Remote-controlled stop of phloem mass flow by biphasic occlusion in Cucurbita maxima

• Published in: Journal of experimental botany 2010-08, Vol.61 (13), p.3697-3708
• Main Authors: Furch, Alexandra C.U, Zimmermann, Matthias R, Will, Torsten, Hafke, Jens B, van Bel, Aart J.E
• Format: Article
• Language: English
• Subjects: Action potentials; Animals; Aphididae; Aphids - metabolism; Behavior, Animal - physiology; Biological and medical sciences; Burns - metabolism; Callose; Cucurbita - metabolism; Cucurbita - parasitology; Cucurbita maxima; Depolarization; Electrophysiology; EPW; Fluorescence; Fundamental and applied biological sciences. Psychology; Glucans - chemistry; Glucans - metabolism; Mass flow; membrane potential; Phloem; Phloem - chemistry; Phloem - metabolism; Plant Leaves - metabolism; Plant veins; Plants; RESEARCH PAPER; Research Papers; Sieve elements; Sieve plates; sieve tube occlusion; Sieve tubes; Time Factors; two-step sieve plate blockage
• ISSN: 0022-0957; 1460-2431
• DOI: 10.1093/jxb/erq181

The relationships between damage-induced electropotential waves (EPWs), sieve tube occlusion, and stop of mass flow were investigated in intact Cucurbita maxima plants. After burning leaf tips, EPWs propagating along the phloem of the main vein were recorded by extra- and intracellular microelectrodes. The respective EPW profiles (a steep hyperpolarization/depolarization peak followed by a prolonged hyperpolarization/depolarization) probably reflect merged action and variation potentials. A few minutes after passage of the first EPW peak, sieve tubes gradually became occluded by callose, with maximum synthesis occurring ~10 min after burning. Early stop of mass flow, well before completion of callose deposition, pointed to an occlusion mechanism preceding callose deposition. This obstruction of mass flow was inferred from the halt of carboxyfluorescein movement in sieve tubes and intensified secretion of aqueous saliva by feeding aphids. The early occlusion is probably due to proteins, as indicated by a dramatic drop in soluble sieve element proteins and a simultaneous coagulation of sieve element proteins shortly after the burning stimulus. Mass flow resumed 30-40 min after burning, as demonstrated by carboxyfluorescein movement and aphid activities. Stop of mass flow by Ca²⁺-dependent occlusion mechanisms is attributed to Ca²⁺ influx during EPW passage; the reversibility of the occlusion is explained by removal of Ca²⁺ ions.