Poster: Hormones
Abs #
622: Two distinct signal transduction pathways participate in auxin-induced swelling of pea epidermal protoplasts.
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Presenter: |
Yamagami, Mutsumi , yamagami@ies.or.jp | Authors | Yamagami, Mutsumi (A) Haga, Ken (B) Napier, Richard M (C) Iino, Moritoshi (B) | | Affiliations: |
(A): Inst. Environmental Sci., Aomori, Japan
(B): Botanical Gardens, Grad. Sch. Sci., Osaka City Univ., Japan
(C): Hort. Res. Int., East Malling, Kent ME19 6BJ, UK
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Protoplasts were isolated from the epidermis of elongating third internodes of red-light-grown pea (Pisum sativum L., cv. Alaska) seedlings. Isolated protoplasts were bathed in a medium (pH 6) containing 10mM KCl and 1mM CaCl2 as the major ions and incubated under red light (50 mmol m-2 s-1). These protoplasts swelled in response to indole-3-acetic acid (IAA) and 1-naphthalene acetic acid (NAA). The swelling occurred with a lag time as short as 10 min and continued for a period of about 2 h. A bell-shaped dose-response curve was obtained with either IAA or NAA. However, the shape of the curves was different between IAA and NAA. With IAA, the ascending arm occurred in a wider concentration range and showed a shoulder. Thus, the response to IAA was biphasic. The antibody prepared against the auxin-binding protein 1 (ABP1) inhibited the response at high IAA concentrations (high [IAA], represented by 10-5 M) but did not inhibit the response at low IAA concentrations (low [IAA], represented by 10-6.5 M). Furthermore, the low [IAA] response required the presence of Ca2+ in the medium, but a major part of the high [IAA] response could be induced in the absence of Ca2+. The response to NAA agreed with the low [IAA] response with regard to effective concentrations, but the effects of the ABP1 antibody and external Ca2+ demonstrated that it rather corresponded to the high [IAA] response. These results have indicated that ABP1-mediated and non-mediated responses contribute to auxin-induced protoplast swelling. The former response occurs at high concentrations of IAA and does not depend on external Ca2+. The latter response occurs at low concentrations of IAA and depends on external Ca2+. NAA is effective for the ABP1-mediated response, but not for the other response.
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