Morphological Adaptations and Membrane Stabilizing Mechanisms of Overwintering Miscanthus (Poaceae)
The bioenergy grass, Miscanthus, demonstrates genotypic variation in cold tolerance. The effect of varying belowground morphological characteristics and growth habit on winter survival of Miscanthus genotypes not been examined. Further, biochemical changes that occur during cold acclimation that stabilize cell membranes in the rhizome and confer increased tolerance to freeze-induced cellular injury and desiccation stress are not well understood. There were two aims of this work: (i) characterize the morphology and growth habit of Miscanthus genotypes that differ in responses to low-temperature stress, (ii) assess the changes in fatty acid saturation state and raffinose family oligosaccharide (RFO) concentrations during autumn cold acclimation. Regrowth viability and membrane stability was tested using field-acclimated plant material to assess the freeze tolerance of three genotypes ‘M114’, ‘M116’, and ‘M1-Select’. Rhizomes of field-grown Miscanthus genotypes were sampled at three time points (early autumn, late autumn, and spring) for fatty acid analysis, and four times during the autumn for RFO analysis in 2010 and 2011. An additional three Miscanthus genotypes were included for morphological measurements of field-grown plants, ‘M118’, ‘M119’, and ‘M161’. There was variation in rhizome length, rhizome growth type, culm growth, tiller recruitment strategy, and clumping habit among the six genotypes. Intravaginal tillering and indeterminate rhizomes may contribute to overwintering success. The lethal freezing temperature (LT50) of Miscanthus pooled across genotypes based on regrowth viability tests was -4.4 oC and was estimated to be between -4.8 0C and -6.6 oC based on electrolyte leakage tests of membrane stability. Double Bond Index (DBI), a measurement of membrane fluidity, increased between early autumn, late autumn and spring, from 1.1 to 1.4. Concentrations of linoleic acid (C18:2n6) and alpha-linolenic acid (C18:3n3) increased by 24% and 36%, respectively between early autumn and spring. RFO concentrations increased over the cold acclimation period in all genotypes, from 2 to 13 mol kg-1 in 2010 and from 3 to 30 mol kg-1 between the first and final sampling in 2011. These findings could be used in the development of a cold tolerance screen for Miscanthus germplasm.