Direct Observation of Reversible and Irreversible Stomatal Responses of Attached Sunflower Leaves to SO₂

Abstract

The effects of S02 on stomatal aperture of attached sunflower leaves were observed with a remote-control light microscope system that permitted continuous observation of stomatal responses over periods of several hours. The relationship between actual stomatal aperture and stomatal conductance, measured with a porometer, also was Stomata play an important role in regulating the uptake of air pollutants such as SO2 (5,10,19,20,22,30), and stomatal aperture therefore is a major factor controlling the amount of leaf injury. Stomatal behavior also is affected by SO2 and stomatal response to SO2 usually has been evaluated by measurement of stomatal conductance or transpiration rate. However, such measurements represent the average behavior of many stomata, and they may be modified by such SO2-induced leaf injury as disorganization ofcells and excessive water loss through the epidermis, independently of stomatal aperture. As a result, measurements based on stomatal conductance or transpiration rate provide no information concerning the response of individual stomata to SO2. They also may not even represent the average response of stomata after the appearance of leaf injury. Omasa and Onoe (27) using a remote-control light microscope, recently observed a transient opening of sunflower stomata exposed to 2 l1-I' of SO2, varying greatly in extent even in neighboring stomata, and occurring before water-soaking was visible in the subsidiary cells. This phenomenon could not have been found without direct, continuous observation of stomatal behavior.There are many reviews of the interrelationships between stomatal response to S02 and leaf injury (4,8,9,14,17,22,31), and several mechanisms have been proposed to explain stomatal responses. However, these explanations are inconsistent with one another and inadequate because they do not fully explain the effects, or differentiate between reversible and irreversible effects. We therefore examined the reversible and irreversible effects of SO2 on stomata of attached sunflower leaves by means of a remote-control light microscope system and attempted to organize the data so as to explain stomatal behavior. We also examined the relationship between stomatal aperture and stomatal conductance during exposure to SO2 to learn the effect of leaf injury on stomatal conductance.

Image Analysis of Chlorophyll Fluorescence Transients for Diagnosing the Photosynthetic System of Attached Leaves

“…The resistance is probably due to the smaller absorption of SO2 in the proximity of veins because of the small stomatal conductance in these areas and/or to the fast dilution of absorbed SO2 by the larger provision of water from the vein (21,23). Therefore, we observed that SO2 injured the leaf heterogeneously and the recovery from the SO2 injury also proceeded heterogeneously on the same leaf.…”

Absorption of Organic and Inorganic Air Pollutants by Plants

“…Relationship between cumulative gas absorption during 4 h (from 1 h to 5 h after gas exposure) (horizontal axis) and the decrease in CO2 absorption rate (net photosynthesis rate) during the same in 15 different woody species exposed to 0.5-ppmv 03' Data are indicated on a unit leaf area basis. (from Omasa et al 2000a) on an attached leaf using a remote-control light microscot>e, Omasa et al (1985Omasa et al ( , 1990 showed that stomata closed when the leaf was exposed to concentrations of 0.1 ppmv S02, N02, or 0 3, but that stomatal opening varied with changes in the pressure balance between guard cells and epidermal cells caused by the watersoaking of epidermal cells. Organic pollutants are also found to change stomatal apertures when present at high concentrations (Omasa et al 2000b).…”

“…Many air pollutants have deleterious effects on leaf tissues and can cause changes in stomatal opening (Heath 1980;Omasa et al 1985Omasa et al , 1990Winner et al 1988;Darrall 1989;Mansfield and Pearson 1996), thus reducing the capacity of plants to act as effective sinks for the pollutants. Both the capacity for foliar absorption and the susceptibility to the pollutants vary widely between species and also between particular growth environments (NIES 1980(NIES , 1984(NIES , 1992Yunus and Iqbal 1996;Sandermann et al 1997;Matyssek et al 1997;De Kok and Stulen 1998).…”

Simultaneous Measurement of Stomatal Conductance, Non-photochemical Quenching, and Photochemical Yield of Photosystem II in Intact Leaves by Thermal and Chlorophyll Fluorescence Imaging

“…Ellenson and Amundson 1982, Omasa et al 1985, Hashimoto et al 1990, Omasa 1990, Kramer and Boyer 1995, Lichtenthaler et al 1996, Chaerle and Straeten 2000, Govindjee and Nedbal 2000, Häder 2000, Omasa et al 2002. In particular, at the level of an intact leaf, thermal imaging and chlorophyll fluorescence imaging techniques have been widely used to assess the dynamics and the heterogeneity of stomatal responses, called stomatal patchiness (Terashima et al 1988, Terashima 1992, Beyschlag and Eckstein 1998, and the photosynthetic activity of the leaf surface.…”