Fight against cold: photosynthetic and antioxidant responses of different bell pepper cultivars (Capsicum annuum L.) to cold stress.

The special metabolites of bell pepper (Capsicum annuum L.) leaves can protect the plant under possibly damaging circumstances, such as high light, UV, unfavorable temperatures, or other environmental effects. In this study, we examined the cold stress tolerance of three different Hungarian pepper varieties (Darina, Édesalma, Rekord), focusing on the antioxidant and photosynthetic responses. The plants were developed in growth chambers under optimal temperature conditions (day/night 25 °C/20 °C) until the leaves on the fourth node became fully developed, then half of the plants received a cold treatment (day/night 15 °C/10 °C). Via a detailed pigment analysis, the PS II chlorophyll fluorescence responses, gas exchange parameters and total antioxidant capacities, leaf acclimation to low temperatures has been characterized. Our results display some of the developing physiological and antioxidant properties, which are among the main factors in monitoring the damaging effects of cold temperatures. Nevertheless, despite their differences, the tested pepper varieties did not show different cold responses.

On the spectrophotometric determination of total phenolic and flavonoid contents.

Spectrophotometric assays assessing total phenol and flavonoid content in plant samples are cheaper and faster and thus more accessible methods than analytical chromatography techniques, although these identify compound categories rather than individual compounds. Most methods are used and are published in several varieties and their general (chemically unspecific) nature is often neglected. The aim of the present in vitro study was to compare five frequently used methods in terms of cross reactivity and sensitivity using pure phenolic substances. Test compounds were selected to represent categories of phenolic compounds of special interest in plant stress studies. Examining the classic Folin-Ciocalteu test we found that in addition to phenolics, it was also reactive to ascorbate. Three flavonoid assays were also examined. These are usually applied to quantify (i) flavonols using aluminium-chloride, (ii) flavanons and flavanonols using 2,4-dinitrophenyl-hydrazine or (iii) flavanols using 4-dimethylamino-cinnamaldehyde. We found that all three methods were unaffected by the presence of ascorbate, but only the last one was specific to the group of compounds aimed at. Our results show that cross reactivities to various flavonoid groups should be taken into account when interpreting data from these assays. Methods utilizing the UV absorption of phenolic compounds were also tested and analyses of whole spectra were found more accurate than estimates based on absorptions at single wavelengths.