Diversity in root architecture and response to P deficiency in seedlings of <Emphasis Type="Italic">Cucumis melo</Emphasis> L.

Breeding for more phosphorus (P)-efficient crops is one strategy to reduce the use of P fertilizers, thus mitigating the environmental and economic impacts of agriculture. Variation in root architecture and the response to P deficiency were studied in C. melo. Forty accessions representing genetic diversity within the species were screened for their root systems in normal and deficient P conditions at the seedling stage. Various parameters of P-uptake and P-use were analyzed in a subset of accessions at 40 days. Significant differences in root architecture were observed, with the taproot systems prevailing among the wild and exotic accessions, and more branched root systems in cultivated stocks. Moreover, differences in the plastic response of roots to P starvation were observed. Variation in different P-use and -uptake traits correlated with the root architecture. Within ssp. melo, the inodorus and flexuosus landraces had larger and more branched roots and more efficient P-uptake, thereby providing a close genepool for breeding. Within ssp. agrestis, conomon and momordica accessions can be sources of interest for the enhancement of variation in root architecture and P-use efficiency into cultivated melons. Therefore, the diversity observed within C. melo species could be useful in breeding P-efficient melon cultivars.     

不同耐低磷水稻基因型秧苗对难溶性磷的吸收利用

选取4个典型耐低磷水稻基因型99011、508、580和99112,并以2个磷敏感基因型99012和99056为参照,采用营养液培养和砂培的方法,研究不同磷处理对秧苗生长的影响以及不同耐低磷基因型对3种难溶性磷源(有机磷、铝磷和磷矿粉)吸收利用能力的差异。结果表明,不同无机磷处理,6个基因型生物量和根干重基本上均为全磷处理（P）>对照+铝磷（CK+Al-P）>对照+磷矿粉（CK+RP）> 对照（CK）;4个耐低磷基因型根干重和根冠比均大于2个磷敏感基因型;对于根冠比,耐低磷基因型580和99011为对照+磷矿粉（CK+RP）>对照+铝磷（CK+Al-P）> 对照（CK）> 全磷处理（P）,耐低磷基因型508、99112和磷敏感基因型99012为CK> CK+RP> CK+Al-P > P,磷敏感基因型99056为CK+Al-P > CK+RP > P>CK;缺磷处理,秧苗活化吸收难溶性磷源的能力均为OP> Al-P> RP,且不同基因型的分解吸收能力对OP为99011> 508> 580> 99012> 99112> 99056（表2）,对Al-P为580> 99011> 99112> 508> 99056> 99012（表3）,对RP为580> 99112> 99011> 508> 99012> 99056（表2）。此外,缺磷即CK处理,508对低浓度的磷吸收最多(表2和表3),而580对磷的利用效率显著高于其他基因型（表3）,这些特征可能也是它们耐低磷的重要贡献因子之一。     

Generation mean analysis of phosphorus‐use efficiency in freely nodulating soybean crosses grown in low‐phosphorus soil

Freely nodulating soybean genotypes vary in their phosphorus (P) uptake and P‐use efficiency (PUE) in low‐P soils. Understanding the genetic basis of these genotypes’ performance is essential for effective breeding. To study the inheritance of PUE, we conducted crosses using two high‐PUE genotypes, two moderate‐PUE genotypes and two inefficient‐PUE genotypes, and obtained F₁, F_2, BC₁ and BC₂ populations. The inheritance of PUE was evaluated using a randomized complete block design. A generation mean analysis of phenotypic data showed that PUE was heritable, with complex inheritance patterns and the presence of additive, dominance and epistatic gene effects. Seed P, shoot P, root P, P‐incorporation efficiency and PUE were largely quantitatively inherited traits. There were dominance, additive × additive and dominance × dominance gene effects on PUE, grain yield, shoot dry weight, 100‐seed weight, root dry weight and shoot dry matter per unit P for populations grown under low‐P conditions. Dominance effects were generally greater than additive effects on PUE‐related indices. These PUE indices can be used to select P‐efficient soybean genotypes from segregating populations.     

Variation in root hairs of barley cultivars doubled soil phosphorus uptake

Length and density (number mm^-1 root) of root hairs of two barley (Hordeum vulgare L.) cultivars Salka and Zita and their capability to absorb phosphorus (P) from nutrient solution as well as from rhizosphere soil were studied. The cultivars were chosen because they differed most among 30 cultivars in ability to absorb P from low P soil in two field conditions. In nutrient solution culture, Salka had 32±4 root hairs mm^-1 root, 1.02±0.22 mm long. Zita had 21±3 hairs mm^-1 root, 0.54±0.14 mm long. In soil, the root hairs of both the cultivars were slightly longer (Salka 1.10 ±0.16 mm; Zita 0.63±0.18 mm) than in solution culture but the difference was non-significant (p<0.05). The root hairs increased the effective root surface area of Salka by 206% and that of Zita by 81%. In solution culture, Salka produced 163±9 m g^-1 and Zita 153±11 m g^-1 dry roots in 21 days. Salka produced 1.65±0.22 g and Zita 1.51±0.31 g of green dry matter (DM). The cultivars did not differ in uptake of P from nutrient solution culture. The P content of DM was 0.42±0.1% in Salka and 0.41±0.08% in Zita. In soil, Salka depleted two times more P from rhizosphere than Zita. The longer root hairs of Salka increased the extension of the depletion zone for NaHCO₃-P_i (inorganic P extracted with 0.5 M NaHCO₃) in the rhizosphere. The cultivars also depleted NaOH-Pi (inorganic P extracted with 0.1 M NaOH) from the rhizosphere soil, but the difference between the cultivars was non-significant (p<0.05). The results suggested that the ability of Salka to absorb more inorganic soil P was due to its longer and denser root hairs. This revised version was published online in July 2006 with corrections to the Cover Date.     

Improving hybrid rice parental lines for blast resistance by introgression of broad-spectrum resistance genes Pi54 and Pi9 by marker-assisted selection

Hybrid rice technology offers a great promise to produce 15% to 20% more yield than pure line varieties. The success of hybrid rice hinges on developing superior parental lines. To improve the blast resistance of hybrid rice parental line RP5933-1-19-2R, crosses were made with donors of two major blast resistance genes namely, Pi54 (Tetep) and Pi9 (IR71033–121-15) and the resulting F₁s were confirmed for their hybridity by using Pi54MAS and NMSMPi9-1 genic markers. The confirmed F₁s were intercrossed to obtain ICF₁s and selected positive plants by markers were backcrossed to the recurrent parent, as well as selfed for advancing further to BC₁F₃ and ICF₄ generations. The segregating plants were phenotyped for blast resistance at Uniform Blast Nursery. The identified complete restorers namely, RP 6619-1, RP 6616-26, RP 6619-3 and RP 6619-11 with Pi9 and Pi54 genes would serve as donors for broad spectrum blast resistance. This could ultimately lead to the development of new rice hybrids with improved resistance to blast disease, which is crucial for sustainable rice production and food security.     

Salt (NaCl)‐Induced Modulation in some Key Physio‐Biochemical Attributes in Okra (Abelmoschus esculentus L.)

Salt (NaCl)‐induced regulation of some key physio‐biochemical characteristics in two okra (Abelmoschus esculentus L.) cultivars (Nirali and Posa Sawni) was examined under greenhouse conditions. Plants of both cultivars were subjected for 30 days to sand culture salinized with four salt levels [0 (control), 50, 100 and 150 mm NaCl] in Hoagland’s nutrient solution. Salt stress significantly reduced the shoot and root fresh weights, transpiration rate, chlorophyll b content, net CO₂ assimilation (A), transpiration rate (E), while enhanced leaf and root Na⁺ and Cl^– concentrations in both cultivars. In contrast, chlorophyll a content, stomatal conductance (g_s), leaf internal CO₂ (C_i), C_i/C_a ratio, water‐use efficiency (A/E) and fluorescence characteristics such as photochemical quenching (qP), non‐photochemical quenching (NPQ), efficiency of PS‐II (F_v/F_m), proline contents, and leaf and root K⁺, Ca^{2 +} and N contents remained almost unaffected in both lines due to salt stress. The efficiency of PSII (F_v/F_m), A, chlorophyll b, root fresh weight and root N were higher in relatively salt tolerant cv. Nirali, whereas leaf Na⁺ and root Cl^– were higher in cv. Posa Sawni. The relatively more reduction in growth in the cv. Posa Sawni was found to be associated with higher accumulation of Na⁺ in its leaves and Cl^– in roots.     

Physiological processes associated with salinity tolerance in an alfalfa half‐sib family

We previously reported an alfalfa half‐sib family, HS‐B, with improved salt tolerance, compared to parental plants, P‐B. In this study, we conducted additional experiments to address potential physiological mechanisms that may contribute to salt tolerance in HS‐B. Vegetatively propagated HS‐B and P‐B plants were treated with a nutrient solution (control) or a nutrient solution containing NaCl (EC = 12 dS/m). Shoots and roots were harvested at various time points after treatment for quantification of proline, soluble sugar, and H₂O₂ using spectrophotometers. Subcellular localization and quantification of Na in roots were conducted using a Na⁺‐specific dye under a confocal microscope. HS‐B produced 86 and 89% greater shoot and root dry biomass, respectively, compared to parental plants, P‐B, under salinity in the greenhouse. Under saline conditions the HS‐B shoots accumulated 115% and roots 55% more soluble sugars than P‐B counterparts. The non‐saline HS‐B shoots, however, showed 72% less soluble sugars than the non‐saline P‐B plants. Under saline conditions HS‐B accumulated 39% less proline in shoots, while roots accumulated 56% more proline, compared to their P‐B parents. HS‐B plants also showed a greater reduction of stomatal conductance under mild saline stress. HS‐B shoots and roots contained 3–4 times less reactive oxygen species (H₂O₂) after salt treatment compared to P‐B plants. Sodium localization and distribution analysis using Na⁺‐specific dye revealed HS‐B plants accumulated 88% and 48% less Na⁺ in stele and xylem vessels compared to P‐B. The study provides insights into the potential mechanisms that may contribute to salt tolerance in HS‐B: maintaining RWC by accumulating soluble sugars while reducing transpiration, maintaining healthy status by reducing oxidative stresses, and preventing salt toxicity by reducing accumulation of Na⁺ inside root cells and xylem.     

Root Growth Inhibition and Lignification Induced by Salt Stress in Soybean

Salt stress was evaluated on root growth, enzyme activities (phenylalanine ammonia‐lyase or PAL and soluble plus cell wall‐bound peroxidase or POD), hydrogen peroxide (H₂O₂) production, total phenolic content and lignin content and composition in soybean (Glycine max L. Merrill) roots. Three‐day‐old seedlings were cultivated in half‐strength Hoagland’s solution (pH 6.0), with or without addition of 50–200 mm of NaCl, into a growth chamber (25 °C, 12/12 h light/dark photoperiod, irradiance of 280 μmol m^?2 s^?1) for 24 h. In general, root length and fresh and dry weights decreased after NaCl treatment. PAL activity decreased, soluble and cell wall‐bound POD activities increased, and H₂O₂ content significantly decreased after NaCl exposure. Consequently, total phenolic and lignin contents and p‐hydroxyphenyl (H) and syringyl (S) monomers of lignin increased in NaCl‐treated roots. Altogether, these results suggest that the effects caused by NaCl may be owing to the enhanced lignin production that solidifies the cell wall and restricts root growth.     

Effect of Phosphorus Nutrition on Growth and Physiology of Cotton Under Ambient and Elevated Carbon Dioxide

Phosphorous deficiency in soil limits crop growth and productivity in the majority of arable lands worldwide and may moderate the growth enhancement effect of rising atmospheric carbon dioxide (CO₂) concentration. To evaluate the interactive effect of these two factors on cotton (Gossypium hirsutum) growth and physiology, plants were grown in controlled environment growth chambers with three levels of phosphate (Pi) supply (0.20, 0.05 and 0.01 mm ) under ambient and elevated (400 and 800 μmol mol^?1, respectively) CO₂. Phosphate stress caused stunted growth and resulted in early leaf senescence with severely decreased leaf area and photosynthesis. Phosphate stress led to over 77 % reduction in total biomass across CO₂ levels. There was a below‐ground (roots) shift in biomass partitioning under Pi deficiency. While tissue phosphorus (P) decreased, tissue nitrogen (N) content tended to increase under Pi deficiency. The CO₂ × Pi interactions were significant on leaf area, photosynthesis and biomass accumulation. The stimulatory effect of elevated CO₂ on growth and photosynthesis was reduced or highly depressed suggesting an increased sensitivity of cotton to Pi deficiency under elevated CO₂. Although, tissue P and stomatal conductance were lower at elevated CO₂, these did not appear to be the main causes of cotton unresponsiveness to elevated CO₂ under severe Pi‐stress. The alteration in the uptake and utilization of N was suggested due to a consistent reduction (18–21 %) in the cotton plant tissue N content under elevated CO₂.     

Salt‐Induced Regulation of Some Key Antioxidant Enzymes and Physio‐Biochemical Phenomena in Five Diverse Cultivars of Turnip (Brassica rapa L.)

A greenhouse experiment was carried out to examine the differential morpho‐physiological responses of five cultivars of turnip (Brassica rapa L.) to salt stress. Five diverse cultivars of turnip (shaljum desi surakh, shaljum purple top, shaljum golden bal, neela shaljum, and peela shaljum) were subjected for 6 weeks to varying levels of NaCl, i.e. 0, 80 and 160 mm in Hoagland’s nutrient solution in sand culture. Imposition of varying levels of salt substantially decreased shoot and root fresh and dry weights, chlorophyll contents, leaf osmotic potential, relative water contents, different gas exchange attributes, total phenolics, malondialdehyde, activities of superoxide dismutase, peroxidase catalase, and leaf and root K⁺ levels while enhanced the proline contents, membrane permeability, level of H₂O₂, leaf and root Na⁺ and Cl^? and leaf Ca²⁺ in all turnip cultivars under study. Of all cultivars, peela shaljum and neela shaljum were consistently higher in their growth than the other turnip cultivars at all salt concentrations of the growth medium. Photosynthetic capacity (A) and stomatal conductance (g_s) were higher in high biomass‐producing cultivars, i.e. peela shaljum and neela shaljum, which provide to be potential selection criteria of salt tolerance in turnip. However, the regulation of antioxidant system was cultivar‐specific under saline conditions.     

Constitutive expression of Cry proteins in roots and border cells of transgenic cotton

Transgenic cotton plants expressing Cry1Ac and Cry2Ab, from the soil bacterium Bacillus thuringiensis (Bt), provide effective control of certain lepidopteran pests, however, little is known about the proteins below ground expression. We used ELISA to quantify in vitro expression of the Cry1Ac and Cry2Ab proteins in mucilage, root border cells and root tips in five transgenic cultivars of cotton compared to conventional cultivar Sicot 189. Expression of Cry proteins in roots and border cells of the transgenic cotton cultivars was constitutive and at detectable levels, with Cry1Ac and Cry2Ab protein expression ranging from <20 ppb to >100 pbb. To determine if genetically modified cotton demonstrated simple differences in properties of the root, when compared to an elite parental line (cv. Sicot 189), we enumerated border cells on seedling radicles. Border cell counts of 14 cultivars ranged from 0.2 to 1.1 × 10⁴ cells per root tip with an average of 5 × 10³ border cells. Border cell production in the transgenic cultivars was generally similar to that of both donor and elite parents, the exception being the cultivar Sicot 189, which had substantially more border cells than all of its transgenic derivatives. Comparison of border cell number with varietal disease resistance ranking found a limited relationship (r ² = 0.65, n = 7) between border cell numbers and the commercial resistance rank against Fusarium wilt of cotton. The implications of differences in cotton cultivar border cell number and root tip expression of Cry proteins for plant–microbe interactions in the rhizosphere and the soil ecosystem are yet to be resolved.     

Rapid survey for presence of a blast resistance gene Pi-ta in rice cultivars using the dominant DNA markers derived from portions of the Pi-ta gene

The Pi‐ta gene in rice confers resistance to strains of the blast pathogen Magnaporthe grisea (Herbert) Borr. (anamorph Pyricularia oryza Cav.) containing the corresponding avirulence gene AVR‐Pita in a gene‐for‐gene fashion. The Pi‐ta gene is a typical nucleotide‐binding site type resistance gene. Nucleotide sequences distinguishing the resistant Pi‐ta and susceptible pi‐ta alleles were previously identified and used for developing DNA markers for a resistant Pi‐ta haplotype and three susceptible pi‐ta haplotypes. In the present study, the existence of the Pi‐ta gene in 141 rice germplasm accessions was rapidly determined using these markers, and the results were confirmed by inoculating rice germplasm with an M. grisea strain containing AVR‐Pita. The Pi‐ta gene was found in accessions from several major rice producing countries, including China, Colombia, Japan, Vietnam, the Philippines, Iran and the United States. The usefulness of DNA markers for rapid determination of the genotype of rice germplasm was thus demonstrated. The Pi‐ta gene also was found in rice cultivar known to contain the Pi‐ta² gene, although the allelic relationship of these genes remains to be determined. The presence of the Pi‐ta gene in landrace cultivars in several different geographical locations, the Philippines and Vietnam, other indica rice cultivars in China and Colombia suggest that the Pi‐ta gene may have spontaneously originated in indica rice cultivars. These results are useful for incorporating the Pi‐ta gene into advanced breeding lines by marker‐assisted selection for rice breeding programmes worldwide.     

富钾基因型烤烟的钾积累及根系生理特性

采用室内营养液培养(钾浓度为3 mmol L^-1)的方法, 以富钾基因型烤烟农大202与2个一般型品种净叶黄、NC89为材料, 研究富钾基因型烤烟钾积累及根系生理特性。结果表明, 3个烤烟品种根和茎中钾积累量无显著差异, 但农大202的叶片钾积累量、根系活力和根系总活力、根系H⁺分泌量、根系阳离子交换量(CEC)、根系可溶性蛋白含量和ATPase活性均极显著高于另两个品种。净叶黄、NC89间除根系活力和根系H⁺分泌量差异达显著水平外, 其他根系生理特性差异均不显著。根系钾吸收动力学参数结果显示,农大202苗期钾离子最大吸收速率(V_max)较高而米氏常数(K_m)和钾离子吸收临界浓度(C_min)较低, 而旺长期的V_max、K_m及C_min均较高, 说明其根系具有较高的钾吸收速率, 但旺长期后耐低钾能力较差。     

Difference in Allelopathic Potential as Influenced by Root Periderm Colour of Sweet Potato (Ipomoea batatas)

Laboratory bioassay and high‐performance liquid chromatography (HPLC) analysis were conducted to determine the allelopathic potentials of aqueous or methanol extracts from three different coloured sweet potato [Ipomoea batatas L. (Lam)] cultivars by plant part. The aqueous extracts applied on filter paper significantly inhibited root growth of alfalfa (Medicago sativa L.). Aqueous leaf leachates at 40 g dry tissue l^?1 (g l^?1) from white sweet potato cultivar ‘Sinyulmi’ showed the highest inhibition against alfalfa, followed by yellow ‘Sinhwangmi’ and purple ‘Jami’. Alfalfa root growth was significantly inhibited by methanol extracts of the same plants as the concentration increased. Aqueous and methanol extracts from leaves showed the most inhibitory effect on alfalfa root growth followed by stems and roots. By means of HPLC analysis, leaf samples of sweet potato had the highest amount of phenolic compounds followed by stems and roots. Total content of these compounds was highest for leaf extracts (37.7 mg 100 g^?1), detected in EtOAc fraction, especially trans‐cinnamic acid (20.9 mg 100 g^?1). These results suggest that sweet potato plants are allelopathic and that their activities differ depending on plant part as well as root periderm colour.     

IAA、GA3和ABA对稻根负向光性和生长的影响

为探明稻根负向光性与内源植物激素含量的关系,以及外源激素对水稻根系生长的影响,以扬稻6号(籼稻)、日本晴(粳稻)和中花11 (粳稻)的OsPIN1a超表达转基因水稻为材料,观察了根负向光性生长的过程,分析了负向光弯曲部位内源生长素(IAA)、赤霉素(GA₃)和脱落酸(ABA)的含量,以及外源激素对水稻根系形态和解剖结构的影响。结果表明, 扬稻6号和日本晴的根都具有负向光性,扬稻6号侧根和不定根的负向光性大于日本晴;2种材料中,IAA、GA₃和ABA在发生负向光弯曲过程中的含量变化基本一致。光照引起3种激素的含量下降;向光侧的含量低于背光侧。单侧光照和外施IAA共同促进了籼稻根毛的大量发生;与普通水稻相比,OsPIN1a超表达稻株的根负向光性角度增大。外源GA₃和ABA处理与稻根负向光性间无直接关系;外源ABA处理显著抑制了根的生长,单株根系总吸收表面积与根数均减少。10 µmol L^-1 ABA处理的水稻根尖生长异常,分生区和根冠发育不良,细胞伸长受抑,成熟区细胞变形使根局部膨胀,并改变了中央维管组织的发育。     

Effects of soil drought during the vegetative phase of seedling growth on the uptake of 14co2 and the accumulation and translocation of 14C in cultivars of field bean (vicia faba L. Var. Minor) and field pea (pisum sativum L.) Of different drought tolerance

During the vegetative phase of growth of two field bean and two field pea cultivars of different drought tolerance, the effect of short and prolonged soil drought on gas exchange (CO₂ i H₂O), leaf water potential (ψ), stomatal diffusive resistance (r_S), uptake of CO₂, and the distribution and accumulation of ¹⁴C was studied. Differences in the response to drought conditions between resistant and susceptible cultivars were marked. After 5 days of soil drought, the decrease in net photosynthesis and transpiration rate and the increase of stomatal resistance were greater in the drought-resistant cultivars than in the drought-susceptible ones. In contrast, after 10 days of drought the decrease of leaf P_N (CO₂ assimilation rate), E (rate of transpiration) and ψ (water potential) was greater in the susceptible cultivars than in the resistant ones. Significant differences between the resistant and the susceptible cultivars were also observed in the assimilation and translocation of ¹⁴C by the green parts of the plant. The amount of carbon accumulation in roots in drought-susceptible cultivars increased less than in the drought-resistant cultivars. For treatments in which optimal soil watering was resumed after 5 or 10 days of drought there was no evidence of effects of drought on the majority of measurements, but the drought-resistant cultivars showed a general tendency for a more rapid recovery. Our results confirm the existence of genetic variability in drought tolerance among the cultivars of field bean and field pea. The recorded differences in the response to drought of experimental cultivars may indicate that, under water deficit in the soil and in plant tissues, they may use different strategies to avoid the damaging effects of temporary limitation of water supply; for example, the drought-resistant cultivars may more effectively conserve tissue hydration through effective stomatal closure. Also, the observed changes in carbon assimilation and accumulation might be the reason for their different responses to drought. The change in radioactivity losses in the control and stressed plants may result from the differences in demand for energy to maintain cell structure and function. Similarly, the less intense carbon accumulation in the roots of the sensitive cultivars could be caused by more harmful effects of drought on root growth.     

Bermudagrass cultivar identification by use of isoenzyme electrophoretic patterns

Summary Isoenzyme analysis has been demonstrated as an effective tool for definitive identification of plant cultivars, but it has not been applied to pasture bermudagrass (Cynodon spp.) cultivars in the USA. Polyacrylamide gel electrophoresis (PAGE) was used to study five isoenzyme systems in mitochondrial, microsomal, and soluble cell fractions of actively growing leaves, stems, and roots of seven vegetatively-propagated pasture bermudagrass (Cynodon spp.) cultivars used in the southern half of the USA. Peroxidase, esterase, and, with one exception, acid phosphatase successfully differentiated between the cultivars in all leaf and stem cell fractions. Fewer cultivar differences were found for amino- and endo-peptidases. Only peroxidase and acid phosphatase were resolved from root cell fractions; and only the microsomal fraction differentiated between all cultivars. Within plant parts, cultivars were distinguishable on the basis of peptidase banding in some cellular fractions, but not in others. Plant part and subcellular fraction-specific isoenzyme variations suggest the existence of multiple molecular forms of various enzymes within the same plant.Journal Article 5746 of the Okla. Agric. Exp. Stn.     

Waterlogging and Hypoxia have Permanent Effects on Wheat Root Growth and Respiration

Waterlogging causes long‐lasting damage to wheat (Triticum aestivum). Root growth and respiration were investigated after heading in waterlogged, pot‐grown, wheat plants and also in hydroponically grown, wheat seedlings exposed to a hypoxic treatment. In the pot experiment, plants were subjected to 8 days of waterlogging after heading. This period of waterlogging resulted in reduced shoot and root growth through to maturity. The root CO₂ emission rates of previously waterlogged and well‐drained plants were about 220 and 140 nmol g^?1 per s, respectively, with the rate differences persisting from 10 days after anthesis through to maturity. In the hydroponic experiments, seedlings (Feekes stage 2.0) were exposed to root‐zone, hypoxic treatment for 10–19 days. The roots showed 27 % higher CO₂ emission rates and 37 % higher O₂ consumption rates, compared with untreated roots. In whole root systems, the high respiration rates found during hypoxic treatment disappeared during recovery under aerated conditions as a result of the appearance of newly initiated roots. However, measurements of the respiration of the previously hypoxic roots showed abnormally high respiration rates. In roots exposed to hypoxic treatment, total sugar concentrations were 3.6‐times higher than in untreated roots indicating that this elevation of sugar may be responsible for the continued high respiration rate. This study shows that roots exposed to waterlogging or to hypoxic treatments do not increase their weights and thus recover from the metabolic disturbances resulting from these treatments.     

低磷胁迫下不同基因型玉米对难溶性磷酸盐的吸收和利用

为了解低磷胁迫下不同基因型玉米对难溶性磷酸盐的吸收利用的差异,以不同磷效率玉米自交系SDKH502和SDLH502为材料,采用营养液培养和砂培的方法,研究不同磷处理对玉米幼苗的生长以及对难溶性磷酸钙、磷酸铁、磷酸铝吸收利用能力的影响。结果表明：正常供磷处理和低磷处理的玉米植株的根系分泌物对难溶性磷酸盐都具有一定的活化能力,低磷胁迫下玉米的根系分泌物对Al-P、Ca-P或Fe-P的活化能力高于正常供磷处理的植株。与足磷下相比,低磷下SDKH502的根系分泌物对Al-P、Ca-P、Fe-P的活化能力依次提高了69.28%、87.34%和51.83%,SDLH502则依次提高了165.67%、141.13%和6.35%。与足磷下相比,低磷下SDKH502和SDLH502的根系分泌的有机酸分别提高了26.96%和18.85%,pH分别降低了0.79、0.57个单位,SDKH502和SDLH502间存在显著差异。在低磷胁迫下,自交系SDKH502和SDLH502活化吸收难溶性磷酸盐能力的不同与SDKH502和SDLH502根系分泌有机酸和质子能力的差异有关。     

Genotypic Variation of Gas Exchange Parameters and Leaf Stable Carbon and Nitrogen Isotopes in Ten Quinoa Cultivars Grown under Drought

Genotypic variations in leaf gas exchange and grain yield were analysed in 10 highland‐adapted quinoa cultivars grown in the field under drought conditions. Trials took place in an arid mountain region of the Northwest of Argentina (Encalilla, Amaicha del Valle, 22°31′S, 65°59′W). Significant changes in leaf gas exchange and grain yield among cultivars were observed. Our data demonstrate that leaf stomatal conductance to water vapour (g_s) is a major determinant of net CO₂ assimilation (A_n) because quinoa cultivars with inherently higher g_s were capable of keeping higher photosynthesis rate. Aboveground dry mass and grain yield significantly varied among cultivars. Significant variations also occurred in chlorophyll, N and P content, photosynthetic nitrogen‐use efficiency (PNUE), specific leaf area (SLA), intrinsic water‐use efficiency (_iWUE) and carboxylation capacity (A_n/C_i). Many cultivars gave promissory grain yields with values higher than 2000 kg ha^?1, reaching for Sayaña cultivar 3855 kg ha^?1. Overall, these data indicate that cultivars, which showed higher photosynthesis and conductances, were also generally more productive. Carbon isotope discrimination (Δ) was positively correlated with the grain yield and negatively with _iWUE, but δ¹⁵N did not show significant correlations. This study provides a reliable measure of specific responses of quinoa cultivars to drought and it may be valuable in breeding programmes.