Stomatal Responses to Two Herbicidal Auxins

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Abstract
The effects of 1-naphthylacetic acid (NAA) and 2-naphthoxyacetic acid (NOXA) on stomatal opening on illumination of excised, turgid leaves of Stachytarpheta indica were investigated by microscopic examination of abaxial epidermises fixed in absolute ethanol. Both chemicals were effective in restricting, but not completely preventing, stomatal opening and suppressing starch hydrolysis and potassium accumulation in the guard cells. The repressive effects were only partly reversed by CO2-free air. It is concluded that NAA and NOXA do not greatly affect passive opening mediated by changes in the leaf water balance, but partly supress photoactive opening by arresting starch hydrolysis and potassium accumulation in the guard cells and partly by disturbing the intercellular CO2 concentration. A possible link between starch hydrolysis and potassium accumulation in the guard cells is briefly mentioned.