutifolius was obtained from mature embryo explants on a medium containing thidiazuron and indole-3-acetic acid. For the P. vulgaris genotype Xan-159, regeneration was achieved from cotyledon explants, but not from embryonic axis explants. Both explants could be used for the P. acutifolius genotype NI 574 but embryonic axes gave the best results. In-vitro-rooted plantlets of P. acutifolius could readily be established in the greenhouse. For P. vulgaris hardening problems with in-vitro-rooted plantlets could be overcome by means of in vitro grafting. The potential of the described procedure for obtaining transgenic P. vulgaris plants is discussed. Received: 31 July 1997 / Revision received: 9 September 1997 / Accepted: 22 December 1997     

Agrobacterium-mediated transformation of Phaseolus acutifolius A. Gray

Agrobacterium-mediated transformation of Phaseolus acutifolius A. Gray has been achieved. Regeneration-competent callus, obtained from bud explants of greenhouse-grown plants, was co-cultivated with Agrobacterium tumefaciens C58C1Rif^R(pMP90) harbouring a binary vector with the neomycin phosphotransferase II (nptII) and β-glucuronidase (uidA) marker genes. Transient expression of uidA was detected in five out of six genotypes tested. Transgenic callus lines of three genotypes were established on geneticin-containing medium. Plants were recovered from one line (genotype NI 576). This line had been transformed with a binary plasmid which, in addition to the marker genes, contained a genomic fragment encoding the Phaseolus vulgaris arcelin-5a protein. This seed storage protein presumably confers resistance to the insect Zabrotes subfasciatus, a major pest of P. vulgaris. Integration of foreign DNA was confirmed by molecular analysis. The introduced genes segregated as a single locus. Arcelin-5a was produced at high levels in seeds. The possibility of using P. acutifolius as a `bridging' species to introduce transgenes into the economically more important species P. vulgaris is discussed. Received: 20 July 1996 / Accepted: 23 August 1996     

内蒙古高原锦鸡儿属植物的形态和生理生态适应性

比较研究内蒙古高原锦鸡儿属(Caragana)中生种,旱生种和强旱生种的叶片形态结构、渗透调节、气孔调节和保护酶,目的是揭示锦鸡儿属不同类型植物的生态适应策略。中生种叶片平展,被稀疏绿色短柔毛;旱生种叶片平展或呈瓦状,被灰色柔毛;强旱生种叶片呈瓦状或卷成筒状,被直立或伏帖绢毛。叶片厚度强旱生种>旱生种>中生种,叶片面积、生物量和比叶面积(SLA)强旱生种<旱生种<中生种。叶片长宽比,强旱生种和旱生种大于中生种。这些形态结构导致保水能力强旱生种>旱生种>中生种,光能利用能力中生种>旱生种>强旱生种。渗透调节物质含量、细胞质离子浓度和细胞渗透势强旱生种>旱生种>中生种。渗透调节物质含量的差异主要表现在强旱生种可溶性糖和无机离子含量远高于旱生种,后者又远高于中生种。叶含水量、自由水含量、叶水势和气孔导度中生种>旱生种>强旱生种,束缚水含量、束缚水/自由水比值、POD和SOD活性正好相反,CAT活性旱生种>中生种>强旱生种。这些生理特性导致抗旱能力强旱生种>旱生种>中生种,但代谢速率正好相反。旱生种和中生种表现出较少的日水分亏缺,强旱生种水分亏缺从清晨到傍晚持续大幅增加。细胞膜相对透性和MDA含量强旱生种>旱生种>中生种。自由基含量表现为旱生种>中生种>强旱生种。这些数据说明虽然旱生种和强旱生种形成了多种特点来适应干旱环境,但仍然是不充分的。结论:(1)分布于半湿润至半干旱区的锦鸡儿属中生种依靠活跃的代谢、大量的水分消耗和快速生长使其在生物环境中取得竞争优势;生活在干旱地区和强干旱地区的旱生种和强旱生种依靠低代谢、节水和高抗旱性来抵抗苛刻的非生物环境。(2) 旱生种和强旱生种主要通过可溶性糖和无机离子的积累,调节细胞质渗透势,保持水分平衡,这是一种相对节省能量的适应对策。     

WATER RELATIONS AND GROWTH CHARACTERISTICS OF PROSOPIS GLANDULOSA VAR. TORREYANA IN A SIMULATED PHREATOPHYTIC ENVIRONMENT

Recent studies of Prosopis glandulosa have demonstrated a unique system of a deeply rooted species with significant water stress tolerance. Several growth and developmental characteristics have been correlated with water stress and nitrogen availability during field studies. Here we present a lab experiment in which a phreatophytic regime is simulated and the availability of nitrogen and water are varied. Increased ground water salinity caused lower plant water potentials and greater osmotic adjustment without significant increases in leaf Na⁺ concentrations. Leaf conductance was higher in the higher salinity treatments. Low water potential was also associated with reduced leaf size, reduced leaf area per plant and increased root to shoot ratio. Specific leaf weight and the transpiration ratio were unaffected by the low water potentials induced by increased salinity. Increasing nitrogen availability caused increased growth rates but did not influence water use efficiency. Net assimilation rates increased with increasing nitrogen availability but relative growth rates were more dependent on overall plant size than treatment conditions. The responses of P. glandulosa to the simulated phreatophytic environment were similar to those predicted by field measurements.     

Root and leaf traits, water use and drought tolerance of maize genotypes

The main components of drought tolerance of six maize genotypes were studied to evaluate crop performance in water limiting environments: (1) the postponement of dehydration by reduced transpiration rate (TR) and an increased efficiency of water acquisition from soil; (2) the tolerance of dehydration by effective physiological water use. The aim was to describe the genotype dependent response to drought in leaf and root traits and water relations using data from controlled environment and field experiments, and using dynamic simulation by the Swedish Coup model. High genetic variation was detected in the root density, acquisition efficiency and water use among the genotypes. The female parent lines had the greatest TR with the smallest dry matter accumulation in water deficiency, whereas hybrids could acquire more water from dryer soil while maintaining a lower TR. Hybrid Mv 444 increased water potential more strongly in leaves than hybrid Norma. The postponement of dehydration was observed for Norma, while more tolerance to dehydration characterized Mv 444. Simulation was an effective tool for testing hypotheses considering water acquisition efficiency and for summarizing the results of the measurements in a formalized structure; it helped to quantify the dynamics of water availability and the impact of drought on the growth of the maize genotypes.     

The evolutionary rate of leaf osmotic strength drives diversification of Primulina species in karst regions

Leaf water storage capacity and osmotic strength are important traits enabling species to adapt to environments that are often moisture limited. However, whether these drought tolerance traits are correlated with the species diversification rate (DR) of plant lineages is yet to be determined. In this study, we selected a species-rich genus (Primulina) of plants widely distributed in karst regions in which species frequently experience variable periods of drought. We measured water storage capacity-related traits (including leaf thickness and water content per mass) and saturated osmotic strength in the leaves of 58 Primulina species growing in a common garden. Subsequently, using phylogenetic methods, we examined the relationships between the rate of species diversification and the drought tolerance traits and between the species DR and evolutionary rates of these traits. We found that neither water storage capacity nor saturated osmotic strength showed significant relationships with the rate of species diversification. However, the evolutionary rate of saturated osmotic strength showed a significant correlation with the species DR, although no comparable significant relationship was detected regarding the evolutionary rate of water storage capacity. Our study indicates that the diversification among Primulina species has typically been accompanied by an extensive divergence of leaf osmotic strength but not a divergence in leaf water storage capacity. These findings will enhance our current understanding of how drought tolerance influences the diversification of plant species in karst regions.     

The relative contribution of elastic and osmotic adjustments to turgor maintenance of woody species.

To determine how tissue water relations vary and contribute to turgor maintenance in species from contrasting ecological zones, seedlings of jack pine ( Pinus banksiana Lamb.), black spruce ( Picea mariana [Mill] B.S.P.) and flooded gum ( Eucalyptus grandis W. Hill ex Maiden) were subjected to an 8 day drought stress by water withholding with and without prior mild water stress conditioning. Jack pine, a deep-rooted species from dry, sandy boreal sites, lost turgor at the lowest relative water content (75–65%) and water potential, and had lowest maximum bulk elastic modulus (E_max of 5.2–5.8 MPa). Although this suggests a high inherent dehydration tolerance, jack pine did not further adjust its elasticity when repeatedly stressed. Black spruce, a shallow-rooted species from predominantly moist sites in the boreal region, lost turgor at intermediate relative water content (86–76%) and water potential, but could adjust its elasticity to maintain turgor in repeatedly stressed tissues. Flooded gum, a deep-rooted species from moist, warm temperate-subtropical regions, had a low inherent drought tolerance since it lost turgor at higher relative water content (88–84%) and water potential, but was capable of some adjustment when the stress was repeated. Elastic adjustment (<3.7 MPa) was more important for turgor maintenance than osmotic adjustment (<0.13 MPa), which was statistically nonsignificant. Maximum bulk modulus of elasticity, but not osmotic potentials at full turgor, was significantly correlated with the relative water content and water potential at zero turgor in droughted seedlings. These results highlight the importance of tissue shrinkage for dehydration tolerance. Both the inherent capacity for turgor maintenance of a species under drought and its ability to adjust to repeated drought should be considered in genetic selections for drought tolerance.     

Thermotolerance of the photosynthetic light reactions in two <Emphasis Type="Italic">Phaseolus</Emphasis> species: a comparative study

The common bean (Phaseolus vulgaris L.) is sensitive to high temperature, while an ecologically contrasting species (Phaseolus acutifolius A. Gray) is cultivated successfully in hot environments. In this study, the two bean species were respectively acclimated to a control temperature of 25 °C and a moderately elevated temperature of 35 °C in order to compare the thermotolerance capabilities of their photosynthetic light reactions. Growth at 35 °C appeared to have no obvious adverse effect on the photosynthetic activities of the two beans, but changed their thermotolerance. After a short period of heat shock (40 °C for up to 4 h), the photosynthetic activities of 25 °C-grown P. vulgaris declined more severely than those of P. acutifolius grown at 25 °C, implying that the basal thermotolerance of P. vulgaris is inferior to that of P. acutifolius. But after acclimating to 35 °C, the thermotolerances of the two species were both greatly enhanced to about the same level, clearly demonstrating the induction of acquired thermotolerance in their chloroplasts, and P. vulgaris could be as good as P. acutifolius. Temperature acclimation also changed plants’ resistance to photoinhibition in a manner similar to those toward heat stress. In addition, acquisition of tolerance to heat and strong irradiance would reduce the dependency of the two beans on xanthophyll pigments to dissipate heat, and also seemed irrelevant to the agents with antioxidant activities such as SOD.     

Effects of water stress on the water relations of Phaseolus vulgaris and the drought resistant Phaseolus acutifolius

The tepary bean ( Phaseolus acutifolius Gray var. latifolius ), a drought resistant species, was compared under water stress conditions with the more drought susceptible P. vulgaris L. cvs Pinto and White Half Runner (WHR). In order to better understand the basis for the superior drought resistance of tepary, this study was designed to determine the relationships among leaf water potential, osmotic potential, turgor potential, and relative water content (RWC).
Plants were prestressed by withholding irrigation water. These stress pretreatments changed the relation between leaf water potential and relative water content of both species so that prestressed plants had lower water potentials than controls at the same leaf RWC. Tepary had lower water potentials at given RWC levels than Pinto or WHR; this can account for part of the superior resistance of tepary. In all genotypes, prestressed plants maintained osmotic potentials approximately 0.2 MPa lower than controls. Tepary reached osmotic potentials that were significantly lower (0.15 to 0.25 MPa) than Pinto or WHR. Both control and prestressed tepary plants had 0.05 to 0.25 MPa more turgor than Pinto or WHR at RWC values between 65 and 80%. Both prestressed and control tepary plants had greater elasticity (a lower elastic modulus) than Pinto or WHR. This greater turgor of tepary at low RWC values could be caused by several factors including greater tissue elasticity, active accumulation of solutes, or greater solute concentration.
Tepary had significantly lower osmotic potentials than the P. vulgaris cultivars, but there was little difference in osmotic potential between Pinto and WHR. Knowledge of differences in osmotic and turgor potentials among and within species could be useful in breeding for drought resistance in Phaseolus.