No abstract

Ethylene is a plant hormone that plays a major role in the elongation of both exploratory and root hair systems. Here, we demonstrate in Brassica napus seedlings that treatments with the ethylene precursor, aminocyclopropane carboxylic acid (ACC) and the ethylene biosynthesis inhibitor, aminoethoxyvinylglycine (AVG), cause modification of the dynamic processes of primary root and root hair elongation in a dose-dependent way. Moreover, restoration of root elongation in AVG-treated seedlings by 1 mM L-glutamate suggested that high concentrations of AVG affect root elongation through nonoverlapping ethylene metabolic pathway involving pyridoxal 5#-P-dependent enzymes of nitrate (N) metabolism. In this respect, treatments with high concentrations of ACC and AVG (10 mM) over 5 d revealed significant differences in relationships between root growth architecture and N uptake capacities. Indeed, if these treatments decreased severely the elongation of the exploratory root system (primary root and lateral roots) they had opposing effects on the root hair system. Although ACC increased the length and number of root hairs, the rate of N uptake and the transcript level of the N transporter BnNrt2.1 were markedly reduced. In contrast, the decrease in root hair length and number in AVG-treated seedlings was overcompensated by an increase of N uptake and BnNrt2.1 gene expression. These root architectural changes demonstrated that BnNrt2.1 expression levels were more correlated to the changes of the exploratory root system than the changes of the root hair system. The difference between treatments in N transporters BnNrt1.1 and BnNrt2

Background and Aims: Both rootstocks and mineral nutrition, particularly nitrogen (N), are known to affect many aspects of plant development including the control of scion vigour. In this study, we investigated the role of the rootstock genotype in grafted grapevine responses to N supply in terms of the root and leaf ionomes, scion vigour and whole plant biomass. Methods and Results: Vitis vinifera cv. Cabernet Sauvignon was grafted on two rootstock genotypes known to confer high and low vigour. Plants were grown for 60 days under three levels of nitrate supply. Stem, leaf, trunk and root biomass, and the concentration of 13 macroelements and microelements in roots and leaves were measured. High scion vigour was associated with a high concentration of elements in the leaves. The concentration of some elements in the leaves, such as phosphorus, was affected by the N supply differently in the two scion/rootstock combinations. Conclusion: Differences in rootstock conferred vigour were associated with particular shoot and root ionome profiles, and these responses were dependent on N supply. Significance of the Study: These results demonstrate that rootstocks alter scion growth and the leaf ionome in response to N supply.

In the last decade, genetic and pharmacological approaches have been used to explore ethylene biosynthesis and perception in order to study the role of ethylene and ethylene/auxin interaction in root architecture development. However, recent findings with pharmacological approaches highlight the non-specificity of commonly used inhibitors. This suggests that caution is required for interpreting these studies and that the use of pharmacological agents is a 'double-edged' tool. On one hand, non-specific effects make interpretation difficult unless other experiments, such as with different mutants or with multiple diversely acting chemicals, are conducted. On the other hand, the non-specificity of inhibitors opens up the possibility of uncovering some ligands or modulators of new receptors such as plant glutamate-like receptors and importance of some metabolic hubs in carbon and nitrogen metabolism such as the pyridoxal phosphate biosynthesis involved in the regulation of the root morphogenetic programme. Identification of such targets is a critical issue to improve the efficiency of absorption of macronutrients in relation to root the morphogenetic programme.