Spectrum of Light as a Determinant of Plant Functioning: A Historical Perspective

Abstract

The significance of the spectral composition of light for growth and other physiological functions of plants moved to the focus of "plant science" soon after the discovery of photosynthesis, if not earlier. The research in this field recently intensified due to the explosive development of computer-controlled systems for artificial illumination and documenting photosynthetic activity. The progress is also substantiated by recent insights into the molecular mechanisms of photo-regulation of assorted physiological functions in plants mediated by photoreceptors and other pigment systems. The spectral balance of solar radiation can vary significantly, affecting the functioning and development of plants. Its effects are evident on the macroscale (e.g., in individual plants growing under the forest canopy) as well as on the meso- or microscale (e.g., mutual shading of leaf cell layers and chloroplasts). The diversity of the observable effects of light spectrum variation arises through (i) the triggering of different photoreceptors, (ii) the non-uniform efficiency of spectral components in driving photosynthesis, and (iii) a variable depth of penetration of spectral components into the leaf. We depict the effects of these factors using the spectral dependence of chloroplast photorelocation movements interlinked with the changes in light penetration into (light capture by) the leaf and the photosynthetic capacity. In this review, we unfold the history of the research on the photocontrol effects and put it in the broader context of photosynthesis efficiency and photoprotection under stress caused by a high intensity of light.

Keywords: action spectrum of photosynthesis; chloroplast photorelocation; inter-leaf light intensity gradient; regulatory and energy-supplying functions of light.

Figure 1

Figure from Senn’s book (1908) [22] illustrating chloroplast distribution in and light paths through Phaseolus vulgaris mesophyll cells.

Figure 2

Absorption spectra of spinach leaves, isolated chloroplasts, and pigment extracts containing equivalent quantities of chlorophyll. Redrawn from [31].

Figure 3

Representative distribution of transmitted (upper plot) and scattered (lower plot) light across Medicago sativa leaf. ‘e’ designates the epidermal layer. Redrawn from [37].

Figure 4

The time course of saturating pulse-activated (F_M) and transient chlorophyll fluorescence (F_O) at blue or red actinic light of moderate irradiance (155 μmol photons m⁻²s⁻¹) and photosystem II efficiency (Φ_PSII) in T. fluminensis leaves [71].