Document Type : Research Article
Authors
Department of Horticultural Sciences, Faculty of Agriculture, Lorestan University, Lorestan, Iran
Abstract
Introduction
The growth and development of plants in arid and semi-arid regions are restricted primarily due to limited water availability. Under these conditions, the physiological and biochemical characteristics of plants undergo significant changes. In these conditions, due to the imbalance of hormones, plant growth decreases. Therefore, the use of plant growth regulators can be an effective factor in improving tolerance to abiotic stresses. Thidiazuron is known to activate stress-responsive genes and promote the accumulation of stress-related signaling molecules, including abscisic acid and proline. Catharanthus roseus is an evergreen ornamental-medicinal plant that is very popular for planting in pots and green spaces.
Materials and Methods
The experiment was conducted as a factorial experiment in a completely randomized design with two factors and four replications in the research greenhouses of Lorestan Agricultural College during the spring and summer of 2022. The first factor was water deficit stress at three levels of 80 (control), 50, and 20% available water content in soil, and the second factor was foliar application of thidiazuron at three levels of 0 (control), 2.5, and 5 mg.L-1. Water deficit stress was imposed and maintained using a pressure plate device and the gravimetric method. Thidiazuron was applied as a foliar spray. Three months after the application of water deficit stress, growth traits (Such as plant height, stem diameter, leaf number and area, flower diameter, root diameter and volume, fresh and dry weight of shoots and roots), gas exchange parameters (photosynthesis rate, transpiration rate, stomatal conductance, mesophyll conductance, and intracellular CO₂ concentration) and biochemical characteristics (relative leaf water content, electrolyte leakage, photosynthetic pigments, malondialdehyde and peroxidase and ascorbate peroxidase enzyme activities) were measured.
Results and Discussion
The results indicated that higher levels of water deficit stress significantly reduced plant growth, gas exchange rates, photosynthetic pigment content, and relative water content, while significantly increasing root length, photosynthetic water use efficiency, electrolyte leakage, malondialdehyde content, and antioxidant enzyme activity in Catharanthus. Foliar application of thidiazuron alleviated the negative impacts of water deficit stress by enhancing antioxidant enzyme activity, improving gas exchange, and maintaining better plant water balance. These results indicate that water deficit stress has detrimental effects on both vegetative and reproductive growth in Catharanthus roseus. However, thidiazuron application reduced these effects and improved plant tolerance to stress by promoting root growth and increasing antioxidant enzyme activity. Water deficit limits plant growth by reducing shoot and root development, which decreases plant dry weight. This reduction is likely due to decreased photosynthesis, reduced cell expansion, and inhibited cell division. Thidiazuron may counteract these effects by promoting cell division, enhancing chlorophyll accumulation, stimulating the biosynthesis of photosynthetic pigments, and delaying leaf senescence through cytokinin stimulation. Drought stress also limits membrane integrity, pigment content, lipid biosynthesis, and hormonal balance by reducing gas exchange and carbon dioxide concentration, thereby reducing plant growth. On the other hand, thidiazuron, known as a cytokinin, has dual auxin and cytokinin effects and may facilitate the accumulation or synthesis of endogenous plant growth hormones, in fact, thidiazuron acts through adenine-type cytokinin activity either by stimulating endogenous cytokinin or by binding to cytokinin receptors. It also enhances plant growth by activating enzymatic and non-enzymatic antioxidant defense systems.
Conclusion
The results of the present experiment showed that thidiazuron enhances plant resistance to water deficit stress by stimulating root growth, enhancing gas exchange, and boosting enzymatic antioxidant activity. However, further research is needed to optimize its application for managing water deficit stress in Catharanthus roseus.
Acknowledgement
This article is based on a master's thesis proposal. The authors would like to thank Lorestan University and the Department of Horticultural Sciences, Faculty of Agriculture, for their support.
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