Studies on the Growth and Respiration of Roots

Publisher Website
Google Scholar
Abstract
Simultaneous observations on extension growth and respiration rate (oxygen consumption) of 2-mm. sections excised from the extension zone of roots of pea ( Pisum sativum ) growing in distilled water and 0·5 per cent. sucrose have yielded results closely similar to those of Brown and Sutcliffe (1950). Respiration rate is not obviously correlated with growth rate either in water or in sucrose, but it is strongly correlated with section length. Respiration rate per unit section length (¬per unit fresh weight) shows a marked downward drift during extension and is affected little by growth conditions. Tentative suggestions are advanced to account for the small differences between drifts in o·5 per cent. sucrose and those in distilled water. Medium agitation produces an immediate and sustained stimulation of growth but no stimulation of oxygen uptake until the later growth stages. Thus respiration per unit section length is unaffected by agitation at any stage. A typical growth response to β-indolylacetic acid (IAA) was obtained, with a maximum stimulation (of about 35 per cent.) at 1 part in 10 11 and inhibitions increasing progressively with concentration beyond the threshold of about i part in 10 9 . Both percentage stimulation and percentage inhibition of growth were independent of the presence of sucrose. Respiratory responses to β-indolylacetic acid were complex. In water no immediate response could be detected with either a growth-stimulatory (10 −11 ) or a growth-inhibitory (10 −-8 ) concentration, while in 0·5 per cent. sucrose the inhibitory concentration prevented the small immediate respiratory rise due to the sucrose, probably by impeding sugar entry. During the subsequent period of rapid growth (up to 36 hours) the small respiratory responses observed closely followed the small growth responses to both concentrations of IAA, suggesting that the former are the direct result of the differences in section length induced by the auxin. When growth ceases (at 48 hours) sections which have grown considerably in sucrose show respiratory rates still closely correlated with section length, whereas in water both concentrations of auxin induce marked depressions in respiration rate. It is concluded that β-indolylacetic acid in both growth-stimulatory and growth- inhibitory concentrations has no direct effect on the activity of the respiratory enzyme system of growing root cells. The small respiratory responses are best explained as resulting from differential changes in section size and correlated changes in the enzyme complements of the growing cell.

This publication has 0 references indexed in Scilit: