Which Is More Intelligent? An iPhone Or A Plant? – Part 4

gyroscope.jpgWhy They Call It A “Smartphone”

Arguably, the new iPhone 4 is the most advanced smartphone currently available.

But is the iPhone 4 so smart that it’s actually smarter than the average flowering plant? (At least when it comes to sensing and responding to its environment.)

This is the question I posed way back here, starting with the iPhone’s light and proximity sensors. Next we examined the compass and then the accelerometer. Last up: the gyroscope.

For an excellent review of the iPhone 4 gyroscope, I’ll refer you to AppleInsider. An excerpt from which covers the basics:

“The iPhone 4 gyroscope adds an additional new electronic sensor for detecting 3-axis angular acceleration around the X, Y and Z axes, enabling precise calculation of pitch, yaw and roll.

While conventional accelerometers measure linear acceleration as a change in velocity (speed increasing or decreasing over time) apart a change of direction, a gyro measures angular acceleration: a change in both velocity and direction at the same time. In iPhone 4, the gyro enables the device to sense slight degrees of rotation while rejecting linear movements and hand jitters, while its accelerometer senses those linear movements.

Combined with data from the accelerometer and compass, the gyro provides detailed, precise information about the device’s six-axis movement in space: the 3 axes of the gyro, combined with the 3 axes of the accelerometer enable the device to recognize how far, fast, and in which direction it has moved in space.”

Wow!

How could a plant match all of that?

Do Plants Have a Gyroscope?

The simple answer is no. (At least not one like the iPhone 4.)

But a gyroscope basically is a device for measuring and maintaining orientation. Do plants have something analogous to a gyroscope?

The simple answer to this question is yes.

Plants obviously have the ability to sense and respond to the Earth’s center of gravity.

Most roots grow toward the center of gravity and most stems do the opposite.

Perceiving the direction of the Earth’s center of gravity is the “sensor” most plants use to maintain their correct orientation.

So, instead of a “gyroscopes” plants have a “gravisensors”.

How Do Plant “Gravisensors” Work?balance.jpg

The gravity sensors in plants are located in the root cap cells and in some cells within the growing regions of stems.

The generally-accepted explanation is that starch grains within these cells are relatively dense and heavy enough to be affected by the Earth’s gravity. Thus, their orientation within the gravisensing cells allows them to tell which way is “down”, that is, the center of gravity.

This theory has been recently refined to indicate that starch-containing organelles within the gravisensing plant cells, likely plastids called amyloplasts, are the bodies that move inside the cells in response to gravity.

The reorientation of these organelles somehow affects the transport of the plant hormone auxin out of the gravisensing cells, which is the chemical signal that mediates the plant’s response to gravity. That is, auxin either stimulates (stems) or inhibits (roots) cell elongation, causing the stems to grow away from the center of gravity and the roots to do the opposite.

How the gravity-responsive organelles redirect auxin efflux in these cells is poorly understood. But it may have something to do with relative forces on the cell’s cytoskeleton, which, in turn, may affect auxin transport at the cell membrane. Think tugging on one edge of a spider’s web.

So, though plants don’t have gyroscopes, they do have arrays of gravisensors that allow them to accurately perceive and grow in response to Earth’s center of gravity.

Next-time: Well, which is more intelligent when it comes to sensing and responding to its environment – an iPhone 4 or a plant? Summary and conclusions.

References

1. Miyo Terao Morita (2010) “Directional Gravity Sensing in Gravitropism.” Annual Review of Plant Biology Vol. 61, pp. 705-720. (Abstract)

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