The hypocotyl chloroplast plays a role in phototropic bending of Arabidopsis seedlings: developmental and genetic evidence

Abstract

Chloroplasts of guard cells and coleoptiles have been implicated in the sensory transduction of blue light. The present study was aimed at establishing whether the chloroplast of the hypocotyl from Arabidopsis, another blue light-responding organ, has similar characteristics to that of sensory-transducing guard cell and coleoptile chloroplasts. Results showed that the phototropic curvature and arch length induced by blue light in Arabidopsis seedlings matched the distribution of mature chloroplasts in the bending hypocotyl. The bending arch consistently included the region of the hypocotyl containing mature chloroplasts, and never extended beyond that region. Manipulation of the extent of greening of dark-grown hypocotyls by varying red light pretreatments elicited blue light-stimulated curvatures and arch lengths that depended on the duration of the red light pretreatment and on the distribution of mature chloroplasts in the hypocotyl. Albino psd2 mutants of Arabidopsis, which lack mature chloroplasts, are devoid of phototropic sensitivity under conditions in which wild-type seedlings show large curvatures. The star mutant of Arabidopsis has a delayed greening and a delayed phototropic response as compared with wild type. Measurements of photosynthetic oxygen evolution and carbon fixation, dark respiration, and light-dependent zeaxanthin formation in the hypocotyl showed features similar to those of guard cells and coleoptiles, and distinctly different from those of mesophyll tissue. These results indicate that the hypocotyl chloroplast has characteristics similar to those associated with guard cell and coleoptile chloroplasts, and that phototropic bending of Arabidopsis hypocotyls appears to require mature chloroplasts.

Phototropism: Mechanism and Outcomes

“…Not quite! In 2001, Jin and colleagues (Jin et al, 2001) found that hypocotyl phototropism in Arabidopsis appears to require mature chloroplasts and suggested the need for a functional xanthophyll cycle. Much of their conclusions are based upon a simple observation that mature chloroplasts are present within the bending region of the hypocotyl, and that RL pretreatments that increase BL-dependent phototropism also broaden the "zone of chloroplast maturation" within the hypocotyl.…”

Identification of repressed gene transcript accumulation in three albino mutants of Bambusa edulis Munro by cDNA microarray analysis

“…The pds2 mutant of Arabidopsis has a defective phytoene desaturase, is completely devoid of chlorophylls, and has an albino phenotype 30. In a blue light‐stimulated phototropic bending test, pds2 seedlings had no phototropic bending 31. Given that plants have more than one light sensory system and that we had only 2034 clones in our array, we cannot conclude that all light sensors are functional in these albino mutants.…”

THE INVOLVEMENT OF A PLASMA MEMBRANE H+‐ATPase IN THE BLUE‐LIGHT ENHANCEMENT OF PHOTOSYNTHESIS IN LAMINARIA DIGITATA (PHAEOPHYTA)1

“…Blue light (BL) is known to specifically affect several physiological processes, such as phototropism ( Jin et al 2001), stomatal aperture (Zeiger 2000), and chloroplast movement ( Jarillo et al 2001) in higher plants; uptake of monovalent anions in microalgae (Quiñones et al 1997); and synthesis of mycosporine‐like amino acids in macroalgae (Franklin et al 2001). One of the effects of BL that has been studied more in detail in macroalgae is the stimulation of red‐light (RL) saturated photosynthesis in brown algae.…”