INFLUENCE OF ABSCISIC ACID ON THE CONTENT OF PROLINE AND ABA PHYTOHORMONE IN COTTON PLANT UNDER SALINITY

INFLUENCE OF ABSCISIC ACID ON THE CONTENT OF PROLINE AND ABA PHYTOHORMONE IN COTTON PLANT UNDER SALINITY

Kuldoshova K.M., Akhunov A.A.

Institute of Bioorganic Chemistry, Academy of Science

zarabarlos90@bk.ru

Abstract: Salinity is one of the most imperative global problems that affect the crop productivity on a large scale. Salinity impairs plant growth and development by imposing various stresses and it is vital to decode those stress factors and identify possible solutions to improve agriculture productivity. The present study was undertaken to determine the effects of exogenous application of abscisic acid (ABA) on salinity tolerance in cotton plant. Some patterns of formation resistance were revealed on the seedlings of two cotton plant varieties: Gulistan (resistant) and C-4727 (sensitive). Their response to salinity by the action of abscisic acid, a plant phytohormone. Besides, we conducted comparative research on antioxidant potential of cotton plant varieties that are different in saline resistance. The contents of amino acid free proline and the quantity of endogenous ABA were determined. The results revealed significant differences of resistant and sensitive cotton plant varieties in response to saline stress. The plant response has been linked with contents of free proline and endogenous abscisic acid. Studies have shown a high constitutive level of proline, endogenous ABA for the resistant variety Gulistan compared to salt stress sensitive variety C-4727.

Introduction. Soil salinity is a major environmental limitation to world agriculture affecting 800 million hectares of land. This estimates over 6 % of the world total land area, affected either by salinity (397 million hectares) or associated forms of sodicity (434 million hectares) [5]. Salt stress alters various biochemical and physiological responses in plants and thus affects almost all plant processes including photosynthesis, growth and development [4]. Studies on salinity stress will be a stride towards the urgent need of developing crop varieties possessing higher growth rate and yield in salt affected environments.

Involvement of phytohormones in the resistance of cotton plant to salt stress is one of significant points that require deeper knowledge. Phytohormones, as the main components of the plant regulatory system, play a key role not only in growth and morphogenetic processes, but also in adaptive reactions associated with exposure to

unfavorable factors. Not enough attention was paid to the involvement of phytohormones in the resistance of plants increasing in the initial period of stress.

In order to improve the adverse outcome of salinity stress on a plant growth, diverse phytohormones are extensively used and one such kind of a phytohormone is abscisic acid (ABA), plant stress hormone which is considered as an important agent in the mechanisms of resistance and adaptation in plants against salt stress conditions [1]. ABA was also found involved in several other physiological processes such as stomatal closure, embryo morphogenesis, development of seeds and synthesis of storage proteins and lipids [7], germination leaf senescence and defense against pathogens [6]. It has been well documented that endogenous ABA accumulates in plants under abiotic stresses [9].

Materials and methods. 7-day-old seedlings of two cotton (Gossypium hirsutum L.) cultivars with different salt tolerances, Gulistan (salt-tolerant) and C-4727 (saltsensitive), were used in this study. The seedlings were grown with tap water, then the samples were subjected to salt stress by exposing them in a solution of 1 % and 4 % NaCl for 1 hour, and then for 24 hours. 10 -7 M concentration of exogenous ABA was used in the experiment. Thus, the seedlings were used for further analyses.

The method of Bates et al. [2] was used for the estimation of proline.

Quantity analyses of ABA phytohormone were conducted in Agilent technologies 1200. The column 250 x 4.6-mm of strong anion exchanger (5- ^m spherical particles of Adsorbosphere SAX, Alltech Associates) was used for the next step of purification. The samples were dissolved in acetonitrile (35 %): 0.1 % phosphoric acid (65 %). Development was gradient with A (acetonitrile) - B (trifluoroacetic acid) at 1 ml min-&. Gradient % B/min, 70-30 % 10 min, 50-50 % 2 min, 50-50 % 3 min, 70-30 % 2 min. A Waters model 440 fixed-wavelength UV absorbance detector (254 nm) were connected in series and used to detect ABA, respectively.

Statistical analysis

Statistical analysis was performed by GraphPad Prism. Values are expressed as mean ± SD of 3 biological replicates.

Results and Discussion. Proline (Pro), as an important osmotic adjustment substance, exists in plant cells in free state and possesses low molecular weight, high water solubility, and no net charge in the physiological pH range. Plant cells tend to accumulate soluble osmotic adjustment substances to alleviate osmotic stress caused by salt stress, especially the biosynthesis of pro is clearly activated. Pro content can be used as a physiological index of plant resistance to stress tolerance [8].

We have conducted several experiments on the determination of exogenous effect of ABA in the content of pro in the seedlings of both varieties of cotton plant (Table 1). It was defined that considerable increase of content of Pro occurs under the

effect of 1% NaCl after 1 hour in resistant variety Gulistan. Exogenous effect of ABA decreases the amount of Pro not only in 1 % but also in higher concentration of the salt.

Like in Gulistan variety, in salt-sensitive C-4727 variety mainly the decrease of Pro was observed mainly after 1 hour under the effect of ABA. After 24 hours 1 and 4 % salinization caused rapid increase of Pro content.

The exogenous effect of ABA on the content of free Pro in cotton seedlings

(n = 3; M ± m)

Samples Gulistan C-4727

Pro, mM / gr fresh weig i

Control 25,25±2,3 20,8±1,64 18,5±1,2 13,4±1,23

*The results are presented as mean ± SD (n = 3).

©\\o o\\o ©\\© ©\\©

Gulistan C-4727

Gulistan C-4727

Figure 1. Content of free abscisic acid in cotton seedlings under chloride salinity. The

results are presented as mean ± SD (n = 3) It was established that the treatment with 1% NaCl and 4% NaCl led to significantly higher accumulation of free ABA in cotton seedlings for 1 hour (Fig.1). It was established that the treatment with 1% NaCl and 4% NaCl led to significantly higher accumulation of free ABA in cotton seedlings for 1 (Fig.1). In the seedlings of control plants of Gulistan variety, a high constitutive content of ABA was revealed. It was found that in the initial period of stress (4% NaCl) after 1 hour, the ABA content increased (on average by 61.&

Under stress conditions ABA can be synthesized quickly from carotenoids through xanthoxin, accumulated and inactivated rapidly into phaseic acid and then into di hydro phaseic acid, which provides a reversible process that can be completely normalized after reducing the concentration of ABA [9].

A prolonged exposure to plants under salinization conditions reduced their survival and the level of ABA, especially at a higher concentration. The resistance of cotton to the short-term effect of chloride salinization is associated with an increased level of ABA. It should be emphasized that the accumulation of ABA in cotton seedlings under the action of salinization was temporary, and further, it decreased. Obviously, in plants grown in saline soil, ABA manifests itself either as a factor that triggers the formation of increased resistance, or as one of the direct participants providing an increase in resistance in the first hours of exposure to this factor [10].

Conclusion. Our studies showed that there are significant differences in response to salt stress of sensitive and resistant cotton varieties. According to results the important role of ABA in tolerance to salt stresses and provide new insights into the molecular mechanism of enhanced salt tolerance by the application of exogenous ABA on crops.

Acknowledgement. Author thanks co-workers of laboratory of Proteins and Peptides chemistry of Institute of Bioorganic Chemistry AS of Uzbekistan. We thank PhD Ishimov U.J. for help on ABA measurements.

The work was supported by state project A-FA-BV-2019-6 "Development for personalization technology of using natural preparations and chemicals in the formation resistance of the new cotton varieties under different soil-climate conditions".

References