A novel approach for reducing water stress on sunflower plants by using medicinal plant extracts rather than artificial growth regulators

One of the most significant physiological stressors that negatively impact plants in numerous vital areas of their growth and metabolism is water stress. This study estimates the effects of natural bio-stimulants (Origanum majorana, Nigella sativa and Curcurma longa) extracts for the first time, on water stress of sunflower plant in comparison with synthetic growth regulators (glycein betaine, proline, indole acetic acid, benzyl adenine and ascorbic acid). Water stress appeared to decrease of lengths, fresh and dry weights of shoot and root. Also caused a significant drop in chlorophylls and carotenoids. Foliar application of these synthetic and natural growth regulators significantly decreased the negative effects of drought stress on all studied morphological parameters and pigment contents of sunflower. HPLC analysis of bio-stimulants appeared six phenolic acids, one phenol and two flavonoids were found in all natural extracts. Gallic, rosmarinic, caffeic, syringic acids and kaempferol are the major phenolic compounds (more than 1000 µg/g) detected in Origanum majorana. While gallic acid, hesperetin and ferulic acid are the major phenolic compounds (more than 1000 µg/g) present in Curcurma longa. Chlorogenic acid, gallic acid, catechin, pyro catechol, coffeic acid and rutin are the dominant phenolic compounds present in Nigella sativa. The Nigella sativa treatment showed the highest decrease in proline levels. This may be due to the high concentration of caffeic acid (2406.97 g/g). The Origanum majorana treatment had the highest levels of chl. a and carotenoid contents, which rose by about 32% and 72%, respectively, compared to the stress-treated plant. The highly decrease in catalase activity, which is considered as most important indicator to water stress, appeared in Origanum majorana treatment. We suggest the use of these natural extracts as an alternative way, which appeared a significant increase in growth and biochemical near to synthetic regulators in the treatment of water stress due to the fact that these extracts contain many important phenolic compounds that have a role in the treatment of water stress.