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Wall yield threshold and effective turgor in growing bean leaves

E. Van Volkenburgh and R.E. Cleland
Planta
Vol. 167, No. 1 (1986), pp. 37-43
Published by: Springer
Stable URL: http://www.jstor.org/stable/23377981
Page Count: 7
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Wall yield threshold and effective turgor in growing bean leaves
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Abstract

The rate of cell enlargement depends on cell-wall extensibility (m) and on the amount of turgor pressure (P) which exceeds the wall yield threshold (Y). The difference (P—Y) is the growth-effective turgor (Pe). Values of P, Y and Pe have been measured in growing bean (Phaseolus vulgaris L.) leaves with an isopiestic psychrometer, using the stress-relaxation method to derive Y. When rapid leaf growth is initiated by light, P, Y and Pe all decrease. Thereafter, while the growth rate declines in maturing leaves, Y continues to decrease and Pe actually increases. These data confirm earlier results indicating that the changes in light-stimulated leaf growth rate are primarily controlled by changes in m, and not by changes in Pe. Seedlings incubated at 100% relative humidity have increased P, but this treatment does not increase growth rate. In some cases Y changes in parallel with P, so that Pe remains unchanged. These data point out the importance of determining Pe, rather than just P, when relating cell turgor to the growth rate.

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