Abstract
Main ConclusionThe drought conditions and the application of ABA reduce the photosynthetic activity, and the processes related to the transpiration of Dracocephalum moldavica L. At the same time, the plant increases the production of phenolic compounds and essential oil as a response to stress conditions.In the semi-arid regions, drought stress is the most important environmental limitations for crop production. Abscisic acid (ABA) plays a crucial role in the reactions of plants towards environmental stress such as drought. Field experiments for two consecutive years in 2016 and 2017 were conducted to evaluate the effect of three watering regimes (well-watered, moderate and severe drought) and five exogenous ABA concentrations (0, 5, 10, 20 and 40 μM) on growth, photosynthesis, total phenolic and essential oil content of Dracocephalum moldavica L. Without ABA application, the highest photosynthetic rate (6.1 μmol CO2 m−2 s−1) was obtained under well-watered condition and, moderate and severe drought stress decreased photosynthesis rate by 26.39% and 34.43%, respectively. Some growth parameters such as stem height, leaf area, leaf dry weight and biological yield were also reduced by drought stress. ABA application showed a decreasing trend in photosynthesis rate and mentioned plant growth parameters under all moisture regimes. The highest seed yield (1243.56 kg ha−1) was obtained under well-watered condition without ABA application. Increasing ABA concentration decreased seed yield in all moisture regimes. The highest total phenolic content (8.9 mg g−1 FW) and essential oil yield (20.58 kg ha−1) were obtained from 20 and 5 μM ABA concentration, respectively, under moderate drought stress.
Highlights
Drought stress is a major constraint to be achieved higher yields in crop plants, especially in the arid and semi-arid regions of the world (Kumar et al 2020; Mahdavi et al 2020; Naservafaei et al 2021; Rad et al 2020; Reza Yousefi et al 2020)
Exogenous Abscisic acid (ABA) application clearly reduced the stomatal conductance in all three moisture regimes (Fig. 3) and the lowest stomatal conductance (0.02 mol m−2 s−1) was obtained from plants treated by ABA 50 μM concentration under severe drought condition (Fig. 3)
We analyzed the roles of exogenous ABA on some physiological, morphological and metabolic parameters of D. moldavica under drought stress
Summary
Drought stress is a major constraint to be achieved higher yields in crop plants, especially in the arid and semi-arid regions of the world (Kumar et al 2020; Mahdavi et al 2020; Naservafaei et al 2021; Rad et al 2020; Reza Yousefi et al 2020). Planta (2021) 253:127 stomatal closure limiting decline in growth and photosynthesis rate (Flexas and Medrano 2002) Both cell expansion and cell division, two primary processes involved in plant growth, can be influenced by relatively mild drought stress, even before photosynthesis or respiration is affected critical processes, such as germination, emergence, leaf expansion, root and shoot development, dry matter accumulation, floral initiation, pollination, fertilization, seed growth and seed yield (Morgan 1984; Roberts 1988). Drought decrease cell size and cell number and can lead to decreased leaf area, stem growth and plant height (Randall and Sinclair 1988; Simonneau et al 1993; Tardieu et al 2000). Drought decreases the seedfilling duration, leading to smaller seed size and seed yield (Frederick et al 1991; De Souza et al 1997; Wardlaw and Willenbrink 2000)
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