Gautam Sarath

Hydrolysis of phosphate esters is a critical process in the energy metabolism and metabolic regulation of plant cells. This review summarizes the characteristics and putative roles of plant acid phosphatase (APase). Although immunologically closely related, plant APases display remarkable heterogeneity with regards to their kinetic and molecular properties, and subcellular location. The secreted APases of roots and cell cultures are relatively non‐specific enzymes that appear to be important in the hydrolysis and mobilization of P i from extracellular phosphomonoesters for plant nutrition. Intracellular APases are undoubtedly involved in the routine utilization of P i reserves or other P i ‐containing compounds. A special class of intracellular APase exists that demonstrate a clear‐cut (but generally nonabsolute) substrate selectivity. These APases are hypothesized to have distinct metabolic functions and include: phytase, phosphoglycolate phosphatase, 3‐phosphoglycerate phosphatase, phosphoenolpyruvate phosphatase, and phosphotyrosyl‐protein phosphatase. APase expression is regulated by a variety of developmental and environmental factors. P i starvation induces de novo synthesis of extra‐ and intracellular APases in cell cultures as well as in whole plants. Recommendations are made to achieve uniformity in the analyses of the different APase isoforms normally encountered within and between different plant tissues.

Switchgrass (Panicum virgatum L.) has been identified as a model herbaceous energy crop for the USA. In this review, we selectively highlight current USDA-ARS research on switchgrass for biomass energy. Intensive research on switchgrass as a biomass feedstock in the 1990s greatly improved our understanding of the adaptation of switchgrass cultivars, production practices, and environmental benefits. Several constraints still remain in terms of economic production of switchgrass for biomass feedstock including reliable establishment practices to ensure productive stands in the seeding year, efficient use of fertilizers, and more efficient methods to convert lignocellulose to biofuels. Overcoming the biological constraints will require genetic enhancement, molecular biology, and plant breeding efforts to improve switchgrass cultivars. New genomic resources will aid in developing molecular markers, and should allow for marker-assisted selection of improved germplasm. Research is also needed on profitable management practices for switchgrass production appropriate to specific agro-ecoregions and breakthroughs in conversion methodology. Current higher costs of biofuels compared to fossil fuels may be offset by accurately valuing environmental benefits associated with perennial grasses such as reduced runoff and erosion and associated reduced losses of soil nutrients and organic matter, increased incorporation of soil carbon and reduced use of agricultural chemicals. Use of warm-season perennial grasses in bioenergy cropping systems may also mitigate increases in atmospheric CO 2 . A critical need is teams of scientists, extension staff, and producer-cooperators in key agro-ecoregions to develop profitable management practices for the production of biomass feedstocks appropriate to those agro-ecoregions. Key words: Bioenergy, biomass conversion technologies, Panicum virgatum L., stand establishment, switchgrass improvement, USDA-ARS