Figure 1.

Heterotrimeric G-Protein α Subunit Is Involved in Sugar Signaling.

(A) Seedlings of wild-type Columbia (Col-0) and gpa1-4 genotypes were sown on normal (1%) and increased (6%) d-glucose and 6% mannitol as an osmotic control. The rate of growth of the primary root was assayed over a 6-d period, beginning 48 h after exposure to light. Shown are interval growth rates for each 24-h period expressed as millimeters of growth per hour. Error bars represent se. n > 10. As shown previously by Ullah et al. (2002), gpa1 mutants have delayed germination on high glucose. Student's t tests were performed with pairwise comparison between wild-type and mutant root growth rate on 6% d-glucose. For days 5 and 6, P < 0.1; for days 4, 7, and 8, P = ∼0.2.

(B) Seedlings overexpressing the constitutively active form of the Gα subunit [GPA1^(Q222L)] are less sensitive to increased d-glucose than are wild-type seedlings. Images show 7-d-old seedlings. Arrows denote root tips and root/shoot junctions.