Stomata from npq1, a Zeaxanthin-less Arabidopsis Mutant, Lack a Specific Response to Blue Light

Abstract

The Arabidopsis mutant npq1, which cannot accumulate zeaxanthin because of a defective violaxanthin deepoxidase, was used to investigate the role of zeaxanthin in the stomatal response to blue light. Neither dark-adapted nor light-treated guard cells or mesophyll cells of the npq1 mutant contained detectable zeaxanthin. In contrast, wild-type guard cells had a significant zeaxanthin content in the dark and accumulated large amounts of zeaxanthin when illuminated. The well-documented red light enhancement of blue light-stimulated stomatal opening, in which increasing fluence rates of background red light result in increased response to blue light, was used to probe the specific blue light response of Arabidopsis stomata. Stomata from the npq1 mutant did not have a specific blue light response under all fluence rates of background red light tested. On the other hand, stomata from leaves of hy4 (cry 1), an Arabidopsis mutant lacking blue light-dependent inhibition of hypocotyl elongation, had a typical enhancement of the blue light response by background red light. The lack of a specific blue light response in the zeaxanthinless npq1 mutant provides genetic evidence for the role of zeaxanthin as a blue light photoreceptor in guard cells.

The guard cell chloroplast: a perspective for the twenty-first century

“…It should also be noted that npq1 stomata in epidermal peels have an apparently normal response to white light (Frechilla et al, 1999). A normal stomatal response to white light in a mutant with a defective blue light-sensing mechanism points to the operation of compensating mechanisms.…”

“…Interestingly, the acclimation time courses of the blue light and CO 2 responses are remarkably similar, suggesting that the regulatory mechanisms controlling the two responses are interrelated. Since the gcc is involved in the sensing of both blue light and CO 2 ( Zhu et al , 1998;Frechilla et al , 1999), both acclimation processes are likely to involve gcc components. One important implication of these findings is that the guard cells' responses to blue light and CO 2 have a remarkable plasticity, modulated by growth conditions.…”

“…The Arabidopsis mutant npq1 has a defective violaxanthin deepoxidase and cannot accumulate zeaxanthin in its mesophyll or guard cells (Niyogi et al , 1998;Frechilla et al , 1999).…”

“…The specific blue light response of npq1 stomata was therefore assessed in experiments measuring the red light-dependent enhancement of the blue light response, which should critically depend on zeaxanthin concentrations. Wild-type stomata showed a typical enhancement of their blue light-stimulated opening by red light, whereas npq1 stomata were devoid of the response (Frechilla et al , 1999). The mutants cry1 and nph1 , which are defective for blue light-stimulated, phototropic bending and hypocotyl elongation have been shown to have normal stomatal responses (Lascève et al , 1999).…”

Blue Light and Phytochrome-Mediated Stomatal Opening in the npq1 and phot1 phot2 Mutants of Arabidopsis

“…The activation of the ATPase is mediated by the phosphorylation of its C terminus by a Ser/Thr kinase, facilitated by the binding of a 14-3-3 protein (Kinoshita and Shimazaki, 1999). Blue lightspecific stomatal opening has an action spectrum, showing a maximum at 450 nm and two minor peaks at 420 and 470 nm (Karlsson, 1986).Genetic, biochemical, and physiological studies have identified the chloroplastic carotenoid, zeaxanthin, as a blue light photoreceptor in guard cells (Frechilla et al, 1999). Two recent studies, however, have reported that stomata from the zeaxanthin-less Arabidopsis mutant, npq1, open in response to blue light (Eckert and Kaldenhoff, 2000;Kinoshita et al, 2001) and questioned the validity of the zeaxanthin hypothesis.…”