Genetic variation of stomatal conductance, blue light sensitivity and zeaxanthin content in guard cells of Pima cotton (Gossypium barbadense)

Pima S-6 (Gossypium barbadense L.) is a modern line with high stomatal conductance, while B368 is a primitive cotton with low conductance. The blue light sensitivity of adaxial guard cells, probed as the blue light-dependent enhancement of the red light-induced chlorophyll a fluorescence quenching, was investigated in these two cotton lines with contrasting stomatal conductance. Adaxial guard cells isolated from Pima S-6 cotton plants had a significantly higher carotenoid content and a higher blue light sensitivity than those isolated from B368 plants. In a growth chamber-grown F-2 population of a cross between these two lines, adaxial stomatal conductances of individual plants segregated over a range exceeding the average conductances of the parents. Carotenoid content and the blue light sensitivity of adaxial guard cells also segregated. The concentrations of xanthophylls and beta-carotene in the adaxial guard cells were poorly correlated with the blue light response, except for zeaxanthin. The co-segregation of stomatal conductance and blue light sensitivity suggested that the stomatal response to blue light may play a role in the regulation of stomatal conductance in the intact leaf, Zeaxanthin content and blue light sensitivity also co-segregated, suggesting that both parameters are under genetic control. The co-segregation of zeaxanthin content, blue light sensitivity and stomatal conductance provides further evidence for a role of zeaxanthin in the blue light photoreception of guard cells.