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Ca2+ has been considered as a necessary ion for alleviation of stress-induced damages in plants. We investigated effects of exogenous Ca2+ on waterlogging-induced damage to pepper and its underlying mechanisms. Pepper seedlings under stress were treated by spraying of 10 mM CaCl2. Applying exogenous Ca2+ increased the biomass of pepper leaves and roots, improved photosynthetic characteristics, membrane permeability, root activity, osmotic substance contents, antioxidant enzyme and alcohol dehydrogenase activities, while it reduced lactate dehydrogenase activity. It maintained hydroxide radical contents and activities of malate dehydrogenase and succinate dehydrogenase relatively high. Our results suggested that applying exogenous Ca2+ could regulate osmotic substance contents, antioxidant system activity, root respiration, and metabolism, and subsequently alleviate waterlogging-induced damages to pepper plants.

Pepper is a thermophilous and heliophilic vegetable. In China, pepper is grown in greenhouse during winter and spring under lower temperature and irradiation. In this study, we investigated the effects of low temperature and low irradiance (LTLI) on the physiological characteristics and the expression of related genes in five pepper species, Capsicum annuum L. (CA), C. baccatum L. (CB), C. chinense Jacquin (CC), C. frutescens L. (CF), and C. pubescens Ruiz & Pavon (CP) in order to screen for greenhouse species that is resistant to such adverse conditions. We observed significant reductions not only in photosynthetic pigments and stomatal conductance but also in proline, total soluble sugar, enzyme activity, and root activity; disordered arrangements of leaf palisade and spongy tissues; and first rising and then falling expression of C-repeat binding factor (CBF3) and cold-regulated genes (CORc410). These results indicate that pepper is not resistant to LTLI. We also found that CP showed significantly higher photosynthetic activity, more proline and total soluble sugar, higher enzyme activity, higher root activity, higher CBF3 and CORc410 expression levels, more tightly packed leaf palisade and spongy tissues, and thicker bundle sheath than the other four species did under LTLI, while CF exhibited the lowest values for these indicators. It demonstrated significant differences in the ability to resist to LTLI among different species, with CP showing the strongest resistance, followed by CB. Therefore, we recommend the introduction of CP and CB to greenhouse cultivation to further screen for low temperature and low light-resistant pepper varieties to increase pepper production by strengthening intervariety hybridization.

The genomic organisation of the seven cultivated Vigna species, V. unguiculata, V. subterranea, V. angularis, V. umbellata, V. radiata, V. mungo and V. aconitifolia, was determined using sequential combined PI and DAPI (CPD) staining and dual-colour fluorescence in situ hybridisation (FISH) with 5S and 45S rDNA probes. For phylogenetic analyses, comparative genomic in situ hybridisation (cGISH) onto somatic chromosomes and sequence analysis of the internal transcribed spacer (ITS) of 45S rDNA were used. Quantitative karyotypes were established using chromosome measurements, fluorochrome bands and rDNA FISH signals. All species had symmetrical karyotypes composed of only metacentric or metacentric and submetacentric chromosomes. Distinct heterochromatin differentiation was revealed by CPD staining and DAPI counterstaining after FISH. The rDNA sites among all species differed in their number, location and size. cGISH of V. umbellata genomic DNA to the chromosomes of all species produced strong signals in all centromeric regions of V. umbellata and V. angularis, weak signals in all pericentromeric regions of V. aconitifolia, and CPD-banded proximal regions of V. mungo var. mungo. Molecular phylogenetic trees showed that V. angularis and V. umbellata were the closest relatives, and V. mungo and V. aconitifolia were relatively closely related; these species formed a group that was separated from another group comprising V. radiata, V. unguiculata ssp. sesquipedalis and V. subterranea. This result was consistent with the phylogenetic relationships inferred from the heterochromatin and cGISH patterns; thus, fluorochrome banding and cGISH are efficient tools for the phylogenetic analysis of Vigna species.

The aim of the study was to investigate the genetic distances and their relationships among pepper species using photosynthetic features under different stresses and genetic variability. The photosynthetic features under drought, waterlogging and low-temperature stresses, rDNA internal transcribed spacer (ITS) sequences of nuclear genome and trnH-psbA sequence of chloroplast genome of 25 varieties from 5 pepper species Capsicum annuum L. (CA), Capsicum baccatum L. (CB), Capsicum chinense Jacquin. (CC), Capsicum frutescens L. (CF) and Capsicum pubescens Ruiz & Pavon (CP) were analyzed and used to construct the dendrograms. The results showed the photosynthetic rate of different pepper species could be greatly but differentially decreased by stresses. For example, CB and CF had the smallest and the highest decrease to drought, CC had the highest decrease to waterlogging, and CP had the smallest decrease to low temperature. The ITS sequences of 25 pepper varieties are 591–619 bp in length and have GC% between 51.1% and 64.5%. Their trnH-psbA sequences are 537–558 bp in length and have GC% between 27.2% and 28.5%. The cluster analysis of the five pepper species based on the changes in PN under stresses is similar to that based on genetic variability, that is, CP clusters with CB, and CC clusters with CA after first clusters with CF. In addition, the clustering methods based on the photosynthetic stress responses and genetic variability are unable to completely distinguish pepper varieties within the same species. The results indicate that similarly to genetic variability, changes in PN under stresses (specifically the stress corresponding to the climate of plant’s original habitat) could be used to identify genetic distance of pepper species.

One of the effective ways to address the effects of abnormal climate change on plant is to find germplasms that have better resistance to adverse environments. In this paper, we studied the responses of 5 pepper species Capsicum annuum L. (CA), C. baccatum L. (CB), C. chinense Jacquin. (CC), C. frutescens L. (CF) and C. pubescens Ruiz & Pavon (CP) as well as a wild pepper C. baccatum var. baccatum (CBY) to waterlogging stress. The results showed that warterlogging treatment greatly decreases photosynthetic pigment content, net photosynthetic rate (P N) and stomatal conductance (g s), and dramatically increases proline content and water-use efficiency (WUE) in all tested pepper, suggesting that pepper has weak resistance to waterlogging stress. The results also showed that changes of the above parameters vary in different species. CP had the smallest decreases in photosynthetic pigment content, P N, and g s and greatest increases in proline content and WUE. By contrast, CC had the greatest decreases in photosynthetic pigment content, P N, and g s and smallest increases in proline content and WUE, indicating that different species had different resistance to adverse environment and species CP and CC had the strongest and the weakest resistances, respectively. In addition, the study also demonstrated that wild pepper CBY had better resistance to adverse environment than all the tested species, indicating loss of the stress resistance genes during the process of domestication. Taking together, our study strongly suggests that pepper species should crossbreed with other species and wild pepper to expand genetic diversity, enlarge genetic distance, promote production, and improve the resistance to adverse environments.

Biao 810S is a chlorina mutant of the thermosensitive genic male sterile (TGMS) rice. We compared photosynthetic characteristics of these two lines. The contents of chlorophylls and carotenoids in Biao 810S were approximately half of those in 810S. However, the net photosynthetic rate (P N) of Biao 810S was higher than that of 810S under high irradiance or low concentration of carbon dioxide, and the photon quantum efficiency was higher than that of 810S. The activity of ribulose-1,5-bisphosphate carboxylase/oxygenase in Biao 810S was only 69.80 % of that in 810S, but the activities of phosphoenolpyruvate carboxylase and NADP-malic enzyme were 79.50 and 69.06 % higher than those of 810S, respectively, suggesting that the efficiency of photon energy utilization in Biao 810S was enhanced by reduction of thermal dissipation and increase of electron transfer rate to generate sufficient assimilation power for the dark reactions. Consequently, the increased activities of C4 photosynthetic enzymes lead to more effective fixation of CO2 and the synergistic effect of light and dark reactions contributed to the higher P N of Biao 810S.

Contents of chlorophylls and carotenoids in yellow-green mutant Biao 810S were approximately half those in control type 810S. Biao 810S had fewer grana lamellae and looser structure than 810S, lower volume of starch granules in chloroplasts, but under high temperature and high irradiance the net photosynthetic rate (PN) of Biao 810S was higher than that of 810S. The chlorophyll fluorescence parameter Fv/Fm of Biao 810S was little higher and photochemical quenching qP was obviously higher than those of 810S. No significant differences in PN and biomass were observed in their hybrid combination. The yellow-green mutant phenotype may be a useful genetic marker of P(T)GMS rice used for hybrid seed production.