Research in Dr. Kostman's lab focuses on how plants regulate calcium. Plants, unlike animals, cannot change their surrounding environment by simply moving when conditions become unfavorable. One major problem thus faced by plants is exposure to excess nutrients. Calcium is a prime example of this. Calcium is a necessary mineral involved in the structure of plant cell walls, in cell signaling, and in control of many metabolic processes within the cell. To be effective, it must be maintained at very low levels within the cytoplasm of the cell. The problem is that most plants have little control over the amount of calcium they take up from the soil, so they are faced many times with huge excesses of calcium in and around their cells. Over time plants have developed several ways of dealing with this problem. A primary method used is formation of calcium oxalate crystals, which tie up the calcium in an insoluble form and thus keep it at low levels within cells. Calcium oxalate crystals form within the vacuoles of specialized cells called crystal idioblasts. Crystal idioblasts are cells modified to serve as sinks for the excess calcium from surrounding cells. Some of these modifications include extensive networks of ER, many mitochondria, and enlarged nucleus, and the presence of specialized plastids. The crystals form within membrane structures thought to control the shape and growth of crystals. Little is known about what triggers crystals idioblast cells to differentiate into crystal forming cells. Another area of interest is how the calcium moves within the crystal cells. Calcium binding proteins such as calreticulin are thought to be involved, but more evidence is needed.
The goal of this REU project is to first identify key proteins involved
in calcium regulation using protein extraction, 1 or 2-D gel electrophoresis,
and MALDI Mass Spectrometry. This will be accomplished by using an
aquatic model plant Pistia stratiotes (water lettuce) that forms large
numbers of calcium oxalate crystals in its leaves. Since it is an
aquatic plant, we can easily place it on a high-calcium medium, which
will kick the calcium regulation system into high gear, then extract
and look for up-regulated proteins- as they are likely involved in
calcium regulation and/or crystal formation. Once key proteins have
been identified, the next step will be to determine the proteome of
the crystal idioblast cell itself and further characterize proteins
unique to these cells that are involved in calcium regulation and
crystal formation. We can then put all of this information together
to hopefully better understand the process of calcium regulation in
plant cells and tissues.
