PLANT PHYSIOLOGY , Vol 106, Issue 4 1395-1402, Copyright © 1994 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
Expression of Sporophytic Storage Proteins in the Corm of the Quillwort (Isoetes echinospora Dur.)
J. D. DeCamp, D. A. Stetler and A. E. DeMaggio
Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire 03755 (J.D.D., A.E.D.)
Parenchyma cells from the corm tissue of the aquatic lycopod Isoetes
echinospora Dur. were shown by electron microscopy to be packed with
amyloplasts, lipid bodies, and protein bodies. The protein bodies are
morphologically similar to those identified in seeds and certain vegetative
tissues of higher plants. Globoid-containing protein bodies (1-10 [mu]m)
isolated in a sucrose gradient possessed a buoyant density of 1.28 g/mL and
contained globulin (salt-soluble) proteins. Sucrose gradient centrifugation
of crude globulins revealed only two components with mean sedimentation
coefficients of approximately 2S and 11S. The 2S component, designated
VSP-IsA, was composed of a 15.7-kD polypeptide. The 11S component,
designated VSP-IsB, had a molecular mass of 215 kD as estimated by gel
filtration and was composed of 39- to 42-kD polypeptides. Two-dimensional
gel electrophoresis showed constituent polypeptides distinguished by
differences in net charge and molecular mass. Affinity-purified antibodies
against VSP-IsA and VSP-IsB prepared and used as probes on immunoblots
cross-react only with their specific antigens, suggesting that the proteins
are not immunologically related. Indirect immunolocalization studies
confirmed that VSP-IsB is deposited in protein bodies. These globulin
proteins, like those from some seeds, form the principal storage reserves
of the corm tissue.