Abstract
In the early growth stage of etiolated Alaska pea seedlings grown in a horizontal or an inclined position under 1 g and simulated microgravity conditions on a 3D clinostat, epicotyls showed negative gravitropism and automorphosis-like growth, respectively. Epicotyls of etiolated agravitropic pea mutant, ageotropum, also showed automorphosis-like growth both under 1 g and simulated microgravity conditions. Auxin polar transport inhibitors, TIBA, NAP and HFCA, inhibited gravitropic response of etiolated Alaska pea epicotyls and changed growth direction of ageotropum pea epicotyls under 1 g conditions. Auxin polar transport activities in the proximal side of etiolated pea epicotyls dramatically changed when gravitropic response of the seedlings was inhibited. Auxin polar transport inhibitors did not affect gene expression of PsPINs and PsAUX1. These results suggest that auxin polar transport activities in the proximal side of epicotyls play an important role in gravitropic response in the early growth stage of etiolated pea seedlings.
