Respiratory enzyme activity and regulation of respiration pathway in seashore mallow (Kosteletzkya virginica) seedlings under waterlogging conditions

We determined the enzyme activities involved in the aerobic and anaerobic respiration of Kosteletzkya virginica on the 0, 10, 20, and 30 d of waterlogging to understand its respiratory characteristics. We also determined the enzyme activities on the 10 and 20 d of recovery after water drainage. Non-waterlogged seedlings were regarded as control during this experiment. All waterlogged seedlings were averagely divided into two parts after the formation of adventitious roots. The first and second treatment groups contain seedlings with retained and removed adventitious roots, respectively. The activities of mitochondrial enzymes, including pyruvate dehydrogenase, isocitrate dehydrogenase, α-ketoglutarate dehydrogenase, succinate dehydrogenase, malate dehydrogenase, and cytochrome c oxidase, were lower in the two seedling groups than in the control. Furthermore, the adventitious root-removed seedlings exhibited the lowest mitochondrial enzyme activities during waterlogging. By contrast, an increase in the activity of fermentation enzymes, including alcoholic dehydrogenase (ADH), pyruvate decarboxylase (PDC), and lactate dehydrogense (LDH), was observed in the two treatments compared with the control. However, the activities of ADH, PDC, and LDH were higher in the adventitious root-removed seedlings than those in the adventitious root-retained seedlings. Subsequently, all enzyme characteristics in waterlogged seedlings were restored gradually during the recovery period. Enzyme activity was analyzed to calculate the amount of released electrons. The contribution of the tricarboxylic acid (TCA) cycle to the survival of stressed plants decreased, whereas that of lactic and alcoholic metabolisms increased during waterlogging. The contributions of TCA (27.8%) and alcoholic fermentation (36.3%) were obviously different from their corresponding control (36.1% and 31.0%, P ≤ 0.05) on the 30 d of waterlogging. The contribution rate of the TCA cycle in the adventitious root-retained seedlings was 6.7% and 5.9% higher (P ≤ 0.05) than that in the adventitious root-removed seedlings during this experiment. In conclusion, adventitious roots can sustain aerobic respiration in the mitochondria to help K. virginica overcome waterlogging.