A systematic relationship between phytochrome-controlled development and species habitat, for plants grown in simulated natural radiation

Abstract

A survey of the responsiveness of plant species, typical of open and shade habitats, to simulated natural shade-light quality (i.e. white light plus supplementary far-red) has demonstrated a systematic relationship between habitat and certain developmental responses. Supplementary far-red light has a much greater effect on stem extension rate, petiole length, and leaf dry weight: stem dry weight ratio of the open habitat, shade-intolerant species. Far-red effects on leaf chlorophyll content show no such systematic grading. These results are discussed in relation to habitat adaptation. In most cases, the relationship between developmental response and the estimated phytochrome photoequilibrium, which is established by the radiation treatment, is linear. This is taken as an indication of phytochrome involvement in shade perception.

Ajustes morfológicos e fisiológicos em plantas jovens de Araucária angustifolia (Bertol.) Kuntze em resposta ao sombreamento

“…No caso de um sombreamento contínuo, como o estabelecido no presente estudo e como aquele que se estabelece no sub-bosque florestal, o mais vantajoso, segundo os mesmos autores, seria a conservação dos recursos por parte da planta. Assim, num primeiro momento, um rápido crescimento em A B C altura estaria associado principalmente a plantas intolerantes ao sombreamento, conforme tem sido sugerido na literatura (Morgan & Smith 1979, Brokaw 1987. Cabe salientar que, mesmo reduzindo drasticamente o alongamento das estruturas caulinares, as plantas S mantiveram, até o final do experimento, um CCE significativamente maior que as plantas controle, indicando uma maior eficiência no uso da massa para alongamento dos eixos caulinares (Poorter 1999).…”

Plasticity to Light Cues and Resources in Arabidopsis Thaliana: Testing for Adaptive Value and Costs

“…Shade-avoidance responses are usually hypothesized to confer a fitness advantage by enhancing light capture in dense stands (Casal and Smith 1989;Schmitt and Wulff 1993;Smith 1995). However, stem elongation is predicted to be maladaptive if the plant cannot overtop the foliage canopy, due to opportunity costs of allocating resources to stem at the expense of resourcecapturing organs (Morgan and Smith 1979;Schmitt and Wulff 1993). Recent data support this prediction for Abutilon theophrasti beneath a corn canopy (Weinig 2000).…”

Foraging for light: photosensory ecology and agricultural implications

“…Smitb and associates developed tbe concept tbat sbade avoidance is elicited primarily by tbe pbotoreceptor pbytocbrome, wbicb in green plants triggers an inctease in stem elongation and apical dominance in response to reduced red (R) to far-red (FR) ratios (R;FR) (references in Smitb 1982(references in Smitb , 1995. Tbeir work substantiated tbe following key points: (1) tbe reduction of tbe R:FR ratio underneatb canopies is a reliable signal of tbe degree of sbading (Holmes & Smitb 1977); (2) tbese cbanges in R:FR lead to large variations in tbe pbotostationary state of pbytocbrome (Smitb & © 1997Blackwell Science Ltd Holmes 1977, and (3) under light levels comparable to those encountered beneath dense canopies, plants respond to reduced R:FR with an increase in elongation rate that is directly correlated with the effect of R:FR on the photostationary state of phytochrome (Morgan & Smith 1979 and references therein).…”