A Low Ratio of Red/Far-Red in the Light Spectrum Accelerates Senescence in Nest Leaves of Platycerium Bifurcatum

Abstract

The fern Platycerium bifurcatum is a valuable component of the flora of tropical forests, where degradation of local ecosystems and changes in lighting conditions occur due to the increasing anthropogenic pressure. In ferns, phytochrome mechanism responsible for the response to changes in the value of R/FR differs from the mechanism observed in spermatophytes. This study analyzed the course of ontogenesis of nest leaves in P. bifurcatum at two values of the R/FR ratio, corresponding to shadow conditions (low R/FR) and intense insolation (high R/FR). The work used only non-destructive research analysis, such as measurements of reflectance of radiation from the leaves, their blue-green and red fluorescence, and the chlorophyll a fluorescence kinetics. This allowed tracing the development and aging processes in the same leaves. Nest leaves are characterized by short, intense growth and rapid senescence. The study identified four stages of development of the studied leaves related to morphological and anatomical structure and changing photochemical efficiency of PSII. Under the high R/FR ratio, the rate of ontogenesis of the leaf lamina was much slower than under the low R/FR value. As shown, the rapid aging of the leaves was correlated with faster decline of the chlorophyll content. It was shown that leaf senescence was accompanied by accumulation of polyphenols, anthocyanins and carotenoids on the basis of reflectance and fluorescence measurements in the blue-green range.Keywords: chlorophyll a fluorescence; fern; nest leaves; photomorphogenesis; R/FR ratio; reflectance Abbreviations:Area -surface area above the chlorophyll fluorescence induction curve; ARI -anthocyanin reflectance index; BRI -browning reflectance index; CRI 1 -carotenoid reflectance index; DI 0 /RC -total energy dissipation not trapped by the PSII reaction center; ET 0 /RC -rate of electron transfer by the active PSII reaction center; F v /F 0 -maximum efficiency of the water-splitting reaction of the donor side of PSII; F v /F m -maximum quantum yield of PS II; H -R/FR higher value of the red/far red ratio; L-R/FR -lower value of the red/far red ratio; PAR -photosynthetically active radiation; PI -PSII vitality index; PSII -photosystem II; Q A -plastochinon Q A ; RC -reaction center; RC/ABS -reaction center density ratio in terms of chlorophyll; R/FR -photon intensity between 660-670 nm/photon intensity between 725-735 nm; TR 0 /RC -energy trapping of one active reaction center; WBI -water band index. * Corresponding authors,

Different response of photosynthetic apparatus to high-light stress in sporotrophophyll and nest leaves of Platycerium bifurcatum

“…1). Long, ribbon-like sporotrophophylls have an assimilatory role, while nest leaves, which support the plant, show different physiological features and even a different type of metabolism (C3 in sporotrophophylls, CAM in nest leaves - Rut et al 2008, Oliwa et al 2017. Heterophylly is very rarely considered in ecophysiological studies.…”

“…Heterophylly is very rarely considered in ecophysiological studies. However, for an assessment of physiological state of the whole plant, conditions of nest leaves should be taken into account, due to possible translocation of metabolites from nest leaves to sporotrophophylls during their terminal stage (Oliwa et al 2017). sporotrophophyll and nest leaves at their second stage of development (according to the classification of Oliwa et al 2017).…”

“…However, for an assessment of physiological state of the whole plant, conditions of nest leaves should be taken into account, due to possible translocation of metabolites from nest leaves to sporotrophophylls during their terminal stage (Oliwa et al 2017). sporotrophophyll and nest leaves at their second stage of development (according to the classification of Oliwa et al 2017). In order to elicit an intense light response, the plants were placed for 7 d under sodium lamps (Philips SON-T AGRO 400W, The Netherlands), and PPFD was increased to a value of ≤ 800 µmol m -2 s -1 .…”

“…Lack of significant changes in the water content under HL conditions compared to control may indicate the absence of disturbances in leaf stomatal conductance. On the other hand, lower WBI values in nest leaves were results of their different morphological and anatomical structure (Oliwa et al 2017).…”

“…4). This can be explained by an entirely different ontogenesis compared to sporotrophophylls, i.e., short period of leaf growth and the following fast aging process, combined with the loss of assimilation properties (Oliwa et al 2017). The study of Lovelock et al (1994) demonstrated that a short leaf life span in some tropical fern species was associated with their ability to regenerate faster after photoinhibition.…”