Assessment of Enzyme Induction and Aerenchyma Formation as Mechanisms for Flooding Tolerance in Trifolium subterraneum 'Park'

Abstract

The objective of this study was to evaluate the role of enzyme induction and aerenchyma formation in prolonged tolerance to soil flooding in a variety of underground clover (Trifolium subterraneum 'Park') previously selected for resistance. Seedlings were grown in hydroponic tanks, initially with aeration for 3 weeks and subsequently in the absence of aeration for up to 3 weeks. After 1 h in the absence of aeration, the oxygen concentration in the hydroponic medium had decreased to 1.5 %. During the 3 weeks of extreme oxygen deficiency, primary roots died and were replaced by considerable numbers of adventitious roots. Activities of many glycolytic and fermentative enzymes increased in adventitious roots. Excised adventitious roots were capable of immediate induction of ethanol in the absence of lactate production, in association with energy charge higher than that in excised roots of aerobically maintained controls. Energy charge was even higher when measured in adventitious roots in planta. Interestingly, haemoglobin protein could be correlated with energy charge. Aerenchyma was readily visualized in adventitious roots by optical microscopy of longitudinal and transverse sections. We conclude that avoidance of root anoxia via aerenchyma is the major mechanism for prolonged root tolerance in Trifolium subterraneum 'Park'.

Prolonged root hypoxia effects on enzymes involved in nitrogen assimilation pathway in tomato plants

“…This is in accordance with the decrease in soluble protein content (Fig. 1D), and the increase in NH 4 + accumulation (Fig. 1C).…”

“…The activities of nitrate and nitrite reductase were enhanced in roots as well as leaves. The higher increase in the Nh 4 + content and in the protease activities in roots and leaves of hypoxically treated plants coincide with a greater decrease in soluble protein contents. Taken together, these results suggest that root hypoxia leaded to higher protein degradation.…”

“…29 The aminating activity of GDH is specially stimulated in certain stress conditions: with senescence, 30 NH 4 + excess, 31,32 dark and atmospheric CO 2 excess. 33 Generally, these conditions lead to a perturbation of the activities of enzymes involved in NH 4 + assimilation, such as inhibition of GS, 34 and GOGAT. 35 However, the effects of root hypoxia on the activities of these enzymes are scarce in the literature.…”

“…In the last decades considerable progress has been made in our understanding of the mechanisms that enable certain plant species and cultivars to withstand periods with excess soil water or even complete submergence. Much of the research has been carried out with crop plant species, such as Oryza sativa, Zea mays, Trifolium subterraneum and Medicago sativa, [2][3][4][5] but wild species originating from wetland habitats have been also used, mostly for comparative studies. 6,7 With transient flooding or irrigation followed by slow drainage, or in natural wetlands, plant roots can become oxygen deficient because of slow transfer of dissolved oxygen in the waterfilled pore space of the soil.…”

Acclimation to soil flooding — sensing and signal-transduction

“…Aerenchyma formation in crop species such as sunflower, bean (Phaseolus vulgaris), tomato (Lycopersicon esculentum - Kawase, 1981) and wheat (Wiengweera et al, 1997) and in tree species like Pinus serotina (Topa and McLeod, 1988) seems under the control of low oxygen concentrations and ethylene, although silver did not affect aerenchyma formation in barley (Larsen et al, 1986). In Trifolium subterraneum a change in protease composition was shown following hypoxia, which correlated with cell lysis during root aerenchyma development and may point to the expression of a specific set of lysis-involved protease genes (Aschi-Smiti et al, 2003). However, the lack of model species that develop inducible aerenchyma and are also suitable for molecular-genetic studies seems to have hindered further progress in the signal transduction chain down-stream of ethylene.…”