PLASMODESMAL-MEDIATED CELL-TO-CELL TRANSPORT IN WHEAT ROOTS IS MODULATED BY ANAEROBIC STRESS

Cell-to-cell transport of small molecules and ions occurs in plants th rough plasmodesmata. Plant roots are frequently subjected to localized anaerobic stress, with a resultant decrease in ATP. In order to deter mine the effect of this stress on plasmodesmal transport, fluorescent dyes of increasing molecular weight (0.46 to 10 kDa) were injected int o epidermal and cortical cells of 3-day-old wheal roots, and their mov ement into neighboring cells was determined by fluorescence microscopy . Anaerobiosis was generated by N-2 gas or simulated by the presence o f sodium azide, both of which reduced the ATP levels in the tissue by over 80%. In the absence of such stress, the upper limit for movement, or size exclusion limit (SEL), of cortical plasmodesmata was < 1 kDa. The ATP analogue TNP-ADP (mw 681) moved across the plasmodesmata of u nstressed roots, indicating that plasmodesmata may be conduits for nuc leotide (ATP and ADP) exchange between cells. Upon imposition of stres s, the SEL rose to between 5 and 10 kDa. This response of plasmodesmat a to a decrease in the level of ATP suggests that they are constricted by an ATP-dependent process so as to maintain a restricted SEL. When roots are subjected to anaerobic stress, an increase in SEL may permit enhanced delivery of sugars to the affected cells of the root where a naerobic respiration could regenerate the needed ATP.