Morphological Responses of Wheat to Changes in Phytochrome Photoequilibrium

Abstract

Wheat plants (Triticum aestivum L.) Tillering in grasses is affected not only by radiation quantity but also by its quality, or SED3, which affects the activity of at least two plant photoreceptors, the blue light receptor(s) and phytochrome (1-3, 9, 10, 16, 19). The characteristic SED of the radiation source determines the activity of each photoreceptor. Responses to blue light, for example, appear to be controlled by the absolute amount of blue light (400-500 nm) received by the plant. Phytochrome responses, on the other hand, are controlled by the ratio of the amount of phytochrome in the active form (Pfr) to the total amount of phytochrome (PtotaI), or Ptr/PtotjI ('P). This ratio ((P) in the plant can be predicted from the SED of the radiation source. Past research has relied mainly on an approximation of'P, called the v ratio, which is based on the relative amounts of radiation at the peak absorption wavelengths for each form of phytochrome, generally considered to be centered around 660 nm for Pr and 730 nm for Pfr. However, exact values for these peak absorbances can vary, and different researchers have used v to represent a range of ratios (5,7,11,17,20,26). In this paper, v represents the ratio of radiation at 660:730 nm unless otherwise specified.Holmes and Smith (17, 25) characterized the relationship between v and 'P for several natural and artificial radiation sources. They found that values for 'P increased from a minimum of 0.04 to about 0.54 (typical sunlight 'P) for corresponding v values of 0.05 and 1.15 (typical sunlight t), respectively. (8) (20) found that wheat tiller number decreased only slightly from 7.5 and 7.1 in response to a large decrease in v (645:735 nm) from 5.0 to 1.5.Lower v ratios in dense canopies due to natural filtration by leaves (shading) appear to have the same effect as lower r ratios artificially created by manipulation of 'P in controlled environments. Lowering of v by either means results in the morphological responses of increased stem elongation (17,18,24,26) and reduced tillering (6,20

Detecting the role of individual species for overyielding in experimental grassland communities composed of potentially dominant species

“…In contrast, vegetative growth of the other grass species and the herbs is characterized by a basal position of the meristem. Studies with several grass species gave evidence that changes in light quality (lower Poa trivialis 10 -1 10 0 10 1 10 2 10 3 10 4 10 5 10 -1 10 0 10 1 10 2 10 3 10 4 10 5 10 -1 10 0 10 1 10 2 10 3 10 4 10 5 10 -1 10 0 10 1 10 2 10 3 10 4 10 5 10 -1 red to far red ratios) result in stem elongation and reduced tillering and may cause a reduced formation of reproductive tillers and expanded leaves and a higher mortality of young vegetative tillers (Smith 1982;Casal et al 1986;Barnes and Bugbee 1991). A down-regulation of tillering in dense stands is in accordance with our observations of constant density in more diverse mixtures, and our data also indicate that a competitive advantage (increased relative yields) of several species (Fig.…”

Differences in the Response of Wheat, Soybean and Lettuce to Reduced Blue Radiation¶

“…Phytochrome photoequilibrium. Plant morphology and growth are presumed to respond to the balance of active phytochrome to total phytochrome, measured as phytochrome photoequilibrium (PPE) (20,21). Researchers have used PPE, measured at the top of the canopy, to estimate phytochrome status.…”

“…However, the in vivo role of chlorophyll altering the radiation absorbed, and thus PPE, is still unknown because the phytochrome response in vivo with chlorophyll present has not yet been measured (20). Nonetheless, many plant morphological responses are attributable to changes in the balance of red and far-red light as measured by PPE (20,21). These morphological differences are typically observed when comparing a PPE of 0.71 (sunlight) with a much lower PPE of 0.3-0.5 (shade).…”

Competitive Interactions between First‐year Seedlings of Timothy (Phleum pratense L.) and Meadow Fescue (Festuca pratensis Huds.)

“…In mixture, however, timothy produced the same number or more tillers than meadow fescue. Tiller production is closely related to nutrient availability and to the quantity and quality of light received down to the stem bases (RYLE 1964, KAYS and HARPER 1974, BARNES and BUGBEE 1991. When plants were exposed to full competition.…”