Green Pericarp Research Articles

Transcriptome, Plant Hormone, and Metabolome Analysis Reveals the Mechanism of Purple Pericarp Formation in 'Zihui' Papaya (Carica papaya L.).

The color of the pericarp is a crucial characteristic that influences the marketability of papaya fruit. Prior to ripening, normal papaya exhibits a green pericarp, whereas the cultivar 'Zihui' displays purple ring spots on the fruit tip, which significantly affects the fruit's visual appeal. To understand the mechanism behind the formation of purple pericarp, this study performed a thorough examination of the transcriptome, plant hormone, and metabolome. Based on the UPLC-ESI-MS/MS system, a total of 35 anthocyanins and 11 plant hormones were identified, with 27 anthocyanins and two plant hormones exhibiting higher levels of abundance in the purple pericarp. In the purple pericarp, 14 anthocyanin synthesis genes were up-regulated, including CHS, CHI, F3H, F3'5'H, F3'H, ANS, OMT, and CYP73A. Additionally, through co-expression network analysis, three MYBs were identified as potential key regulators of anthocyanin synthesis by controlling genes encoding anthocyanin biosynthesis. As a result, we have identified numerous key genes involved in anthocyanin synthesis and developed new insights into how the purple pericarp of papaya is formed.

Potential locus W and candidate gene McPRR2 associated with pericarp pigment accumulation in bitter gourd (Momordica charantia L.) revealed via BSA-seq analysis

Pericarp color is a prominent agronomic trait that exerts a significant impact on consumer and breeder preferences. Genetic analysis has revealed that the pericarp color of bitter gourd is a quantitative trait. However, the underlying mechanism for this trait in bitter gourd remains largely unknown. In the present study, we employed bulked segregant analysis (BSA) to identify the candidate genes responsible for bitter gourd pericarp color (specifically, dark green versus white) within F2 segregation populations resulting from the crossing of B07 (dark green pericarp) and A06 (white pericarp). Through genomic variation, genetic mapping, and expression analysis, we identified a candidate gene named McPRR2, which was a homolog of Arabidopsis pseudo response regulator 2 (APRR2) encoded by LOC111023472. Sequence alignment of the candidate gene between the two parental lines revealed a 15-bp nucleotide insertion in the coding region of LOC111023472, leading to a premature stop codon and potentially causing a loss-of-function mutation. qRT-PCR analysis demonstrated that the expression of McPRR2 was significantly higher in B07 compared to A06, and it was primarily expressed in the immature fruit pericarp. Moreover, overexpression of McPRR2 in tomato could enhance the green color of immature fruit pericarp by increasing the chlorophyll content. Consequently, McPRR2 emerged as a strong candidate gene regulating the bitter gourd pericarp color by influencing chlorophyll accumulation. Finally, we developed a molecular marker linked to pericarp color, enabling the identification of genotypes in breeding populations. These findings provided valuable insights into the genetic improvement of bitter gourd pericarp color.

McAPRR2: The Key Regulator of Domesticated Pericarp Color in Bitter Gourd.

Pericarp color is a crucial commercial trait influencing consumer preferences for bitter gourds. However, until now, the gene responsible for this trait has remained unidentified. In this study, we identified a gene (McAPRR2) controlling pericarp color via a genome-wide association study (GWAS) utilizing the resequencing data of 106 bitter gourd accessions. McAPRR2 exhibits three primary haplotypes: Hap1 is a wild type with a green pericarp, Hap2 is a SA (South Asian) and SEA (Southeast Asia) type with a green pericarp, and Hap3 is primarily a SEA type with a light green pericarp. The McAPRR2 haplotype is significantly correlated with both pericarp color and ecological type. Importantly, McAPRR2 with the light green pericarp demonstrated premature termination due to a 15 bp sequence insertion. The phylogenetic tree clustered according to pericarp color and ecological type, using SNPs located in the McAPRR2 gene and its promoter. High πwild/SEA and πSA/SEA values indicate high nucleotide diversity between wild and SEA types and between SA and SEA types in the McAPRR2 gene. The haplotypes, phylogenetic tree, and nucleotide diversity of McAPRR2 suggest that McAPRR2 has undergone domestication selection. This study identifies McAPRR2 as the key gene determining pericarp color in bitter gourds and introduces a novel insight that McAPRR2 is subject to domestication selection.

Asymmetric distribution of mineral nutrients aggravates uneven fruit pigmentation driven by sunlight exposure in litchi.

Sunlight boosts anthocyanin synthesis/accumulation in sunny pericarp of litchi fruit, directly leading to uneven pigmentation. Distribution discrepancy of mineral element aggravates uneven coloration by modulating synthesis/accumulation of anthocyanin and sugar. Uneven coloration, characterized by red pericarp on sunny side and green pericarp on shady side, impacts fruit quality of 'Feizixiao' (cv.) litchi. The mechanisms of this phenomenon were explored by investigating the distribution of chlorophyll, flavonoids, sugars, and mineral elements in both types of pericarp. Transcriptome analysis in pericarp was conducted as well. Sunny pericarp contained higher anthocyanins in an order of magnitude and higher fructose, glucose, co-pigments (flavanols, flavonols, ferulic acid), and mineral elements like Ca, Mg and Mn, along with lower N, P, K, S, Cu, Zn and B (P < 0.01), compared to shady pericarp. Sunlight regulated the expression of genes involved in synthesis/accumulation of flavonoids and sugars and genes functioning in nutrient uptake and transport, leading to asymmetric distribution of these substances. Anthocyanins conferred red color on sunny pericarp, sugars, Ca and Mg promoted synthesis/accumulation of anthocyanins, and co-pigments enhanced color display of anthocyanins. The insufficiencies of anthocyanins, sugars and co-pigments, and inhibition effect of excess K, S, N and P on synthesis/accumulation of anthocyanins and sugars, jointly contributed to green color of shady pericarp. These findings highlight the role of asymmetric distribution of substances, mineral elements in particular, on uneven pigmentation in litchi, and provide insights into coloration improvement via precise fertilization.

Fine Mapping and Identification of SmAPRR2 Regulating Rind Color in Eggplant (Solanum melongena L.)

Rind color is an economically important agronomic trait in eggplant that impacts consumer preferences. In this study, bulked segregant analysis and competitive allele-specific PCR were employed to identify the candidate gene for eggplant rind color through constructing a 2794 F2 population generated from a cross between "BL01" (green pericarp) and "B1" (white pericarp). Genetic analysis of rind color revealed that a single dominant gene controls green color of eggplant peel. Pigment content measurement and cytological observations demonstrated that chlorophyll content and chloroplast number in BL01 were higher than in B1. A candidate gene (EGP19168.1) was fine-mapped to a 20.36 Kb interval on chromosome 8, which was predicted to encode the two-component response regulator-like protein Arabidopsis pseudo-response regulator2 (APRR2). Subsequently, allelic sequence analysis revealed that a SNP deletion (ACT→AT) in white-skinned eggplant led to a premature termination codon. Genotypic validation of 113 breeding lines using the Indel marker closely linked to SmAPRR2 could predict the skin color (green/white) trait with an accuracy of 92.9%. This study will be valuable for molecular marker-assisted selection in eggplant breeding and provides theoretical foundation for analyzing the formation mechanism of eggplant peel color.

Metabolome and transcriptome analysis of terpene synthase genes and their putative role in floral aroma production in Litchi chinensis.

Volatile organic compounds (VOCs) are essential traits of flowers since they attract pollinators, aid in seed distribution, protect the plant from internal and external stimuli, and are involved in plant-plant and plant-environment interactions. Apart from their role in plants, VOCs are used in pharmaceuticals, fragrances, cosmetics, and flavorings. Litchi (Litchi chinensis Sonn.) is a popular fruit due to its enticing red appearance, exotic taste, and high nutritional qualities. Litchi flowers bloom as inflorescences primarily on the shoot terminals. There are three distinct flower types, two male and one female, all of which are produced on the same panicle and rely on insect pollination. Herein, we used a comprehensive metabolomic approach to examine the volatile profile of litchi fruit (green pericarp, yellow pericarp, and red pericarp) as well as male and female flowers (bud stage, half open and full bloom). From a quantitative examination of the volatiles in L. chinensis, a total of 19, 22, and 21 VOCs were discovered from female flowers, male flowers, and fruits, with the majority of them belonging to sesquiterpenes. Multivariate analysis revealed that the volatile profiles of fruits differ from those of male and female flowers. Three VOCs were unique to male flowers and ten to the fruit, while eight VOCs were shared by both male and female flowers and eleven by both male and female flowers and the fruit. Furthermore, for the first time, we identified and comprehensively studied the TERPENE SYNTHASE genes (TPS) using the litchi genome and transcriptome database, which revealed 38 TPS genes unevenly distributed across the 15 chromosomes. A phylogenetic study showed that LcTPS were grouped into TPS-b, TPS-c, TPS-e, TPS-f, and TPS-g subfamilies, with TPS-b having the most genes. The conserved motifs (RRX8 W, NSE/DTE, and DDXX D) were studied in LcTPSs, and significant variation between subfamilies was discovered. Furthermore, after integrating the metabolome and transcriptome datasets, several VOCs were shown to be development-specific and highly linked with distinct LcTPS genes, making them promising biomarkers. Interestingly, LcTPS17/20/23/24/31 were associated with monoterpene edges, while the rest were connected to sesquiterpene edges, indicating their probable participation in the aroma biosynthesis mechanism of certain compounds.

Pigment and oil content estimation in seeds of Bixa orellana L.

Bixa orellana L. is an economic tree native to the Neotropics. It is perennial in nature growing up to a height ranging from 2 to 8 m. Bixa orellana L. shows phenotypic variation in flower color, pod color, pod shape, height as well as girth. The tree gives a natural colorant called ‘Annatto’ that is second most demanded dye in the world. Selection of trees based on high pigment content becomes a must for this economic tree. Identification of phenotypic character for selection of trees with desirable pigment content was the aim of the study. It was found that cordate pods with green pericarp and maroon bristles gave the highest bixin content, although norbixin content was found to be similar in all pod shapes, cordate pods with maroon pericarp and bristles were advantageous. For selection for oil content conical pods with maroon pericarp and bristles were the most appropriate amongst all.

Identification of candidate genes and clarification of the maintenance of the green pericarp of weedy rice grains.

The weedy rice (Oryza sativa f. spontanea) pericarp has diverse colors (e.g., purple, red, light-red, and white). However, research on pericarp colors has focused on red and purple, but not green. Unlike many other common weedy rice resources, LM8 has a green pericarp at maturity. In this study, the coloration of the LM8 pericarp was evaluated at the cellular and genetic levels. First, an examination of their ultrastructure indicated that LM8 chloroplasts were normal regarding plastid development and they contained many plastoglobules from the early immature stage to maturity. Analyses of transcriptome profiles and differentially expressed genes revealed that most chlorophyll (Chl) degradation-related genes in LM8 were expressed at lower levels than Chl a/b cycle-related genes in mature pericarps, suggesting that the green LM8 pericarp was associated with inhibited Chl degradation in intact chloroplasts. Second, the F2 generation derived from a cross between LM8 (green pericarp) and SLG (white pericarp) had a pericarp color segregation ratio of 9:3:4 (green:brown:white). The bulked segregant analysis of the F2 populations resulted in the identification of 12 known genes in the chromosome 3 and 4 hotspot regions as candidate genes related to Chl metabolism in the rice pericarp. The RNA-seq and sqRT-PCR assays indicated that the expression of the Chl a/b cycle-related structural gene DVR (encoding divinyl reductase) was sharply up-regulated. Moreover, genes encoding magnesium-chelatase subunit D and the light-harvesting Chl a/b-binding protein were transcriptionally active in the fully ripened dry pericarp. Regarding the ethylene signal transduction pathway, the CTR (encoding an ethylene-responsive protein kinase) and ERF (encoding an ethylene-responsive factor) genes expression profiles were determined. The findings of this study highlight the regulatory roles of Chl biosynthesis- and degradation-related genes influencing Chl accumulation during the maturation of the LM8 pericarp.

Examining samarium sorption in biochars and carbon-rich materials for water remediation: batch vs. continuous-flow methods

Samarium (Sm) sorption from aqueous solutions was evaluated in biochars (derived from castor meal (CM), eucalyptus forest residues (CE), sugarcane bagasse (SB) and green pericarp of coconut (PC)) and in other carbon-rich materials (coal fines (CF); two commercial activated charcoals (GAC, NGAC)) by applying batch and continuous-flow sorption experiments. Batch experiments revealed great Kd values, in the range of 104–105 L kg−1, and high Sm sorption percentages (>97%, except for SB) in the range of environmental representative concentrations, using as-received materials, with no further treatments. Maximum sorption capacities were derived from sorption isotherms using the Langmuir model (from 1.2 to 37 mg g−1). Continuous-flow sorption experiments permitted to obtain maximum sorption capacities by mass balance and by fitting the experimental breakthrough curves to Thomas and Yan models. CF exhibited the greatest maximum sorption capacity (40 mg g−1) besting the commercial activated charcoals, while CM was established as the best biochar (7.2 mg g−1), with similar results to NGAC (12 mg g−1) but worse than GAC (36 mg g−1). The contribution of cation exchange in Sm sorption was confirmed to be significant for most materials based on the analyses of cations leached during continuous-flow sorption experiments. Maximum sorption capacities derived from Langmuir fitting correlated well with maximum sorption capacities obtained from continuous-flow experiments. Both methods were confirmed to be suitable to determine the maximum Sm sorption capacity of the materials and then to propose the most suitable materials that can act as alternative to commercial activated charcoals.

Transcriptome and metabolome profiling revealing anthocyanin and phenolic acid biosynthetic mechanisms in sweet osmanthus pericarp

During the maturation process of sweet osmanthus fruit, its pericarp color gradually changes from green to purple-black. Moreover, the chemical composition changes in the pericarp of sweet osmanthus fruit during its color change; however, the mechanisms by which the major medicinal chemicals and anthocyanins are produced remain unclear. This study adopts a metabolomic approach to analyze the chemical composition of green, light purple, and purple-black pericarps during the sweet osmanthus fruit maturation process. Phenolic acids and lignans were more diverse and higher in the green pericarp than in the purple-black pericarp, especially chlorogenic acid and phillygenin that were upregulated by 1.78-and 4.55-fold, respectively, in the green pericarp, whereas flavonoids and anthocyanins were higher in the purple-black pericarp than in the green pericarp, especially cyanidin-3-O-rutinoside and peonidin-3-O-rutinoside that were upregulated by 6.68- and 16.98-fold, respectively, in the purple-black pericarp. Thus, the purple-black color of the sweet osmanthus pericarp is primarily because of a high content of cyanidin-3-O-rutinoside. Transcriptome sequencing analysis showed that the expression level of genes related to the phenolic acid and lignan synthesis pathways, such as HCT, CCoAOMT, CCR, and F5H, demonstrated significant upregulation in the green pericarp, whereas genes such as CHS, CHI, F3H, DFR, and ANS involved in the flavonoid metabolism pathway were significantly downregulated in the green pericarp. These gene expression differences result in a higher content of phenolic acids and lignans in the green pericarp and a higher content of anthocyanins in the purple-black pericarp. The results of this study provide a theoretical basis for the development and utilization of medicinal components, such as chlorogenic acid, phillygenin, and flavonoids in the pericarp of sweet osmanthus fruit for medicinal, health, and food additive use.

Durio tanjungpurensis (Malvaceae), a new species and its one new variety from west Kalimantan, Indonesia

A new species and a new variety of Durio Adanson from West Kalimantan are described namely, Durio tanjungpurensis Z.I. Navia, sp. nov. and D. tanjungpurensis var. tembaganensis Navia, var. nov. The new species has small fruits (5 - 8 cm in diam), brown to yellowish green pericarp, milky white thin aril (&lt;1 mm), and not edible. It is related to D. testudinarum Becc. Durio tanjungpurensis varies in its flower and fruit characters. The new variety differed from D. tanjungpurensis Z.I. Navia, sp. nov. in six characters, i.e. leaf ovate, petal oblanceolate with apex round, fruits on the branches, on the stem, at the base of trunk, no-spine area in fruit apex, pericarp green to yellowish green, aril only 20 - 40% covering the seeds.

Observation and Investigation of Starch Granules Within Wheat Pericarp and Endosperm

The pericarp and endosperm are two important wheat caryopsis sinks containing starch granules. In order to further clarify developmental characteristics of starch granules within wheat pericarp and endosperm, caryopses of hard and soft wheat at different days after pollination were used as experimental materials and their sections were observed with light and electron microscopy in this paper. The results indicated: (1) Pericarp parenchyma cells contained two types of starch granules: single-granule starch granules (ISG) and compound-granule starch granules (CSG). Pericarp parenchyma cells underwent degeneration from the part adjacent to cross cells to the part near the pericarp epidermis. Along with degeneration of pericarp parenchyma cells, CSG were transformed into ISG and all of ISG were gradually disintegrated. (2) There were denser chloroplasts present within the green pericarp cells around the vascular system in hard wheat than in soft wheat. (3) The tiny ISG appeared in aleurone cells at 9 days after pollination, but disappeared in the high-level differentiated aleurone cells. (4) ISG of the inner-layer endosperm transfer cells, sub-aleurone cells and the central starchy endosperm cells developed better in hard wheat than in soft wheat. This was probably because endosperm transfer cells had stronger nutrient transport function and the green pericarp cells provided more photosynthates for the endosperm in hard wheat than in soft wheat.

Observation and comparison of structure changes in wheat caryopsis maternal tissues and endosperm

During the caryopsis development, maternal tissues provide protection and nutrients for the endosperm. Wheat caryopses were observed using different microscopies to investigate structure characteristics of wheat caryopsis maternal tissues and endosperm. The results were as the following: (1) Maternal tissues, especially nucellar cells and pericarp parenchyma cells, degenerated to supply space to the endosperm growth. A thick cuticle layer adhered to the outer integument existed till the endosperm matured. The thick cuticle layer not only made sure that nutrients from the vascular system got into the endosperm through the chalaza but also was probably the key reason why integuments could affect the endosperm growth. (2) The green pericarp contained chloroplasts and perhaps played an important part in nursing other maternal tissues and limiting nutrients from phloem to be transported toward pericarp parenchyma cells. (3) Sieve tubes of the vascular system increased in response to the enhanced endosperm sink strength. Chalazal cell walls and inclusions probably changed to regulate the flux of nutrients transported into the endosperm. In one word, structure changes of maternal transport tissues had a close relationship with the endosperm development.

'만풍배'의 생육기별 해부학적 구조와 과실품질

This study was carried out to understand the physiological characteristics of 'Manpungbae' (Pyrus pyrifolia Nakai) pears through the seasonal changes of pericarp structure and anatomical differences between bagging and non-bagging treatment, and also fruit quality and peel coloration characteristics at the harvest time. The pericarp at full bloom was consists of outer epidermis, hypodermis, parenchyma cell, and inner epidermis from the exterior. The cell layers from the outer epidermis to vascular bundle increased rapidly 7-10 layers to 18-26 layers from full bloom (FB) to 77 days after full bloom (DAFB) and did not change significantly until maturity. Thus, the cell division period of 'Manpungbae' pear was until 77 DAFB and during this period, the thickness from hypodermis to vascular bundle increased from 73.1 µm to 195 µm in this period. Stone cells were formed from seven to 21 DAFB and stone cell clusters were formed around 49 DAFB. The cork cell layer was formed between 49 and 77 DAFB. 'Manpungbae' fruit pericarp was consists of 4.5 layers of the cork cell layers and seven layers of hypodermis which has the tannin at harvest time (161 DAFB). Comparison of the fruit enlargement and fruit structure development by bagging or non-bagging showed that 'Manpungbae' fruits without bagging had more than three cork cell layer than those with bagging at maturity. The size of stone cell clusters were varied in two treatments. Fruit weight was higher in the non-bagging treatment but there was no difference in soluble solid contents (SSC) between two treatments. The weight of the 'Manpunbae' fruit was distributed from 301 g to more 900 g and the average fruit weight was 677.2 g at harvest time, and fruits in the range of 551-800 g accounted for 71.6% of total production. The SSC, acidity and SSC/acidity ratio was 10.2-12.1 °Brix, 0.10-1.24% and 9.76-14.31 respectively, and the SSC was higher in bigger fruit which had a very higher positive correlation with a fruit weight. However, the fruit firmness tended to be lower with fruit size which had a very higher negative correlation with the fruit weight and SSC. The cork cell layer numbers between yellowish brown and green pericarp were not different significantly, in 3.8 and 3.5 respectively.

Inhibition of SnRK1 by metabolites: Tissue-dependent effects and cooperative inhibition by glucose 1-phosphate in combination with trehalose 6-phosphate

SnRK1 of the SNF1/AMPK group of protein kinases is an important regulatory protein kinase in plants. SnRK1 was recently shown as a target of the sugar signal, trehalose 6-phosphate (T6P). Glucose 6-phosphate (G6P) can also inhibit SnRK1 and given the similarity in structure to T6P, we sought to establish if each could impart distinct inhibition of SnRK1. Other central metabolites, glucose 1-phosphate (G1P), fructose 6-phosphate and UDP-glucose were also tested, and additionally ribose 5-phosphate (R5P), recently reported to inhibit SnRK1 strongly in wheat grain tissue. For the metabolites that inhibited SnRK1, kinetic models show that T6P, G1P and G6P each provide distinct regulation (50% inhibition of SnRK1 at 5.4 μM, 480 μM, >1 mM, respectively). Strikingly, G1P in combination with T6P inhibited SnRK1 synergistically. R5P, in contrast to the other inhibitors, inhibited SnRK1 in green tissues only. We show that this is due to consumption of ATP in the assay mediated by phosphoribulokinase during conversion of R5P to ribulose-1,5-bisphosphate. The accompanying loss of ATP limits the activity of SnRK1 giving rise to an apparent inhibition of SnRK1. Inhibition of SnRK1 by R5P in wheat grain preparations can be explained by the presence of green pericarp tissue; this exposes an important caveat in the assessment of potential protein kinase inhibitors. Data provide further insight into the regulation of SnRK1 by metabolites.

Pyridine 2,4-Dicarboxylate Downregulates Ethylene Production in Response to Mechanical Wounding in Excised Mature Green Tomato Pericarp Discs

Pyridine 2,4-dicarboxylate (PDCA) is a structural analog of 2-oxoglutarate and a potent inhibitor of 2-oxoacid-dependent dioxygenases (2-ODDs), such as prolyl 4-hydroxylases (P4Hs). It has been reported that PDCA inhibited the in vitro activity of P4Hs in cut carnation flowers and delayed petal senescence due to suppression of climacteric ethylene production. In this study, the effect of PDCA on ethylene evolution in response to mechanical wounding due to excision of mature green tomato pericarp discs was investigated. Ethylene evolution was induced within 1 h of mechanical wounding in control discs and gradually increased throughout 24 h, whereas it was partially suppressed in PDCA-treated discs during the first 12 h of a 24-h experimental period. This transient, partial suppression of ethylene production can be attributed to the lack of induction and the downregulation of ethylene biosynthetic genes within 1 h and after 12 h of wounding, respectively. However, it cannot be attributed to the suppression of ACC oxidase, a well-known 2-ODD, because no significant change in enzymatic activity was observed in PDCA-treated discs. In addition, the transcript abundance of wound-induced and ethylene-regulated PIN1, PIN2, and E4 genes was also partially suppressed in PDCA-treated discs. PDCA was also shown to be involved in ethylene evolution and color development of mature green and turning fruit discs. Overall, these results indicate that PDCA downregulates ethylene production in response to mechanical wounding and during ripening of preclimacteric and climacteric tomato fruit discs.

Thermostabilities of plant phenol oxidase and peroxidase determining the technology of their use in the food industry

Stabilities of phenol oxidase and peroxidase from tea plant (Camellia sinensis L.) clone Kolkhida leaves, apple (Malus domestica L.) cultivar Kekhura fruits, walnut (Juglans regia L.) green pericarp, and horseradish (Armoracia lapathifolia Gilib) roots were studied using different storage temperature modes and storage duration. It was demonstrated that both enzymes retained residual activities (approximately 10%) upon 20-min incubation at 80 degrees C. Phenol oxidases from tea, walnut, and, especially, apple, as well as tea peroxidase were stable during storage. A technology for treatment of plant oxidases was proposed, based on the use of a natural inhibitor phenol oxidase and peroxidase, isolated from tea leaves, which solving the problem of residual activities of these enzymes, arising during pasteurization and storage of beverages and juices. It was demonstrated that browning of apple juice during pasteurization and beer turbidity during storage could be efficiently prevented using the natural inhibitor of these enzymes.

Induction and Control of Chromoplast-specific Carotenoid Genes by Oxidative Stress

The differentiation of chloroplasts into chromoplasts involves a series of biochemical changes that culminate with the intense accumulation of long chain chromophore carotenoids such as lycopene, rhodoxanthin, astaxanthin, anhydroeschsoltzxanthin, capsanthin, and capsorubin. The signal pathways mediating these transformations are unknown. Chromoplast carotenoids are known to accumulate in green tissues experiencing stress conditions, and studies indicate that they provide efficient protection against oxidative stress. We tested the role of reactive oxygen species (ROS) as regulators of chromoplast carotenoid biosynthesis in vivo. The addition of ROS progenitors, such as menadione, tert-butylhydroperoxide, or paraquat and prooxidants such as diamide or buthionine sulfoximine to green pericarp discs of pepper fruits rapidly and dramatically induce the simultaneous expression of multiple carotenogenic gene mRNAS that give rise to capsanthin. Similarly, down-regulation of catalase by amitrole induces expression of carotenogenic gene mRNAs leading to the synthesis of capsanthin in excised green pericarp discs. ROS signals from plastids and mitochondria also contribute significantly to this process. Analysis of the capsanthin-capsorubin synthase promoter in combination with a beta-glucuronidase reporter gene reveals strong activation in transformed pepper protoplasts challenged with the above ROS. Collectively these data demonstrate that ROS act as a novel class of second messengers that mediate intense carotenoid synthesis during chromoplast differentiation.

Enzymic properties and capacities of developing tomato (Lycopersicon esculentum L.) fruit plastids

To characterize the developmental stage of tomato fruits, chlorophyll content, photosynthetic O 2 evolution and CO 2 fixation of pericarp slices were determined. During the first developmental stages a higher expression level of the triose phosphate translocator was detected. Transport measurements revealed that both the hexose phosphate and the triose phosphate translocator are very likely to be active at this time. Plastidic and cytosolic fructose-1,6-bisphosphatase are active in green fruit pericarp, whereas in red pericarp only the cytosolic form is present. Tomato fruit chloroplasts are able to synthesize starch from Glc6P. Starch synthesis is strongly dependent on the addition of 3PGA and ATP and on plastid illumination. Fruit chloroplasts exhibit very low CO 2 fixation rates and so the capacities of green pericarp slices were investigated. In relation to chlorophyll content, pericarp slices show the same capacity of starch synthesis as spinach or potato leaves. To investigate the presence of further reactions consuming the products of photosynthetic electron transport, the GOGAT activity was measured. In the light, glutamine/2-oxoglutarate-dependent formation of glutamate occurred with a high activity. In the presence of Glc6P only 18% of the light activity was obtained. Since the Glc6P-dependent activity is rather low, the release of 14 CO 2 from labelled [1- 14 C]-Glc6P was also measured. In the dark, the formation of glutamate and oxidation of Glc6P are very tightly coupled to each other in fruit chloroplasts.

Decarboxylative metabolism of [1′-14C]indole-3-acetic acid by tomato pericarp discs during ripening

The rate of decarboxylation of [1′-14C]indole-3-acetic acid (IAA) infiltrated into tomato (Lycopersicon esculentum Mill.) pericarp discs was much more rapid in green than in breaker and pink tissues. Studies were carried out in order to determine whether the decarboxylative catabolism occurring in the green pericarp discs was associated with ripening or was a consequence of wound-induced peroxidase activity and/or ethylene production. After a 2-h lag, the decarboxylative capacity of the green pericarp discs increased exponentially during a 24-h incubation period. This increase was accompanied by increases in IAA-oxidase activity in cell-free preparations from the intercellular space and cut surface of the discs. Although higher IAA-oxidase activity was detected in extracts from the tissue residue, which comprises mainly intracellular peroxidases, this activity did not increase during the 24-h incubation period. Analysis of the cell-free preparations by isoelectric focusing revealed the major component in all samples was a highly anionic peroxidase (pI=3.5) the levels of which did not increase during incubation. However, the intercellular and cut-surface preparations contained additional anionic and cationic peroxidases which increased in parallel with the increases in both the IAA-oxidase activity of the preparations and the decarboxylative capacity of the green pericarp discs from which they were derived. Treatment of green discs with the ethylene-biosynthesis inhibitors aminooxyacetic acid and CoCl2, inhibited the development of an enhanced capacity to decarboxylate [1′-14C]IAA but the inhibition was not counteracted by exogenous ethylene. Another ethylene-biosynthesis inhibitor, aminoethoxyvinyl glycine, also reduced ethylene levels but did not affect IAA decarboxylation, indicating that the decarboxylation was not a consequence of wound-induced ethylene production. The data obtained thus demonstrate that the enhanced capacity to decarboxylate [1′-14C]IAA that develops in green tomato pericarp discs following excision is not associated with ripening but instead is attributable to a wound-induced increase in anionic and cationic peroxidase activity in the intercellular fluid and at the cut surface of the excised tissues.