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Polyethylene Glycol (peg)-treated Hydroponic Culture Reduces Length and Diameter of Root Hairs of Wheat Varieties

Arif Hasan Khan Robin
Department of Genetics and Plant Breeding, Bangladesh Agricultural University, Mymensingh 02202, Bangladesh

Md. Jasim Uddin
Department of Genetics and Plant Breeding, Bangladesh Agricultural University, Mymensingh 02202, Bangladesh

Khandaker Nafiz Bayazid
Department of Genetics and Plant Breeding, Bangladesh Agricultural University, Mymensingh 02202, Bangladesh

Abstract/ Executive Summary:

Wheat is an important cereal crop worldwide that often suffers from moisture deficits at the reproductive stage. Polyethylene glycol (PEG)-treated hydroponic conditions create negative osmotic potential which is compared with moisture deficit stress. An experiment was conducted in a growth chamber to study the effects of PEG on root hair morphology and associated traits of wheat varieties. Plants of 13 wheat varieties were grown hydroponically and three different doses of PEG 6000 (w/v): 0% (control), 0.3% and 0.6% (less than −1 bar) were imposed on 60 days after sowing for 20 days’ duration. A low PEG concentration was imposed to observe how initial low moisture stress might affect root hair development. PEG-treated hydroponic culture significantly decreased root hair diameter and length. Estimated surface area reduction of root hairs at the main axes of wheat plants was around nine times at the 0.6% PEG level compared to the control plants. Decrease in root hair diameter and length under PEG-induced culture decreased “potential” root surface area per unit length of main root axis. A negative association between panicle traits, length and dry weight and the main axis length of young roots indicated competition for carbon during their development. Data provides insight into how a low PEG level might alter root hair development.

Keywords: Wheat; Root hairs; Root morphology; Phytomer; PEG

Location: Department of Genetics and Plant Breeding, Bangladesh Agricultural University, Mymensingh

Start Date: 00-08-2013

End Date: 00-02-2014

Program Area: Variety and Species

Commodity: Wheat

Objectives:

To explore how Polyethylene glycol (PEG) treated hydroponic culture affects root hair development and associated traits.

Methodology:

Plant Culture and Management: The experiment was conducted at the Department of Genetics and Plant Breeding, Bangladesh Agricultural University for the period between August 2013 and February 2014. Seeds of 13 elite wheat varieties were collected from the Wheat Research Centre of the Bangladesh Agricultural Research Institute, Gazipur. Seeds were germinated in clean tap water floated in foam net inside the plastic trays in a growth chamber. Around 200 seeds were germinated per tray for each variety in order to select 18 healthy seedlings with synchronized leaf appearance in hydroponic nutrient solution at transplanting. Seed germination process took 5–7 days. Seedlings were transplanted in hydroponic solution following a completely randomized design with three treatments and six replicates per treatment for each of the 13 varieties. An individual plant was considered as a single replicate as root variables were measured in individual plants. There were 18 individual trays for setting up the whole experiment, six trays for each treatment. Each tray contained 13 plants, one from each variety. Plants were cultured at 20 ± 2 °C temperature and at 50 ± 2 PPFD (photosynthetic photon flux density) light intensity with cool white fluorescent lamps in a 12:12 h day:night cycle. Leaf appearance interval of all varieties was monitored for two weeks and that was calculated at around 10 days (90 °C days). Plants were fed with following nutrient solution: 1mM·NH₄NO₃, 0.6mM·NaH₂PO₄·H₂O, 0.6mM·MgCl₂·H₂O, 0.3mM·K₂SO₄, 0.3mM·CaCl₂·H₂O, 50μM·H₃BO₃, 90μM·Fe-EDTA, 9μM·MnSO₄·4H₂O, 0.7μM·ZnSO₄·7H₂O, 0.3μM·CuSO₄·5H₂O, 0.1μM·NaMoO₄·2H₂O dissolved in water [40]. The nutrient solution was refreshed weekly. All 234 plants were under similar management until they were 60 days old. There were 4–6 live leaves, 3–6 seminal roots and 6–12 adventitious roots per main tiller 60 days after transplantation depending on varieties (p < 0.001). Three different polyethylene glycol (PEG 6000, Sigma-Aldrich, Steinheim, Germany) treatments were imposed when the plants were 60 days old. Those were: 0% (control), 0.3% and 0.6% PEG levels. The highest level of PEG 0.6% can potentially create an osmotic potential less than one bar at 20 °C. Even though PEG concentrations are low, however intuitively, these low concentrations of PEG can cause a significant reduction in root hydraulic conductivity, and, therefore, significant water stress, depending on the varieties of wheat.

Measurements and Data Collection: Data were recorded on 20 days and 40 days after the PEG treatment by two separate destructive harvests. Three individual plants out of six from each variety × treatment combination were destructively harvested 20 days after treatment, and the remaining three 40 days after treatment. Number of live leaves per main tiller was recorded on the same day. Measurements of root traits were carried out during the destructive harvest. Root measurements include number of root bearing phytomers, number of adventitious roots, mean number of roots per phytomer, number of seminal roots, main axis length at the root bearing phytomer position (Pr) 1, 2, 3, and 4 (youngest root bearing phytomer was considered as reference point), main axis diameter at Pr1, number of root hairs per mm main axis at Pr1, length and diameter of the root hairs at Pr1. Diameter of the main axis, number of root hairs per mm main axis, length and diameter of root hair were measured at 100× magnification under a light microscope. A safranin solution of 0.5% prepared in 50% alcohol was used for staining root hairs. Shoots and roots of the plants at the destructive harvest were dried in an air draft oven for 72 h at 60 °C before recording their dry weights. Panicle length was recorded at the second destructive harvest 40 days after treatment, when plants were 100 days old. Dry weights of the panicles were recorded after 72 h drying at 60 °C in an air draft oven.

Estimation of Root Hair Density and Root Hair Surface Area: To estimate root hair density in no. mm⁻² main axis, individual main axis was considered as cylinders. Then, the surface area of the main axis per mm length was calculated as: π × D (mm) × 1 mm length. Number of root hairs per mm² surface area was obtained using the following equation:

Root hair density (no. mm−2) =Number of root hairs counted per mm length of main axisSurface area of main axis for per mm length of main axis............(1)

Surface area produced by the root hairs at different PEG levels was calculated from the following equation:

Root hair surface area (mm2) =Root hair density (no. mm−2) × π × RHD × RHL....................................................................................................................(2)

where RHD and RHL respectively represent root hair diameter and root hair length.

Statistical Analysis: Analysis of variance was carried out following a generalized linear model, using MINITAB 16 statistical software package (Minitab Inc., State College, PA, USA) to find variations among treatments, varieties and treatment × varieties. To test the significant variations among the measured variables, a user defined model was used where the replications within treatment were the error term. Principal component analysis was carried out for some selected traits, the majority of which accounted for either a significant treatment effect or treatment × varieties effect. Analysis of variance of the PC scores was carried out for treatment and variety effects following a generalized linear model.

Source of Information: Agronomy 2015, 5(4), 506-518; ISSN 2073-4395, doi:10.3390/agronomy5040506

Article Link (Online Journal): http://www.mdpi.com/2073-4395/5/4/506/htm

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

One objective of this study was to measure development of root hairs at the reproductive stage under PEG-treated hydroponic culture. This study found that PEG-treated culture decreased the length and diameter of root hairs. Reduction of root hair diameter and root hair length reduced the root surface area of an individual root. In addition, this study revealed a contrast between main axis length and panicle traits with significant differences among varieties, which suggested competition in dry matter partitioning. As low exposure of PEG alters the diameter and length of root hairs, in future experimentation, it will be important to observe how these alterations are associated with growth, development and yield of the wheat varieties under low moisture stress. Moreover, data relevant to root hydraulic conductance or leaf water potential against each of the PEG levels would provide further validation of the experimental results.

Knowledge Management: Journal