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- Author or Editor: James R. Carpenter x
Abstract
Red maple (Acer rubrum L.) and baldcypress (Taxodium distichum (L.) Rich.) seedlings were very tolerant of extended flooding, whereas shoots of sugar maple (Acer saccharum Marsh) seedlings experienced desiccation after 8 days of flooding, and leaf death after 14 days. Shoot desiccation occurred after 14 days of flooding. Roots of all 3 species utilized O2 with similar efficiency prior to flood stress. However, the respiratory capacity of sugar maple roots declined substantially during the first 8 days of flooding, and more gradually from 8 to 22 days, at 21, 5, or 0.5% O2. Red maple roots declined gradually in respiratory capacity over the entire flooding period at 21 and 5%, but not at 0.5% O2. After an initial sharp decline, baldcypress roots gradually regained capability to utilize O2 from 8 to 22 days of flooding at all 3 levels of O2. When tested at 21% O2, both red maple and baldcypress roots had 2- to 3-fold higher respiratory capacities than did sugar maple roots after 22 days of flooding. Presoaking root sections from flooded red and sugar maple in a sucrose solution mildly stimulated respiration rates measured at 21% O2, but did not fully restore respiratory capacity lost by flooding either species.
Abstract
Effects of cyanide (as KCN) and/or salicylhydroxamic acid (SHAM) on respiratory rates (QO2 ) of excised tree roots were evaluated before and after flooding intact plants. CN, an inhibitor of cytochrome oxidase, stimulated QO2 in flood-intolerant sugar maple (Acer saccharum Marsh.) and Japanese yew (Taxus cuspidata Sieb. and Zucc.), but not in flood-tolerant red maple (Acer rub rum L.), and inhibited QO2 in very flood-tolerant baldcypress (Taxodium distichum (L.) Rich). Eight days of flooding eliminated CN-stimulation of QO2 in sugar maple. SHAM, an inhibitor of the alternative oxidase, had little effect on QO2 of any species when used alone, but greatly inhibited QO2 of all species when combined with KCN, indicating the presence of substantial amounts of both respiratory pathways in flood-tolerant and intolerant species, as well as the ability of electrons to flow from one pathway to another when one is blocked by a specific inhibitor. Flooding reduced root respiration capacity in all species, affecting intolerant species the most and tolerant the least. The exception was QO2 of dormant Taxus roots, which was not inhibited by flooding. CN-sensitive QO2 was lost from roots of intolerant species in particular, and to a lesser extent from more tolerant species. A limiting leveL of O2 (0.5%) suppressed SHAM-sensitive QO2 more than CN-sensitive QO2 indicating a greater affinity for O2 by the CN-sensitive path-way. The evidence is consistent with a model for relative flood tolerance based upon differential damage to the aerobic respiratory mechanism.