| 其他摘要 | Terrestrial plants inhale CO 2 through stomata on leaves in photosynthesis, and
meanwhile water dissipate out of stomata as stomatal transpiration. Water consumed by
transpiration is supplied by the root and stem. The driving force for the water supply
derives from transpiration, i.e. water supply is controlled by water demand. On the other
hand, transpiration relies on water supply that is usually restricted. Plants regulate stomatal
conductance to control transpiration. Soil humidity and air humidity are two important
environmental factors relative to stomatal regulation.
Stomata respond to transpiration rate rather than air humidity per se. The model of
Buckley et al. and Dewar’s model both can model the general stomatal response to water
vapor deficit at leaf surface (D s ): stomatal conductance decreases linearly as transpiration
rate increases because of rising D s . The absolute value of the slope increases with the
effective hydraulic resistance from soil to leaf epidermis in the model of Buckley et al. In
Dewar’s model, however, the absolute value of the slope is determined by the hydraulic
resistance from epidermal cells to guard cells instead. Several researches support the model
of Buckley et al. in this regard.
The most sensitive response of plants to drought is stomatal closing. As regards the
mechanism of this response, there are two contrasting theories: the theory of root-sourced
chemical signal and that of hydraulic signal. Both of them have convincing evidence while
neither of them is complete. They should be integrated. The model of Buckley et al. offers
a basis for an integrated model of stomatal conductance.
The core hypothesis of the model of Buckley et al. is “hydro-active local feedback”:
guard cell osmotic pressure is actively regulated in response to water status in the
immediate vicinity of guard cells in the epidermis. Evidence had indicated that guard cells
of Vicia faba respond actively to osmotic stress. However, Grantz and Schwartz found that
guard cells of Commelina communis L. did not respond actively to osmotic stress in detached epidermis. They had incubated detached epidermis in relatively high
concentration of KCl in ambient air. We incubated detached epidermis in 40 mM KCl in
CO 2 -free air. Mannitol was added by solution replacement without interrupting CO 2 -free
air. Solute accumulation in guard cells was restricted in response to osmotic stress. ABA
greatly enhanced this active response. Furthermore, ABA stimulated active response of
guard cells of initially open stomata to osmotic stress: guard cell osmotic pressure was
reduced actively. Our results support “hydro-active local feedback” hypothesis, and
suggest that ABA should enhance guard cell sensitivity to epidermal water potential if
ABA is to be introduced into the model.
The model of Buckley et al. can accommodate physiological properties concerning
stomatal regulation, such as ABA synthesis in the shoot and the root, the interaction of
ABA and hydraulic signal, some potential chemical signals, the effect of pH on the
movement of ABA, changes in the hydraulic conductance of plants including xylem
embolism, and water storage in plants. We introduced root-sourced ABA and the
interaction between ABA and hydraulic signal into the model, and successfully modeled
isohydric behavior and stomatal response to D s in Regime C. After xylem embolism was
introduced in addition, stomatal response to D s in Regime B was modeled. Simulation also
showed that moderate xylem embolism enhanced stomatal closing and the homeostasis of
leaf water potential.
Key Words：soil humidity, air humidity, root-sourced chemical signal, hydraulic signal,
model of stomatal conductance |
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