Chapter 36, Problem 1Q

Summary Introduction

To review:

The data observed from the given experiment in relation to the role of four phytochrome genes in leaf development.

Given:

Effect of differential expression of phy genes that code for phytochromes in Arabidopsis was studied by overexpression of these genes. Later, genetic screens were conducted to identify the mutant strains and their effect on the leaf elongation and size of leaf area was recorded.

Introduction:

Phytochromes are a type of photoreceptors that are present in plants. Photoreceptors detect light to which plant is exposed to and initiates a number of responses that lead to different developmental pathways in plants. These developments range from germination, de-etiolation to development of plant architecture, such as leaf area.

Explanation of Solution

The data given in the table indicate that four phytochromes present in Arabidopsis are involved in different developmental functions like the development of leaf architecture such as length of the leaves and area of the leaves. Since the mutants of these phytochromes show different phenotype from the wild-type, suggests that phytochromes play an important role in determining the area and length of leaves in the plant.

Gene expression	Leaf area (mm2)
Wild-type	22
phyA overexpressed	21
phyB overexpressed	21
phyC overexpressed	31
phyD overexpressed	22

Table: Phytochrome genes phyA, phyB, phyC, and phyD were separately overexpressed in Arabidopsis, and 18-day-old seedlings were examined with regard to leaf area.

These results also indicate that in some cases, the role of some of these phytochromes may be redundant. Redundancy means that the same function can be performed by a different phytochrome. In other cases, their roles may be overlapping or synergistic. The synergistic role means that two phytochromes may work together to create a certain effect on development. Some phytochromes play a greater role in controlling certain phenotypes such as phytochrome C, whose deficiency leads to the enhanced effect on the elongation of leaf, indicating it plays a role in suppression of leaf length.

Conclusion

Therefore, it can be concluded that the four phytochromes play different roles in the development of leaf area as well as elongation of leaf and these functions may be synergistic or redundant.