Conjugated Polyamines in Root Plasma Membrane Enhanced the Tolerance of Plum Seedling to Osmotic Stress by Stabilizing Membrane Structure and Therefore Elevating H+-ATPase Activity.

Hongyang Du,Huaipan Liu,Qiang Li,Ronald Kurtenbach,Benxue Chen

doi:10.3389/fpls.2021.812360

Hongyang Du, Huaipan Liu + Show 3 more

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https://doi.org/10.3389/fpls.2021.812360

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Abstract

Polyamines are small positively charged molecules in plants and play important functions in many biological processes under various environmental stresses. One of the most confounding problems relating to polyamines (PAs) in stresses is the lack of understanding of the mechanisms underlying their function(s). Furthermore, a limited number of studies have addressed this issue at the sub-cellular level, especially in tree plants under drought stress. Therefore, in this research, by simulating natural drought stress with polyethylene glycol (PEG) osmotic stress, the relationship between the levels of conjugated polyamines and the activity of H+-ATPase in the plasma membrane was elucidated with the roots of two plum (Prunus salicina L.) cultivars, which were different in drought tolerance, as experimental materials. Furthermore, free PA levels and the activities of S-adenosylmethionine decarboxylase (SAMDC) and transglutaminase (TGase), which were closely associated with the levels of free and conjugated PAs, were also detected. Results showed that under osmotic stress, the increases of the levels of non-covalently conjugated (non-CC) spermidine (Spd) and spermine (Spm), covalently conjugated (CC) putrescine (Put) and Spd in the plasma membrane of drought-tolerant Ganli No. 5 were more significant than those of drought-sensitive Suli No. 3, indicating that these conjugated PAs might be involved in the tolerance of plum seedlings to stress. Furthermore, the conjugated PAs were closely correlated with plum seedling growth, water retention capacity, plasma membrane damage degree, and hydrogen (H+)-ATPase activity in the plasma membrane. To get more complementary pieces of evidence, we subjected plum seedlings to combined treatments of PEG and exogenous PA (Spd and Spm), and an inhibitor of SAMDC [methylglyoxal-bis (guanylhydrazone), (MGBG)] or TGase (o-phenanthroline). These results collectively suggested that non-CC Spd and Spm, CC Put and Spd in plasma membrane might function in enhancing the tolerance of plum seedlings to osmotic stress by stabilizing membrane structure and therefore elevating H+-ATPase activity.

Highlights

The index relative increase rate of seedling dry weight (RIRSDW) was used to estimate the tolerance of plum seedlings to osmotic stress and the effectiveness of the treatment with every reagent at the different concentrations used in this research (Figure 1)
After the plum seedlings were treated with 25% polyethylene glycol (PEG) (−0.85 MPa) for 7 days, there was a marked difference between the two plum cultivars in the index (Figure 1A)
To verify the drought tolerance of the two plum cultivars, we examined the indexes of RIRSDW, relative water content of root (RWCR), relative plasma membrane permeability (RPMP), and MDA content in the study, since the obvious reaction of plants to environmental stresses is shown as growthinhibiting and the plant drought resistance is closely related with relative water content and growth, which is determined by the accumulation of biomass and dry matter (Kaur and Asthir, 2017)

Summary

Introduction

Abiotic environmental factors, such as drought (Maheswari et al, 2016; Ouyang et al, 2020; Ebmeyer et al, 2021), temperature (Xu et al, 2018), heavy metal (Rakicet al., 2021), and salinity (Zheng et al, 2016; Zhong et al, 2020), are significant plant stressors with a major impact on plant development and productivity, causing serious agricultural yield losses. Gong et al (2010) report that early activation of root hair cell H+-ATPase in the plasma membrane of drought-tolerant oat seedlings triggers the increases in major osmolytes, e.g., proline and glycine betaine, which lead to the up-regulation of the water maintenance system. For another example, the study of Cheng et al (2021) demonstrate that arbuscular mycorrhizal fungus stimulates H+-ATPase activity in response to drought stress, which results in active physiological and biochemical processes, such as great nutrient uptake, root growth, photosynthetic and transpiration rate, etc., coupled with the enhanced tolerance of trifoliate orange seedlings to drought stress. As an important protein, plasma membrane H+-ATPase is closely correlated to drought stress

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