Exogenous application of 5-aminolevulinic acid on wheat seedlings under drought stress enhances the transcription of psbA and psbD genes and improves photosynthesis

Abstract

The compound 5-aminolevulinic acid (ALA) is an essential precursor for the biosynthesis of porphyrins, including chlorophyll, heme, and cytochromes. The protective effects of ALA on photosynthesis and the expression of photosynthetic genes in wheat under drought stress are not well understood. Two wheat cultivars, drought-tolerant Aikang-58 and droughtsensitive Chinese Spring, were exposed to drought stress induced by 20% polyethylene glycol (PEG-6000) after foliar pretreatment with ALA for 3 days. The results showed that exogenous application of ALA protected the drought-stressed wheat seedlings by significantly inhibiting the decrease in relative water and chlorophyll contents. The ALA-mediated alleviation of stress was similar between the drought-tolerant and drought-sensitive wheat cultivars. Meanwhile, compared to seedlings under drought treatment alone, the ALA-pre-treated wheat seedlings under drought stress maintained higher photosystem II (PSII) functional indexes. The ALA pretreatment reduced the drought-driven accumulation of both H 2 O 2 and ABA and increased the stomatal conductance. Real-time PCR analysis showed that the psbA and psbD gene transcripts were both upregulated under drought stress following ALA pretreatment. The present study suggests that the exogenous foliar application of ALA alleviates the drought stress on wheat seedlings, which is associated with the enhancement of PSII function by inducing chlorophyll synthesis and psbA and psbD transcription. Moreover, the protective effect of ALA pretreatment was not related to the decline in stomatal conductance caused by ABA or H 2 O 2 accumulation.

The iTRAQ-based chloroplast proteomic analysis of Triticum aestivum L. leaves subjected to drought stress and 5-aminolevulinic acid alleviation reveals several proteins involved in the protection of photosynthesis

“…The accumulation of Gap benefits the transduction of the ROS hydrogen peroxide (H 2 O 2 ) signal in response to drought stress, and a knockout of Gap decreases stomatal sensitivity to ABA and renders plants less responsive to water deficits than the wild type [57]. When wheat seedlings were pretreated with ALA, the downregulation of Gaps was coordinated with a lower content of H 2 O 2 in a previous report [23], which was most likely associated with the accumulation of the ROS scavengers GPX and POD.…”

“…The ambient environmental temperature and relative humidity were controlled at 25°C/22°C (day/night) and 75~85%, respectively. The wheat seedlings were watered with 400 mL of water every 2 d until two leaves were fully expanded, and 100 mg L − 1 ALA was foliar applied according to our previous evaluation results [23]. Three days after ALA treatments, the seedlings were subjected to drought stress by a cessation of watering, while the control group was watered as normal.…”

“…Fresh seedling leaves were sampled from three replicates under each treatment. RWC was calculated by the following formula: RWC (%) = (FW -DW) / (TW -DW) × 100 [23]. The chlorophyll content was determined by spectrophotometry according to Porra et al [66].…”

“…Under drought stress, the exogenous application of ALA has been proven to alleviate the damage, which was shown in reports on Kentucky bluegrass [18], alfalfa (Medicago varia Martyn.) [19], Leymus chinensis [20], canola (Brassica napus L.) [21], and wheat [22,23]. For wheat, the use of ALA is more attractive because this substance was reported to promote growth and alleviate the yield loss caused by dry conditions [24].…”

“…According to the existing evidence, the exogenous application of ALA increases the chlorophyll content, activates antioxidant enzymes, reduces lipid peroxidation of the membrane [13], promotes photosynthesis [15], enhances the tetrapyrrole biosynthetic pathway and proline accumulation [14], improves the metabolism of polyamines [17], regulates nitrogen metabolism, absorption, aggregation and distribution of nutrient ions [22,25], inhibits the microstructural damage in chloroplasts by increasing the proportion of intact thylakoids [26], and regulates the expression of genes [27]. Our previous study showed that ALA pretreatment enhanced the photosynthetic capacity of droughtstressed wheat seedlings [23], but the regulatory mechanism behind this effect is still unknown.…”