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While ameliorating effects of melatonin (MT) on abiotic stress tolerance in plants are widely reported, the mechanism that underlies this process remains elusive. This work investigated mechanisms by which MT improved drought tolerance in pepper (Capsicum annuum) plants. A foliar spray of 0.1 mM MT treatment was applied to plants grown at 80% and 40% of full field capacity for 3 days. Drought stress caused a significant decrease in plant dry weight, relative water content, leaf water potential, PSII efficiency (Fv/Fm ratio), chlorophyll, soluble protein, leaf and root nitrogen content. Drought increased hydrogen peroxide, malondialdehyde (MDA), nitrate, ammonium, free amino acids, soluble sugars, proline and glycine betaine. Drought also increased peroxidase (POD), glutathione S-transferase (GST) and catalase (CAT) activities, electrolyte leakage (EL) and methylglyoxal (MG). MT pre-treatment reduced oxidative stress and improved nitrogen metabolism by activating various enzymes such as nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), glutamate synthetase (GOGAT) and glutamine dehydrogenase (GDH) activities. It also activated enzymes related to the glyoxalase system (Gly I and Gly II) and decreased NO3-, NH4+ and free amino acid content. Our study suggests a cost-effective and sustainable solution to improve crop productivity in water-limited conditions, by enhancing plant growth, photosynthesis and nitrogen content. [ABSTRACT FROM AUTHOR]

High-throughput automated plant phenotyping has recently received a lotofattention. Leaf area isan important characteristic in understanding plant performance, but time-consuming and destructive to measure accurately. In this research, we describe a method to use a histogram of image intensities to automatically measure plant leaf area of tall pepper (Capsicum annuum L.) plants in the greenhouse. With a device equipped with several cameras, images of plants were recordedat5-cm intervals over aheightof3 m,at a recording distance of less than60 cm. The images were reduced to a small set of principal components that defined the design matrix in a regression model for predicting manually measured leaf area as obtained from destructive harvesting. These regression calibrations were performed for six different developmental times. In addition, development of leaf area was investigated by fitting linear relations between predicted leaf area and time, with special attention given to the genotype by time interaction and its genetic basis in the form of quantitative trait loci (QTLs). The experiment comprised parents,F1progeny and eight genotypes of a recombinant inbred population of pepper. Although the current trial contained a limited number of genotypes, an earlier identified QTL related to leaf area growth could be confirmed. Therefore, image analysis, as presented in this paper, provides a powerful and efficient way to study and identify the genetic basis of growth and developmental processes in plants. [ABSTRACT FROM AUTHOR]

Nickel (Ni) contamination hinders plant growth and yield. Nitric oxide (NO) and thiourea (Thi) aid plant recovery from heavy metal damage, but their combined effects on pepper (Capsicum annuum) plant tolerance to Ni stress need more study. Sodium nitroprusside (0.1 mM, SNP) and 400 mg L−1 Thi, alone and combined, were studied for their impact on pepper growth under Ni toxicity. Ni stress reduces chlorophyll, PSII efficiency and leaf water and sugar content. However, SNP and Thi alleviate these effects by increasing leaf water, proline and sugar content. It also increased the activities of superoxide dismutase, catalase, ascorbate peroxidase and peroxidase. Nickel stress lowered nitrogen assimilation enzymes (nitrate reductase, nitrite reductase, glutamine synthetase, glutamate synthase and glutamate dehydrogenase) and protein content, but increased nitrate, ammonium and amino acid content. SNP and Thi enhanced nitrogen assimilation, increased protein content and improved pepper plant growth and physiological functions during Ni stress. The combined treatment reduced Ni accumulation, increased Ni in leaf cell walls and potentially in root vacuoles, and decreased Ni concentration in cell organelles. It effectively mitigated Ni toxicity to vital organelles, surpassing the effects of SNP or Thi use alone. This study provides valuable insights for addressing heavy metal contamination in agricultural soils and offers potential strategies for sustainable and eco-friendly farming practices. Nickel contamination hinders plant growth and yield. Nitric oxide (NO) and thiourea aid plant recovery from heavy metal damage, but their combined effects on pepper (Capsicum annuum) tolerance to Ni stress need more study. Combined use of NO and thiourea alleviates Ni stress effects on pepper by enhancing leaf water, proline, sugar content, antioxidant enzyme activities and Ni distribution. These findings contribute valuable insights for addressing heavy metal contamination in agricultural soils and promoting sustainable and eco-friendly farming practices. [ABSTRACT FROM AUTHOR]

The presence of melatonin, a known animal hormone, has been confirmed in many evolutionary distant organisms, including higher plants. It is known that melatonin increases tolerance to stress factors as a wide spectrum antioxidant. Tolerant genotypes have generally higher melatonin content than sensitive ones, and exposure to stressful conditions is known to increase endogenous melatonin levels. However, endogenous melatonin levels in seeds have never been used to select genotypes tolerant to abiotic stresses. Thus, in this study, the existence of possible relationship between seed melatonin levels of 28 pepper (Capsicum annuum L.) genotypes and their germination and emergence performance under chilling conditions (15°C) was investigated. The results indicated that these parameters were much better for pepper genotypes with higher seed melatonin contents while those having less than 2 ng g−1 additionally exhibited elevated levels of MDA and H2O2 but lower antioxidant enzyme activities. Thus, a positive relationship between seed melatonin content and chilling stress tolerance has been shown, suggesting a possible use of endogenous melatonin levels as a criterion in selecting chilling stress tolerant varieties. To save considerable time, money and labour, it is recommended that genotypes with lower melatonin contents are excluded from breeding programmes that aim to develop new stress tolerant genotypes. Endogenous melatonin content in pepper (Capsicum annuum L.) seeds may be used as a marker of cold stress tolerance. Thus, eliminating low melatonin seed varieties from the breeding programs could significantly improve their effectiveness and save considerable time, money and labour. [ABSTRACT FROM AUTHOR]

Drought is one of the major factors limiting global crop yield. In Mexico, agriculture is expected to be severely affected by drought. The Capsicum genus has several crop species of agricultural importance. In this work, we analysed the Capsicum chinense plant physiological responses and differentially expressed genes under water stress mainly focused on the responses elicited following recovery through repetitive stress. Plants were cultivated in an experimental block. Each block consisted of plants under water deficit and a control group without deficit. Morphometric and functional parameters, and the expression of genes related to resistance to abiotic stresses were measured. Morphological differences were observed. Plants subjected to water deficit showed impaired growth. Nonetheless, in the physiological parameters, no differences were observed between treatments. We selected abiotic stress-related genes that include heat-shock proteins (HSPs), heat-shock factors (HSFs), transcription factors related to abiotic stress (MYB, ETR1, and WRKY), and those associated with biotic and abiotic stress responses (Jar1 and Lox2). HSF, HSP, MYB72, ETR1, Jar1, WRKYa, and Lox2 genes were involved in the response to water-deficit stress in C. chinense plants. In conclusion, our work may improve our understanding of the morphological, physiological, and molecular mechanisms underlying hydric stress response in C. chinense. [ABSTRACT FROM AUTHOR]

Phytoene synthase (PSY) is the first committed enzyme in carotenoid biosynthesis, which plays important role in ripen fruit colour. However, the roles of CaPSY genes are not explained detail in ripen pepper fruit colour. In this study, three CaPSY genes (CaPSY1 , CaPSY2 and CaPSY3) were identified through basic local alignment search tool (BLAST) in pepper genome. Among them, CaPSY1 was predicted as putative candidate based on relative expression values using five developmental stages of fruit in Zunla-1 cultivar and also in ripen fruits of five contrasting pepper lines. The CaPSY1 was characterised functionally through virus-induced gene silencing (VIGS) in ripen fruits and overexpression in Arabidopsis thaliana (L.) Heynh. Silencing of CaPSY1 gene altered colour with increased lutein and decreased zeaxanthin content in pepper fruits. The transgenic Arabidopsis line CaPSY1 gene showed higher expression of PSY1 gene compared with WT and dwarf phenotype due to reduction of GA3 (gibberellic acid) and higher abscisic acid (ABA) content. Our results confirmed that CaPSY1 gene involved in carotenoid metabolism in ripen pepper fruit and provide clue to develop bright red coloured pepper lines through breeding. Phytoene synthase (PSY) is the first enzyme in carotenoid biosynthesis, which plays important role in fruit coloration at ripening. CaPSY1 was predicted as putative candidate based on relative expression values using five fruit developmental stages of Zunla-1 and in ripen fruits of five contrasting pepper lines. The CaPSY1 gene was validated functionally through silencing and overexpression by VIGS in ripen fruits and in Arabidopsis thaliana respectively. [ABSTRACT FROM AUTHOR]

Optimal plant growth in many species is achieved when the two major forms of N are supplied at a particular ratio. In this pot experiment, the effects of five different ammonium : nitrate ratios (ANRs) (0 : 100, 12.5 : 87.5, 25 : 75, 37.5 : 62.5, and 50 : 50) on photosynthesis efficiency in chilli pepper (Capsicum annuum L.) plants were evaluated. The results showed that an ANR of 25 : 75 increased the contents of chl a , leaf area and dry matter, whereas chl b content was not affected by the ANRs. Regarding chlorophyll fluorescence, an ANR of 25 : 75 also enhanced the actual photochemical efficiency, photochemical quenching and maximum photosynthetic rate. However, the 0 : 100 and 50 : 50 ANRs resulted in higher values for nonphotochemical quenching. An inhibition of maximal photochemical efficiency was found when 50% NH4+ was supplied at the later stage of plant growth. The addition of 25% or 37.5% NH4+ was beneficial for gas exchange parameters and the 25% NH4+ optimised the thylakoid of chloroplasts. Compared with nitrate alone, 12.5–50% NH4+ upregulated glutamate dehydrogenase (GDH), the large subunit and the small subunit of Rubisco. It can be concluded that the 25 : 75 ANR accelerated N assimilation through active GDH, which provides a material basis for chloroplast and Rubisco formation, resulting in the increased photosynthetic rate and enhanced growth in chilli pepper. The unbalanced application of N fertilizer has resulted in enormous energy consumption and adverse environmental consequences worldwide. Optimum development is attainable when ammonium and nitrate are supplied to the plants at an appropriate ratio. This experiment reveals that an ammonium : nitrate ratio of 25 : 75 is the most appropriate for improved photosynthetic capacity in chilli pepper. This can improve the growth and development of this popular vegetable for the benefit of farmers. [ABSTRACT FROM AUTHOR]

In this work, we analysed the natural variation in mechanisms for protection against salt stress in pepper varieties (Capsicum chinense Jacq. cv. Rex, Chichen-Itza and Naranja and Capsicum annuum L. cv. Padron), considering primary root growth and viability of the post-stressed seedlings. NaCl-induced K+ and H+ efflux in roots was also studied by ion-selective microelectrodes under application of pharmacological agents. In these pepper varieties, the magnitude of theK+ leakage in the roots positively correlated with growth inhibition of the primary root in the presence of NaCl, with Rex variety showing a higher level of tolerance than Chichen-Itza. The K+ leakage and the activity of the H+ pump in the roots were dependent on the NaCl concentration. Pharmacological analysis indicated that the NaCl-induced K+ leakage was mediated by TEA+-sensitive KOR channels but not by NSCC channels. In addition, we present evidence for the possible participation of proline, and a Na+-insensitive HAK K+ transporter expressed in habanero pepper roots for maintaining K+ homeostasis under salt stress conditions. [ABSTRACT FROM AUTHOR]