Dr. Thomas Rost  




Dr. Edwin P. Groot

(Postdoctoral Researcher - epgroot@ucdavis.edu)

Abstract from the 1999 International Botanical Congress:

Groot, E.P. Section of Plant Biology, U.C., Davis, CA. - APPLICATION OF THE PLASTOCHRON INDEX TO ANALYZE GROWTH AND DEVELOPMENT IN ARABIDOPSIS THALIANA.   The use of the plastochron index (PI) as a numerical measure of leaf developmental age was introduced for A. thaliana. A standardized statistical methodology was formulated to validate the PI for leaf development. The PI was the ideal choice for determining leaf age because it lowered the temporal variation relative to using plant age in days. Tooth development was compared between the Columbia-1 (Col-1) ecotype and se, a mutant with deeper teeth. The se mutant initiated teeth earlier in leaf development than did Col-1. Besides leaves, the PI can serve as the time variable for other modules such as: flowers, inflorescences, internodes, and stem units. The PI has found utility in physiology, anatomy and growth modeling, but it ought to be used more in quantitative studies of molecular genetics, plant development and testing hypotheses of heterochrony in plants.


Eva Grotkopp Kuo

(Doctoral Student - ekgrotkopp@ucdavis.edu)

Abstract from the 1999 International Botanical Congress:

Eva Grotkopp, Marcel Rejmánek, and Thomas L. Rost. University of California, Davis, CA, 95616, USA. - WHAT ATTRIBUTES DETERMINE INVASIVENESS OF PINES.   We found that seedling relative growth rate is negatively correlated with genome size and positively correlated with invasiveness of thirty pine species. Relative growth rate has two components: leaf area ratio and net assimilation rate. Leaf area ratio, the major contributor to relative growth rate in pines, was negatively correlated with genome size while net assimilation had no correlation with genome size. Ecologists have noted the negative correlation between seed size and relative growth rate, as well as the positive correlation between seed size and genome size. Using path analysis, we found that seed size does not directly influence relative growth rate. Instead, we hypothesize the following causal chain: genome size (+) --> seed size (-) --> specific leaf area (+) --> leaf area ratio (+) --> relative growth rate (+) --> invasiveness in disturbed areas.

Eva - statement of research project:

Eva, working in the laboratories of Dr. Thomas Rost and Dr. Marcel Rejmanek, is studying how genome size affects invasiveness of plants. Her work with thirty species of pines (16-36 pg of DNA per genome) shows a significant negative relationship between genome size and relative growth rate, an important aspect of invasiveness. She is presently correlating genome size with cell size and cell cycle times to see how these cellular consequences of genome size influence relative growth rate. Her next project will be to study the separate effects of genome size and ploidy in 22 species of the angiosperm genus, Centaurea (Asteraceae).


Sue Nichol

(Postgraduate Researcher - sanichol@ucdavis.edu)

Effect of growth zones on soil quality in the rhizosphere

The ability of the root to change the pH of the soil in its immediate vicinity affects the uptake of both beneficial and phytotoxic metals and thus regulates the rate of introduction of mineral elements into the food chain.  This is a pilot project designed to examine the effect of root growth zones on the pH of the rhizosphere.  The overall project obejective is to characterize interactions between rhizosphere pH and root growth.  Preliminary results indicate that for maize primary roots growing slowly at 20oC or rapidly at at 26oC, the pH pattern of the rhizosphere is the same.  Thus the plant can synchronize H+ fluxes with expansion rates to regulate the pH of the rhizosphere.  Measurements of rhizosphere pH are made with both an agar gel to which the indicator Bromocresol purple is added as well as with microelectrodes.  A parallel theoretical study showed quantitatively the effects of root growth rate, H+ diffusivity, and plant H+ fluxes on predicted pH patterns around the growth zone in the rhizosphere.  The classical theory for root induced pH patterns in the rhizosphere was modified to include a moving reference frame and spatial variation in H+ flux.  Nondimensional analysis reveals that a version of the Peclet number, P, of transport theory can characterize the time dependence of the rhizosphere pH.  For small P, corresponding to high H+ diffusivity relative to root growth rates, the rhizosphere becomes more acidic over time; while for larger P, the pH field around the growth zone can be time invariant.  The pH field predicted by theory has agreed well with empirical measurements made with microelectrodes.


Dr. Joseph Dubrovsky

Sabbatical visitor (Presently professor at CIBNOR, La Paz, Mexico - jdubrov@cibnor.mx)

Abstract from the 1999 International Botanical Congress:

Joseph G. Dubrovsky. CIBNOR, La Paz, Mexico. - ADAPTATION STRATEGIES IN ROOT DEVELOPMENT OF ARID CACTACEAE.   I analyze adaptive strategies evolved in root development of Sonoran Desert Cactaceae and propose the following adaptation principles. 1. Developmental shift. Usually root hair formation starts when cell elongation is completed. In Stenocereus gummosus the first hairs are formed before cell elongation starts. Early exhaustion of the meristem is another example of the principle. 2. Developmental maximization. If a process is significant for survival, then the development of a related structure is maximized. In S. gummosus, each epidermal cell forms a root hair whereas in most non-arid species not all cells do. 3. Short developmental programs. The related strategies (such as short period of root growth, its determinate pattern, short cell cycle, limited number of cycles) are important for plant survival in a desert. 4. Principle of economy operates as a combination of principles 2 and 3. As a result, the first root system is relatively small but is sufficient for rapid seedling establishment and does not require much carbon input and water for growth and construction.


Dr. Joseph G. Dubrovsky from the Center for Biological Research, La Paz, Mexico, is working in the laboratory during his sabbatical leave. Generally he is studying various problems of root biology, particularly cellular bases of root growth and development. Lately, he researched the developmental aspects of plant roots from the perspective of plant adaptation to real environment. Working with roots of Cactaceae of the Sonoran Desert, he was able to find some unique adaptive features of root in these species. In the Rost Laboratory Dr. Dubrovsky is now studying lateral root development in Arabidopsis. You are welcome to visit his Internet page (in English) and to consult list of his publications at http://www.cibnor.mx/be/idubrov.html


Kathy Tong

Laboratory Assistant (Presently a med student at Northwestern University, Chicago - ktong003@md.nwu.edu)

My research focuses on the development of the primary root tip in Trifolium repens (white clover). Clover primary roots were harvested after one, two, and three weeks of growth and embedded in plastic for thin sectioning. Longitudinal sections through the root tips revealed the presence of T-divisions, periclinal, formative divisions that have been documented in roots with closed apical organization. Clover root tips have open apical organization, so the presence of T-divisions in clover suggests a common developmental event in both open and closed root tips. Serial cross sections of clover root tips were used to determine where T-divisions had occurred in the roots. Gaining an understanding of the location of T-divisions is an important step towards determining the temporal sequence of T-divisions and how that may affect the placement of different tissues in the root.


Dr. Carol Wenzel

Graduate Researcher (Presently at the University of York, UK - clw7@york.ac.uk)

Spiral growth in Arabidopsis thaliana roots.

Wenzel, CL and Rost, TL. Arabidopsis thaliana roots have closed apical organization where cell files originate from a specific tier of initial cells. The root cap/protoderm (RCP) initials are arranged in a collar around the columella initials. Periclinal division of the RCP initials give rise to the peripheral root cap cells and the first protoderm cell forming a T-junction. Transverse sections at the level of the initial tier reveal a spiral pattern of peripheral root cap cells in 2 week old Arabidopsis thaliana ws roots grown in sand. The spiral pattern was suggested to be derived from sequential divisions of the RCP initials in a particular direction around the collar of initials (1). Externally, spiral patterns of root growth are also seen in the epidermal cell file rotations and in the cork-screwing pattern of roots as they drill downwards. Here we correlate the internal and external spiral patterns of Arabidopsis thaliana roots grown in agar and in sand. We test the hypothesis that the cell division pattern causes differential cell expansion around the axis of the root creating a torque which would lead to cell file rotations and the cork-screwing growth pattern of roots. 1. Root apical organization of Arabidopsis thaliana. 1. Root cap and protoderm. Protoplasma 192: 178-188.


The T-Division Project

Abstract from the 1999 International Botanical Congress:

T.L. Rost, C.L. Wenzel, and K. Tong. (Sect. Plant Biol., Univ. of Calif., Davis, CA 95616, USA). - ROOT APICAL MERISTEM ORGANIZATION: A COMMON PROTOCOL FOR THE DEVELOPMENT OF THE EPIDERMIS AND ROOT CAP.   Patterns of organization of the root apical meristem of Arabidopsis thaliana and Trifolium repens will be discussed. One common event, a T-division, leads to the initiation of the epidermis and peripheral root cap even though these roots have different apical organization. This suggests a common developmental pathway for the epidermis and peripheral root cap from initiation to maturation. The peripheral root cap and epidermal cells are produced from periclinal T-divisions of the root cap protoderm (RCP) initial cells. Lineages derived from each initial cell were followed in A. thaliana and T. repens root tips. Subsequent proliferative divisions of cell lineages forming 'packets' of epidermal and peripheral root cap cells, and their relation to the columella root cap cells will be described.