Abstract
Leaf senescence provides a unique window to explore the age-dependent programmed degradation at organ label in plants. Here, spectral domain optical coherence tomography (SD-OCT) has been used to study in vivo senescing leaf microstructural changes in the deciduous plant Acer serrulatum Hayata. Hayata leaves show autumn phenology and change color from green to yellow and finally red. SD-OCT image analysis shows distinctive features among different layers of the leaves; merging of upper epidermis and palisade layers form thicker layers in red leaves compared to green leaves. Moreover, A-scan analysis showed a significant (p < 0.001) decrease in the attenuation coefficient (for wavelength range: 1100–1550 nm) from green to red leaves. In addition, the B-scan analysis also showed significant changes in 14 texture parameters extracted from second-order spatial gray level dependence matrix (SGLDM). Among these parameters, a set of three features (energy, skewness, and sum variance), capable of quantitatively distinguishing difference in the microstructures of three different colored leaves, has been identified. Furthermore, classification based on k-nearest neighbors algorithm (k-NN) was found to yield 98% sensitivity, 99% specificity, and 95.5% accuracy. Following the proposed technique, a portable noninvasive tool for quality control in crop management can be anticipated.
Highlights
The lifespan and microstructure of leaves are crucial for the overall development of plants
In Optical coherence tomography (OCT), A-scan is referred for depth scan; while B-scan is referred to sagittal, or transverse sections such as XZ, or YZ plane
Our results showed that the total chlorophyll concentrations of the yellow and red leaves are significantly decreased (p < 0.001) compared to the green leaves by ~65.29% and ~79.80% respectively; further, the chlorophyll content decreases by ~41.77% (p < 0.001) for red leaves compared to yellow leaves (Fig. 5(b))
Summary
The lifespan and microstructure of leaves are crucial for the overall development of plants. Changes in leaf microstructure are closely associated with the photosynthetic activity, which usually degrades during senescence[12] Imaging modalities such as scanning electron microscopy (SEM)[13], transmission electron microscopy (TEM)[14] and X-ray computed tomography[15] have been widely used for quantitative visualization microstructural biomarkers in leaves. Are valuable for non-destructive study of leaf senescence at the cellular, molecular, as well as microstructural level Though these techniques provide interesting findings, are limited by penetration depth and sometimes needs physical sectioning. Non-destructive and fast optical imaging modality with high penetration depth to monitor the microstructural changes in leaves during senescence is required. SD-OCT and OCT, in general, have the potential to become an invaluable tool in agriculture and plant science
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