Photosynthesis and Dark Respiration in Leaves of Different Ages of Partly Flooded Maize Seedlings

Maize seedlings were flooded for periods from 1 to 15 days, and the leaves of different ages were then taken to examine photosynthesis, dark respiration, transpiration, chlorophyll content, and some morphometric parameters. The responses of leaves to root submergence essentially depended on the leaf layer and the treatment duration. A short-term flooding (1–24 h) induced primary stress responses in the first leaf. Photosynthesis and respiration in this leaf oscillated around the control levels with amplitudes of ±15–25% and ±40–60%, respectively. After a longer flooding, the CO₂ exchange in the second leaf was suppressed, while oxygen uptake was stimulated. In the third leaf, which was formed during submergence, the photosynthetic rate increased and the respiratory activity decreased. The transpiration rate did not change in these leaves for 15 days of flooding. The hypoxic treatment, at its early stages, retarded growth and disturbed the source–sink relations. At later stages the plants adapted to hypoxic environment: the seedling growth was restored, which elevated the demand for assimilates and stimulated photosynthesis. It is concluded that plants overcome negative impact of the root hypoxia at the systemic level.     

Ethylene Production and Activation of Hydrolytic Enzymes during Acclimation of Maize Seedlings to Partial Flooding

The effects of partial flooding on the partial pressure of oxygen and carbon dioxide in water around the roots, ethylene production by intact maize (Zea mays L.) seedlings, the activities of hydrolytic enzymes (pectinase, xylanase, and cellulase) in adventitious roots, and the growth of adventitious and main roots were studied. Aggravated hypoxia resulted in the accelerated ethylene production and the activation of enzymes destroying cell walls in the adventitious roots; as a result, the latter changed their growth pattern. The conclusion is that the interrelated responses are adaptive ones, and the adventitious roots play a key role in plant adaptation.