In vivo measurements of the optical properties of plant leaves, by spectrophotometric methods, could potentially provide very useful information for the assessment of the plant’s health. This paper describes a novel experimental set-up that enables continuous measurements of the optical reflection and transmission coefficients of broad-leaved plants. The optical spectral characteristics of leaves, in the broad wavelength range, are often a discussed topic in the scientific literature. Nevertheless, to the best of our knowledge, the real-time spectral analyses of the leaf haven’t been reported so far. Monitoring the evolution of the plant activity in real-time has resulted in the graph of the spectral Circadian rhythm as a function of time. The set-up was tested on Phaseolus vulgaris and the results of the measurements are presented and discussed.

Chloroplast movement rapidly ameliorates the effects of suboptimal light intensity by accumulating along the periclinal cell walls, as well as the effects of excess light by shifting to the anticlinal cell walls. These acclimation responses are triggered by phototropins located at the plasma membrane and chloroplast envelope. Here, we used a recently developed non-invasive system sensitive to very small changes in red light leaf transmittance to perform long-term continuous measurements of dark–light transitions. As a model system, we used variegated Pelargonium zonale leaves containing green sectors (GS) with fully developed chloroplasts and achlorophyllous, white sectors (WS) with undifferentiated plastids, and higher phototropin expression levels. We observed biphasic changes in the red-light transmittance and oscillations triggered by medium intensities of white light, described by a transient peak preceded by a constant decrease in transmittance level. A slight change in red-light transmittance was recorded even in WS. Furthermore, the chloroplast position at lower light intensities affected the rapid light curves, while high light intensity decreased saturated electron transport, maximum quantum efficiency of photosystem II, and increased non-photochemical quenching of chlorophyll fluorescence and epidermal flavonoids. Our results extend the knowledge of light-dependent chloroplast movements and thus contribute to a better understanding of their role in regulating photosynthesis under fluctuating light conditions.

Well-balanced nutrition is important for the successful cultivation of healthy plants. In this paper, we demonstrate a nondestructive optical method that can sense a deficiency of certain nutrients. The setup was tested on hydroponically grown Ocimum basilicum. The plants were subjected to nutrient deficiency by the exclusion of one of the essential elements (Fe, Mg, P, N) from the hydroponic solution. A control group of plants, fed by the balanced hydroponic solution, was also grown under the same conditions. The proposed method tracks and records the optical transmittance of the plants' leaves. All groups exhibit clearly defined day-night Circadian rhythms. When compared to the control group, the treated plants exhibited modified circadian rhythms of the optical transmission, suggesting an early indicator of the plants' stress. The condition of the plants under test was also assessed by the more common (destructive) methods such as: measurements of the determination of the photosynthetic pigment content, dray weight determination and the efficiency of PSII. Several biological parameters were observed, calculated and compared to the graphs of optical transmission dependence in real time. Presented results have demonstrated a significant potential of the proposed optical method for the early detection of plants' stress in hydroponic cultivation.

Optical detection of plant stress in real-time is crucial as it enables timely interventions to mitigate potential damage. This study presents a detailed evaluation of a system that detects changes in plant metabolism in real-time by distributing optical signals across the leaf. The methodology facilitates continuous monitoring of changes in the optical properties of plant leaves through measurements of optical transmission coefficients using a 665 nm LED light signal, thereby recording the circadian rhythm over time. Given that the photosynthetic processes within the leaves are closely linked to the plant’s overall health, this system can detect stress caused by various factors and identify metabolic changes by analysing the circadian rhythm patterns of the observed plants.For inducing metabolic changes, the plant Vriesea carinata Wawra, a verified representative of dual metabolism, was subjected to high light intensity stress. To validate the method, the collected results were compared with data obtained through chemical methods to establish a correlation between the traditional, destructive method and the non-destructive, optical method.The findings successfully identify circadian rhythms as parameters for recognizing changes in plant metabolism, demonstrating the significance of the proposed method in researching plant physiology through the optical identification of biological processes.