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. 2022 Oct 28;8(11):1140.
doi: 10.3390/jof8111140.

Abscisic Acid May Play a Critical Role in the Moderating Effect of Epichloë Endophyte on Achnatherum inebrians under Drought Stress

Xuelian Cui  1 , Wen He  1 , Michael John Christensen  2 , Jinfeng Yue  1 , Fanbin Zeng  1 , Xingxu Zhang  1 , Zhibiao Nan  1 , Chao Xia  1
Affiliations

Abscisic Acid May Play a Critical Role in the Moderating Effect of Epichloë Endophyte on Achnatherum inebrians under Drought Stress

Xuelian Cui et al. J Fungi (Basel). .

Abstract

Water scarcity is a major constraint that adversely affects plant development and growth. Abscisic acid (ABA) is a plant stress hormone that is rapidly synthesized and can induce stomatal closure to conserve water, thereby alleviating the drought stress of plants. The Epichloë endophyte enhances the drought tolerance of Achnatherum inebrians (drunken horse grass, DHG). To better understand how the Epichloë endophyte enhances drought tolerance, DHG plants without (EF) and with (EI), an Epichloë endophyte, were grown under 20% and 60% soil water conditions (SWC), and the leaves of the three treatments of EF and EI plants were sprayed with ABA solution (1 mg/L); fluridone (FLU), the ABA biosynthesis inhibitor solution (1 mg/L); and distilled water, respectively. Four-weeks later, the results indicated that the exogenous ABA application promoted plant growth, stomatal conductance, and photosynthetic rate, while the opposite effect occurred with plants sprayed with FLU. The differences between EI and EF plants in tiller number, height, chlorophyll content, stomata conductance, and photosynthetic rate were highest when sprayed with ABA. Thus, it is concluded that ABA might be involved in the moderating effect of Epichloë endophytes on DHG plants exposed to drought by maintaining growth and improving photosynthetic efficiency.

Keywords: Epichloë endophyte; abscisic acid; drought stress; photosynthesis.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Plant height and tiller number of A. inebrians seedlings, endophyte-uninfected (EF) and infected (EI), under different exogenous ABA content and two soil water contents. Columns with non-matching lowercase letters indicate a significant difference between different treatments under the same water content at p < 0.05. Columns with non-matching capital letters indicate a significant difference between different ABA treatments under the same water content at p < 0.05. The same below. (a,c): 20% water content, (b,d): 60% water content.
Figure 2
Figure 2
Shoot dry biomass and root dry biomass of two different soil water contents of A. inebrians seedlings, endophyte-uninfected (EF) and infected (EI) under different exogenous ABA content (g). (a,c): 20% water content, (b,d): 60% water content.
Figure 3
Figure 3
Chlorophyll content of two different soil water contents of A. inebrians seedlings, endophyte-uninfected (EF) and infected (EI) under different exogenous ABA content (mg/dm2). (a): 20% water content, (b): 60% water content.
Figure 4
Figure 4
Photosynthetic rate (μmol CO2 m−2s−1), transpiration rate (mmol H2O m−2s−1), stomatal conductance (mmol H2O m−2s−1), and intercellular carbon dioxide concentration (μmol CO2 mol−1) of endophyte-uninfected (EF) and infected (EI) A. inebrians seedlings, at two soil water contents and different exogenous ABA contents. (a,c,e,g): 20% soil water content, (b,d,f,h): 60% soil water content.
Figure 5
Figure 5
The final model results of structural equation modeling (SEM) analysis for endophyte, abscisic acid, and water factors on biomass of A. inebrians seedlings. Dotted arrows, insufficient statistical evidence for path coefficients (p > 0.05). Blue arrows indicate evidence for negative relationships, and red arrows indicate evidence for positive relationships. The proportion of variance explained (R2) appears alongside each response variable in the model. Width of the arrows shows the strength of the causal relationship, and the numbers adjacent to arrows are standardized path coefficients, which reflect the extent of the relationship, while asterisks indicate statistical significance (*** p < 0.001; ** p < 0.01; * p < 0.05). The final model adequately fitted the data: χ2 = 0.662, P = 0.956, RMSEA < 0.001, GFI = 0.997, AGFI = 0.978, RFI = 0.992.
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