In some plant species, an endodermis is present in both...

Name: Problem 13, Chapter 37: Biology: The Dynamic Science
Uploaded: 2021-09-16T21:58:14-08:00
Duration: 2 min 41 s
Channel: Caroline Jones
Description: In some plant species, an endodermis is present in both stems and roots. In experiments, the shoots of mutant plants lacking differentiated endodermis in their root and shoot tissue do not respond normally to gravity, but roots of such plants do respond normally. Explain this finding, based on your reading in this chapter.

In some plant species, an endodermis is present in both stems and roots. In experiments, the shoots of mutant plants lacking differentiated endodermis in their root and shoot tissue do not respond normally to gravity, but roots of such plants do respond normally. Explain this finding, based on your reading in this chapter.

Key Concepts

Gravitropism

Gravitropism is the directional growth response of plants to gravity. This process involves gravity perception, signal transduction, and the differential distribution of growth hormones, such as auxin, leading to bending toward or away from the gravitational pull. It is a central concept in plant physiology that explains how plants orient their growth in response to environmental cues.

Endodermis Function in Gravity Sensing

The endodermis is a tissue layer found in both roots and shoots in some plant species that plays a crucial role in gravity perception, particularly in the shoot. It contains specialized cells that can sense gravity through mechanisms like amyloplast sedimentation. In the context of gravitropism, a differentiated endodermis is essential for shoots to detect and respond to changes in orientation relative to gravity.

Statocytes and Amyloplast Sedimentation

Statocytes are specialized gravity-sensing cells that contain amyloplasts—starch-rich organelles that sediment in response to gravity. The movement of these amyloplasts within statocytes provides a physical signal that is translated into a biochemical cascade, leading to differential hormone distribution and subsequent growth adjustments. This mechanism underpins the sensitivity of plant tissues to gravitational cues.

Organ-Specific Mechanisms in Gravity Response

Although both roots and shoots have tissues involved in gravity sensing, the two organs can utilize different structures for this purpose. In roots, aside from the endodermis, gravity perception is largely performed by columella cells in the root cap, which serve as alternative gravity sensing sites. This redundancy explains why roots may maintain normal gravitropic responses even when the differentiated endodermis is absent, whereas shoots, which rely more heavily on the endodermis for gravity detection, display abnormal responses.

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