Abstract
The aim of the study was to demonstrate the potential of the promotion and regulation of plant physiology and growth under control and copper stress conditions, and the impact of the exogenous application of methyl jasmonate on this potential. Runner bean plants were treated with methyl jasmonate (1 or 10 µM) (J; J1 or J10) and Cu (50 µM), and inoculated with a bacterial isolate (S17) originating from Spitsbergen soil, and identified as Pseudomonas luteola using the analytical profile index (API) test. Above- and under-ground plant parts were analyzed. The growth parameters; the concentration of the photosynthetic pigments, elements, flavonoids (FLAVO), phenolics (TPC), allantoin (ALLA), and low molecular weight organic acids (LMWOAs); the activity of antioxidant enzymes and enzymes of resistance induction pathways (e.g., superoxide dismutase (SOD), catalase (CAT), ascorbate (APX) and guaiacol (GPX) peroxidase, glucanase (GLU), and phenylalanine (PAL) and tyrosine ammonia-lyase (TAL)), and the antioxidant capacity (AC) were studied. The leaves exhibited substantially higher ALLA and LMWOA concentrations as well as PAL and TAL activities, whereas the roots mostly had higher activities for a majority of the enzymes tested (i.e., SOD, CAT, APX, GPX, and GLU). The inoculation with S17 mitigated the effect of the Cu stress. Under the Cu stress and in the presence of J10, isolate S17 caused an elevation of the shoot fresh weight, K concentration, and TAL activity in the leaves, and APX and GPX (also at J1) activities in the roots. In the absence of Cu, isolate S17 increased the root length and the shoot-to-root ratio, but without statistical significance. In these conditions, S17 contributed to a 236% and 34% enhancement of P and Mn, respectively, in the roots, and a 19% rise of N in the leaves. Under the Cu stress, S17 caused a significant increase in FLAVO and TPC in the leaves. Similarly, the levels of FLAVO, TPC, and AC were enhanced after inoculation with Cu and J1. Regardless of the presence of J, inoculation at Cu excess caused a reduction of SOD and CAT activities, and an elevation of GPX. The effects of inoculation were associated with the application of Cu and J, which modified plant response mainly in a concentration-dependent manner (e.g., PAL, TAL, and LMWOA levels). The conducted studies demonstrated the potential for isolate S17 in the promotion of plant growth.
Highlights
Elicitors are chemicals able to trigger morphological and physiological responses in the plant organism, activating or reducing a defined set of compounds [1]
In our previous studies [35], the S17 isolate was biochemically identified as Gram-negative (Figure 1A) Pseudomonas luteola, and characterized by growth on oligotrophic and coptotrophic media, the activity of ACC (1-aminocyclopropane-1-carboxylate) deaminase, the concentration of indoleacetic acid (IAA), and the Minimal Inhibitory Concentration (MIC) for Cu
The activities of antioxidant enzymes such as superoxide dismutase (SOD), CAT, and peroxidases increased in Pseudomonas and Bacillus inoculated plants, which is partially in agreement with our findings, but our results suggested a dependency on the presence and concentration of J [3,12]
Summary
Elicitors are chemicals able to trigger morphological and physiological responses in the plant organism, activating or reducing a defined set of compounds [1]. Methyl jasmonate (J) is an important naturally occurring plant growth regulator that modulates plant status by activation of the signal transduction pathways [2]. Jasmonate acid (JA), just as ethylene, is involved in the induction of systemic resistance (ISR), which is mediated by plant growth-promoting bacteria (PGPB) capable of stimulating plant growth [3]. Being involved in plant signaling pathways, J participates in the generation of highly reactive oxygen species (ROS), which stimulate the plant defense system by the production of various enzymatic and non-enzymatic antioxidant mechanisms. To study its potential in the plant organism, J can be applied exogenously [5,6,7]
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