Abstract
Excessive aluminum ions (Al3+) in acidic soil can have a toxic effect on watermelons, restricting plant growth and reducing yield and quality. In this study, we found that exogenous application of nitric oxide (NO) could increase the photochemical efficiency of watermelon leaves under aluminum stress by promoting closure of leaf stomata, reducing malondialdehyde and superoxide anion in leaves, and increasing POD and CAT activity. These findings showed that the exogenous application of NO improved the ability of watermelon to withstand aluminum stress. To further reveal the mitigation mechanism of NO on watermelons under aluminum stress, the differences following different types of treatments—normal growth, Al, and Al + NO—were shown using de novo sequencing of transcriptomes. In total, 511 differentially expressed genes (DEGs) were identified between the Al + NO and Al treatment groups. Significantly enriched biological processes included nitrogen metabolism, phenylpropane metabolism, and photosynthesis. We selected 23 genes related to antioxidant enzymes and phenylpropane metabolism for qRT-PCR validation. The results showed that after exogenous application of NO, the expression of genes encoding POD and CAT increased, consistent with the results of the physiological indicators. The expression patterns of genes involved in phenylpropanoid metabolism were consistent with the transcriptome expression abundance. These results indicate that aluminum stress was involved in the inhibition of the photosynthetic pathway, and NO could activate the antioxidant enzyme defense system and phenylpropane metabolism to protect cells and scavenge reactive oxygen species. This study improves our current understanding by comprehensively analyzing the molecular mechanisms underlying NO-induced aluminum stress alleviation in watermelons.
Highlights
Introduction published maps and institutional affilWatermelon (Citrullus lanatus (Thunb.) Matsum. et Nakai) is an annual vine belonging to the Cucurbitaceae family and widely cultivated all over the world [1]
During Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, we found that 1107 differentially expressed genes (DEGs) identified between CK and Al groups were annotated into 89 metabolic pathways, and 511 DEGs obtained from the Al vs. Al + nitric oxide (NO) comparison were successfully annotated into 65 metabolic pathways
We found that aluminum stress significantly inhibited root elongation and the growth of watermelons, while the addition of NO alleviated growth inhibition, consistent with the literature [22,23]
Summary
Introduction published maps and institutional affilWatermelon (Citrullus lanatus (Thunb.) Matsum. et Nakai) is an annual vine belonging to the Cucurbitaceae family and widely cultivated all over the world [1]. According to the FAO data in 2019 (https://scienceagri.com/10-worlds-biggest-watermelon-producing-countries/, accessed on 27 October 2021), China is the world’s largest producer of watermelon, with the planting area, output, and consumption ranking first in the world. It has been reported that the acidification of the soil led to increased mobile aluminum contents, being one of the reasons for continuous cropping obstacle of watermelon [2]. Aluminum stress has been documented to inhibit the growth and development of watermelon on acid soil and seriously affect the yield and quality. Acidic soil accounts for about 30% of the world’s ice-free land area [3]. Given that acidic soils are widely distributed in southern China, aluminum toxicity in acidic soils has been reported as a significant factor limiting local crop production [4].
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