Hiromi Eguchi

Dynamic analysis of stomatal responses by an improved method of leaf heat balance

Abstract Dynamic stomatal responses to drastic changes in environment were analyzed in an on-line system using an improved heat balance method. The boundary layer resistance (rAH) of a rough cucumber leaf was much smaller than that of a smooth artificial leaf (an aluminum plate similar in shape to the cucumber leaf). The effect of free convection on rAH for mixed convection could be described exactly by a model in which the resistance for free convection was connected in parallel with the resistance for forced convection. The intact cucumber leaf was exposed to oscillating air temperatures (TA) and water vapor densities (WA) in a growth chamber, and the heat balance Method was used to calculate transpiration rate and leaf conductance using rAH obtained from the parallel resistance model developed for the real leaf. The calculated transpiration rate agreed well with the value measured by weight change. Oscillations of TA and WA with periodicities of 6 and 12 min induced rapid stomatal oscillations which were synchronized with evaporative demand. The rapid stomatal oscillations were attributed to hydraulic interaction between guard and epidermal cells in the stomatal compelx exposed directly to the ambient air. Slower oscillations of TA and WA with a periodicity of 24 min perturbed the water balance of the whole leaf and induced slow and strong stomatal oscillations which were not synchronized with evaporative demand. Thus, the improved heat balance method was applicable for analysis of dynamic stomatal responses to the environment.

Digital image processing in polarized light for evaluation of foliar injury

Abstract Foliar injury simulated in cucumber leaves by using air pollutants of SO 2 and O 3 resulted in variation of the polarization of light reflected at the leaf surface. The injured area was visualized at earlier stages in vertically polarized light having electric field vibration parallel to the plane of incidence. The injured leaf image was taken by a vidicon camera in vertically polarized light and digitized for computation. This digitized image was denoted as a matrix of reflectances of the vertically polarized light. The injured area was disciminated in the matrix by setting a threshold level of the reflectance at 3%. The ratio of reflectances in the injured area to those in the normal area was found useful for representing the degree of the injury. These results suggest that this method of image processing can be applied to the evaluation of foliar injury using on-line measurement.