Abstract
Several inorganic and organic compounds including glycine betaine (GB) are presently being used as an exogenous application to enhance tolerance in plants to different environmental stresses. The current study assessed to what extent exogenously applied GB could improve the gaseous exchange capacity and primary and secondary metabolites in two accessions (16178 and 16180) of safflower (Carthamus tinctorius L.) plants under drought stress. Three-week-old plants of both safflower accessions were subjected to well-watered (control) or water-deficit conditions (60% field capacity (FC)). Three levels of GB (control, 50 mM and 100 mM) were sprayed to the foliage of the control and stressed plants after one month of drought application. After two weeks of foliar application of GB, gas exchange characteristics and other biochemical parameters were determined. The results showed that water deficiency markedly suppressed plant biomass, chlorophyll contents, photosynthesis rate (A), water use efficiency (A/E), stomatal conductance (gs) and relative water contents (RWC) of both accessions of safflower, while it enhanced the levels of osmolytes (GB and proline), hydrogen peroxide (H2O2) and total phenolics. Foliar application of GB was effective in enhancing the plant biomass, chlorophyll contents, gs, sub-stomatal CO2 concentration (Ci), Ci/Ca ratio, osmolytes, H2O2, ascorbic acid (AsA), total phenolics and RWC in safflower plants under water shortage. Thus, exogenous application of GB could be used as an effective strategy to improve plant growth, photosynthetic attributes and secondary metabolites in safflower plants under water deficit conditions.
Highlights
All plant processes are greatly influenced by deficiency of water as water is vital for their functioning [1,2]
A marked (p ≤ 0.001) decrease was observed in the biomass production of both accessions (16178 and 16180) of safflower under drought stress (Table 1)
No significant difference was observed between both accessions of safflower in terms of biomass production (Figure 1)
Summary
All plant processes are greatly influenced by deficiency of water as water is vital for their functioning [1,2]. Water deficiency even for a short time can disturb the growth and decrease the productivity of plants by disturbing photosynthesis [3,4]. Water-deficiency-induced impairment in photosynthesis is attributed to damaged composition of thylakoid membranes in chloroplasts as the lipid contents of cell membranes are susceptible to the ROS species produced as a result of drought [3,4,5]. Plants possess defensive systems primarily as antioxidants, which can effectively reduce the drastic effects of ROS species caused by water deficiency [13,14,15,16,17]. Its oil is used to cook food for patients with cardiovascular diseases as it has a high content of linoleic acid antioxidants such as vitamin E [20,21]. In view of a number of reports, it is evident that this crop, with an inherent characteristic of a deep root system, is resistant to water deficiency and can be grown successfully in semi-arid and arid countries of the world facing problems of water shortage [22,23,24]
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