ISHS Acta Horticulturae 630: XXVI International Horticultural Congress: Nursery Crops; Development, Evaluation, Production and Use
ULTRASTRUCTURE OF NODULES FROM ALNUS MARITIMA |
| Authors: | H.A. Kratsch, W.R. Graves |
| Keywords: | nitrogen fixation, alder, Frankia, hyphae, vesicles, symbiosis |
| Abstract:
Alnus maritima (Marsh.) Muhl. ex Nutt. (seaside alder) is an attractive woody perennial, is the only North American alder that flowers in autumn, and is considered threatened in its three small, disjunct natural habitats. An understanding of the conditions that foster or limit growth of seaside alder is crucial to its use and, perhaps, to its existence. Establishment of effective symbioses between Alnus and Frankia bacteria is sensitive to the concentration of oxygen in the root zone. A. maritima, in contrast to other alders, is an obligate inhabitant of flooded soils. Our hypothesis is that low oxygen in flooded soils affects nodule structure and function and may be essential to symbiotic compatibility. The objective of this work was to describe the morphology and structure of nodules from indigenous plants as a first step in testing our hypothesis. Roots of A. maritima subsp. maritima Schrader & Graves were excavated from saturated, sandy soils of Sussex County, Delaware and Dorchester County, Maryland. Nodules were excised from the roots and processed for microscopy. The nodules are coralloid structures from 1-4 cm in diameter and comprised of one to many nodule lobes. Areas of Frankia-infected tissue within a lobe surround the vascular cylinder, which grows out from and is continuous with the vascular bundle of the plant root. Phenolic-containing cells delimit areas of Frankia infection in a way that hints at the eventual differentiation of the nodule into discreet lobes. Frankia hyphae invade new tissues acropetally and differentiate into septate multilaminar vesicles at their terminus. The ultrastructure of nodules from A. maritima has never been described and will serve as a basis for comparison in later work on oxygen relations in the Frankia-Alnus maritima symbiosis. | |
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