PARENT SESSION
Posters P4C Controling CO₂: Stomates and carbon concentrating mechanisms. Abstracts (631-642)

ABA response in CO₂ insensitive Arabidopsis mutants, ht1 and ht2. Mimi Hashimoto^*,1, Juntaro Negi¹, Koh Iba¹, ¹ Department of Biology, Faculty of Science, 6-10-1 Hakozaki, Higashi-ku, Fukuoka, Japan

ABSTRACT- Carbon dioxide and abscisic acid (ABA) are two major signaling molecules that bring about stomatal closure. In contrast to ABA, comparatively little is known about the molecular mechanism by which increased CO₂ concentration brings about reduction of stomatal pore size. We have taken a genetic approach to analyzing the molecular mechanism of CO₂ sensing in stomatal guard cells. Transpiration through the stomata causes leaf cooling. Therefore, leaf temperature provides an indicator of stomatal pore size. We isolated two higher leaf temperature mutants under low CO₂ concentration (high leaf temperature; ht1 and ht2) by thermography. In these mutants, low CO₂-induced stomatal opening and increasing of stomatal conductance were inhibited. Leaf temperature change related to CO₂ level indicated that both of the ht mutants exhibited reduced sensitivity to CO₂. ABA responsiveness in the stomatal closure of the ht mutants was similar to the ABA hyper-sensitive mutants, era1 [Pei et al. (1998) Science 282: 287] and abh1 [Hugouvieux et al. (2001) Cell 106: 477]. The ht mutants also showed ABA hypersensitivity in seed germination. These results indicated that the HT gene products operate downstream in the ABA and CO₂ signaling pathway.

KEY WORDS: stomata, carbon dioxide, abscisic acid