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Title: A new aspect of flower abscission: involvement of a specific alkalization of the cytosol in the abscission zone cells

item SUNDARESAN, SRIVIGNESH - Hebrew University Of Jerusalem
item PHILOSOPH-HADAS, SONIA - Agricultural Research Organization Of Israel
item RIOV, JOESEPH - Agricultural Research Organization Of Israel
item BELAUSOV, EDUARD - Agricultural Research Organization Of Israel
item KOCHANEK, BETTINA - Agricultural Research Organization Of Israel
item Tucker, Mark
item MEIR, SHIMON - Hebrew University Of Jerusalem

Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2014
Publication Date: 12/10/2014
Citation: Sundaresan, S., Philosoph-Hadas, S., Riov, J., Belausov, E., Kochanek, B., Tucker, M.L., Meir, S. 2014. A new aspect of flower abscission: involvement of a specific alkalization of the cytosol in the abscission zone cells. Journal of Experimental Botany. 66:1355-1368.

Interpretive Summary: We are interested in characterizing plant signals that regulate cell separation events, e.g., abscission (organ separation) and nematode infection of plant roots. We recently discovered that the cytoplasm of cells in the separation layer of the abscission zones of model plants, become more alkaline immediately prior to when the cell walls begin to disintegrate and separation occurs. The alkalinization of the cytoplasm was shown to occur in three different model plant species: tomato, Arabidopsis and wild rocket. Moreover, in mutant plants that display a delayed abscission response, alkalinization of the cytoplasm was also delayed. A better understanding of signals involved in soybean development and nematode infection of soybean roots will greatly improve the ability of scientists and industrial partners to control nematode infection of soybean and other agriculturally important plants.

Technical Abstract: The correlation between organ abscission and pH changes in the abscission zone (AZ) cells, visualized by the pH-sensitive and intracellularly trapped dye, 2',7'-bis-(2-carboxyethyl)-5(and-6)-carboxyfluorescein-acetoxymethyl (BCECF-AM) ester derivative, combined with confocal microscopy was studied. A specific and gradual increase in the cytosolic pH of AZ cells was observed during natural abscission of flowers and flower organs in Arabidopsis thaliana Col. and wild rocket (Diplotaxis tenuifolia), as well as during pedicel abscission induced by flower removal in tomato (Lycopersicon esculantum Mill). The alkalization pattern in the first two species paralleled the acceleration or inhibition of flower organ abscission induced by ethylene and 1-methylcyclopropene (1-MCP), respectively. Similarly, 1-MCP pretreatment of tomato flower explants abolished the pH increase induced in AZ cells by flower removal and pedicels abscission. Examination of pH changes in the AZ cells of several Arabidopsis mutants defective in both ethylene-induced (ctr1, ein2, eto4) and ethylene-independent (ida, nev7, dab5) abscission pathways confirmed these results. The data indicate that pH changes in the AZ cells are part of both the ethylene-sensitive and -insensitive abscission pathways and occur concomitantly with the execution of organ abscission. Regulation of pH in the AZ by ethylene could occur via modification of AZ-specific transporters, which might affect cytosolic pH. Indeed, four genes associated with pH regulation, Vacuolar H+-ATPase, Putative high-affinity nitrate transporter, and two GTP-binding proteins, were specifically upregulated in tomato flower AZ following abscission induction, and 1-MCP reduced or abolished their increased expression. Taken together, our results open a new and challenging direction for abscission research.