Relation of Photochemical Reflectance Indices Based on Different Wavelengths to the Parameters of Light Reactions in Photosystems I and II in Pea Plants

Abstract

Measurement and analysis of the numerous reflectance indices of plants is an effective approach for the remote sensing of plant physiological processes in agriculture and ecological monitoring. A photochemical reflectance index (PRI) plays an important role in this kind of remote sensing because it can be related to early changes in photosynthetic processes under the action of stressors (excess light, changes in temperature, drought, etc.). In particular, we previously showed that light-induced changes in PRIs could be strongly related to the energy-dependent component of the non-photochemical quenching in photosystem II. The aim of the present work was to undertake comparative analysis of the efficiency of using light-induced changes in PRIs (∆PRIs) based on different wavelengths for the estimation of the parameters of photosynthetic light reactions (including the parameters of photosystem I). Pea plants were used in the investigation; the photosynthetic parameters were measured using the pulse-amplitude-modulated (PAM) fluorometer Dual-PAM-100 and the intensities of the reflected light were measured using the spectrometer S100. The ∆PRIs were calculated as ∆PRI(band,570), where the band was 531 nm for the typical PRI and 515, 525, 535, 545, or 555 nm for modified PRIs; 570 nm was the reference wavelength for all PRIs. There were several important results: (1) ∆PRI(525,570), ∆PRI(531,570), ∆PRI(535,570), and ∆PRI(545,570) could be used for estimation of most of the photosynthetic parameters under light only or under dark only conditions. (2) The combination of dark and light conditions decreased the efficiency of ∆PRIs for the estimation of the photosynthetic parameters; ∆PRI(535,570) and ∆PRI(545,570) had maximal efficiency under these conditions. (3) ∆PRI(515,570) and ∆PRI(525,570) mainly included the slow-relaxing component of PRI; in contrast, ∆PRI(531,570), ∆PRI(535,570), ∆PRI(545,570), and ∆PRI(555,570) mainly included the fast-relaxing component of PRI. These components were probably caused by different mechanisms.Plants were cultivated hydroponically (a half-strength Hoagland-Arnon medium) in a Binder KBW 240 climatic chamber (Binder GmbH, Tuttlingen, Germany) at 23 • C under a 16/8 light/dark photoperiod. The measurements were performed on 2-3-week-old plants. The reflectance and photosynthetic parameters were investigated in the second mature leaves.2.2. The Procedure of the Measurements of the Photosystem II Fluorescence, Photosystem I Light Absorption, and Reflected Light Intensity in Pea Figure 1a shows the schema of simultaneous measurements of the intensity of the reflected light, fluorescence of PSII, and light absorption of PSI in pea leaves, which was previously described in detail [64]. The leaves were fixed in the measuring system before the experimental procedure.The PSII fluorescence and PSI absorption measurements were performed using a standard Dual-PAM-100 measuring system (Heinz Walz GmbH, Effeltrich, Germany).The system analyzed photosynthetic parameters on basis of method of the pulse...

Proximal Imaging of Changes in Photochemical Reflectance Index in Leaves Based on Using Pulses of Green-Yellow Light

“…However, our meta-analysis [35] shows that the relation of the non-photochemical quenching to PRI can be strongly varied under sunlight, however using artificial illumination increases correlations between the parameters. Additionally, our previous results demonstrate that light-induced changes in PRI (∆PRI) are more sensitive to the nonphotochemical quenching than absolute value of PRI [36,41,45]. The results show that measuring PRI with using artificial illumination under different light conditions, which is necessary for ∆PRI estimation, is an important problem for remote and proximal plant photosynthetic sensing.…”

“…Our previously developed modality of PRI measurements [36,41] was based on 30 s GYL pulses which could influence PRI because the fast component of changes in the photochemical reflectance indices is formed within a few seconds or less [38]. In contrast, the newly reported system can generate both short-term GYL pulses (18 ms), which are significantly shorter than the durations of all potential mechanisms of the PRI changes [34,36,38], and pulses with controlled durations, which induce fast changes in PRI. The property increases the efficiency of proximal imaging of photosynthetic processes in plants with the use of the developed system (e.g., the fast component of PRI changes can be measured or excluded from measurements).…”

“…The result confirms a hypothesis by Evain et al [38] on the possibility of changes in PRI with duration less than several seconds. Changes in the light scattering at 530-546 nm which are caused by illumination (including light with weak intensity [62]) and following chloroplast lumen acidification [63][64][65] and modifies the leaf light absorbance [66][67][68] are potential mechanism of PRI changes in ranges of seconds and minutes [36,40]. It is known [40,65] that the first component of the changes in the light scattering under illumination is extremely fast (less than several seconds) and potentially related to electrochromic pigment absorbance shift which is caused by forming electrical potential gradient across thylakoid membranes [65,69,70].…”

“…A photochemical reflectance index (PRI), which was proposed by Gamon et al (1992) [32], is the perspective optical parameter for early revealing photosynthetic changes [33][34][35]. Traditionally, Equation ( 1) is used for PRI calculation [33][34][35]; however, using modified spectral changes can be also effective for revealing photosynthetic changes (e.g., [36]):…”

Influence of Local Burning on Difference Reflectance Indices Based on 400–700 nm Wavelengths in Leaves of Pea Seedlings

“…It is known that photosynthetic processes are strongly related to plant optical properties, including fast changes in leaf reflectance (e.g., reflectance in the green spectral range [66,68,[75][76][77][78][88][89][90], which is caused by acidification of the lumen of chloroplasts). Thus, it seems highly probable that VP-induced photosynthetic changes should be accompanied by changes in leaf reflectance, which can potentially be used for their remote sensing.…”