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 F₂ 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 β‐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.