Gabaculine does not inhibit cytokinin-stimulated biosynthesis of chlorophyll in Pinus nigra seedlings in the dark

Chlorophyll (Chl) accumulation was monitored during black pine (Pinus nigra L.) seed germination for 14 days in the light and in the dark in the presence of gabaculine (GAB) and cytokinin in order to elucidate the regulation of gymnosperm seedling greening in the dark, primarily at the level of aminolevulinic acid formation. In the light, GAB inhibited chlorophyll accumulation in a manner dependent on concentration and developmental stage, and in the dark it showed no effect. Cytokinin, 10(-5) M benzyl adenine (BA) partly overcame GAP-induced inhibition in the light, mainly during earlier developmental stages. In the seedlings grown in the dark, an equal quantity of Chi accumulated in the presence of cytokinin with and without GAB and it was approximately 20-40% higher than in the control seedlings or in the seedlings grown only in the presence of GAP. 5-Amino-levulinic acid (ALA) synthesis was equal in the light and in the dark in seedlings of the same age and seedlings treated with GAP grown in the dark. In the light, GAP inhibited ALA synthetic activity. The results indicate that ALA synthesis is not a rate-limiting step within Chi biosynthesis in pine seedlings grown in the dark. (C) 2000 Published by Elsevier Science Ireland Ltd. All rights reserved.