Extrastomatal Control of Transpiration in Leaves of Yellow Lupin (Lupinus luteusvar. Weiko III) after Drought or Abscisic Acid Treatment

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Abstract
Stornata of leaves of non-stressed yellow lupin plants were closed with phenylmercuric acetate (PMA) and viscous flow resistance and apparent diffusive resistance were measured for both leaf surfaces. Viscous flow resistance was proportional to the yth power of apparent diffusive resistance with y = 1.19 ± 0.10 for the upper surface and y = 1.58 ± 0.11 for the lower surface, i.e. viscous flow resistance changed faster than apparent diffusive resistance. However, in three separate experiments where lupin plants were watered with 10−4 M abscisic acid (ABA) for 1 week, the y values were between 0.29 and 0.59 for the upper surface and between 0.18 and 1.00 for the lower surface. Similarly, drought-hardened plants showed y values between 0.45 and 0.52 for the upper surface, and between 0.43 and 0.88 for the lower surface. Both ABA. and drought-induced changes in y values were statistically different from PMA results at the 1% confidence level. Upon rewatering, drought-stressed plants and ABA-treated plants recovered within 2 and 5 d respectively. Thus with both treatments there was a considerable increase in apparent diffusive resistance (and thus a decrease in transpiration) which could not be accounted for by a comparable increase in viscous flow resistance (i.e. stomatal closure). These results suggest that drought stress and ABA treatment cause an extrastomatal resistance to transpiration in the leaves of yellow lupin plants.

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