How Plants Find Light in Patchy Canopies. A Comparison between Wild-Type and Phytochrome-B-Deficient Mutant Plants of Cucumber

Foraging for light: photosensory ecology and agricultural implications

“…For instance, it has been shown that the projection of shoots towards canopy gaps is controlled by a blue light (B) photoreceptor and by negative phototropic responses to reflected FR radiation, which are mediated by phytochrome (references in Ballare et al 1995b). Interestingly, positive phototropism towards FR has recently being documented in the parasite Cuseuta sp., which suggests that this weed uses FR to detect remotely the proximity of prospective plant hosts (Orr, Haidar & Orr 1996).…”

“…Robson et al 1993). The involvement of phyB-like phytochrotnes in foraging processes in canopies has also been tested in ecological experiments, with the following results: (1) the //; mutant of cucumber presents reduced or no elongation responses to leaf shading; this mutant also displays reduced phototropic responses in horizontally patchy canopies and, in contrast to the wild type (WT), does not preferentially deploy new growth into canopy gaps (Ballare et al 1995b, and references therein); (2) phyB Arabidopsis mutants grown under sunlight do not respond to light reflected from nearby plants (Yanovsky, Casal & Whitelam 1995) and, (3) when grown in even-aged stands, present highly attenuated responses to crowding; this behaviour is indistinguishable from that of mutants believed to be functionally deficient in all phytochromes (e.g. hyl) (Ballare & Scopel 1997).…”

“…cryptocbromes) also control plant morphological plasticity in canopies, for example by triggering pbototropic responses of leaves and stems (references in Ballare et al 1995b). The involvement of a cryptocbrome in elongation responses to crowding is supported by tbe following observations: (1) tbe B pboton fluence rate received by tbe stems of plants grown in even-heigbt stand falls off sbarply wben tbe canopy begins to close, and (2) if tbe B irradiance received by tbe stems of fully de-etiolated plants grown under sunligbt is reduced, elongation is greatly promoted (references in Ballare et al 1995a).…”

“…(2) Not only elongation, but also branch numbers and angles, leaf orientation, and otber arcbitectural parameters define tbe ability of tbe plant to deploy and maintain pbotosyntbetic tissue in bigb-ligbt patcbes (see Hutcbings & DeKroon 1994). (3) Most of tbese arcbitectural parameters are controlled by informational pbotoreceptors (references in Ballare et al 1995b). (4) A cucumber mutant impaired in pbototropic and otber arcbitectural responses mediated by pbytocbrome is mucb less efficient tban tbe corresponding WT at colonizing canopy gaps (Ballare et al 1995b).…”

“…(3) Most of tbese arcbitectural parameters are controlled by informational pbotoreceptors (references in Ballare et al 1995b). (4) A cucumber mutant impaired in pbototropic and otber arcbitectural responses mediated by pbytocbrome is mucb less efficient tban tbe corresponding WT at colonizing canopy gaps (Ballare et al 1995b).…”