Journal Article

Rapid effects of nitrogen form on leaf morphogenesis in tobacco

Pia Walch‐Liu, Günter Neumann, Fritz Bangerth and Christof Engels

in Journal of Experimental Botany

Published on behalf of Society for Experimental Biology

Volume 51, issue 343, pages 227-237
Published in print February 2000 | ISSN: 0022-0957
Published online February 2000 | e-ISSN: 1460-2431 | DOI: https://dx.doi.org/10.1093/jexbot/51.343.227
Rapid effects of nitrogen form on leaf morphogenesis in tobacco

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Ammonium (NH+4) instead of nitrate (NO3) as the nitrogen (N) source for tobacco (Nicotiana tabacum L.) cultivated in a pH‐buffered nutrient solution resulted in decreased shoot and root biomass. Reduction of shoot fresh weight was mainly related to inhibition of leaf growth, which was already detectable after short‐term NH+4 treatments of 24 h, and even at a moderate concentration level of 2 mM. Microscopic analysis of the epidermis of fully expanded leaves revealed a decrease in cell number (50%) and in cell size (30%) indicating that both cell division and cell elongation were affected by NH+4 application. Changes in various physiological parameters known to be associated with NH+4‐induced growth depression were examined both in long‐term and short‐term experiments: the concentrations of total N, soluble sugars and starch as well as the osmotic potential, the apparent hydraulic conductivity and the rate of water uptake were not reduced by NH+4 treatments (duration 1–12 d), suggesting that leaf growth was neither limited by the availability of N and carbohydrates, nor by a lack of osmotica or water supply. Although the concentration of K+ in leaf press sap declined in expanding leaves by approximately 15% in response to NH+4 nutrition, limitation of mineral nutrients seems to be unlikely in view of the fast response of leaf growth at 24 h after the start of the NH+4 treatment. No inhibitory effects were observed when NH+4 and NO3 were applied simultaneously (each 1 mM) resulting in a NO3/NH+4 net uptake ratio of 6 : 4. These findings suggest that the rapid inhibition of leaf growth was not primarily related to NH+4 toxicity, but to the lack of NO3‐supply. Growth inhibition of plants fed solely with NH+4 was associated with a 60% reduction of the zeatine+zeatine riboside (Z+ZR) cytokinin fraction in the xylem sap after 24 h. Furthermore Z+ZR levels declined to almost zero within the next 4 d after start of the NH+4 treatment. In contrast, the concentrations of the putative Z+ZR precursors isopentenyl‐adenine and isopentenyl‐adenosine (i‐Ade+i‐Ado) were not affected by NH+4 application. Since cytokinins are involved in the regulation of both cell division and cell elongation, it seems likely that the presence of NO3 is required to maintain biosynthesis and/or root to shoot transfer of cytokinins at a level that is sufficient to mediate normal leaf morphogenesis.

Keywords: Ammonium; nitrate; leaf growth; cytokinin.; CK, cytokinin; DAS, days after sowing; i‐; Ade, isopentenyl‐adenine; i‐Ado, isopentenyl‐adenosine; Z, zeatine; ZR, zeatine riboside.

Journal Article.  7221 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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