In three-day-old maize (Zea mays L.) seedlings, we removed the endosperm, coleoptile with leaflets, and adventitious roots. Primary roots were exposed to 0–10−3 M salicylic acid (SA) for 1–5 h; scutellum, to 10−2 M 2-desoxy-D-glucose (2dG). 2dG-sucrose synthesized from 2dG was transported from scutella to the roots along the phloem. Its accumulation in 5-mm-long root tips was the measure of phloem unloading. At the concentrations higher than 10−4 M, SA suppressed unloading. Simultaneously, the uptake of 14C-5,5-dimethyloxazolidinedione (DMO) by root segments was inhibited, indicating cytoplasm acidification. 10−3 M SA also inhibited root respiration and growth. The lower SA concentrations (10−5 and 10−6 M) activated unloading under conditions of weak sucrose phloem transport to the root. They did not affect DMO uptake, respiration, and growth. 10−4 M SA stimulated unloading during 1- or 2-h exposure but did not affect it at longer treatments. A dependence of SA action on its concentration and exposure duration implies its involvement in the control of phloem unloading in the root tip.
Russian Journal of Plant Physiology – Springer Journals
Published: Sep 8, 2009
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