Immunological Evidence of Connexin‐like Proteins in the Plasma Membrane of Vicia faba L.

Abstract

_ . _ --Plasma membranes from three week old leaves of Vicia foba L. were enriched by aqueous twophase partitioning to high purity. Plasma membrane proteins were immunoblotted with polyclonal, monospecific antibodies raised against mouse liver connexins (ex) 32 and 26. Immunostaining after treatments with ex BSA: 32 antibodies revealed the existence of a 29 kDa protein, clearly enriched in the plasma membrane fraction, An additional immunoreactive band of 20 kDa, possibly a degradation product of the 29 kDa protein, was found in the soluble fraction. When immunoblots were incubated with ex 26 antibodies, a 40 kDa band with a strong immunoresponse appeared, assumed to present the dimeric form of a 21 kDa, ex 26-like plant protein. The monomeric form could be only obtained when intact leaf material or mesophyll protoplasts from three week old plants were directly SDS-extracted. Furthermore, in young, one week old leaves, the monomer seems to exist in larger amounts, Tris:I together with another crossreacting 35 kDa protein. The 29 kDa (ex 32-related) as well as the 40 kDa (ex 26-. related) polypeptide is obviously located in the plasma

Iron uptake by leaf mesophyll cells: The role of the plasma membrane-bound ferric-chelate reductase

“…Table 4 shows the inhibition of membrane-bound ATPase (pH 6.1) activity by various inhibitors in PMs and crude microsomes. The PM preparations showed a purity similar to that ob- in one out of three independent preparations with similar results tained with green leaves from other species (Kjellbohm and Larssen 1984;Briiggemann and Janiesch 1989;Hunte et al 1992). In the course of the preparation, NADH-dependent FCR activity increased from 3.75+0.15 (leaf crude microsomes) to 7.25+2.39 (leaf PM) nmol 9 (mg protein)-1 .…”

Plasmodesmata: composition, structure and trafficking

“…First biochemical and molecular information on plasmodesmata came from studies demonstrating the presence of animal connexin-homologous proteins in plants [33,34,36,41,42,43,44,59,81,82]. Schindler and co-workers noted numerous functional homologies between plasmodesmata and between animal gap junctions, structures involved in cytoplasmic cell-to-cell communication in animals.…”

“…These functional analogies included similar behavior with regard to SEL tracer dyes, similar electrical properties and similar modes of down-regulation by effectors of protein kinase C. It was suggested that there may be biochemical homologies between gap junction proteins and plasmodesmatal proteins. Immunological data suggested that dicotyledonous plants contain peptides immunologically related to the mammalian gap junction proteins, connexin32 [33,41,42,44,81], and connexin26 [33,34,59]. Indirect evidence suggested that these crossreacting proteins [33,34,59,81] may be plasmodesma-associated.…”

“…Immunological data suggested that dicotyledonous plants contain peptides immunologically related to the mammalian gap junction proteins, connexin32 [33,41,42,44,81], and connexin26 [33,34,59]. Indirect evidence suggested that these crossreacting proteins [33,34,59,81] may be plasmodesma-associated. More definitive evidence for the presence of a connexin homologous protein in plants was provided by immunocytochemical studies in maize by Yahalom et al [82].…”

“…At present no sequence data are available either for the two confirmed plasmodesma-associated maize proteins PAP26 and PAP27 [82] or for the Viciafaba 21 kDa wail-associated protein that cross-reacted with antibodies to mouse liver connexin26 [33]. It would be of great interest to see if these proteins are truly connexin-homologous or only show very limit homologies at a small number of epitopes.…”