Kinetics of IRP1 Gene Expression in Gravistimulated Maize Pulvini

Date of Award

2007

Document Type

Thesis

Degree Name

Bachelors

Department

Natural Sciences

First Advisor

Clore, Amy

Keywords

Plant Cell Biology, Cellular Signaling, Gravitropism, Gravistimulation

Area of Concentration

Biology

Abstract

During a plant's lifespan, it is bound to encounter and respond to many stimuli, including changes in orientation with respect to the gravity vector. During harsh storms or gusts of wind, a plant may tip over, and it is necessary for it to right itself in order to continue reasonably normal growth. Many monocots achieve this reorientation by differential growth in specialized discs of tissue along the stem known as pulvini. Following stimulation, the cells in the lower half of the pulvini elongate, leading to an upward curvature of the stem. Gravity perception occurs in specialized cells known as statocytes, which contain amyloplasts that sediment upon reorientation. How this sedimentation leads to a change in growth is still largely unknown. Although recent studies have begun tackling the pieces of the signaling pathway, little is understood about the changes in gene expression that lead to differential growth. Preliminary results of Clore et al. (in preparation) suggest that the iron regulatory protein 1 (irp1) gene is upregulated soon after gravistimulation in maize (Zea mays), and that IRP1 may play a part in the early signaling pathway prior to differential growth. We aimed to further test this hypothesis by measuring the levels of irp1 mRNA at various timepoints after gravistimulation in both upper and lower halves of the pulvinus. To do so, we used the sensitive and quantitative technique of real time reverse-transcriptase polymerase chain reaction (real-time RT-PCR). We have determined that there appears to be a pattern of synchronous rises and falls of irp1 transcript levels in both the upper and lower halves of the pulvinus, whereas gene expression is reasonably steady in vertical pulvini and in gravistimulated internode tissue. Somewhat unexpectedly, modest increases in expression did occur in node tissues as well as leaf sheath tissue immediately around the pulvinus. Possible explanations for this result are discussed. We hypothesize that IRP1 may be part of a cascade that leads from gravity perception to asymmetrical growth and propose future experiments to study this possibility further.

Rights

This bibliographic record is available under the Creative Commons CC0 public domain dedication. The New College of Florida, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.

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