Exogenously-Applied Glycinebeyaine is Not Rapidly Re-Translocated in Cotton
Apr 26, 2019
The redistribution of methyl-14C-glycinebetaine was examined after local application to young cotton plants at first flowering. Labelled glycinebetaine in a solution containing Tween-20 (0.05%) was applied to the surface of young or old leaves of cotton (cv. CIM-443) using a syringe. In some cases a self-sealing plastic bag was used to maintain high humidity around the fed leaf. Plants were subsequently grown for 7-10 days in a greenhouse or in a controlled-environment room. Fed leaves were carefully washed prior to sampling. Movement of label was detected in three ways. Plants dried 5 days after treatment and subjected to autoradiography for 5 days showed concentrated labelling in the fed leaf, with lower activity in the attached petiole and the adjacent stem. Long-distance transport of label (as happens in rapeseed etc.) was not observed. More quantitative data were obtained by dividing the plants into stem, petioles, leaves and sympodial branches, drying the samples and burning them in a sample oxidizer. This confirmed that there was little movement of label to other main-stem leaves or to the shoot apex, but some movement into the adjacent main stem and sympodial structures. In these experiments it is assumed that glycinebetaine is not easily metabolized in cotton, and remains in solution. Extraction of sap from different parts of the plants produced a similar pattern of label distribution to sample oxidation. Only when methyl-14C-glycinebetaine was directly injected into a petiole was there substantial movement of label - mostly into the attached leaf and the adjacent stem.