Root-zone temperature and salinity: Interacting effects on tillering,growth and element concentration in barley

The effects of root-zone salinity (0, 30, and 60 mmol L^–1 of NaCl) and root-zone temperature (10, 15, 20, and 25°C) and their interactions on the number of tillers, total dry matter production, and the concentration of nutrients in the roots and tops of barley (Hordeum vulgare L.) were studied. Experiments were conducted in growth chambers (day/night photoperiod of 16/8 h and constant air temperature of 20°C) and under water-culture conditions. Salinity and root temperature affected all the parameters tested. Interactions between salinity and temperature were significant (p<0.05) for the number of tillers, growth of tops and roots, and the concentration of Na, K, P in the tops and the concentration of P in the roots. Maximum number of tillers and the highest dry matter were produced when the root temperature was at the intermediate levels of 15 to 20°C. Effect of salinity on most parameters tested strongly depended on the prevailing root temperature. For example, at root temperature of 10°C addition of 30 mmol L^–1 NaCl to the nutrient solution stimulated the growth of barley roots; at root temperature of 25°C, however, the same NaCl concentration inhibited the root growth. At 60 mmol L^–1, root and shoot growth were maximum when root temperature was kept at the intermediate level of 15°C; most inhibition of salinity occurred at both low (10°C) and high (25°C) root temperatures. As the root temperature was raised from 10 to 25°C, the concentration of Na generally decreased in the tops and increased in the roots. At a given Na concentration in the tops or in the roots, respective growth of tops or roots was much less inhibited if the roots were grown at 15–20°C. It is concluded that the tolerance of barley plant to NaCl salinity of the rooting media appears to be altered by the root temperature and is highest if the root temperature is kept at 15 to 20°C.     

Effect of sub-optimal root zone temperatures at varied nutrient supply and shoot meristem temperature on growth and nutrient concentrations in maize seedlings (Zea mays L.)

Maize seedlings were grown for 10 to 20 days in either nutrient solution or in soils with or without fertilizer supply. Air temperature was kept uniform for all treatments, while root zone temperature (RZT) was varied between 12 and 24°C. In some treatments the basal part of the shoot (with apical shoot meristem and zone of leaf elongation) was lifted up to separate the indirect effects of root zone temperature on shoot growth from the direct effects of temperature on the shoot meristem.Shoot and root growth were decreased by low RZT to a similar extent irrespective of the growth medium (i.e. nutrient solution, fertilized or unfertilized soil). In all culture media Ca concentration was similar or even higher in plants grown at 12 as compared to 24°. At lower RZT concentrations of N, P and K in the shoot dry matter decreased in unfertilized soil, whereas in nutrient solution and fertilized soil only the K concentration decreased.When direct temperature effects on the shoot meristem were reduced by lifting the basal part of the shoot above the temperature-controlled root zone, shoot growth at low RZT was significantly increased in nutrient solution and fertilized soil, but not in unfertilized soil. In fertilized soil and nutrient solution at low RZT the uptake of K increased to a similar extent as plant growth, and thus shoot K concentration was not reduced by increasing shoot growth rates. In contrast, uptake of N and P was not increased, resulting in significantly decreased shoot concentrations.It is concluded that shoot growth at suboptimal RZT was limited both by a direct temperature effect on shoot activity and by a reduced nutrient supply through the roots. Nutrient concentrations in the shoot tissue at low RZT were not only influenced by availability in the substrate and dilution by growth, but also by the internal demand for growth.     

Aluminum stress in the roots of naked barley

Phytotoxicity of aluminum (Al) is the major limiting factor for the crops grown in acid soils rapidly inhibiting root elongation. In this study, changes in root growth, total activity and isozyme patterns of antioxidant enzymes such as peroxidase, ascorbate peroxidase, catalase and glutathione reductase by Al stress were investigated in the roots of naked barley (Hordeum vulgare L. cv. Kwangwhalssalbori). As Al concentration increased up to 500 M, the rooting rate and root elongation substantially decreased. Growth results suggested that this cultivar is an Al-sensitive species. Total activities of antioxidant enzymes generally increased at lower Al concentrations and then gradually decreased at higher Al concentrations. They also increased when the exposure time to Al was extended up to 48 hr. Changes in the isozyme patterns of antioxidant enzymes were investigated byin situ enzyme activity staining on a non-denaturing PAGE gel. They generally coincided with the changes in the total activity in parallel. Changes in the total activity of antioxidant enzymes also coincided with the changes of the root growth. Since growth reduction in the roots by Al stress could be related with the changes in the activities of antioxidant enzymes, these results suggested that Al might cause the oxidative stress in the roots of this cultivar of naked barley.     

Heat shock temperature acclimation of normal secretory protein synthesis in barley aleurone cells

Exposure of barley (Hordeum vulgare L. cv. Himalaya) aleurone layers to 40°C for a period of 3 h results in the selective suppression of the synthesis and secretion of hydrolytic enzymes; other normal cellular protein synthesis continues during heat shock. This suppression is correlated with secretory protein mRNA destabilization and the dissociation of stacked ER lamellae during heat shock (Belanger et al. 1986, Proceedings of the National Academy of Sciences USA 83, pp. 1354–1358). In this report we examined the effect of exposure to extended periods of heat shock. If exposure to 40°C was continued for a period of 18 h, the synthesis of α-amylase, the predominant secreted hydrolase, resumed. This was accompanied by increased α-amylase mRNA levels and the reformation of ER lamellae. Though initial exposure (3 h) to 40°C reduced protein secretion to ～10% of that observed in aleurone cells maintained at 25°C, exposure for prolonged periods (16–20 h) permitted the resumption of protein secretion to ～66% of non-heat-shocked control levels. The resumption of normal secretory protein synthesis during prolonged exposure to 40°C was correlated with an increase in the incorporation of [¹⁴C]glycerol into phosphatidylcholine and an increase in the ratio of saturated to unsaturated fatty acids in lipids isolated from ER membrane preparations. Increased fatty acid saturation has been demonstrated to enhance thermostability in biological membranes, and such changes in membrane composition may be important to the recovery of secretory protein synthesis at the ER.     

A laser ablation technique maps differences in elemental composition in roots of two barley cultivars subjected to salinity stress

In saline soils, high levels of sodium (Na⁺) and chloride (Cl^?) ions reduce root growth by inhibiting cell division and elongation, thereby impacting on crop yield. Soil salinity can lead to Na⁺ toxicity of plant cells, influencing the uptake and retention of other important ions [i.e. potassium (K⁺)] required for growth. However, measuring and quantifying soluble ions in their native, cellular environment is inherently difficult. Technologies that allow in situ profiling of plant tissues are fundamental for our understanding of abiotic stress responses and the development of tolerant crops. Here, we employ laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) to quantify Na, K and other elements [calcium (Ca), magnesium (Mg), sulphur (S), phosphorus (P), iron (Fe)] at high spatial resolution in the root growth zone of two genotypes of barley (Hordeum vulgare) that differ in salt‐tolerance, cv. Clipper (tolerant) and Sahara (sensitive). The data show that Na⁺ was excluded from the meristem and cell division zone, indicating that Na⁺ toxicity is not directly reducing cell division in the salt‐sensitive genotype, Sahara. Interestingly, in both genotypes, K⁺ was strongly correlated with Na⁺ concentration, in response to salt stress. In addition, we also show important genetic differences and salt‐specific changes in elemental composition in the root growth zone. These results show that LA‐ICP‐MS can be used for fine mapping of soluble ions (i.e. Na⁺ and K⁺) in plant tissues, providing insight into the link between Na⁺ toxicity and root growth responses to salt stress.     

Regulation of protein synthesis in root, shoot and embryonic tissues of germinating barley during salinity stress

Abstract Protein synthesis during seed germination, a stage vulnerable to salinity stress, was investigated. The responses of barley genotypes, CM72 (California Mariout 72) and Prato, toward salinity were different during seed germination. Germination of CM72 was unaffected up to 0.34 kmol m^?3 (2%) NaCl, but that of Prato was reduced 30% by 0.17 kmol m ³ NaCl and 75% by 0.34 kmol m^?3 NaCl. Therefore, the former genotype is relatively more salt-tolerant than the latter. Protein synthesis in roots, shoots, and embryos was investigated in these two genotypes before and after salinity stress. The uptake of S-methionine and its incorporation into protein were significantly reduced by salinity in both genotypes. The inhibition of global protein synthesis was significant in roots and shoots. Proteins from different tissues were resolved by single and two dimensional gels. The steady-state protein levels were maintained remarkably well during salinity stress in roots and shoots. Likewise, proteins in germinating embryos were stable except for a 42-kilodalton protein unique to the salt tolerant genotype which was apparently degraded during salinity stress. Salinity, around 0.34 kmol m^?3 NaCl, induced both quantitative and qualitative changes in the expression of some proteins labelled in vivo. The quantitative changes included repression or enhancement of synthesis of selected groups of proteins. Around 8% of the nearly 400 resolved proteins in a tissue was affected this way. Some of the proteins in this category were specific to each genotype. About 1 % of the total showed qualitative changes; these proteins were expressed only during salinity stress. In roots, two proteins (28, 41.7 kilodaltons) were detected in CM72 and five (28, 45, 60.5, 76.5, 82.5 kilodaltons) in Prato; only the 28-kilodalton protein was common to both genotypes. In shoots, four proteins (45, 60.5, 76.5, 82.5 kilodaltons) were found only in Prato and these were similar to those induced in roots. The four new proteins (32, 37.5, 89, 92 kilodaltons) in germinating embryos were apparently induced only in CM72; these were distinctly different from those detected in developed roots and shoots. The unique protein changes induced by salinity stress during germination (this study) and seedling growth studies reported earlier (Ramagopal, 1987b) are apparently different. The findings demonstrate that ontogeny plays an important role in the expression of tissue-specific proteins during salinity stress in the salt tolerant and sensitive barley genotypes.     

高温和干旱胁迫对西红柿幼苗生长、养分含量及元素利用效率的影响

全球气候变化将增加未来高温与干旱的发生频率和强度,然而高温与干旱的交互作用对农作物生长、养分含量及其利用效率的影响还不甚清楚。因此,研究高温与干旱交互作用对农作物生理生态的影响将为准确评价农作物对未来极端气候条件的响应提供科学依据。选取全球第四大经济作物——西红柿为研究对象,在人工智能气候箱中模拟高温和干旱环境。共设置两个水分处理(正常浇水;干旱)与两个温度处理(常温-26℃/19℃(白天/夜间);高温-42℃/35℃(白天/夜间)(7d))。主要测定指标包括生物量以及生物量分配、比叶面积、养分含量(全氮、全磷)、光合元素利用效率(光合氮素利用效率、光合磷素利用效率)。研究表明,高温、干旱单独作用以及交互作用均显著降低了根、茎、叶生物量以及总生物量,并且高温干旱交互作用使总生物量降低最多。在生物量分配方面,高温单独作用显著降低了根质量分数以及根冠比,而干旱单独作用增加了根质量分数、茎质量分数以及根冠比,但降低了叶质量分数。在养分含量方面,高温单独作用导致叶片全氮、全磷含量显著降低、茎全磷含量显著增加、根全磷含量显著降低。干旱单独作用导致叶片、茎全磷含量显著降低、根全氮含量显著升高。高温与干旱交互作用对生物量分配及养分含量的影响与干旱胁迫单独作用类似。在光合元素利用效率方面,高温、干旱单独作用均降低了幼苗光合氮素利用效率、光合磷素利用效率,并且高温加剧了干旱对光合磷素利用效率的影响。因此,在未来气候变化情况下,高温与干旱交互作用可能会对农作物产生更大威胁。     

Effect of temperature and salinity stress on growth and lipid composition of Shewanella gelidimarina

The maximum growth temperature, the optimal growth temperature, and the estimated normal physiological range for growth of Shewanella gelidimarina are functions of water activity (a(w)), which can be manipulated by changing the concentration of sodium chloride. The growth temperatures at the boundaries of the normal physiological range for growth were characterized by increased variability in fatty acid composition. Under hyper- and hypoosmotic stress conditions at an a(w) of 0.993 (1.0% [wt/vol] NaCl) and at an a(w) of 0.977 (4.0% [wt/vol] NaCl) the proportion of certain fatty acids (monounsaturated and branched-chain fatty acids) was highly regulated and was inversely related to the growth rate over the entire temperature range. The physical states of lipids extracted from samples grown at stressful a(w) values at the boundaries of the normal physiological range exhibited no abrupt gel-liquid phase transitions when the lipids were analyzed as liposomes. Lipid packing and adaptational fatty acid composition responses are clearly influenced by differences in the temperature-salinity regime, which are reflected in overall cell function characteristics, such as the growth rate and the normal physiological range for growth.     

Phosphorus (P) uptake and growth of a root hairless barley mutant (bald root barley, brb) and wild type in low- and high-P soils

The recently isolated root‐hairless mutant of barley (Hordeum vulgare L), bald root barley, brb offers a unique possibility to quantify the importance of root hairs in phosphorus (P) uptake from soil. In the present study the ability of brb and the wild‐type, barley genotype Pallas producing normal root hairs to deplete P in the rhizosphere soil was investigated and the theory of diffusion and mass flow applied to compare the predicted and measured depletion profiles of diffusible P. Pallas depleted twice as much P from the rhizosphere soil as brb. The P depletion profile of Pallas uniformly extended to 0.8 mm from the root surface, which was equal to the root hair length (RHL). The model based on the theory of diffusion and mass flow explained the observed P‐depletion profile of brb, and the P depletion outside the root‐hair zone of Pallas, suggesting that the model is valid only for P movement in rhizosphere soil outside the root‐hair zone. In low‐P soil (P in soil solution 3 µm ) brb did not survive after 30 d, whereas Pallas continued to grow, confirming the importance of root hairs in plant growth in a P‐limiting environment. In high‐P soil (P in soil solution 10 µm ) both brb and Pallas maintained their growth, and they were able to produce seeds. At the high‐P concentration, RHL of the Pallas was reduced from 0.80 ± 0.2 to 0.68 ± 0.14 mm. In low‐P soil, P‐uptake rate into the roots of Pallas was 4.0 × 10^?7 g mm^?1 d^?1 and that of brb was 1.9 × 10^?7 g mm^?1 d^?1, which agreed well with the double amount of P depleted from the rhizosphere soil of Pallas in comparison with that of brb. In high‐P soil, the P uptake rates into the roots of brb and Pallas were 3.3 and 5.5 × 10^?7 g mm^?1 d^?1, respectively. The results unequivocally confirmed that in a low‐P environment, root hairs are of immense importance in P acquisition and plants survival, but under high‐P conditions they may be dispensable. The characterization of phenotypes brb and Pallas and the ability to reproduce seeds offers a unique possibility of molecular mapping of QTLs and candidate genes conferring root‐hair formation and growth of barley.     

低磷胁迫下磷高效基因型大麦的根系形态特征

在根袋土培盆栽条件下,以磷高效基因型DH110+、DH147和低效基因型DH49大麦为试验材料,利用根系分析系统分析不同施磷(P₂O₅)水平(极低磷25 mg·kg^-1、低磷50 mg·kg^-1和正常磷75 mg·kg^-1)下,磷高效基因型大麦的根系形态特征及其与植株磷素吸收的关系.结果表明： 低磷胁迫显著降低大麦生物量和磷吸收量,其中磷高效基因型的生物量和磷吸收量在各施磷水平下分别为低效基因型的1.24～1.70和1.18～1.83倍;大麦的总根长、总根表面积、平均根系直径、不定根长及其根表面积、侧根长及其根表面积均随施磷水平的降低而显著降低,其中磷高效基因型大麦在各施磷水平下的总根长、总根表面积、比根长、侧根长及根表面积分别为低效基因型的1.46～2.06、1.12～1.51、1.35～1.72、1.69～2.42和1.40～1.78倍,而平均根系直径为低效基因型的70.6%～90.2%;主成分分析表明,平均根系直径、比根表面积和比根长受基因型差异的影响较为明显,是区分两类磷效率基因型大麦根系形态差异的主要指标;偏最小二乘回归分析表明,各施磷水平下,总根长、总根表面积对大麦植株磷素吸收贡献均较大,随施磷水平降低,不定根长、不定根表面积对大麦植株磷素吸收的贡献明显降低,而平均根系直径、比根长、侧根长及其根表面积的贡献明显增加.磷高效基因型大麦可通过维持侧根的生长、根细度和比根长的增加来适应低磷胁迫.     

温度和盐度对皱肋文蛤幼贝存活与生长的影响

在室内控制条件下,研究了不同海水温度和盐度对皱肋文蛤(Meretrix lyrata)幼贝存活与生长的影响。结果表明:皱肋文蛤幼贝适宜生存温度为12.2-35.6℃,最适生存温度为24-30℃;适宜生长温度为23.5-33.0℃,最适生长温度为27-30℃,属典型的南方滩涂贝类。皱肋文蛤幼贝适宜生存盐度为4.3-40.5,最适生存盐度为11-31;适宜生长盐度为17.1-33.4,最适生长盐度为19-23,属广盐性滩涂贝类。该贝低温和高温敏感起始点分别为21℃和33℃;低盐和高盐敏感起始点分别为9和33。皱肋文蛤幼贝对极端温、盐度具有一定的耐受力:在37℃下仍可保持6d,100%不死亡,在39、41℃下分别在3d和5d内全部死亡;在4、6、8、10、12℃下则可分别100%存活3、4、6、9、11d;在盐度为0、5、7、9时保持100%存活的时间分别为5、8、10、10d;在盐度为33、35、37、39时保持100%存活的时间分别为7、5、3、3d,盐度41时当天即出现死亡。     

Developmental patterns of a large set of barley (Hordeum vulgare) cultivars in response to ambient temperature

Ambient temperature plays an important role in plant development. In cereals, little is known about the exact effects of ambient temperature in the range between it being a vernalising agent and an abiotic stress factor; thus the genetic determinants involved in the registering and response to ambient temperature, and their natural variation has not been dissected either. Principally, we wished to establish the level of natural variation in response to ambient temperature in barley via studying plant phenological development. The responses to temperature of 168 barley genotypes of different provenances and seasonal growth habit groups were observed in controlled environments. The effects of four temperature regimes (13°C, 16.5°C, 18°C and 23°C) on the duration of plant phenophases were examined. The plant development was characterised in a series of consecutive phenophases that span the plant life cycle from germination through flowering to attainment of maximum plant height. Ambient temperature affected significantly plant development, with substantial variation in responses among the genotypes. Six major types of responses were identified, which depended strongly on seasonal growth habit, with only a small degree of overlap. Although the differences in the timing of development among clusters were significant under each temperature regime, the 23°C treatment resulted in the largest diversity of responses, with significant changes in the ranking of the six clusters compared to other treatments. Two clusters showed particularly unusual responses to 23°C: the development of one winter barley cluster was extremely accelerated by the 23°C treatment, whereas the development of one spring barley cluster was significantly delayed. Ambient temperature assumes importance as a regulatory cue in the intricate and complex temporal and spatial regulation network of plant development in cereals and acts mostly through its regulatory effect on certain developmental phases such as the onset and duration of the intensive stem elongation.     

Plasma membrane proteome analysis identifies a role of barley membrane steroid binding protein in root architecture response to salinity

Although the physiological consequences of plant growth under saline conditions have been well described, understanding the core mechanisms conferring plant salt adaptation has only started. We target the root plasma membrane proteomes of two barley varieties, cvs. Steptoe and Morex, with contrasting salinity tolerance. In total, 588 plasma membrane proteins were identified by mass spectrometry, of which 182 were either cultivar or salinity stress responsive. Three candidate proteins with increased abundance in the tolerant cv. Morex were involved either in sterol binding (a GTPase‐activating protein for the adenosine diphosphate ribosylation factor [ZIGA2], and a membrane steroid binding protein [MSBP]) or in phospholipid synthesis (phosphoethanolamine methyltransferase [PEAMT]). Overexpression of barley MSBP conferred salinity tolerance to yeast cells, whereas the knock‐out of the heterologous AtMSBP1 increased salt sensitivity in Arabidopsis. Atmsbp1 plants showed a reduced number of lateral roots under salinity, and root‐tip‐specific expression of barley MSBP in Atmsbp1 complemented this phenotype. In barley, an increased abundance of MSBP correlates with reduced root length and lateral root formation as well as increased levels of auxin under salinity being stronger in the tolerant cv. Morex. Hence, we concluded the involvement of MSBP in phytohormone‐directed adaptation of root architecture in response to salinity.     

Boron toxicity in barley (Hordeum vulgare L.) seedlings in relation to soil temperature

Boron (B) is an essential micronutrient in crop growth but its sufficiency range is narrow. Boron toxicity is a widespread problem in arid and semi-arid areas with cold weather. We investigated the effect of soil temperature (5, 10 and 15°C) on development of symptoms of B toxicity, plant growth and plant development, and on content and concentration of B in tissue of seedlings of four barley lines grown in soil with high level of available B (12 mg kg^–1). Visual symptoms of toxicity were first observed in the high B soil concentration treatment at 5 °C at 12 days after emergence. Concentration of B in tissue decreased with increasing soil-temperatures. There was no effect of soil temperature on B content or B concentration in plant tissue at the final sample (17 days after emergence). High soil B reduced seedling and leaf emergence rates, although the final seedling emergence and number of leaves were unaffected. Barley lines differed in concentration of B in tissues and visual toxicity symptom development. Adaptation to high B was either through maintaining low tissue B concentration or through tolerance to high tissue B concentration. While the investigated range of temperature does influence B toxicity in barley seedlings, it remains to be determined whether it affects crop yield.     

Pre-germination effects on mechanically impeded root growth of barley (Hordeum vulgare L)

The effects of conditions pre-dating germination on growth rate of impeded barley cv. Harrington roots were measured using an agar-capillary tube technique. Seedling root tips were directed into glass capillary tubes twothirds filled with agar at eight concentrations ranging from 1.6 to 9.6%, equivalent to penetrometer resistances of 25 to 1240 kPa. The rate of unrestricted root elongation (growth in air) of seed stored for 13 months (old seed), and of seed grown for a second generation without subsequent storage (new seed) was compared with growth in agar over a 24-hour interval. Root elongation rate of old and new seed was identical in the absence of resistance. At low to intermediate agar concentrations, elongation was significantly slower in roots from old, compared with new seed. At high agar concentrations root growth of old and new seed was the same. In both old and new seed, root growth through agar was greater in seed that germinated after 24, compared with 48 h. Differences in impeded root growth between old and new seed were lost in progeny of the test seed. Environmental factors that pre-date germination are an important influence on the ability of seedling roots to elongate through soil.LRS Contribution no. 3879349LRS Contribution no. 3879349     

Vertical gradient in soil temperature stimulates development and increases biomass accumulation in barley

We have detailed knowledge from controlled environment studies on the influence of root temperature on plant performance, growth and morphology. However, in all studies root temperature was kept spatially uniform, which motivated us to test whether a vertical gradient in soil temperature affected development and biomass production. Roots of barley seedlings were exposed to three uniform temperature treatments (10, 15 or 20°C) or to a vertical gradient (20-10°C from top to bottom). Substantial differences in plant performance, biomass production and root architecture occurred in the 30-day-old plants. Shoot and root biomass of plants exposed to vertical temperature gradient increased by 144 respectively, 297%, compared with plants grown at uniform root temperature of 20°C. Additionally the root system was concentrated in the upper 10cm of the soil substrate (98% of total root biomass) in contrast to plants grown at uniform soil temperature of 20°C (86% of total root biomass). N and C concentrations in plant roots grown in the gradient were significantly lower than under uniform growth conditions. These results are important for the transferability of 'normal' greenhouse experiments where generally soil temperature is not controlled or monitored and open a new path to better understand and experimentally assess root-shoot interactions.     

Influence of water activity, temperature and time on mycotoxins production on barley rootlets

AIMS: The objective of this study was to determine the ochratoxin (OT) and aflatoxin (AF) production by three strains of Aspergillus spp. under different water activities, temperature and incubation time on barley rootlets (BR). METHODS AND RESULTS: Aspergillus ochraceus and Aspergillus flavus were able to produce mycotoxins on BR. Aspergillus ochraceus produced ochratoxin A (OTA) at 0.80 water activity (a(w)), at 25 and 30 degrees C as optimal environmental conditions. The OTA production varies at different incubation days depending on a(w). Aflatoxin B(1) (AFB1) accumulation was obtained at 25 degrees C, at 0.80 and 0.95 a(w), after 14 and 21 incubation days respectively. Temperature was a critical factor influencing OTA and AFB(1) production. CONCLUSIONS: This study demonstrates that BR support OTA and AFB(1) production at relatively low water activity (0.80 a(w)) and high temperatures (25-30 degrees C). SIGNIFICANCE AND IMPACT OF THE STUDY: The study of ecophysiological parameters and their interactions would determine the prevailing environmental factors, which enhance the mycotoxin production on BR used as animal feed.     

Interactions between diurnal temperature fluctuations and salinity on expansion growth and water status of young tomato plants

Expansion growth is limited if the difference between day and night temperature (DIF) is negative. Growth is also limited high salinity. Expansion growth of tomato seedlings was studied under day/night temperatures of 16/24°C and 24/16°C, and nutrient solution salinities of 3 and 15 mS cm^-1 to ascertain whether interactions exist between the two stress forms. Water status was also studied in order to assess possible mechanisms of growth retardation. A significant interaction between DIF and salinity was found for all recorded growth variables. Hypocotyl length, plant height, leaf area and fresh and dry weight were lower at negative DIF than at positive, the reduction being greater at low salinity than at high. Increased salinity also reduced growth, more so at positive DIF than at negative. Growth reduction at negative DIF was accompanied increased shoot water and osmotic potentials. Pressure potential was unaffected DIF. Growth reduction at high salinity was accompanied reduced water and osmotic potentials. Pre-dawn pressure potential was increased at high salinity, whereas no effect of salinity on pressure potential at midday was found. The differences in effects on water status between the two stress forms may suggest differing mechanisms of growth retardation.