Respiration Rate of Barley Roots: its Relation to Growth, Substrate Supply and the Illumination of the Shoot

The respiration rate of roots on intact barley plants grown in 16 h light 8 h dark cycles shows an exponential decay in the dark, rises on re-illumination and there is a transient fall 12–14 h into the photoperiod Roots of plants placed in the dark for up to 48 h show a continued exponential decay, and a rather small fall in soluble carbohydrate levels The respiration of roots excised from predarkened plants does not rise on addition of sucrose to the medium bathing them Respiration rate, measured 10 h into the photoperiod, shows a constant relation to root weight in plants 8–24 days old, during which time root carbohydrate content first falls and later rises It is concluded that root respiration rate is not a simple function of carbohydrate supply from the shoot The importance of root respiration in the carbon budget of barley plants is evaluated and the levels of control operating on root respiration rate are briefly discussed