Reductions in maize root tip elongation by salt and osmotic stress do not correlate with apoplastic .O2- levels.

BUSTOS, DOLORES; LASCANO, HR; VILLASUSO, AL; MACHADO, E; SENN, ME; CÓRDOBA, A; TALEISNIK, E

ANNALS OF BOTANY

OXFORD UNIV PRESS

Año: 2008 vol. 102 p. 551 - 559

0305-7364

SUMMARY Background and Aims Experimental evidence in the literature suggests .O2- produced in the elongation zone of roots and leaves by plasma membrane NADPH oxidase activity, is required for growth. This work explores, whether growth changes along the root tip induced by hyperosmotic treatments and the distribution of apoplastic .O2- are associated. It was performed with Zea mays L. roots. Methods Stress treatments were imposed using 150 mM NaCl or 300 mM sorbitol. Root elongation rates and the spatial distribution of growth rates in the root tip were measured. Apoplastic .O2- was determined with nitro blue tetrazolium, and H2O2 with 2?, 7?-dichlorofluorescin. Key results In non-stressed plants, the distribution of accelerating growth and highest .O2- levels coincided along the root tip. Salt and osmotic stress of the same intensity had similar inhibitory effects on root elongation but .O2- levels increased in sorbitol-treated roots, and were depressed by NaCl treatments. Conclusions The lack of association between apoplastic .O2- levels and root growth inhibition under hyperosmotic stress suggests that under those conditions apoplastic .O2- may predominantly participate in signalling processes, conveying information on the nature of the substrate the growing root is exploring.