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Gas Exchange and Chlorophyll Fluorescence Parameters in Four Maize Genotypes Influenced by First Phase of Salt Stress

MN Uddin
Department of Crop Botany, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh.

MIU Hoque
Department of Crop Botany, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh.

S Monira
Department of Agronomy, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh.

MAA Bari
Department of Genetics and Plant Breeding, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh.

Abstract/ Executive Summary:

Responses in photosynthesis, transpiration, stomatal conductance, chlorophyll fluorescence characteristics and chlorophyll content of four maize (Zea mays L.) genotypes were examined under first phase of salt stress. In the experiment four maize genotypes viz. indigenous yellow pure line, indigenous yellow, hybrid, and indigenous white were tested in two levels of salinity (control: without NaCl application; salinity: 12 dS m^-1 by applying NaCl). The experiment was laid out following completely randomized design (CRD) with four replications in the net house of Department of Crop Botany, Bangladesh Agricultural University, Mymensingh. Plants were harvested on day 21 after 7 d application of full salt stress (12 dS m^-1). The reductions of shoot fresh masses under salinity were 70, 57, 55 and 61% in indigenous yellow pure line, indigenous yellow, hybrid, and indigenous white, respectively. Some core physiological parameters viz. net photosynthesis rate (Pn), transpiration rate (E), stomatal conductance (gs), and the chlorophyll content decreased in all the maize genotypes except indigenous white under first phase of salt stress. In contrast, the ratio of variable fluorescence to maximal fluorescence (Fv/Fm) of photosystem II significantly decreased only in indigenous yellow pure line under salinity stress. Thus the first phase of salt stress seemed to be deleterious on its response to shoot fresh mass production in all the tested four maize genotypes with the concomitant decrease in rate of photosynthesis, rate of transpiration, stomatal conductance and chlorophyll content in all genotypes except indigenous white.

Keywords: Photosynthesis; Transpiration; Stomatal conductance; Fv/Fm, Maize

Location: Department of Crop Botany, Bangladesh Agricultural University, Mymensingh

Start Date:

End Date:

Program Area: Variety and Species

Commodity: Maize, Soil salinity

Objectives:

To investigate gas exchange parameters, chlorophyll fluorescence of photosystem II and chlorophyll content in four maize genotypes as influenced by first phase of salt stress.

Methodology:

Experimental layout and salinity development: The pot experiment was conducted in net house in the Department of Crop Botany, Bangladesh Agricultural University, Mymensingh, followed by a completely randomized design (CRD) with four replicates of each treatment. Four maize genotypes namely indigenous yellow pure line (IYPL), indigenous yellow (IY), hybrid, and indigenous white (IW) were tested against 12 dS m^-1 salinity. Plastic containers (10 L) were filled with 12 kg of air-dried subsoil fertilized with standard fertilizer doses and then water content was adjusted to 60% of total water holding capacity (WHC). Seeds of all maize genotypes were soaked in the aerated water overnight and then placed four seeds of each genotype to the plastic containers covering all replications. After germination only one healthy plant was kept in each container. To develop salinity, NaCl was applied to reach an EC value of 12 dS m^-1. One fourth of the total NaCl was applied on day 11 of seed sowing. On the following three consecutive days the rest amount of salt was applied, each time one fourth of the total NaCl. From day 14 until harvest (at 21 days after planting) the soil water was maintained at 60% of WHC. Chlorophyll measurement with SPAD: The chlorophyll content as SPAD value was measured with a chlorophyll meter (Minolta Co. Ltd., Japan). It is a relative measurement of leaf greenness. In each treatment data was recorded for 6^th fully expanded leaf as an average of three measurements. Measurement of Fv/Fm ratio: The ratio of fluorescence to maximal fluorescence (Fv/Fm) of Chl- a, an indicator of the efficiency of the photosyntem II (PS II), was measured using Pocket PEA portable fluorometer (Hansatech Instruments, King’s Lynn, Norfolk, UK). The same leaf from which chlorophyll was measured conveniently dark adapted for 30 minutes prior to measurement using the leaf-clips. Fluorescence was induced by saturating, red actinic light with energy of 3.500 µmol m-² s^-1. Gas exchange parameters: In parallel to the Chl-a fluorescence measurement of 6^th leaf, photosynthetic rate (A), transpiration rate (E) and stomatal conductance (Gs) were determined using a portable photosynthesis system (ADC Bio-scientific Ltd., UK) from the same leaf.

Source of Information: Progressive Agriculture, Vol. 30, Suppl. 1: 26-32, 2019

Article Link (Online Journal): DOI: https://doi.org/10.3329/pa.v30i0.41554

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

In general, measurement of stomatal resistance provides effectual comparison for determining the degree of stress in plants. Salinity increased the stomatal resistance, which could be explained by inhibition of plant growth due to water stress. There was found a strong negative correlation between stomatal resistance and NaCl stress. Stomatal factors have also a more significant effect on photosynthesis. Possible mechanism in which photosynthesis is reduced under salt stress is not so clear. Salt stress disturbs the balance between production of reactive oxygen species (ROS) and antioxidant defense causing accumulation of reactive oxygen species, whboxylase (PEPCase), and NADP-malic enzyme (NADP-ME). Moreover, noncyclic electroich induces oxidative stress. Increase in tissue Na+ causes ion toxicity, which decreases the leaf growth, and results in early leaf abscission, which reduces the carboxylation. Salt stress limits photosynthesis due to a decline in activities of Rubisco, phosphoenolpyruvate carn transport is down regulated to match the reduced requirements of reduced (nicotinamide adenine dinucleotide phosphate) production and thus reduces adenosine triphosphate synthesis.

Knowledge Management: Journal