Chlorophylls and carotenoids are responsible for harnessing the photon energy ultimately used in the splitting of a water molecule in photosynthesis (Buchanan, 2015). Two primary chlorophylls responsible for photosynthesis in plants—Chl a and Chl b—differ slightly in their absorption spectra. Carotenoids are important phytochemical pigments responsible for the color of most yellow, orange, and red fruits and vegetables. They are classified into two groups: carotenes and xanthophylls. Carotenes such as α-carotene and β-carotene are pure hydrocarbons and are highly lipophilic (Buchanan, 2015). Xanthophylls, on the other hand, have one or more hydroxyl groups attached to one or both of the flanking rings, making them much less lipophilic than carotenes (Buchanan, 2015). In plants, carotenoids aid directly in photosynthesis, increasing the range of light absorption, acting as powerful antioxidants to quench singlet oxygen, and also providing valuable precursors for abscisic acid, which is a plant hormone vital to fruit maturity (Buchanan, 2015). Carotenoids have also been observed to aid in heat dissipation during high rates of photosynthesis (Ma et al., 2016). Capsicum species are widely used as excellent models for the study of carotenoid biosynthesis because of their high accumulation of numerous carotenoids in the fruit (Gomez-Garcia and Ochoa-Alejo, 2013).
Lutescens, or lutescent, plant mutants produce leaves that are abnormally light yellow-green compared with standard plants and have been observed in multiple species of Capsicum and other genera such as Zea, Oryza, and Oenothera (Csillery, 1980; Daskalov and Poulos, 1994; de Vries, 1918; Ma et al., 2017; Shortess et al., 1968). Capsicum leaves do not generally contain the same dangerous alkaloids that render many solanaceous plants inedible and are often consumed as vegetables in the Philippines and other parts of Asia (Bosland, 1999). The poor vigor and high disease susceptibility of chlorophyll-related leaf mutants, such as the Capsicum lutescens, has limited their integration into commercial agriculture (Stommel and Griesbach, 2008). Mutations affecting leaf color are valuable morphological markers for breeding (e.g., male sterility) and provide novel genes for breeders as well as valuable tools in the phenotyping of Capsicum species (Ma et al., 2016; Sun et al., 2017). The distinction between lutescens mutants in Capsicum remains to be fully elucidated as a result of the current lack of study of the relationship between all lutescens accessions.
Previous research of lutescens mutants in Capsicum centered on describing their genetic characteristics and their association with male sterility, and comparatively little is known about the phytochemical constituents of the leaves of lutescent mutants (Ma et al., 2016; Rodriguez, 2017; Sun et al., 2017). A complementation study on 43 lutescens accessions conducted by Rodriguez (2017) found some hybridizations restored a dark-green leaf phenotype whereas others did not, indicating that the phenotype represented a unique genotype. Other research on a lutescent yellow-bud mutant Capsicum was also conducted recently and found that early leaves of yellow-bud mutants exhibited a very high Chl a/b ratio and elevated carotenoid concentrations, as well as ultrastructural signs of delayed chloroplast development (Ma et al., 2016). A similar study of the leaves of yellow-green rice (Oryza sativa) mutants revealed the yellow-leaf mutants to have low Chl b levels and delayed chloroplast development (Ma et al., 2017). Chang and Troughton (1972) concluded that Chl a/b ratios were dependent on environmental conditions, development stage, nutrient availability, and plant species. The correct Chl a/b ratio is vital in modulating the size of the photosynthetic antenna complex (Havaux and Tardy, 1997; Jansson, 1994; Klein et al., 1988; Oster et al., 2000).
Phytochemical phenotyping of lutescens mutants can provide the foundational evidence needed by future studies of the lutescent leaf phenotype. Phenotyping may also reveal an untapped market potential of lutescens accessions as novel photosynthetic profiles. In addition, multivariate leaf phenotyping may yield a better understanding of the regulation of chlorophyll and carotenoid biosynthesis in chloroplasts (Stommel and Griesbach, 2008). Most importantly, no model plant has been established for the study of carotenoid biosynthesis, and this group of profiled lutescent mutant accessions will be valuable to future studies of chloroplast development and carotenoid biosynthesis in vegetative tissue.
By profiling the photosynthetic pigments and obtaining International Commission on Illuminations CIEL*a*b* (CIELAB) readings for the leaves of 25 accessions of lutescens Capsicum species mutants and ‘Jupiter’ bell pepper (Capsicum annuum), our primary objective was to create an accurate and detailed phytochemical portrait of the lutescent phenotype. We hypothesized that all lutescent mutants would exhibit similar phenotypes and therefore would have similar pigment concentrations and CIELAB readings. In addition, we hypothesized that the lutescent mutant phenotype would be correlated with either high amounts of carotenoids or low amounts of chlorophyll.
Coon, D., Barchenger, D.W. & Bosland, P.W. 2017 Evaluation of dwarf ornamental chile pepper cultivars for commercial greenhouse production HortTechnology 27 128 131 doi: 10.21273/HORTTECH03452-16
Csillery, G. 1980 Gene mapping of the pepper needs more initiatives (contributions to the gene list) Proc. 4th Eucarpia Meeting of Capsicum Working Group 17–19 May 1980 Wageningen, The Netherlands 5 9
Csillery, G. 1983 New Capsicum mutants found on seedling, growth type, leaf, flower and fruit Proc. 5th Eucarpia Meeting of Capsicum and Eggplant Working Group 4–7 July 1983 Plovdiv, Bulgaria 127 130
Gomez-Garcia, M. del R. & Ochoa-Alejo, N. 2013 Biochemistry and molecular biology of carotenoid biosynthesis in chili peppers (Capsicum spp.) Intl. J. Mol. Sci. 14 19025 19053 doi: 10.3390/ijms140919025
Guzman, I., Yousef, G.G. & Brown, A.F. 2012 Simultaneous extraction and quantitation of carotenoids, chlorophylls, and tocopherols in Brassica vegetables J. Agr. Food Chem. 60 7238 7244 doi: 10.1021/jf302475d
Havaux, M. & Tardy, F. 1997 Thermostability and photostability of photosystem II in leaves of the chlorina-f2 barley mutant deficient in light-harvesting chlorophyll a/b protein complexes Plant Physiol. 113 913 923 doi: 10.1104/pp.113.3.913
Jansson, S. 1994 The light-harvesting chlorophyll a b-binding proteins BBA Bioenergetics 1184 1 19 doi: 10.1016/0005-2728(94)90148-1
Keyhaninejad, N., Richins, R.D. & O’Connell, M.A. 2012 Carotenoid content in field-grown versus greenhouse-grown peppers: Different responses in leaf and fruit HortScience 47 852 855 doi: 10.21273/HORTSCI.47.7.852
Klein, R.R., Gamble, P.E. & Mullet, J.E. 1988 Light-dependent accumulation of radiolabeled plastid-encoded chlorophyll a-apoproteins requires chlorophyll a Plant Physiol. 88 1246 1256 doi: 10.1104/pp.88.4.1246
Ma, Z.H., Sun, G.S., Zhang, C.W., Wang, Q., Dai, Z.L., Sun, C.Q. & Pan, Y.P. 2016 Chlorophyll content, chloroplast ultrastructure and transcriptome analysis in wild-type and yellow-bud-mutant hot peppers J. Agr. Sci. Technol. 18 1065 1078
Ma, X., Xiaoqiu, S., Li, C., Huan, R., Sun, C., Wang, Y., Xiao, F., Wang, Q., Chen, P., Ma, F., Zhang, K., Wang, P. & Deng, X. 2017 Map-based cloning and characterization of the novel yellow-green leaf gene ys83 in rice (Oryza sativa) Plant Physiol. Biochem. 111 1 9 doi: 10.1016/j.plaphy.2016.11.007
Oster, U., Tanaka, R., Tanaka, A. & Rudiger, W. 2000 Cloning and functional expression of the gene encoding the key enzyme for chlorophyll b biosynthesis (CAO) from Arabidopsis thaliana Plant J. 21 305 310 doi: 10.1046/j.1365-313X.2000.00672.x
Richins, R.D., Kilcrease, J., Rodriguez-Uribe, L. & O’Connell, M.A. 2014 Carotenoid extraction and quantification from Capsicum annuum Bio Protoc. 4 e1256 doi: 10.21769/BioProtoc.1256
Rodriguez, K.K. 2017 Characterization of lutescens mutants in chile pepper (Capsicum spp.) New Mexico State University Las Cruces, NM MS thesis
Shortess, D.K., Wright, J.E. & Bell, W.D. 1968 The lutescent mutant in maize: I. Inheritance patterns and environmental effects Genetics 58 227 235
Smith, S.D. 2014 Quantifying color variation: Improved formulas for calculating hue with segment classification Appl. Plant Sci. 2 1300088 doi: 10.3732/apps.1300088
Stommel, J.R. & Griesbach, R.J. 2008 Inheritance of fruit, foliar, and plant habit attributes in Capsicum J. Amer. Soc. Hort. Sci. 133 396 407 doi: 10.1017/S0022109000004178
Sun, G.S., Dai, Z.L., Bosland, P.W., Wang, Q., Sun, C.Q., Zhang, Z.C. & Ma, Z.H. 2017 Characterizing and marker-assisting a novel chili pepper (Capsicum annuum L.) yellow bud mutant with cytoplasmic male sterility Genet. Mol. Res. 16 1 doi: 10.4238/gmr16019459