[R] Greek letters and subscripts in axis labels or titles

[Andersson, Henrik]

A very brief question.

I have managed to put greek letters in my axis labels using
expression().

Question is, is there an easier (shorter) way than typing 

plot(runif(10),ylab=expression(NH[4]~(mu~M)),xlab="Time (h)")

to get the subscripts and micro sign.

Like NH$_4$ $\mu M$ would be nice :)
-------------------------------------------------------------
Henrik Andersson
Netherlands Institute of Ecology -
Centre for Estuarine and Marine Ecology
P.O. Box 140
4400 AC Yerseke
Phone: +31 113 577473
h.andersson at nioo.knaw.nl
http://www.nioo.knaw.nl/ppages/handersson