Flowering - Relationships Between Leaves and Flowers

(An Introduction to SEM)

Introduction:

Up to this point in the term we have been investigating vegetative development in angiosperms with a recent focus on leaf development. This week we will begin our investigation of the genetic regulation of reproductive development which will carry us through the rest of the term. Today you will look at the relationship between leaves and floral parts in a floral mutant of pea, pim (proliferating inflorescence meristem). This is one of two floral mutants you will investigate for the last half of the term. pim plants have abnormal floral meristems that proliferate as inflorescence branches and produce many abnormal flowers with defective or absent petals. There are many leaf like structures and sepals appear to be morphologically similar to stipules. Today you will examine the floral parts of pim and wild type plants and compare them with pea leaves that you have already characterized. The pim and wild-type plants are segregating from the same cross so you will be comparing siblings. Some of the segregating populations are st st and will have reduced stipules. Other populations are St St and will have wild-type stipules. Pay careful attention to the effect of st on the sepals of pim and wild-type flowers. You may use gross morphological traits, leaf prints (method from last week) and scanning electron microscopy in your characterization. The question you should answer is: "What evidence is there that pim inflorescences revert to vegetative growth?"

Figure 1. Inflorescence of the pim mutant of pea.

Goals for the week:

1) Gain expertise in scanning electron microscopy.

2) Become familiar with floral architecture in pea.

3) Begin examining the transition from vegetative to reproductive development in angiosperms.

4) Continue to build your skills in designing experiments that will yield evidence to support or refute hypotheses.

What to do:

1) Begin by examining wild-type and pim inflorescences in both the st and St backgrounds under a dissecting microscope. Determine what type of comparisons you would like to make. How are you going to address the question of whether or not there is vegetative reversion in the pim mutant? In addition to descriptive data, is there a way to quantitate any of your observations?

2) In addition to the methods you have already mastered in Developmental Botany lab, you should examine the developing flowers with the scanning electron microscope. Directions for sample preparation and use of the SEM are on our home page. I will demonstrate how to prepare your samples and use the SEM this week. SEM images can also be saved in your server account.

What to turn in:

1) At the start of lab next week, you should show me six samples that have been critical point dried and gold coated. If you choose to work in groups, six samples per group will be sufficient. The following week, I will expect to see six scanning electron micrographs.

2) In two weeks, you will turn in a lab report addressing the question of vegetative reversion in the pim mutant. Your lab report will consist of an abstract accompanied by figures and tables with legends.