Relative Shoot Length Research Articles

Genome-wide association study to identify candidate loci and genes for Mn toxicity tolerance in rice.

Manganese (Mn) is an essential micro-nutrient for plants, but flooded rice fields can accumulate high levels of Mn2+ leading to Mn toxicity. Here, we present a genome-wide association study (GWAS) to identify candidate loci conferring Mn toxicity tolerance in rice (Oryza sativa L.). A diversity panel of 288 genotypes was grown in hydroponic solutions in a greenhouse under optimal and toxic Mn concentrations. We applied a Mn toxicity treatment (5 ppm Mn2+, 3 weeks) at twelve days after transplanting. Mn toxicity caused moderate damage in rice in terms of biomass loss and symptom formation despite extremely high shoot Mn concentrations ranging from 2.4 to 17.4 mg g-1. The tropical japonica subpopulation was more sensitive to Mn toxicity than other subpopulations. Leaf damage symptoms were significantly correlated with Mn uptake into shoots. Association mapping was conducted for seven traits using 416741 single nucleotide polymorphism (SNP) markers using a mixed linear model, and detected six significant associations for the traits shoot manganese concentration and relative shoot length. Candidate regions contained genes coding for a heavy metal transporter, peroxidase precursor and Mn2+ ion binding proteins. The significant marker SNP-2.22465867 caused an amino acid change in a gene (LOC_Os02g37170) with unknown function. This study demonstrated significant natural variation in rice for Mn toxicity tolerance and the possibility of using GWAS to unravel genetic factors responsible for such complex traits.

CORRELATION AND HERITABILITY ESTIMATION OF VARIOUS SEEDLING TRAITS IN BRASSICA NAPUS L. UNDER WATER DEFICIT CONDITIONS

Brassica napus L. contains edible oil ensuring safe limits for human health. But farmers prefer to use their fertile land for main crops and only marginal lands for oilseed. Those marginal lands usually face water scarcity and other a-biotic stresses that affect the normal growth and development of plant. Here we tested three levels of water deficit stress (control, medium and high) under controlled conditions. Seedlings were analyzed for various seedling traits to measure the relative effect of different levels water deficit stress. Graphical trends depicts that increasing level of water deficit stress causes declines in leaf area, root length, shoot length, fresh and dry weight of roots and shoots. Correlation coefficients exposed positive significant correlation of fresh shoot weight with chlorophyll contents, relative water contents, leaf area and shoot length at both genotypic and phenotypic level. Path coefficient analysis displayed high direct effects on fresh shoot weight were due to relative water content, root to shoot ratio. Chlorophyll contents, relative water content, leaf area, root length and shoot length showed high broad sense heritability (h2BS) coupled with high genetic advance (GA). These traits could be focused while breeding for water deficit conditions.

Exploring Aluminum Tolerance at Seedling Stage in Rice (Oryza sativa, Linn) by Using Modified Magnavaca Nutrient Solution

<p>Aluminum (Al) toxicity is considered as one of the main constraints for crop production in acidic soil. This study was subjected to observe the response of root and shoot growth of eight rice varieties under Al stress in hydrophonic solution. A modified Magnavaca’s solution was used to compare the effect of Al stress using different variables which were relative root elongation (RRE), relative shoot length (RSL) and relative root weight (RRW). The experiment was conducted in split-plot experimental design. Eight rice varieties were screened in four Al levels (0 μM, 540 μM, 750 μM, and 1,300 μM). Root length, shoot length,<br />and root dry weight were measured after 7 days of treatment, then the RRE, RSL, and RRW were calculated. The results showed that Al significantly reduced RRE and RSL but increased RRW. RSL was reduced as the Al concentration increased while RRE reduction started only at 750 μM Al concentration. It was observed that RRW was significantly higher under 540 and 750 μM Al concentration. However, no significant difference was observed in 1,300 μM Al concentration. The increase in root weight is partly attributed by the thickening of the root wall, but this effect was diminished due to root hair inhibition under 1,300 μM Al concentration. Among these three variables observed, root and shoot lengths indicated better variables in determining Al tolerance in rice, compared to root weight. However, these variables were not sufficient to represent root and shoot growth inhibition, and not sufficient to be used solely for Al toxicity screening</p>

Responses of contrasting rice genotypes to excess manganese and their implications for lignin synthesis

Manganese (Mn) toxicity is frequently encountered in crops grown on soils with low pH or low redox potential, and harmful to plant development and growth. This study aimed at exploring adaptive mechanisms to Mn toxicity in rice, and investigated the effects of Mn toxicity on shoot lignification. Sixteen rice genotypes were grown in hydroponic solutions and exposed to normal (0.5 mg dm−3) or toxic (5 mg dm−3) Mn concentrations for three weeks. Morphological responses to Mn toxicity included a significant reduction in shoot length and the formation of visible symptoms scored as leaf damage index (LDI). Based on shoot Mn concentrations in the Mn toxic treatment, genotypes were classified as Mn includers and excluders. Across different genotypes, shoot Mn concentrations were significantly negatively correlated with relative shoot length and positively correlated with LDI. Consequently, the most tolerant genotypes in terms of morphology were all excluders, while the most sensitive genotypes were includers. The sensitive genotypes were also more responsive to manganese in terms of lipid peroxidation than tolerant genotypes. Shoots of rice plants grown in the high Mn treatment showed a higher level of lignification measured as thioglycolic acid lignin (TGAL), especially among Mn includers. TGAL was positively correlated with shoot Mn concentration and the levels of phenolics. In contrast, peroxidase activity was not responsive to the Mn treatment and was not significantly correlated with shoot lignification. In conclusion, exclusion is a dominant tolerance mechanism to Mn toxicity in rice. Further, Mn stimulated lignin biosynthesis in rice, especially in genotypes that were unable to exclude Mn.

Morphological, physiological, biochemical characteristics and bud success responses of myrobolan 29 c plum rootstock subjected to water stress

Water stress treatments on some morphological, biomass, physiological, biochemical characteristics and budding success of apricot and plum cultivars/Myrobolan 29 C plum rootstock have been studied in a pot-experiment trial. Three different water stress levels (control-100 %, medium-75 %, and severe-50 % of the pot capacity) were applied. The results showed that measured morphological, biomass, physiological and biochemical characteristics as well as budding success of cultivars on the rootstocks were affected by water stress. Water stress, both moderate and severe, significantly decreased the relative shoot length, diameter and shoot stem cross sectional area, plant total fresh and dry weights. Increases in water stress led to increases in peroxidase activities, phenol and proline contents in plum rootstock. Increases in water stress also resulted in reduction in budding success in both Formosa (plum cv)/Myrobolan 29 C (90.00 % and 48.33 %) and San Castrese (apricot cv)/Myrobolan 29 C (87.50 % and 42.83 %).

Screening of chickpea genotypes against salinity stress

The experiment was conducted during the period from December 13, 2010 to May 13, 2011 at the Crop Physiology Lab, Agronomy Division, Bangladesh Agricultural Research Institute (BARI). In Hoagland culture solution, 70 (Seventy) genotypes of chickpea were tested during germination and seedling stage at 0, 5, 10 and 15 dS/m salinity levels. Distilled water (0 dS/m) was used as a control. Germination percentage (GP), relative germination percentage (RGP), germination rate (GR), relative germination rate (RGR), root length (RL), relative root length (RRL), shoot length (SL), relative shoot length (RSL), vigor index, total dry matter (TDM) and relative total dry matter (RTDM) were found to be affected by salinity. Genotypes BD-6061, BD-6066 BD-6071, BD- 6060, BD-6067 and BD 6078 performed better at 10 dS/m and survived up to 15 days after germination as evaluated on the basis of germination percentage (GP), relative germination percentage (RGP), total dry matter (TDM) and relative total dry matter (RTDM). These genotypes could be selected for further investigation under pot culture and field evaluation in the saline area. DOI: http://dx.doi.org/10.3329/bjar.v39i4.22539 Bangladesh J. Agril. Res. 39(4): 605-619, December 2014

The effect of water stress on some morphological, physiological, and biochemical characteristics and bud success on apple and quince rootstocks.

The effects of different water stress (control, medium, and severe) on some morphological, physiological, and biochemical characteristics and bud success of M9 apple and MA quince rootstocks were determined. The results showed that water stress significantly affected most morphological, physiological, and biochemical characteristics as well as budding success on the both rootstocks. The increasing water stress decreased the relative shoot length, diameter, and plant total fresh and dry weights. Leaf relative water content and chlorophyll index decreased while electrolyte leakage increased with the increase of water stress in both rootstocks. An increase in water stress also resulted in reduction in budding success in Vista Bella/M9 (79.33% and 46.67%) and Santa Maria/MA (70.33% and 15.33%) combinations. However, the water stress in Santa Maria/MA was more prominent. The increase in water stress resulted in higher peroxidase activities as well as phenol contents in both rootstocks. Although catalase activity, anthocyanin, and proline contents increased with the impact of stress, this was not statistically significant. The results suggest that the impact of stress increased with the increase of water stress; therefore, growers should be careful when using M9 and MA rootstocks in both nursery and orchards where water scarcity is present.

Assessment of Arsenite, Arsenate, and Chromate Phytotoxicity Based on the Activity of Seed Germination and Growth (Root & Shoot) of Various Plant Seeds

ABSTRACT Effects of different concentrations of arsenite, arsenate, and chromate on seed germination, root length (RL), and shoot length (SL) in four seed types, chosen from preliminary tests with eight seed types, were investigated to assess the toxicity of the tested metals. The sensitivities of the four different seed types toward germination, relative RL (RRL), and relative SL (RSL) varied with each metal. In a comparison, the germination of the seeds was more sensitive to the tested metals than the other chosen endpoints (RL and SL). Arsenite was generally more restrictive to all the endpoints (germination, root, and shoot growth) than arsenate and chromate. Lactuca (garden lettuce) was also generally more sensitive to the tested metals than the other seed types. The correlation between RRL and RSL varied depending on the seed type and metal tested. However, significant correlations (r2 > 0.85) of these were observed with Lactuca seeds, which appeared to be an optimal plant with respect to the tolerance of the tested metals. The differences in the toxicities of metals toward different plant species should be taken into account in the bioassessment of metals-contaminated sites. Thus, this study encourages the need to combine the three endpoints of various seeds in the evaluation of toxicities of metals.

Comparison of Salt Tolerance in Brassicas and Some Related Species

In this paper the salt tolerance in Brassicas and some related species was compared. When seedlings germinated on sand cultures with liquid MS medium were considered, the relative germination rate, root length, shoot length and fresh seedling weight were significantly correlated with each other (P 0.01), and only the relative shoot lengths were significantly different among the tested genotypes (P 0.05); When both seedlings germinated on MS and MS plus 0.4% NaCl were considered, only the relative shoot length of seedlings germinated on MS was significantly different from that germinated on MS + 0.4% NaCl (P 0.05), and also only the relative shoot lengths were significantly different among the tested genotypes (P 0.01). Raphanus sativa cv. Changfeng, B. juncea cv. JC and Brassica napus cv. ZS 10 showed low salt tolerance in terms of relative germination rate, root length, shoot length and fresh seedling weight; B. oleracea cv. JF-1, Sinapis alba cv. HN-2 showed high salt tolerance in terms of relative germination rate, root length, shoot length and fresh seedling weight. Based on our result we suggest that relative shoot length might be convenient to rank the salt tolerance but cluster analysis based on multiple parameters of relative germination rate, root length, shoot length and fresh seedling weight might be more accurate in screening for salt tolerance in Brassicas and related species.

Response to Sodium Chloride Stress at Germination and Seedling and Identification of Salinity Tolerant Genotypes in Foxtail Millet Landraces Originated from China

One hundred and ninety-four Chinese foxtail millet [Setaria italica (L.) P. Beauv.] landraces were screened at germina-tion and seedling stages for salinity tolerance with 150 or 250 mmol L-1 NaCl treatments. On the basis of relative seed germina-tion rate (RSG), relative shoot length (RSL), and relative root length (RRL), the landraces Honggu, Xiaohuanggu, and Sanbian-chou, were identified to be the most salt-tolerant while Yegu 5 and Yanggu sensitive to salt stress. Correlation analysis indicated that RSG was not closely correlated with relative plant height (RPH) and relative leaf area (RLA) of the first true leaf at seedling stage. However, Yegu 5 and Yanggu with poor salinity tolerance at germination stage were also sensitive to salt stress at seedling stage. The RPH of Honggu, Xiaohuanggu, and Sanbianchou, were smaller than those of Yegu 5 and Yanggu. Under high concen-trations of NaCl, the RLA of Xiaohuanggu was smaller than that of other landraces.

Influence of Sulfate Concentration in Mineral Solution on Ryegrass Grown at Different pH and Aluminum Levels

The objective of this study was to clarify the effects of sulfate and phosphate at different sulfate concentrations, pH levels, and aluminum (Al) concentrations on aluminum phytotoxicity in ryegrass grown in mineral solution. The results demonstrated that, in general, both a high sulfate concentration and phosphate in the mineral solution had a positive effect on the detoxification of Al. Increased sulfate concentrations did not have a clear effect on the sulfur (S) or phosphorus (P) content within the shoot or root, because their uptake is regulated by Al uptake in the ryegrass, but a very good relationship was found between the P root content and Al root content (r = 0.944**; p ≤ 0.01). The P and S root content and the aluminum:phosphorus molar ratio in roots were negatively correlated to shoot dry weight (r = −0.747**, −0.619** and −0.816**, respectively; p ≤ 0.01), suggesting that Al tolerance is related to P nutrition. Relative root dry weight (RTI) measured at 90 d was a more sensitive indicator of Al toxicity than relative root or shoot length (RRL, RSL). This study showed that the most important Al detoxifying mechanisms in the ryegrass were apparently physiological Al-PO4 precipitation inside the root and chemical AlSO4 + complex formation in the nutritive solution.

Root and Shoot Growth Responses to Salinity in Maize and Soybean

AbstractSalinity generally reduces shoot growth of crops more than root growth, based on dry weight rather than length measurements. The objective of this study was to compare changes in root length to changes in shoot height under conditions of salinity, using the minirhizotron technique. The experiment was conducted in soil containers (55 cm long, 15 cm diam.), using greenhouse‐grown soybean [Glycine max (L.) Merr.] and field‐grown maize (Zea mays L.) as test crops. Segmented, nonlinear regression analysis showed changes in root length as viewed through minirhizotron tubes to be more sensitive to salinity than changes in shoot height, while there was no response to salinity treatment for final root dry weight. The regression coefficients of changes in relative shoot and root length vs. the electrical conductivity of the soil saturation extract (ECe) were 5.3 ± 4.0% per dS m−1 for soybean shoots and 6.6 ± 4.3% per dS m−1 for soybean roots. For maize, the values were 6.9 ± 1.6% per dS m−1 for shoots and 9.0 ± 4.9% per dS m−1 for roots. The regression coefficients of relative shoot height vs. relative root length of soybean and maize were 0.61 ± 0.27 and 0.66 ± 0.20, both significantly smaller than one. The discrepancy between the response in root length as measured by the minirhizotron technique and the response as measured in final root dry weights was attributed to the fact that changes in root length, as viewed in the minirhizotron video frames, depend more on new lateral root initiation than on extension of individual existing roots. Root extension is a turgor‐dependent process, as is shoot elongation, while lateral root initiation is not turgor dependent, and thus may be more sensitive to salinity. One might also speculate that the young, thin lateral roots are more sensitive to salt stress than the older, thicker main root system. Additionally, final root weight is insensitive to the addition of lateral roots if salinity treatments are initiated after the main root system is established, as was the case in this experiment.

A Model of Chrysanthemum Stem Elongation

The relative progression of lateral shoot elongation from pinch to flower of chrysanthemum [Dendranthema grandiflora (Ramat.) Kitamura `Bright Golden Anne'] plants grown under 2 to 22 mol·day-1·m-2 photosynthetic photon flux and 10 to 20C was modeled using Richards function. Parameters for the function were determined by first transforming data of shoot length and time from pinch (start of short photoperiods) to flower to a relative scale of 0.0 to 1.0 by dividing all intermediate shoot lengths and measurement dates by final shoot length and number of days to flower, respectively. Data used for parameter estimation originated with plants grown at a daily average of ≤20C, since those grown at a daily average above 20C exhibited delayed morphological flower induction and reached 50% of the final shoot length earlier in development. Relative shoot elongation was described by Richards function in the following form: Relative shoot length = SF × {1 + [(SF/SO)N-1] e-SF Kt}-1/N where t (relative time) = 0.0 to 1.0, SF (maximum relative shoot length) = 1.018, SO (relative shoot length at t = o) = 0.0131, N (model parameter related to the shape of the curve) =0.3923, and K (model parameter related to mean relative growth rate) = 5.8138.