Effects of Drought Stress on the Physiological Characteristics of Flue-Cured Tobacco during the Vigorous Growing Period

To systematically examine the tolerance of flue-cured tobacco K326 to soil drought stress, this study set up different water content trials for K326 at 60%, 40%, and 20% levels during the vigorous growing period by greenhouse pot planting. Pigment content, chlorophyll fluorescence parameters, antioxidant enzyme activity, and SPS and GS activities associated with carbon and nitrogen metabolism were investigated in the K326 tobacco leaves. The results showed that chlorophyll a and chlorophyll b contents decreased, non-photochemical quenching coefficient Y(NPQ) decreased in the later stage of vigorous growth, and energy dissipation quantum yield Y(NO) levels increased under the drought stresses, suggesting a decrease in the efficiency of conversion by light to electricity in the PSII reaction center. SOD and CAT activities were elevated during the early stage of drought stresses but sharply declined during the later stage of drought stresses. POD enzyme activity was less affected by moderate drought stress, but it was inhibited by severe drought stress. Additionally, moderate drought stress increased the SPS activity and reduced GS activity in K326 tobacco leaves in the later growth stage, indicating that moderate drought stress can promote the transduction from nitrogen metabolism to carbon metabolism in tobacco leaves in the later growth stage, which will help to improve the internal chemical quality of tobacco leaves.