Abstract
5-aminolevulinic acid (ALA), a key precursor in the biosynthesis of porphyrins, can improve plant tolerance to various environmental stresses. However, it is unclear whether ALA can improve tolerance in poplar. Here, we investigated the effects of ALA on poplars under drought and salt stresses. ALA pretreatment exhibited less morphological damage, reduced leaf malonaldehyde content (MDA) and electrolyte leakage (EL), and increased leaf relative water content (RWC), proline (PRO), superoxide dismutase (SOD), and peroxidase (POD) content under stresses. Furthermore, exogenous ALA mitigated the decrease in photosynthetic capacity, and restored the chlorophyll content (Chl), net CO2 assimilation rate, stomatal conductance (Gs), transpiration rate (Tr), maximal photochemical quantum yield of PSII (Fv/Fm), actual quantum yield of photosynthesis (YII), and electron transfer rate (ETR) of poplar under various stresses. qRT-PCR showed that ALA up-regulated the expression of antiporters and aquaporins genes, which are associated with Na+ exclusion in the leaf cells and the transport activity of aquaporins. In summary, ALA pretreatment significantly improved the stress tolerance of poplar, decreasing the degree of membrane lipid peroxidation and promoting the photosynthesis and antioxidant capacity of leaves. In addition, our results showed that ALA might mediate Na+ transporter and aquaporins activity, thereby increasing the salt tolerance of poplar.
Highlights
Our findings suggested that drought and salt stresses displayed a negative effect on membrane integrity, which may be the reason for the enhanced electrolyte leakage
Our current results showed that aminolevulinic acid (ALA) pretreated plants have lower electrolyte leakage and higher relative water content (RWC) compared to the drought and salt treatment groups under drought and salt stresses (Figures 1 and 2)
ALA pretreatment did not improve the stomatal conductance under drought stress, but Fv/Fm increased and slightly improved photosynthetic CO2 assimilation of ALA pretreated plants (Tables 3 and 5). These results indicated that the photochemistry of photosynthesis was damaged by drought and salt stresses, and ALA pretreatment resulted in less damage to the photosynthetic system and improved the drought and salt tolerance of poplar seedlings
Summary
5-aminolevulinic acid (ALA), a key precursor in the biosynthesis of porphyrins, can improve plant tolerance to various environmental stresses. ALA pretreatment significantly improved the stress tolerance of poplar, decreasing the degree of membrane lipid peroxidation and promoting the photosynthesis and antioxidant capacity of leaves. Poplar has many advantages such as rapid growth, easy survival, and strong adaptability to soil [1,2,3] Abiotic stresses such as drought and salt have a negative impact on plant growth. Water deficit has a negative effect on the production and accumulation of plant biomass. It causes a series of damages to the plant, which are harmful to the growth of poplar [4,5,6].
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