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Annals of Botany 39: 43-55, 1975
© 1975 Annals of Botany Company

RESEARCH-ARTICLE

The Effects of Irradiance on Uptake and Assimilation of Nitrate by Young Barley Seedlings

G. M. FELIPPE, J. E. DALE and CAROL MARRIOTT

Botany Department, University of Edinburgh King's Buildings, Edinburgh 9, Scotland

Received: 22 February 1974   

The nitrogen economy of barley plants growing in a range of irradiances from full shade (less than 0·5 W m–2) to 119 W m–2 has been examined by analysing levels of total, organic and nitrate nitrogen, and by determining nitrate reductase activity in leaf extracts. It has been confirmed that root growth is reduced in low irradiances which are also associated with a lower level of total nitrogen in the plant, and hence with a lower uptake of nitrate. In all parts of the plant the level of organic nitrogen is higher in high light intensity but nitrate-nitrogen as a proportion of the total is greatest in low irradiances. In the first leaf accumulation of free nitrate is substantially greater in low irradiances.

The data indicate a higher level of nitrate assimilation in high irradiances and nitrate reductase activity in leaf extracts is higher in such conditions. When the first leaf is shaded nitrate reductase activity falls to undetectable levels after about 4 days, but in the case of the second leaf, where this is shaded, some reductase activity is always found, although this is substantially less than that in unshaded conditions.

It is concluded that in vitro rates of nitrate reduction may over-estimate nitrate assimilation determined as increase in organic nitrogen.


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