Effects of salt stress on some morphology, physiology properties and proline accumulation in relation to osmotic adjustment during early seedling growth of soybean [Glycine max (L.) merr]

ABSTRACT EFFECTS OF SALT STRESS ON SOME MORPHOLOGY, PHYSIOLOGY PROPERTIES AND PROLINE ACCUMULATION IN RELATION TO OSMOTIC ADJUSTMENT DURING EARLY SEEDLING GROWTH OF SOYBEAN [Glycine max (L.) Merr] Küçükkılıç B. Aydın Adnan Menderes University, Natural Science Enstitüsü, Field Crops Program, Master Science, Aydın, 2023. Objective: In this study, 10 soybean varieties belong to different maturation days and different thousand-grain weights were investigated to the response of these cultivars under three different salt concentrations (0, 3 and 6 dS m-1) during from the seedling development period to the V4 (third triple leaf node) period. The purpose of study was to investigate the changes in morphological, physiological and biochemical reactions and the relations between these parameters under different salt stress. Material and Methods: The experiment was carried out in a randomized parcel design with 2 (two) factors with 5 (five) replications (2 plants in each replication) under semi-controlled greenhouse conditions at Faculty Agriculture of Aydın Adnan Menderes University. Plant height, stem diameter, plant fresh weight, plant dry weight, leaf area, rwc (relative water content), rmp (relative membrane permability), mda (Malondialdehyde), chlorophyll a, chlorophyll b, carotenoid and proline accumulation properties of 10 soybean genotypes were investigated under three different salt stress conditions. Results: It was revealed that the plant height, fresh weight, dry weight, leaf area, rwc (relative water content), Chlla, Chllb, spad, karatoneid values of all soybean varieties decreased depending on the increased salt stress concentration, whereas rmp, proline and MDA values of the leaves were increased. This study showed that there was a 0,821** positive correlation between salt stress and rmp with the increasing salt stress, besides leaf permeability increased significantly in the leaves of all cultivars has got negatively significant correlation relationships with other measured traits, because of oxidative membrane damage. It was determined that the mda content of the leaf was increased with the increasing salt stress, however, the amount of proline in the leaf increased linearly and at high value (r2=0,9381). It was found that the result of an important and high (r2=0,9698) relationship between relative membrane conductivity and proline accumulation in leaves explaned salinity increased plant leaf mda and rmp values, and at the same time, leaf proline values of all cultivars were increased to prevent membrane stability. It was determined that the increases or decreases in all measured characteristics of the cultivars were different at different salt stress levels. Cinsoy cultivar showed the highest value in terms of leaf area, plant height, fresh weight, leaf relative water content (rwc), dry matter production, with the least reduction of oxidative damage in plant tissues and membranes by increasing the accumulation of proline in its leaves under 3 and 6 dS m-1 salt stress conditions. It was concluded that Cinsoy was more resistant to salt stress than that of other soybean cultivars. It was also thought that İksoy and Gapsoy cultivars can be recommended under moderate salt stress conditions (3 dS m-1), due to the high dry matter production. Conclusion: A different result of the study was that the Mersoy cultivar's higher dry matter production than many other cultivars, was thought to be due to the different physiological characteristics of the Mersoy cultivar, although both mda content and proline accumulation content of the leaves of the Mersoy are low level under 3 and 6 dS m-1 salt stress conditions. For these reasons, it was concluded that the Mersoy soybean cultivar should be useful in investigating different physiological parameters in order to better understand the mechanism of resistance to salt stress. Although it was generally concluded that cultivars with the high mda content and the low proline content produced lower dry matter under salt stress, this theory found that the amounts of proline or mda content varied for each in a different plant cultivar. Key Words: Oxidative and Mechanical responses, Proline, Salt stress, Soybean.