Analysis of photoprotection and apparent non-photochemical quenching of chlorophyll fluorescence in Tradescantia leaves based on the rate of irradiance-induced changes in optical transparence

Abstract

The kinetics of irradiation-induced changes in leaf optical transparence (ΔT) and non-photochemical quenching (NPQ) of chlorophyll fluorescence in Tradescantia fluminensis and T. sillamontana leaves adapted to different irradiance in nature was analyzed. Characteristic times of a photoinduced increase and a dark decline of ΔT in these species were 12 and 20 min, respectively. The ΔT was not confirmed to be the main contributor to the observed middle phase of NPQ relaxation kinetics (τ = 10-28 min). Comparison of rate of photoinduced increase in ΔT and photosystem II quantum yield recovery showed that the former did not affect the tolerance of the photosynthetic apparatus (PSA) to irradiances up to 150 µmol PAR·m·s. Irradiance tolerance correlated with the rate of "apparent NPQ" induction. Considering that the induction of apparent NPQ involves processes significantly faster than ΔT, we suggest that the photoprotective mechanism induction rate is crucial for tolerance of the PSA to moderate irradiance during the initial stage of light acclimation (first several minutes upon the onset of illumination).

Hyperspectral and Chlorophyll Fluorescence Analyses of Comparative Leaf Surfaces Reveal Cellular Influences on Leaf Optical Properties in Tradescantia Plants

“…Chlorophyll fluorescence primarily indicates the photosynthetic efficiency of leaf surface cells, thereby emphasising the functional implications of morphological variation [ 2 , 28 , 30 , 66 , 67 ]. By measuring the fluorescence emitted by a flash or detection between two sensors that penetrated the mesophyll tissue profile, we ascertained that the internal leaf signals diminished upon the sensor return [ 1 , 11 , 14 , 68 ]. For example, this determines how light dispersion varies among different cellular layers and the impact of adaxial and abaxial hypodermal cells, which contain purple pigments, on the epidermis.…”

“…Differential pigment accumulation not only augments the visual appearance of these species but also significantly contributes to primary and secondary metabolic processes within the leaves [12,88]. The kinetic fluorescence emission properties of chlorophyll a in Tradescantia leaves were similar to those of typical plant cells in high absorption areas [2,[8][9][10][11]14]. However, regions with intensified pigment concentrations, such as those in purple leaves, exhibited altered absorbance and fluorescence emission owing to self-absorption across all measurement configurations [8,9,14].…”

“…The kinetic fluorescence emission properties of chlorophyll a in Tradescantia leaves were similar to those of typical plant cells in high absorption areas [2,[8][9][10][11]14]. However, regions with intensified pigment concentrations, such as those in purple leaves, exhibited altered absorbance and fluorescence emission owing to self-absorption across all measurement configurations [8,9,14].…”

“…Cells 2024, 13, x FOR PEER REVIEW 3 of 31 In this study, VIS-NIR-SWIR hyperspectral and chlorophyll a fluorescence techniques were employed to acquire precise spectral profiles that correlate cellular and ultrastructural data with the physiological status of plants. This method facilitates an in-depth analysis of the influence of cellular composition and arrangement on the optical properties of leaves, and improves understanding of the modulation of light across both standard and nonstandard leaves, as well as analysing the spectral and fluorescence curves on both adaxial and abaxial surfaces [9,11,14,29]. By integrating detailed microscopic analyses of cellular structures with advanced spectral techniques, we aim to enhance our understanding of the complex interplay between plant cell morphology and function [11,28,30].…”

“…The chlorenchyma, composed of chlorophyll-bearing cells, is vital for photosynthesis [ 12 ]. Its structural arrangement strongly affects how well light is captured and converted into chemical energy, and influences chlorophyll a fluorescence (ChlF) dynamics [ 11 , 14 ]. Moreover, chloroplasts within the chlorenchyma cells, which have light-harvesting complexes and a photosynthetic electron transport chain, are essential for photosynthesis in deeper layers [ 2 , 15 , 16 ].…”