Measurement of Stomatal Aperture by Digital Image Processing

We developed a new digital image processing technique for exactly measuring the degree of stomatal opening, that is, the ratio of the width to the maximum length of a stomatal pore, and the pore area. We applied this technique to evaluate responses to SO2 of neighboring stomata in a small region of an intact attached leaf, with the following results: 1) The pore region could be exactly extracted even when the original digital image was of poor quality. The standard errors in the evaluation of the pore area, the pore length, and the pore width were 10 jum2, 0.3 fim and 0.3 jim, respectively. 2) A wide variety of responses to SO2 was found among neighboring stomata in a small region of an attached leaf. The differences were especially remarkable before water-soaking and wilting. When these began, kj showed a local maximum value, and then all the stomata began to close. These results suggest that stomatal responses of intact growing plants to air pollutants should be examined from the standpoint of not only the average movement of many stomata but also the movement of each stoma and that the interrelationship among movements of neighboring stomata should be investi-gated to clarify the mechanism of stomatal responses to air pollutants