Precision farming in arable agriculture and horticulture allows conservative use of resources that are applied according to
plant needs. The growing concern for sustainability in crop production has accentuated the significance of our work to
develop a rapid, sensitive and non-destructive spectroscopic method for real-time monitoring of plant water stress.
Elucidation of crop water status before the onset of irreversible cellular damage is critical for effective water
management to ensure maximum crop yield and profit margin.
A two-component bio-sensing system comprising transgenic 'Indicator Plants' and a spectrometer-linked stereoscopic
microscope was developed to detect early signs of water stress before the permanent wilting point is reached. The
'Indicator Plants' are transgenic Petunia hybrida genetically engineered with a drought-responsive promoter-linked
enhanced green fluorescent protein marker gene (EGFP). No EGFP fluorescence was detected prior to induction of
dehydration stress. Fluorescence emission intensity increased with dehydration period and was found mainly in the stems,
leaf veins and leaf tips. While fluorescence emission above endogenous background was detectable after 2 hours of water
stress treatment, the plants reached permanent wilting point after 6 hours, showing that our system was able to detect
water stress prior to plant entry into the stage of irreversible damage. Future work will be geared towards overcoming
biological and instrument-related difficulties encountered in our initial detection system.
<i>Brassica chinensis</i> var <i>parachinensis</i> was grown in a recirculating water culture system until the '6-leaf stage' when the plants were separated into two groups: a 'Control' group where plant growth was continued in complete nutrient solution and a '-Ca' group in which the plants were grown in calcium-deficient nutrient solution. Leaf reflectance data was collected daily for eight days, starting from the day before the two treatments were imposed. No visual difference was found between 'Control' and '-Ca' groups during the experimental period. Total calcium content in '-Ca' plants decreased significantly from about 20,000 ppm to steady-state levels at 5,000 ppm by Day 5 while leaf chlorophyll levels in both 'Control' and '-Ca' were relatively similar. However, as the plants matured in the two nutrient solutions, the position of the red edge inflection point (REIP defined as the maximum first derivative of the reflectance spectrum in the 680 nm to 750 nm region) in 'Control' plants shifted towards longer wavelengths, while that in the '-Ca' plants remained relatively unchanged. Good correlation was found between Δ[Ca] and Δ[REIP] of 'Control' and '-Ca' plants. Our results showed that monitoring REIP shifts can provide invaluable spectral cues for pre-visual diagnosis of calcium deficiency in plants.
This article investigates calcium deficiency symptoms of the plants grown under hydroponics conditions. Leaf reflectance data were collected from plants, and then transformed to L*, a*, b* values, which provide color information of the leaves. After comparing the color information of deficient plants to control plants, a set of deficiency criterion was established for early detection of calcium deficiency in the plants. Calcium deficiency could be detected as early as two days from the onset of stress in mature plants when optical data were collected from terminal young leaves. Young plants subjected to calcium stress for 9 days could not be distinguished from nutrient sufficient plants.