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In the northwest of China, the area of facility watermelon cultivation continuously expands with popularization. In order to explore an efficient water-saving irrigation system of watermelon growth in plastic greenhouses, the experiment was conducted to investigate the influence of different mulched drip irrigation frequency on growth, yield, quality, and water use efficiency of watermelons in plastic greenhouses during each growth stage under regulated deficient irrigation. According to preliminary study, a diameter of 20 cm evaporating dish was used to measure water surface evaporation so as to control irrigation water. Three different levels of irrigation frequency were designed including high frequency (once every 2 days), intermediate frequency (once every 4 days), and low frequency (once every 6 days). Each treatment was kept at the same total irrigation amount with 0.4 evaporation amount measured by dish (Ep) during the seedling period, 0.8Ep during the flowering fruit-bearing period, 1.6Ep at the fruit enlargement period, and 0.8Ep at the mature period, respectively. The experiment had measured plant morphological index, photosynthetic indexes, fruit quality index, fruit yield, and water use efficiency. The results showed that irrigation with intermediate frequency at seedlings stage, high frequency at flowering fruit-bearing stage, intermediate frequency at fruit enlargement period, and low frequency at the mature stage (T4 treatment) were the best treatment in all of the nine treatments. In the seedling, flowering, fruit enlargement, and mature periods, this treatment displayed the best growth potential in plant height and stem diameter with a relatively high level of chlorophyll content, net photosynthetic rate, transpiration rate, stomatal conductance, and leaf water use efficiency. This high ability of photosynthesis assimilation in turn contributed to the fruit enlargement and had more advantages against adversity stress early spring. The results of plant height and stem diameter showed that from the stage of seedling to flowering fruit-bearing, the high-frequency irrigation promoted plant height, while intermediate frequency and low frequency irrigation benefited the increase of stem diameter, and because of the different irrigation water during different stages, there were an obvious compensation effect between plant height and stem diameter, in the aspect of quality. T4 treatment had the thinnest peel, which was only 8.30 mm, larger edible part, higher content of total vitamin C, and the highest total center soluble solid content, total edge soluble solid content, as well as soluble protein, which reached 12.85%, 10.80%, 0.35 mg/g respectively. In addition, the fruit sweetness of the T4 treatment was high and had a better quality. In the aspect of fruit production, this treatment also had higher fruit rate, single fruit weight, the highest total fruit production 63.72 t/hm2, and the highest water use efficiency 303.64 kg/(hm2.mm). Therefore, considering the growth potential, yield, quality, and irrigation water use efficiency, the T4 treatment is the best irrigation frequency plan for the whole watermelon growth period, that is, once every 4 days irrigation at seedling stage, once every 2 days irrigation at flowering fruit-bearing stage, once every 4 days irrigation at fruit enlargement stage, and once every 6 days irrigation at the mature stage. T4 is the best treatment in all the nine treatments and the best irrigation frequency scheme for watermelon irrigation in greenhouses under regulated deficit irrigation in early spring of the northwest region. The research could provide valuble information for high efficiency and water-saving irrigation facilities cultivation in the spring of northwest in greenhouse watermelon. [ABSTRACT FROM AUTHOR]

This study was to set up a new model for good quality and high yield evaluation of water-saving watermelon cultivation in the arid regions of northwest China. The coupling effects of water and fertilizers on plant growth, yield and fruit quality of watermelon under plastic film mulch using drip irrigation were studied in a field experiment. Nine treatments were designed including three irrigation amount levels (W1, 450 m3/hm2; W2, 900 m3/hm2; and W3, 1350 m3/hm2) and three fertilizer levels (F1, N 81.53 kg/hm2+ P2O5 33.43 kg/hm2+ K2O 101.09 kg/hm2; F2, N 163.05 kg/hm2+ P2O5 66.85 kg/hm2+ K2O 202.18 kg/hm2; and F3, N 244.58 kg/hm2+ P2O5 100.28 kg/hm2+ K2O 303.27 kg/hm2). The results indicated that at the same fertilizer level, plant height increased but stem diameter decreased with increasing irrigation quantity. Compared with the other treatments, F2W2 showed much higher chlorophyll content in each growth stage. In the seedling stage, treatments with increased supplying of water and fertilizer gave rise to increases in leaf net photosynthetic rate and transpiration rate, and the net photosynthetic rate and transpiration rate in leaf were not significantly different between F2W2 and the other treatments. After the flowering stage, F2W2 treatment revealed a relatively high photosynthesis (with no significant difference with F3W3) in leaves, leading to the highest fruit yield (which was 3.6% higher than F3W3) and the highest water use efficiency (35.73% higher than F3W3) at the end of the experiment. For the fruit quality, F2W1 treatment and F3W2 treatment showed the highest soluble sugar content and total vitamin C content (but no significant difference with F2W2), respectively. The F2W2 treatment revealed the best performance with high content of total soluble solids (TSS), soluble protein and lycopene in fruits as well as good sugar acid ratio and excellent taste. The supply of water and fertilizer in the F2W2 treatment could meet needs for the watermelon growth, making plant grow strongly (with high photosynthesis capability in leaves and good quality as well as high yield in fruits) by economical irrigation water use efficiency. So, the F2W2 treatment was recommended as the best combination of water and fertilizer for the production of watermelon under drip irrigation and plastic film mulch in the arid area of northwest China. [ABSTRACT FROM AUTHOR]

Cold stress is a major environmental factor that detrimentally affects plant growth and development. Melatonin has been shown to confer plant tolerance to cold stress through activating the C-REPEAT BINDING FACTOR (CBF) pathway; however, the underlying modes that enable this function remain obscure. In this study, we investigated the role of H2O2 and Ca2+ signaling in the melatonin-induced CBF pathway and cold tolerance in watermelon (Citrullus lanatus L.) through pharmacological, physiological, and genetic approaches. According to the results, melatonin induced H2O2 accumulation, which was associated with the upregulation of respiratory burst oxidase homolog D (ClRBOHD) during the early response to cold stress in watermelon. Besides, melatonin and H2O2 induced the accumulation of cytoplasmic free Ca2+ ([Ca2+]cyt) in response to cold. This was associated with the upregulation of cyclic nucleotide-gated ion channel 2 (ClCNGC2) in watermelon. However, blocking of Ca2+ influx channels abolished melatonin- or H2O2-induced CBF pathway and cold tolerance. Ca2+ also induced ClRBOHD expression and H2O2 accumulation in early response to cold stress in watermelon. Inhibition of H2O2 production in watermelon by RBOH inhibitor or in Arabidopsis by AtRBOHD knockout compromised melatonin-induced [Ca2+]cyt accumulation and melatonin- or Ca2+-induced CBF pathway and cold tolerance. Overall, these findings indicate that melatonin induces RBOHD-dependent H2O2 generation in early response to cold stress. Increased H2O2 promotes [Ca2+]cyt accumulation, which in turn induces H2O2 accumulation via RBOHD, forming a reciprocal positive-regulatory loop that mediates melatonin-induced CBF pathway and subsequent cold tolerance. [ABSTRACT FROM AUTHOR]

Ethylene plays diverse roles in post-harvest processes of horticultural crops. However, its impact and regulation mechanism on the postharvest physiological deterioration (PPD) of cassava storage roots is unknown. In this study, a notable delay in PPD of cassava storage roots was observed when ethephon was utilized as an ethylene source. Physiological analyses and quantitative acetylproteomes were employed to investigate the regulation mechanism regulating cassava PPD under ethephon treatment. Ethephon was found to enhance the reactive oxygen species (ROS) scavenging system, resulting in a significant decrease in H 2 O 2 and malondialdehyde (MDA) content. The comprehensive acetylome analysis identified 12,095 acetylation sites on 4403 proteins. Subsequent analysis demonstrated that ethephon can regulate the acetylation levels of antioxidant enzymes and members of the energy metabolism pathways. In summary, ethephon could enhance the antioxidant properties and regulate energy metabolism pathways, leading to the delayed PPD of cassava. • Ethephon effectively delays postharvest physiological deterioration (PPD) in cassava. • Ethephon enhances the antioxidant system in cassava, reducing malondialdehyde and H 2 O 2 levels. • Ethephon inhibits browning by regulating polyphenol oxidase activity. • This represents a comprehensive global acetylation profile conducted in cassava. • Ethephon regulates acetylation of antioxidant enzymes and energy metabolism pathways to delay PPD. [ABSTRACT FROM AUTHOR]

Melatonin plays a crucial role in regulating plant cold tolerance, but the mechanisms underlying signal transduction remain elusive. In this study, we discovered that overexpression of the melatonin biosynthetic gene caffeic acid O-methyltransferase1 (COMT1) enhanced watermelon (Citrullus lanatus) cold tolerance, accompanied by the accumulation of cytosolic free calcium ([Ca2+]cyt), a stimulation of Ca2+ influx, and upregulation of 4 Ca2+-permeable channel genes (CNGC2/10/17/20). Conversely, the knockout of COMT1 exhibited contrasting effects compared with its overexpression. Knocking out the 4 CNGC genes revealed that only cyclic nucleotide-gated ion channel 20 (CNGC20) mediates melatonin-induced Ca2+ influx in response to cold stimuli. CNGC20 deletion impeded watermelon callus redifferentiation, prompting us to employ a virus-induced gene silencing strategy to suppress its expression. Silencing CNGC20 compromised COMT1 overexpression-induced [Ca2+]cyt accumulation, Ca2+ influx, and watermelon cold tolerance. Yeast 2-hybrid, bimolecular fluorescence complementation, firefly luciferase complementation imaging, and pull-down assays revealed an interaction between CNGC20 and calmodulin7 (CaM7). Overexpressing CaM7 inhibited melatonin-induced [Ca2+]cyt accumulation, Ca2+ influx, and watermelon cold tolerance. Conversely, silencing CaM7 increased [Ca2+]cyt accumulation, Ca2+ influx, and cold tolerance, whereas COMT1 overexpression failed to further enhance these responses in CaM7-silenced plants, indicating the negative regulation role of CaM7 in melatonin-mediated cold responses. Overall, these findings provide insights into the molecular mechanisms underlying melatonin-enhanced plant cold tolerance via Ca2+ signaling, holding potential for breeding/engineering cold-tolerant cucurbit varieties., Competing Interests: Conflict of interest statement. None declared., (© The Author(s) 2024. Published by Oxford University Press on behalf of American Society of Plant Biologists. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Melatonin is a pivotal bioactive molecule that enhances plant cold stress tolerance, but the precise mechanisms remain enigmatic. Here, we have discovered that overexpressing melatonin biosynthetic gene ClCOMT1 or applying exogenous melatonin activates the C-repeat binding factor (CBF)-responsive pathway and enhances watermelon cold tolerance. This enhancement is accompanied by elevated levels of nitric oxide (NO) and hydrogen sulfide (H 2 S), along with upregulation of nitrate reductase 1 (ClNR1) and L-cysteine desulfhydrase (ClLCD) genes involved in NO and H 2 S generation respectively. Conversely, knockout of ClCOMT1 exhibits contrasting effects compared to its overexpression. Furthermore, application of sodium nitroprusside (SNP, a NO donor) and NaHS (a H 2 S donor) promotes the accumulation of H 2 S and NO, respectively, activating the CBF pathway and enhancing cold tolerance. However, knockout of ClNR1 or ClLCD abolished melatonin-induced H 2 S or NO production respectively and abrogated melatonin-induced CBF pathway and cold tolerance. Conversely, supplementation with SNP and NaHS restored the diminished cold response caused by ClCOMT1 deletion. Additionally, deletion of either ClNR1 or ClLCD eliminated NaHS- or SNP-induced cold response, respectively. Overall, these findings suggest a reciprocal positive-regulatory loop between ClNR1-mediated NO and ClLCD-mediated H 2 S, which plays a crucial role in mediating the melatonin-induced enhancement of cold tolerance., (© 2025 Society for Experimental Biology and John Wiley & Sons Ltd.)

High salinity can severely inhibit the growth and development of watermelon ( Citrullus lanatus L.). WRKY proteins are believed to mediate the adaptation of plants to abiotic stresses. Here, we identified the ClWRKY61 gene, which positively regulates the tolerance of watermelon to salt stress. Knockout of the ClWRKY61 reduced salt tolerance, while overexpression of the ClWRKY61 enhanced salt tolerance in watermelon according to phenotypic and physiological analyses. Yeast two-hybrid assays revealed that ClWRKY61 interacts with the ClLEA55 protein, and this interaction was further confirmed by luciferase complementation imaging, transient bimolecular fluorescence complementation, and GST pull-down assays. Knockout of the ClLEA55 resulted in lower salt tolerance compared to the wild-type plants. RNA-seq analysis indicated 421 up-regulated and 133 down-regulated genes in the ClWRKY61 knockout line under salt stress, containing 293 differentially expressed genes with W-box in their promoters. Thirteen genes encoding phytoene synthase, MYB transcription factor, sucrose synthase, alpha/beta-hydrolases superfamily protein, glutathione reductase, sugar transporter, LEA protein, WRKY transcription factor, ERF transcription factor, alpha-glucan water dikinase, and calcium-dependent protein kinase showed transcriptional changes in ClWRKY61 knockout line, ClWRKY61 overexpression line, and ClLEA55 knockout line under salt stress. These results provide an opportunity to mediate the regulation of salt stress in watermelon with WRKY proteins., Competing Interests: None declared., (© The Author(s) 2025. Published by Oxford University Press on behalf of Nanjing Agricultural University.)

Precocious leaf senescence can reduce crop yield and quality by limiting the growth stage. Melatonin has been shown to delay leaf senescence; however, the underlying mechanism remains obscure. Here, we show that melatonin offsets abscisic acid (ABA) to protect photosystem II and delay the senescence of attached old leaves under the light. Melatonin induced H 2 O 2 accumulation accompanied by an upregulation of melon respiratory burst oxidase homolog D (CmRBOHD) under ABA-induced stress. Both melatonin and H 2 O 2 induced the accumulation of cytoplasmic-free Ca 2+ ([Ca 2+ ] cyt ) in response to ABA, while blocking of Ca 2+ influx channels attenuated melatonin- and H 2 O 2 -induced ABA tolerance. CmRBOHD overexpression induced [Ca 2+ ] cyt accumulation and delayed leaf senescence, whereas deletion of Arabidopsis AtRBOHD, a homologous gene of CmRBOHD, compromised the melatonin-induced [Ca 2+ ] cyt accumulation and delay of leaf senescence in Arabidopsis under ABA stress. Furthermore, melatonin, H 2 O 2  and Ca 2+ attenuated ABA-induced K + efflux and subsequent cell death. CmRBOHD overexpression and AtRBOHD deletion alleviated and aggravated the ABA-induced K + efflux, respectively. Taken together, our study unveils a new mechanism by which melatonin offsets ABA action to delay leaf senescence via RBOHD-dependent H 2 O 2 production that triggers [Ca 2+ ] cyt accumulation and subsequently inhibits K + efflux and delays cell death/leaf senescence in response to ABA., (© 2022 John Wiley & Sons Ltd.)