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UPTAKE AND TRANSLOCATION OF NITROGEN BY MILDEWED BARLEY SEEDLINGS
Author(s) -
MURRAY A. J. S.,
AYRES P. G.
Publication year - 1986
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/j.1469-8137.1986.tb02903.x
Subject(s) - shoot , xylem , powdery mildew , spore , biology , mycelium , nitrate , phloem , horticulture , nitrogen , botany , chromosomal translocation , conidium , root system , chemistry , ecology , organic chemistry , biochemistry , gene
S ummary The uptake of nitrogen (N) by roots, reciprocal transport of N between root and shoot, and reduction of nitrate in both root and shoot were examined in order to determine how the use of N in barley seedlings is affected by powdery mildew infection in both pre‐ and post‐sporulation phases. Plants were grown in culture solution supplying only nitrate‐N. The amount of N translocated in the xylem was calculated as the product of the concentration of N in the xylem sap and the flow rate of sap through the plant. The difference between this amount and the net increment of N in the shoot, which (like that of the root) was measured directly, was taken as being equal to the amount of N translocated in the phloem from the shoot to the root. Infection inhibited N uptake and lowered total amounts of N in roots and shoots both before and during sporulation. Effects of mildew on N content per unit dry weight of tissue were more complex and depended on the stage of infection. The rates of nitrate reduction by the shoots and roots were also altered by infection. Before sporulation, nitrate reduction in the shoots was unaffected by infection, while the rate of reduction in the roots was depressed. After sporulation began, nitrate reduction stopped in the shoots but increased in the roots. Relatively small amounts of N were measured in the fungal mycelium and conidia, and it was concluded that direct losses of N from leaves did not markedly affect the nitrogen budget. During sporulation, infection stopped the normally important recycling of N from the shoots to the roots. In both healthy and infected plants, the proportion of N recycled to the roots was higher when plants were grown on a low N supply than when grown on a high N supply. Root growth was affected by infection to a greater extent on the lower supply of N. The significance of the change in the rate of recycling of N to the roots for growth is discussed.