Photocontrol of stem elongation in light-grown plants of Fuchsia hybrida

Abstract

Stems of the caulescent long-day plant, Fuchsia hybrida cv Lord Byron, showed 2 types of response to light. In one, internode length was increased by far-red irradiation given at the end of an 8 h photoperiod: the response was no greater with prolonged exposure and was less when the start of far-red was delayed. The effect of far-red was reversible by a subsequent exposure to red light. Internode length was inversely proportional to the Pfr/P ratio established before entry to darkness and there was no evidence for loss of Pfr during a 16 h dark period. The inhibitory effect of Pfr acted at a relatively late stage of internode growth. With the development of successive internodes a second response appeared in which stems lengthened following prolonged daily exposures to red or far-red light, or mixtures of the two, or to brief breaks with red or white light. In these later internodes, a short exposure to far-red near the middle of the night was not reversible by red because red alone promoted elongation at this time. Internode length increased with increase in the daily duration of light and, when light was given throughout an otherwise dark period of 16 h, with increase in illuminance to a saturation value of 200 lx from tungsten lamps. Elongation increased as a linear function of decrease in photostationary state of phytochrome down to Pfr/P≃0.3; however, internodes were shorter in far-red light than in 25% red/red+far-red. It was concluded that stem length is a net response to two modes of phytochrome action. An inductive effect of Pfr inhibits a late stage in internode expansion, and a phytochrome reaction which operates only in light (and may involve pigment cycling) promotes an early stage of internode development. Stem elongation is thus a function both of the daily duration of light and its red/red+far-red content. The outgrowth of axillary buds was controlled by the first type of phytochrome action only.

Responses of growth, photosynthesis, and leaf conductance to white light irradiance and end‐of‐day red and far‐red pulses in Fuchsia magellanica Lam.

“…In short term experiments, Impatiens parvifiora (an annual shade tolerator) shows a large increase in stem extension in response to low R: FR under / = 13 //mol m"'^ s^^ (Whitelam & Johnson, 1982). Promotion of internode elongation by FR end-of-day irradiations has been previously observed in Fuchsia hybrida (Vince-Prue, 1977). In Fuchsia ?nagellanica the effect of end-of-day R-FR on internode length was small under HL, but large under LL.…”

Phytochrome A Enhances the Promotion of Hypocotyl Growth Caused by Reductions in Levels of Phytochrome B in Its Far-Red-Light-Absorbing Form in Light-Grown Arabidopsis thaliana

“…61%) for phyB, but only hourly pulses photoconvert newly synthesized phyA Pr to Pfr. In Sinningia speciosa (Satter and Whetherell, 1968), Fuschia kybrida (Vince-Prue, 1977), Pkaseolus vulgaris, and Glycine max (Buck and Vince-Prue, 1985) prolonged R+FR provided during the night was also more effective in promoting stem growth than an EOD R+FR pulse.…”

Leaf photosynthesis, plant growth and nitrogen allocation in rice under different irradiances

“…Generally, plants growing under low irradiance show increased plant length or stem elongation, decreased branching or tillering, and wider and thinner leaf development (Crookston et al 1975;Vince-Prue 1977;Inada and Nishiyama 1987). Those researchers interpret the wider and thinner leaf development as an adaptive phenomenon to capture insucient irradiance more eciently.…”