Abstract
Phytochemical analyses of pepper fruit metabolites have been reported; however, much less is known about the influence of different forms of nitrogen (N), which is critical for plant growth and fruit quality formation. The “Longjiao No. 5” variety (Capsicum annuum L.) grown in Northwestern China was profiled using liquid chromatography–mass spectrometry (LC–MS) coupled with multivariate data analysis to explore the composition of different metabolites in pericarp and placenta, and to investigate the effect of three ammonium (NH4+) to-nitrate (NO3−) ratios (0:100, 25:75, and 50:50). A total of 215 metabolites were obtained by qualitative analysis, where 31 metabolites were the major differential metabolite components of pepper fruits between placenta and pericarp, and 25 among N treatments. The addition of ammonium up-regulated carbohydrates, such as α-lactose and sucrose, as well as phenylalanine lyase (PAL) of placenta tissue. The supply of 25% NH4+–N and 75% NO3−–N exhibited a relatively higher levels of ascorbic acid in pericarp and amino acids, capsaicin, and dihydrocapsaicin in placenta, and led to higher fruit weight among the ammonium-to-nitrate ratios. The expression and activities of glutamic acid synthetase (GOGAT) and glutamine synthetase (GS) that are involved in ammonium assimilation were affected by adjusting the ammonium–N proportion, and they were significantly positively correlated with capsaicin, dihydrocapsaicin contents, capsaicinoid synthetase (CS), as well as the relative expression levels of genes related to capsaicinoid biosynthesis, such as acyltransferase 3 (AT3) and acyl-ACP thioesterase (FatA).
Highlights
Nitrate (NO3 − ) and ammonium (NH4 + ), as the two main soil nitrogen (N) sources available to plants, exert different effects on biochemical processes in higher plants
Metabolites in microorganisms playssignificantly a vital role incompared the biosynthesis of planttissues; secondary metabolites, in addition placenta tissues and changed with pericarp the former may be to participating biosynthesis of protein,ammonia-lyase flavonoid, lignin, and many other compounds more sensitive in to the Phenylalanine is widely found in plants and a[44]
Our metabolome data showed that the compounds in “Longjiao No 5” pepper fruit were affected by the ratio of ammonium and nitrate, the metabolites in the placenta were more sensitive to the change of N source
Summary
Nitrate (NO3 − ) and ammonium (NH4 + ), as the two main soil nitrogen (N) sources available to plants, exert different effects on biochemical processes in higher plants. Assimilation of ammonium from root absorption, biological fixation, nitrate reduction, and photorespiration is largely accomplished by the glutamine synthetase (GS)–glutamate synthetase (GOGAT) pathway. In this pathway, GS combines glutamic acid with NH4 + to form glutamine, and the increase of glutamine level in plants stimulates the activity of GOGAT [2]. For the past few years, a large number of studies have focused on the utilization of NO3 − and NH4 + fertilization [3,4] and the effects on plant growth and development, such as plant photosynthetic physiology [5], rhizosphere environment [6], and abiotic stress tolerance [7]. Few studies have been conducted to evaluate the relationship between
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