MORPHOLOGICAL AND PHYSIOLOGICAL STUDIES ON THE ROLE OF SOME BIOREGULATORS TO REDUCING WATER STRESS IN THYMUS VULGARIS L

Abstract

Two pot experiments were conducted on the 17th and 11th of March of 2015 and 2016 respectively at the Experimental Farm, Faculty of Agriculture, Ain Shams University, Shoubra El-Kheima, Egypt to investigate the effect of foliar application of potassium citrate (KC, 1.63 or 3.26 mM), proline (Pro, 50 or 100 mM), putrescine (Put, 0.1 and 0.2 mM) and distilled water as control on thyme plants (Thymus vulgaris L) under water deficit conditions. Two irrigation levels according to the water holding capacity (WHC) were investigated; the well-watered plants were irrigated when the value of field capacity (FC) between 70-80% whereas; the water-stressed plants were irrigated when the value of FC between 30-40%. The results indicated that water stress caused significant (P≤0.05) decreases in the studied growth parameters including the fresh and dry weights for shoot and root whereas, there was a significant increase in shoot/root dry matter ratio. Moreover water stress induced multiple significant changes in the biochemical constituents including the photosynthetic pigments (Chl a, Chl b, Chl a/b ratio and carotenoids), reactive oxygen species as indicated by increasing the concentration of H2O2 and the rate of lipid peroxidation in term of malondialdehyde (MDA), osmolytes (soluble sugars, proline and free amino acids (FAA)), total soluble phenols and phenolic related enzymes (Phenylalanine ammonia-lyase (PAL). Polyphenol oxidase (PPO), and peroxidase (POD)) Furthermore, water deficit caused several changes at the morphological and anatomical levels of the thyme plants.