Effects of humidity on light-induced stomatal opening: evidence for hydraulic coupling among stomata |
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Authors: | Mott K; Shope J; Buckley T |
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Institution: | Biology Department, Utah State University, Logan, UT 84322-5305, USA; Corresponding author e-mail: kmott@biology.usu.edu |
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Abstract: | A mechanism for co-ordinating behaviour of stomata within an areole during
patchy stomatal conductance has recently been proposed. This mechanism
depends on hydraulic interactions among stomata that are mediated by
transpiration-induced changes in epidermal turgor. One testable prediction
that arises from this proposed mechanism is that the strength of hydraulic
coupling among stomata should be proportional to evaporative demand and,
therefore, inversely proportional to humidity. When a leaf is illuminated
following a period of darkness, there is typically a period of time, termed
the Spannungsphase, during which guard cell osmotic
and turgor pressure are increasing, but the pore remains closed. If
hydraulic coupling is proportional to evaporative demand, then variation
among stomata in the duration of the Spannungsphase
should be lower for leaves at low humidity than for leaves at high
humidity. A similar prediction emerged from a computer model based on the
proposed hydraulic mechanisms. These predictions were tested by measuring
individual stomatal apertures on intact transpiring leaves at low and high
humidity and on vacuum-infiltrated leaf pieces (to eliminate transpiration)
as PFD was increased to high values from either darkness or a low value.
Results showed that the range of Spannungsphasenamong
stomata was reduced at low humidity compared to high humidities.
Experiments that began at low PFD, rather than at darkness, showed no delay
in stomatal opening. These results are discussed in the context of the
proposed hydraulic coupling mechanisms. |
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