The Families of the Monocotyledons

Outline of the classification of flowering plants (Magnoliophyta)

Large areas of the tropics and subtropics are too arid or degraded to support food crops, but Agave species may be suitable for biofuel production in these regions. We review the potential of Agave species as biofuel feedstocks in the context of ecophysiology, agronomy, and land availability for this genus globally. Reported dry biomass yields of Agave spp., when annualized, range from o 1t o 34Mgha � 1 yr � 1 without irrigation, depending on species and location. Some of the most productive species have not yet been evaluated at a commercial scale. Approximately 0.6Mha of land previously used to grow Agave for coarse fibers have fallen out of production, largely as a result of competition with synthetic fibers. Theoretically, this crop area alone could provide 6.1billionL of ethanol if Agave were reestablished as a bioenergy feedstock without causing indirect land use change. Almost one-fifth of the global land surface is semiarid, suggesting there may be large opportunities for expansion of Agave crops for feedstock, but more field trials are needed to determine tolerance boundaries for different Agave species.

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The global potential for Agave as a biofuel feedstock

From mesic to arid: Leaf epidermal features suggest preadaptation in Miocene dragon trees (Dracaena)

Agaves are perennial crassulacean acid metabolism (CAM) plants distributed in tropical and subtropical arid environments, features that are attractive for studying the heat-shock response. In agaves, the stress response can be analysed easily during leaf development, as they form a spirally shaped rosette, having the meristem surrounded by folded leaves in the centre (spike) and the unfolded and more mature leaves in the periphery. Here, we report that the spike of Agave tequilana is the most thermotolerant part of the rosette withstanding shocks of up to 55 degrees C. This finding was inconsistent with the patterns of heat-shock protein (Hsp) gene expression, as maximal accumulation of Hsp transcripts was at 44 degrees C in all sectors (spike, inner, middle and outer). However, levels of small HSP (sHSP)-CI and sHSP-CII proteins were conspicuously higher in spike leaves at all temperatures correlating with their thermotolerance. In addition, spike leaves showed a higher stomatal density and abated more efficiently their temperature several degrees below that of air. We propose that the greater capacity for leaf cooling during the day in response to heat stress, and the elevated levels of sHSPs, constitute part of a set of strategies that protect the SAM and folded leaves of A. tequilana from high temperatures.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-3040.2009.02035.x

K. Jewers

Papers

The comparative leaf anatomy of Agave, Beschorneria, Doryanthes and Furcraea species (Agavaceae: Agaveae)