Plant Growth Analysis & Time-lapse Characterization Of Arabidopsis Starch Metabolism Mutants

Plant Growth Analysis & Time-Lapse Characterization of Arabidopsis Starch Metabolism Mutants

sex1

Columbia

Zachary J. Jarou*, Sean E. Weise & Thomas D. Sharkey Department of Biochemistry & Molecular Biology, Michigan State University

Introduction During the early exponential growth phase of plants, the majority of photoassimilates are reinvested into new leaf material. Once the photosynthetic capacity to reach sufficient carbon mass has been achieved, carbon metabolism can be redirected to cause the accumulation of end products, such as starch and oil. To optimize the timing of this redirection, we have developed growth analysis methods to minimize yield penalty.

Classical Growth Analysis

Measuring Leaf Area with Photoshop The irregular shape of leaves can make measurement by traditional means difficult, especially for large numbers of plants. By taking a digital picture of the leaves to be measured, along with an object of known size, the pixel area of the leaves can be can quantified into physicial units. This is accomplished using the color range and histogram tools in Adobe Photoshop. A screen capture demonstration of this process is available on YouTube (http://www.youtube.com/watch?v=E3O-V6WLw0g).

Relative growth rate (RGR) is defined as the net dry biomass increase per unit dry mass per day and can be further factorized into three components, specific leaf area (SLA), leaf mass fraction (LMF), and unit leaf rate (ULR).

ln(M2) - ln(M1) = SLA x LMF x ULR t2 - t1

SLA is calculated by dividing the leaf area by the leaf mass. LMF is defined as the leaf mass divided by the total plant mass. ULR is the increase of biomass per unit leaf area per day. It can be calculated from plant mass and leaf area on two time points or by gas exchange.

Arabidopsis Hydroponics Systems Growth analysis requires that the masses of each plant component be determined each harvest, including the roots. Because of the difficulties associated with root washing, hydrponic cultivation is ideal as the roots are easily accessible. Seeds are germinated in small, rockwoolfilled microfuge tubes with the bottoms cut off. Once the roots have protruded out of the bottom, the tubes are transferred into the predrilled lids of 50mL centrifuge tubes, which also have their bottoms removed. This method prevents tangling of roots while growing in aerated nutrient solution.

(images from Grant Cramer, University of Nevada)

Time-Lapse Characterization

Leaf area, one of many growth parameters, has been examined by time-lapse photography in Arabidopsis starch metabolism mutants. Weekly time-course images of Columbia and severe starch excess plants (sex1) are shown (far above). Measurement of rosette areas (below) shows that mild starch accumulation (sex4) imposed very little yield penalty. Videos of these and additional mutants are available on YouTube (http://www.youtube.com/watch?v=b-XSnuuXFE4).

Rosette area (cm^2)

RGR =

Weeks of Development