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Drought and Salinity Affect Leaf and Root Anatomical Structures in Three Maize Genotypes

Md. Injamum-Ul-Hoque
Department of Crop Botany, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

Md. Nesar Uddin
Department of Crop Botany, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

Md. Solaiman Ali Fakir
Department of Crop Botany, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

Md. Rasel
Department of Genetics and Plant Breeding, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

Abstract/ Executive Summary:

Salt and drought stresses are being quite similar considered as two major constraints in maize production. To explore the anatomical bases of resistance to salt and drought stresses, 14 days old seedlings of three maize hybrid genotypes were subjected to salt (100 mM NaCl) and drought stress (equiosmotic PEG6000) under hydroponic conditions. The experiment was laid out following a completely randomized design having four replicates. Root protoxylem and metaxylem thickness and root diameter were found to be unaffected in both of the drought resistant genotypes in response to salt and drought stresses whereas root protoxylem thickness increased (33.8 and 112.8% by salt and drought stress, respectively) in sensitive genotype (BARI hybrid maize-7). Bundle sheath thickness was found to increase in response to stresses (58.4 and 59.3% by salt and drought stress, respectively) in BARI hybrid maize-12. BARI hybrid maize 12 showed unaffected response in leaf epidermal thickness, phloem area, xylem area and total leaf thickness under both salt and drought stresses.

Keywords: Salinity, PEG, Protoxylem, Metaxylem, Epidermis

Location: The experiment was conducted with hydroponic culture at hydroponic growth chamber, Plant Physiology Laboratory, Bangladesh Agricultural University, Mymensingh.

Start Date:

End Date:

Program Area: Risk Management in Agriculture

Non-commodity: Drought

Objectives:

This study explored changes in leaf and root anatomical structures due to drought and first phase of salt stresses, and also genotypic differences.

Methodology:

Plant materials and seedling growth Three genotypes were used in this experiment and they were collected from Bangladesh Agricultural Research Institute (BARI), Joydevpur, Gazipur. They are BARI hybrid maize-7, BARI hybrid maize-12, and BARI hybrid maize-13. Among them, the first one is a drought and salt sensitive, whereas the later two are newly released drought resistant genotypes. The caryopsis was soaked in an aerated plastic container for 24 h. Germination took place in the dark at 25 ⁰C in sandwich culture. The caryopses were placed between two layers of foam with oil paper moistened with water. On day 5, plants were exposed to the light. The experiment was conducted with hydroponic culture at hydroponic growth chamber, Plant Physiology Laboratory, Bangladesh Agricultural University, Mymensingh. Experimental layout and salt and drought simulation The hydroponic experiment was laid out following a Completely Randomized Design (CRD) with three treatments (control with 1 mM NaCl, salt treatment with 100 mM NaCl and drought treatment with equiosmotic PEG-6000) with 4 replications. As C4 photosynthesis is favoured by low level of Na+, control plants had been supplied with 1 mM NaCl, and the hydroponic experiment was executed following a slightly modified protocols (Uddin et al., 2014; Uddin et al., 2016). The salt treatment started on day 14 with 25 mM NaCl, and drought treatment started with equiosmotic PEG-6000. It was increased daily with 25 mM NaCl and corresponding equiosmotic PEG-6000, respectively, till a concentration of 100 mM NaCl and equiosmotic PEG6000 were reached on day 17 which was maintained till harvest on day 23. Nutrient solution was changed on every alternate day after reaching full strength concentration. After 7 d full exposure of salt and drought stresses, basal 2 cm of 5th leaves of each genotype was isolated for leaf anatomical studies. For root anatomical studies, 1 cm root segments were collected after discarding 2 cm from root tip. Both leaf and root segments were kept in ethanol till transverse sections were made to observe the differences in anatomical structures. Root and Leaf anatomical structures measurement Root and leaf anatomy of stressed and controlled plants were observed by light microscope (Axioscop; Carl Zeiss, Oberkochen, Germany). Here 10x and 40x of images were observed and captured. Images were processed for taking various anatomical parameters using the ZEISS ZEN digital imaging software for light microscopy. For root, metaxylem thickness and protoxylem thickness were measured from the same xylem strand. Vascular cylinder area and total root diameter were also measured. For leaf anatomy, four epidermal cells from both sides of the stomata were taken to measure epidermal thickness. In each cell three positions were selected to take thickness values and then the average was calculated. Phloem and xylem areas were measured carefully. Total leaf thickness was calculated from three sides of the leaf by measuring distance between upper and lower epidermal layers, and then average value was calculated for each sample. Metaxylem and bundle sheath thickness was measured in the same radial line. Data analysis The statistical analyses of the experimental data were carried out using Mini Tab 17.3 and Microsoft Excel 10.0 software packs. Statistical differences between treatments were adjusted using Fisher test.

Source of Information: J Bangladesh Agril Univ 16(1): 47–55, 2018 ISSN 1810-3030 (Print) 2408-8684 (Online)

Article Link (Online Journal): doi: 10.3329/jbau.v16i1.36480

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Root protoxylem and metaxylem thickness and root diameter were found to be unaffected in both the drought resistant genotypes in either of the two stresses, while root protoxylem thickness increased in the sensitive genotype BARI hybrid maize-7 under both salt and drought stresses. In BARI hybrid maize-12, bundle sheath thickness increased under salt and drought. In contrast, leaf epidermal thickness, phloem area, xylem area and total leaf thickness were unaffected under both salt and drought stresses in this genotype. Relative response data revealed that all the genotypes responded identically between drought and salt stresses for root vascular cylinder area, thickness of leaf, leaf epidermis and bundle sheath thicknesses. In contrast, genotypes differ in their relative response between salt and drought stresses in root protoxylem and metaxylem thickness, root diameter, leaf phloem and xylem areas and leaf metaxylem thickness. Thus, it can be concluded that drought stress and first phase of salt stress are quite similar in their responses to some anatomical parameters but differ also in some other anatomical aspects in three maize hybrids studied.

Knowledge Management: Journal