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Signature Optical Cues: Emerging Technologies for Monitoring Plant Health

View Article: PubMed Central

ABSTRACT

Optical technologies can be developed as practical tools for monitoring plant health by providing unique spectral signatures that can be related to specific plant stresses. Signatures from thermal and fluorescence imaging have been used successfully to track pathogen invasion before visual symptoms are observed. Another approach for non-invasive plant health monitoring involves elucidating the manner with which light interacts with the plant leaf and being able to identify changes in spectral characteristics in response to specific stresses. To achieve this, an important step is to understand the biochemical and anatomical features governing leaf reflectance, transmission and absorption. Many studies have opened up possibilities that subtle changes in leaf reflectance spectra can be analyzed in a plethora of ways for discriminating nutrient and water stress, but with limited success. There has also been interest in developing transgenic phytosensors to elucidate plant status in relation to environmental conditions. This approach involves unambiguous signal creation whereby genetic modification to generate reporter plants has resulted in distinct optical signals emitted in response to specific stressors. Most of these studies are limited to laboratory or controlled greenhouse environments at leaf level. The practical translation of spectral cues for application under field conditions at canopy and regional levels by remote aerial sensing remains a challenge. The movement towards technology development is well exemplified by the Controlled Ecological Life Support System under development by NASA which brings together technologies for monitoring plant status concomitantly with instrumentation for environmental monitoring and feedback control.

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Spectral and morphological effects of calcium deprivation in Brassica sp. (A) REIP shifts in unstressed (Ctrl) and Ca-deprived (-Ca) plants as a function of time. The REIP position stabilizes around 714 nm in the nutrient-sufficient plants (green line) and 708 nm in Ca-deprived plants (red line). Significant deviation in REIP position between nutrient-sufficient and Ca-deprived plants from day 3-4 onwards (highlighted in the blue oval) coincides with obvious cellular breakdown shown in panel C. (B) Linear relationship between ΔREIP and ΔCa. The red line indicates the critical ΔREIP and ΔCa values above which plants are deduced to have entered into a deficiency state (adapted from Li et al. 2005 [78]). (C) Breakdown of cell structure in the abaxial epidermal surface with progression of calcium deprivation.
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f4-sensors-08-03205: Spectral and morphological effects of calcium deprivation in Brassica sp. (A) REIP shifts in unstressed (Ctrl) and Ca-deprived (-Ca) plants as a function of time. The REIP position stabilizes around 714 nm in the nutrient-sufficient plants (green line) and 708 nm in Ca-deprived plants (red line). Significant deviation in REIP position between nutrient-sufficient and Ca-deprived plants from day 3-4 onwards (highlighted in the blue oval) coincides with obvious cellular breakdown shown in panel C. (B) Linear relationship between ΔREIP and ΔCa. The red line indicates the critical ΔREIP and ΔCa values above which plants are deduced to have entered into a deficiency state (adapted from Li et al. 2005 [78]). (C) Breakdown of cell structure in the abaxial epidermal surface with progression of calcium deprivation.

Mentions: In our lab, we used a different combination of spectral features to tease out signature diagnostic information of mineral deficiencies in a model leafy plant, Brassica chinensis L. var parachinensis (Bailey) grown under hydroponics conditions. Leaf reflectance spectra (R) over the visible range from 380–780 nm were collected, and normalized inner reflectance (NRI) spectra were calculated to remove the effects of external reflectance and inner leaf scattering [95]. NRI was then transformed into CIELAB color values, which simplified the whole visible spectrum into three values. We used REIP shifts and CIE L*, a* and b* values as composite predictors of specific elemental stresses. It was found that REIP shifts towards shorter wavelengths provided useful pre-visual cues for Ca deficiency in plants [78]. A linear relationship between the differences in the REIP (ΔREIP) and leaf Ca content (Δ[Ca]) of Ca-stressed and unstressed plants was found (r2 = 0.95). Significant deviations in red edge position and leaf Ca content were observed as early as three days after the imposition of calcium deprivation in young terminal leaves and these corroborated well with concomitant changes in the breakdown of cell structure on the abaxial epidermal surface (Figure 4). There were no significant differences in the ΔL*, Δa* and Δb* values between Ca-deficient and Ca-sufficient young plants [96].


Signature Optical Cues: Emerging Technologies for Monitoring Plant Health
Spectral and morphological effects of calcium deprivation in Brassica sp. (A) REIP shifts in unstressed (Ctrl) and Ca-deprived (-Ca) plants as a function of time. The REIP position stabilizes around 714 nm in the nutrient-sufficient plants (green line) and 708 nm in Ca-deprived plants (red line). Significant deviation in REIP position between nutrient-sufficient and Ca-deprived plants from day 3-4 onwards (highlighted in the blue oval) coincides with obvious cellular breakdown shown in panel C. (B) Linear relationship between ΔREIP and ΔCa. The red line indicates the critical ΔREIP and ΔCa values above which plants are deduced to have entered into a deficiency state (adapted from Li et al. 2005 [78]). (C) Breakdown of cell structure in the abaxial epidermal surface with progression of calcium deprivation.
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Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC3675540&req=5

f4-sensors-08-03205: Spectral and morphological effects of calcium deprivation in Brassica sp. (A) REIP shifts in unstressed (Ctrl) and Ca-deprived (-Ca) plants as a function of time. The REIP position stabilizes around 714 nm in the nutrient-sufficient plants (green line) and 708 nm in Ca-deprived plants (red line). Significant deviation in REIP position between nutrient-sufficient and Ca-deprived plants from day 3-4 onwards (highlighted in the blue oval) coincides with obvious cellular breakdown shown in panel C. (B) Linear relationship between ΔREIP and ΔCa. The red line indicates the critical ΔREIP and ΔCa values above which plants are deduced to have entered into a deficiency state (adapted from Li et al. 2005 [78]). (C) Breakdown of cell structure in the abaxial epidermal surface with progression of calcium deprivation.
Mentions: In our lab, we used a different combination of spectral features to tease out signature diagnostic information of mineral deficiencies in a model leafy plant, Brassica chinensis L. var parachinensis (Bailey) grown under hydroponics conditions. Leaf reflectance spectra (R) over the visible range from 380–780 nm were collected, and normalized inner reflectance (NRI) spectra were calculated to remove the effects of external reflectance and inner leaf scattering [95]. NRI was then transformed into CIELAB color values, which simplified the whole visible spectrum into three values. We used REIP shifts and CIE L*, a* and b* values as composite predictors of specific elemental stresses. It was found that REIP shifts towards shorter wavelengths provided useful pre-visual cues for Ca deficiency in plants [78]. A linear relationship between the differences in the REIP (ΔREIP) and leaf Ca content (Δ[Ca]) of Ca-stressed and unstressed plants was found (r2 = 0.95). Significant deviations in red edge position and leaf Ca content were observed as early as three days after the imposition of calcium deprivation in young terminal leaves and these corroborated well with concomitant changes in the breakdown of cell structure on the abaxial epidermal surface (Figure 4). There were no significant differences in the ΔL*, Δa* and Δb* values between Ca-deficient and Ca-sufficient young plants [96].

View Article: PubMed Central

ABSTRACT

Optical technologies can be developed as practical tools for monitoring plant health by providing unique spectral signatures that can be related to specific plant stresses. Signatures from thermal and fluorescence imaging have been used successfully to track pathogen invasion before visual symptoms are observed. Another approach for non-invasive plant health monitoring involves elucidating the manner with which light interacts with the plant leaf and being able to identify changes in spectral characteristics in response to specific stresses. To achieve this, an important step is to understand the biochemical and anatomical features governing leaf reflectance, transmission and absorption. Many studies have opened up possibilities that subtle changes in leaf reflectance spectra can be analyzed in a plethora of ways for discriminating nutrient and water stress, but with limited success. There has also been interest in developing transgenic phytosensors to elucidate plant status in relation to environmental conditions. This approach involves unambiguous signal creation whereby genetic modification to generate reporter plants has resulted in distinct optical signals emitted in response to specific stressors. Most of these studies are limited to laboratory or controlled greenhouse environments at leaf level. The practical translation of spectral cues for application under field conditions at canopy and regional levels by remote aerial sensing remains a challenge. The movement towards technology development is well exemplified by the Controlled Ecological Life Support System under development by NASA which brings together technologies for monitoring plant status concomitantly with instrumentation for environmental monitoring and feedback control.

No MeSH data available.


Related in: MedlinePlus