Seasonal patterns of cell‐to‐cell communication in Chara corallina Klein ex Willd. I. Cell‐to‐cell communication in vegetative lateral branches during winter and spring

Cell‐to‐cell communication in lateral branches of limited growth in male Chara corallina plants has been studied using fluorescent plasmalemma‐impermeable probes. The extent of cell‐to‐cell communication was found to be seasonal. In winter, branch internodes were characterized by relatively low plasmalemma potential differences (–121·2±23·2 mV; [K+]o 0·5 mol m−3; pH 7·6), quiescent dactyls isolated from the symplast (conic tips) and by restricted cell‐cell communication (frequency of intercellular transport of six carboxyfluorescein = 42·9%). Cell‐to‐cell communication was inhibited during action‐potentials, and was more extensive between cells which did not give an action potential in response to a current pulse. An inhibitor of the action potential, La3+, promoted cell‐to‐cell communication. These may be characteristic features of winter dormancy in lateral branches of Chara. In spring, morphological and electrophysiological changes occurred immediately prior to the onset of fertility. Characteristic changes in morphology included increased abundance of spherosomes and glycosomes, elongation of stipulodes and development of active branch dactyls. Spring branch inter‐nodes were characterized by high plasmalemma PDs (–210·5±30·8mV; [K+]o 0·5 mol m−3; pH 7·6), predominantly active, non‐isolated dactyls (spinaceous tips), and extensive intercellular communication (frequency of intercellular transport of 6 carboxyfluorescein = 89·2%). Artificial elevation of the intracellular calcium ion concentration by application of ionophore A23187 or Ca2+ microinjection significantly restricted intercellular communication to a level similar to that found in winter. The depression of intercellular communication in winter tissues is suggested to be due to high sensitivity to action potentials and/or to Ca2+ fluxes. Changes in intracellular Ca2+ distribution may be involved in the transition between the morphologically distinct states of dormancy and incipient fertility.