Effects of Mg on chlorophyll degradation and leaf chroma during the airing of cigar tobacco leaves

Magnesium (Mg) is the central atom of the chlorophyll porphyrin ring and plays an important role in the degradation of chlorophyll. In this study, the Mg contents in cigar tobacco leaves (Folium cigarum) under different fertilization (no (CK), NPK (NPK), and NPK+MgO (NKP+Mg)) were investigated by a field experiment, and the effects of Mg in cigar tobacco leaves on the chlorophyll degradation and leaf chroma during airing period were analyzed. The results showed that the application of Mg fertilization significantly increased Mg contents in cigar tobacco leaves. The chromaticity values (luminance value L*, red-green value a*, yellow-blue value b*, and total color difference value ΔE) of cigar tobacco leaves in NPK+Mg treatment were lower than other treatments during the airing. The contents of chlorophyll a (Chl a), chlorophyll b (Chl b), and total chlorophyll (TC) were decreased rapidly in the first eight airing days, and the decreasing trend of total chlorophyll/carotenoid (TC/Car) was more smoothly in NPK+Mg treatment than other treatments. The chromaticity values (L*, a*, b*, ΔE) were extremely significantly negatively correlated with pigment contents (Chl a, Chl b, TC, Car), which indicated that the leaf color was determined by the pigment contents. The activities of pheophytin pheophorbide hydrolase (PPH) in NPK+Mg treatment were the highest, while the activities of chlorophyllase (CLH) had no significant difference among the three treatments. The PPH activities were extremely significantly positively correlated with pigment contents (Chl a, Chl b, TC, Car), and significantly negatively correlated with ΔE values, but the CLH activities were not correlated with pigment contents and ΔE. Therefore, the application of Mg fertilizer was beneficial to chlorophyll degradation by increasing the PPH activities of cigar tobacco leaves, and then it regulated the formation of leaf color.