PHYTOGRAM™

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The PHYTOGRAM™ is an electrochemical monitoring capability designed to assess (1) inside-the-plant hydration (extracellular water content), (2) changes in proton or hydrogen peroxide concentration, and (3) the level of metabolic activity of the plants, seedlings, or trees and their response to natural and artificial environmental influences. The PHYTOGRAM™ consists of a sensor and equipment to apply electrochemical testing procedures to the sensor circuit.

The sensor is a thin rod (about three times the size of a human hair and made of precious metal) inserted inside the plant, seedling, or tree. It is implanted in the extracellular region of the tissue in a non destructive manner and as such provides an indication of the normal transfer of constituents into and out of cells adjacent to its surface. The sensor functions as a "chemical window" inside the plant through which one can observe changes in extracellular constituents due to cellular activity.

Measurement of inside-the-plant Water Content (US Patent 6,870376 B1)

On a diurnal time scale water moves out of the cells and into the extracellular region in the morning and back into the cells in the late afternoon and evening. This leads to a diurnal cycle in the extracellular water content. The magnitude of the diurnal cycle gives a measure of the cross sectional area of the extracellular region that is filled with water during the daytime period. Over a multi-day period, the minimum value of the diurnal cycle will vary in proportion to the water content of the plant as a whole. As the plant dries out, both the magnitude of the diurnal cycle and the minimum value decrease.

Water in the extracellular region wets the surface of the sensor. Ionized oxygen within this water forms one charge layer of a parallel plate electrical capacitor. The other charge layer is present within the metal surface of the sensor. The electronics in the POD measures the capacitance of this parallel plate capacitor which is in turn proportional to the area of the wetted surface. The total sensor surface within the plant is measured with a caliper. The ratio of the wetted surface within the plant expressed as a value of electrical capacitance to the total surface within the plant expressed as a length of the cylindrical sensor within the plant gives a measure of water content in units of nanofarads/millimeter. This ratio changes with changes in sensor wetted surface area. The ratio can then he used as a measure of plant water content which is independent of the time and conditions of the measurement. This permits comparison of the ratio from day to day, year to year and site to site. The day-to-day variation, termed a water content profile, can be used as a criterion of plant water content. The magnitude and timing of irrigation events can he set to maintain a desired water content profile. See Water Content of Specific Crops.

Data obtained from monitoring the internal hydration status from an individual field site (every half hour from 15 petioles and 15 berries) generates a significant amount of statistical data. The collected data is averaged to produce a single point per day (minimum value) graph or a 48 point per day (each half hour) graph for review by the Viticulturist or Irrigation Manager of plant's response to irrigation and/or weather .

Measurement of Proton or Hydrogen Peroxide Concentration

Protons are employed in many cellular membrane cotransport processes. Changes in proton concentration in the extracellular region can be used as a measure of the timing and magnitude of these processes. The PHYTOGRAM™ sensor measures changes in the proton concentration by means of changes in the electrical potential between the sensor surface and the extracellular fluid. The difference between the maximum and minimum sensor electrical potential values yields a single numerical daily index of metabolic activity. (See separate discussion below.)

Under the special condition wherein a pathogen is present in the extracellular fluid, the cells increase the concentration of hydrogen peroxide in the extracellular fluid. When this happens, the potential between the sensor surface and the fluid is set by the relative proton and hydrogen peroxide concentration. Proton concentration sets the potential value (the proton mode) over a range of potential up to 700 millivolts relative to the standard hydrogen electrode. Above this level, the concentration of hydrogen peroxide sets the sensor electrical potential (the peroxide mode).

This gives rise to a special application of the PHYTOGRAM™ in plant pathology and plant immunology. Hydrogen peroxide is a major constituent of the active oxygen defense mechanism. The PHYTOGRAM™ can be used to measure the magnitude, timing and spread of this mechanism through the plant.

Metabolic Activity Index (MA4)

An index of daily petiole and berry metabolic activity, MA4, will be placed on a graph on the Internet. This index gives a quantitative measure of the phase and magnitude of the petiole or berry water content cycle relative to the phase of the sun cycle. The value of the MA4 index is set by water content, weather and tissue age.

This index measures whether the vine performs its major water related metabolic activity during the daytime or nighttime. It will perform its major metabolic activity during the daytime if it is not water stressed. This will result in positive values of the daily MA4 index. The vine will shift its major water related metabolic activity to the nighttime if it is water stressed. This will result in a shift in the daily MA4 index to negative values.

This index is anticipated to be positive during the first part of the season when the vines have ample water and then shift negative during the second part of the season. Negative values are desirable near harvest. Irrigation scheduling can be based on the single point minimum value of the diurnal cycle and the value of the MA4 index.

Each block will have three graphs for petioles and three graphs for berries. If a quick appraisal is desired, the single point graphs are more useful. If a more detailed appraisal is desired, the diurnal cycle (48 point) graphs can be examined. For irrigation scheduling, the MA4 graphs can be examined in conjunction with the single point graphs throughout the season but become more useful in the berry ripening period.

The graph of the cumulative value of the daily MA4 index gives a measure of petiole or berry tissue activity over an extended time period. It is analogous to a graph of temperature degree-days in production agriculture.

Monitoring of Irrigation

The PHYTOGRAM™ is also used to determine whether there is water in above-surface drip lines. The output of this Drip Line Sensor indicating the presence or absence of water in the line is recorded at the same acquisition rate (48 measurements per sensor - every half hour of the day) as the PHYTOGRAM™ electrochemical sensors. Information on the exact beginning and ending of irrigation provides the Irrigation Manager with confirmation that irrigation equipment is functioning as intended. See Irrigation Management

General characteristics and applications of the PHYTOGRAM™ are shown below.