Investigation of mechanisms involved in seed germination enhancement, enzymatic activity and seedling growth of rice (Oryza Sativa L.) using LPDBD (Ar+Air) plasma

Highlights

• Seed germination rate enhanced up to 89.75% due to LPDBD plasma.

• Improved morphological and physiological characteristics.

• Enhanced the photosynthetic pigments (a & b).

• Total soluble sugar and protein significantly increased in rice plantlets.

Abstract

The study investigates the effect of LPDBD (Low Pressure Dielectric Barrier Discharge) (Ar + Air) plasma on seed germination, seedling growth and antioxidant enzyme activity of rice. Rice seeds were treated with LPDBD (Ar + Air) plasma for 2min, 4min, 6min, 8min and 10min. Seed germination rate, seedling growth, total chlorophyll content, enzymatic activity, total soluble sugar and protein concentration were increased in plants grown from the LPDBD (Ar + Air) plasma treated seeds. It was observed that the sprouting of seeds and the growth of seedlings of rice depends on the feed gases used to generate plasma and plasma processing time. In the case of plantlets germinated from the plasma-treated seeds of rice, the H₂O₂ level was increased significantly both in leaves and roots for 6min, 8min and 10min treatment respectively. No significant change was observed in Nitric Oxide (NO) concentration in seed, leaf, or root of plants grown from LPDBD (Ar + Air) plasma-treated seeds. The amount of total soluble sugar and protein increased significantly in the case of 2min, 4min, 6min, 8min and 10min seed treatment. Although plants exhibited no significant increase in APX activities, but a significant increase of CAT and SOD activity in the leaf and root was found. This study reveals that LPDBD (Ar + Air) plasma is involved in the elevation of ROS species in leaf and root of rice plants which is tightly regulated by the upregulation of CAT activity that ultimately enhances the seed germination and growth of rice plantlets.

Introduction

Rice (Oryza sativa L.) is one of the leading cultivated cereal food crops in Bangladesh. The position of Bangladesh is sixth in the world due to the production of an adequate amount of rice. It is the most staple food for almost half of the world's population. It supplies 60% of calories to the consumed people all over Asia [1]. Additionally, it contains large amount of starch and mainly functions by binding with water which helps gelatinization of temperature, paste clarity, paste viscosity, solubility and swelling power [2]. In most farming systems in our country, the rice seeds are immersed in the water to break down the dormancy for influencing the seeds to be germinated, and then the germinated seeds are sown in the bed.

Thereafter, seedlings are transplanted to the desired field. Due to the increased population gradually, and for the rapid economic development, it is the key need to increase food production. To increase the rice production, it is necessary to study both in storage and safety. The rapid production depends on various factors including photosynthesis, conversion of assimilates to biomass, and segregation of assimilates to grains [3]. For this reason, several physiological, biochemical and enzymatic changes were required. The conventional methods involve the improvement of irrigation and the rapid use of chemical fertilizer [[4], [5], [6], [7], [8]] which harass the environment. Another method is to physically breakdown of seed dormancy [9].

Plasma technology can be a solution to the current problems. Atmospheric pressure non-thermal plasma promotes seed germination and stimulates plant growth in some crops without the use of nonorganic fertilizer [10]. Additionally, it is known that the Atmospheric Pressure Plasma Jet (APPJ) can cure fungus in plants and improve resistance to some plant diseases [11,12] reported that the seedling growth during germination involves two key steps (a) primary cell elongation of the axial part of the embryo, and (b) simultaneous or delayed cell division in the radicle meristem. Plasma technology is drawing much attention because of its potentiality to treat the seeds in a chemical-free way to grow plants. Besides, Atmospheric Pressure Cold Plasmas (APCPs) are effective to seed germination, water uptake mechanisms, and drought tolerance [13,14]. Improvement in seed germination and growth has been reported in a few plant species [[15], [16], [17], [18]] by APCP. It was [19] reported that the seed germination is the initiation of embryo breaking the dormant stage which always start with the imbibition of water. Seed germination activity involves several physiological and biochemical changes, such as - protein synthesis, enzyme activation and starch metabolism [20]. However, Low Pressure Dielectric Barrier Discharge (LPDBD) technique is a vital source of non-thermal plasma due to its stability and high volume capacity as compared to Atmospheric Pressure Dielectric Barrier Discharge (APDBD) source. Its potential effects are also applicable to the environment and energy conversion [[21], [22], [23]].

To the best of our knowledge, the effects of rice seeds treatment with specifically LPDBD (Ar + Air) plasma on seed germination, seedling growth, total soluble protein and sugar, and antioxidant enzyme activities, altogether, have not been reported yet. The objective of the present study is to investigate the effect of LPDBD (Ar + Air) plasma on the germination rate and growth of rice plantlets and to optimize the gas composition, frequency and treatment time to produce LPDBD (Ar + Air) plasma to treat rice seeds for agronomic improvement.