Growing healthy plants is essential for the advancement of Arabidopsis thaliana (Arabidopsis) research. Over the last 20 years, the Arabidopsis Biological Resource Center (ABRC) has collected and developed a series of best-practice protocols, some of which are presented in this chapter. Arabidopsis can be grown in a variety of locations, growth media, and environmental conditions. Most laboratory accessions and their mutant or transgenic derivatives flower after 4-5 weeks and set seeds after 7-8 weeks, under standard growth conditions (soil, long day, 23 ºC). Some mutant genotypes, natural accessions, and Arabidopsis relatives require strict control of growth conditions best provided by growth rooms, chambers, or incubators. Other lines can be grown in less-controlled greenhouse settings. Although the majority of lines can be grown in soil, certain experimental purposes require utilization of sterile solid or liquid growth media. These include the selection of primary transformants, identification of homozygous lethal individuals in a segregating population, or bulking of a large amount of plant material. The importance of controlling, observing, and recording growth conditions is emphasized and appropriate equipment required to perform monitoring of these conditions is listed. Proper conditions for seed harvesting and preservation, as well as seed quality control, are also described. Plant transformation and genetic crosses, two of the methods that revolutionized Arabidopsis genetics, are introduced as well.

Biomass increase, C and N content, C2H2 reduction, percentage dry weight and chlorophyll a/b ratios were determined for clones of Azolla caroliniana Willd., A.filiculoides Lam., A. mexicana Presl., and A. pinnata R.Br. as a function of nutrient solution, pH, temperature, photoperiod, and light intensity in controlled environment studies. These studies were supplemented by a glasshouse study.

The infectivity of the soybean symbiont Rhizobiumjaponicum changed two-to fivefold with culture age for strains 110 ARS, 138 Str Spc, and 123 Spc, whereas culture age had relatively little effect on the infectivity of strains 83 Str and 61A76 Str. Infectivity was measured by determining the number of nodules which developed on soybean primary roots in the zone which contained developing and preemergent root hairs at the time of inoculation. Root cells in this region of the host root are susceptible to Rhizobium infection, but this susceptibility is lost during acropetal development and maturation of the root cells within a period of 4 to 6 h (T. V. Bhuvaneswari, B. G. Turgeon, and W. D. Bauer, Plant Physiol. 66:1027-1031, 1980. Profiles of nodulation frequency at different locations on the root were not affected by the age of the R. japonicum cultures, indicating that culture age affected the efficiency of Rhizobium infection rather than how soon infections were initiated after inoculation. Inoculum dose-response experiments also indicated that culture age affected the efficiency of infection. Two strains, 61A76 Str and 83 Str, were relatively inefficient at all culture ages, particularly at low inoculum doses. Changes in infectivity with culture age were reasonably well correlated with changes in the proportion of cells in a culture capable of binding soybean lectin. Suspensions of R. japonicum in water were found to retain their viability and infectivity. nm per 100 ml), and grown to the desired growth phase for use as inocula. Inocula were prepared by straight dilution of cultures with sterile water. Rhizobium cell numbers were determined by direct counting in Pe-443 on August 5, 2020 by guest

Three Rhizobiumjaponicum strains and two slow-growing cowpea-type Rhizobium strains were found to remain viable and able to rapidly nodulate their respective hosts after being stored in purified water at ambient temperatures for periods of 1 year and longer. Three fast-growing Rhizobium species did not remain viable under the same water storage conditions. After dilution of slow-growing Rhizobium strains with water to 103 to 105 cells ml-', the bacteria multiplied until the viable cell count reached levels of between 106 and 107 cells ml-1. The viable cell count subsequently remained fairly constant. When the rhizobia were diluted to 107 cells ml-1, they did not multiply, but full viability was maintained. If the rhizobia were washed and suspended at 109 cells ml-', viability slowly declined to 107 cells ml-' during 9 months of storage. Scanning electron microscopy showed that no major morphological changes took place during storage. Preservation of slow-growing rhizobia in water suspensions could provide a simple and inexpensive alternative to current methods for the preservation of rhizobia for legume inoculation.

Arabidopsis thaliana, a model system for plant research, serves as the ideal organism for teaching a variety of basic genetic concepts including inheritance, genetic variation, segregation, and dominant and recessive traits. Rapid advances in the field of genetics make understanding foundational concepts, such as Mendel's laws, ever more important to today's biology student. Coupling these concepts with hands-on learning experiences better engages students and deepens their understanding of the topic. In our article, we present a teaching module from the Arabidopsis Biological Resource Center as a tool to engage students in lab inquiry exploring Mendelian genetics. This includes a series of protocols and assignments that guide students through growing two generations of Arabidopsis, making detailed observations of mutant phenotypes, and determining the inheritance of specific traits, thus providing a hands-on component to help teach genetics at the middle and high school level.