Effects of SO₂ on Stomatal Metabolism in Pisum sativum L

• Published in: Plant physiology (Bethesda) 1983-06, Vol.72 (2), p.573-577
• Main Authors: I. Madhusudana Rao, Amundson, Robert G., Alscher-Herman, Ruth, Anderson, Louise E.
• Format: Article
• Language: English
• Subjects: Chloroplasts; Enzymes; Epidermis; Guard cells; Light modulation; Peas; Photosynthesis; Plants; Sulfites; Thiols
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.72.2.573

Pea (Pisum sativum L. cv 'Little Marvel') plants were exposed to SO2 for short term (3 hours) and long term (2 days) at 0.2 and at 0.5 microliter per liter (ppm) levels. The effect of this treatment on the activity of phosphoenolpyruvate carboxylase, NAD- and NADP-malate dehydrogenases, and alanine aminotransferase from epidermis and whole leaves was investigated. Short-term exposure to SO2 at 0.2 or 0.5 ppm decreased the activity of the carboxylase and the dehydrogenases in the epidermis. In contrast, the activity of the same three enzymes increased in whole leaves with either short- or long-term exposure to SO2. Alanine aminotransferase in epidermis or whole leaves was not much affected by short-term exposure, but the epidermal activity was decreased and whole leaf activity was increased with long-term exposure. SO2 exposure which was initiated prior to illumination decreased the free thiol content of both epidermis and of whole leaf. Net photosynthesis was reversibly inhibited by long-term exposure to SO2 at 0.5 ppm. No effect of 0.5 ppm SO2 on stomatal conductance was detectable after 3 hours. Stomatal conductance appeared to decrease after longer exposure times (2 days) at 0.5 ppm.