D7 Growth and Tropism Monitoring

Topic

Plant growth and movement occur at vastly different rates depending on the process being observed—ranging from signals triggered in fractions of a second to trunk thickening noticeable only over years—and a suite of measurement tools allows each of these rates to be tracked with a temporal resolution appropriate to the relevant timescale.

The fastest rate involves the electrical signals traveling through plant tissues; electrophysiology is the tool used to record these signals with sub-second temporal resolution, capturing changes that often precede any visible plant movement or growth.

Slightly slower than electrical signals—yet still rapid compared to growth—is the pace of tropisms and nastic movements. Time-lapse photography (using a camera that captures images at regular intervals and plays them back in accelerated sequence) allows these to be tracked with a temporal resolution ranging from minutes to hours, revealing both tropisms—which reorient growth in a direction determined by a physical signal—and nastic movements, where the direction of movement is independent of the triggering signal's direction.

Even slower is the rate of plant axis elongation, measured by linear displacement transducers with a temporal resolution of hours to days; these devices record the extent to which the stem or taproot lengthens as cells divide and elongate.

The slowest rate of all is trunk thickening, measured by band dendrometers—straps encircling the trunk that record increases in circumference—with a temporal resolution of days to years, tracking growth that accumulates perceptibly only over entire seasons.

In addition to tracking these rates in a single plant, high-throughput phenotyping platforms repeat these same growth and movement measurements across hundreds of plants simultaneously, enabling comparisons of how these rates and movements vary from one plant to another. Collectively, electrophysiology, time-lapse photography, linear displacement transducers, band dendrometers, and high-throughput phenotyping platforms cover plant growth and movements with a temporal resolution ranging from seconds to years; this temporal coverage enables the diagnosis of growth alterations and tropism disturbances as soon as they begin to manifest, rather than only detecting them once growth or tropisms have already clearly deviated from their normal course.

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