Study of drought and salt stress tolerance in the ligno-cellulosic species giant reed

The production of agricultural biomass and its exploitation for the production of energy and bio-chemicals can contribute to alleviate several problems, such as the dependence on import of non-renewable raw materials, the pollution provoked by the use of fossil feedstocks or the abandonment of land by farmers for lack of profitability Giant reed (Arundo donax L.), a rhizomatous perennial grass which can tolerate a large diversity of ecological conditions, represents a promising biomass crop for second generation biofuels and bio-chemicals in marginal lands where food and feed crops cannot be cultivated. This ligno-cellulosic species is particularly interesting since its biomass production and photosynthesis are higher than other C3 grasses and similar to C4 species. Thus, it is one of the most cost effective and environmental friendly energy crops. Despite its enormous potential, very little is know about the mechanisms it uses to cope with abiotic stresses, allowing cultivation in sub-optimal environments (damaged, e.g. saline or polluted, soils; non irrigated land; etc.).In order to develop a suitable system for screening several A. donax clones collected in the Campania region, also thanks to the kind collaboration of dr. M. Mori (UNINA-Dip. di Agraria), for their ability to grow in soils affected by salinity or drought conditions, we tested different NaCl and polyethylene glycol (PEG) concentrations and different time-courses under controlled conditions in hydroponic systems. Giant reed sprouts were grown in a randomized design with 6-14 replicates; salt stress was applied at three different levels, i.e. 50, 100 and 150 mM NaCl. Water stress was achieved through the addition of the osmolyte PEG 8000 at 5% to the nutrient solution. Biometric (shoot and root growth, leaf width etc.) and physiological (fluorescence emission and electronic transport) parameters were monitored to evaluate stress response. Overall, using either 50 or 100 mM NaCl or 5% PEG most of the analyzed clones showed no differences in shoot biomass between control and stressed samples after 10 days. On the contrary, shoot and root biomass decreased after 21 days in both 150 mM NaCl and 5% PEG treatments. For the above treatments leaf number and 4th leaf width were also monitored at 7-14-21 days and found to decrease in stressed compared with control plants at each of the monitored times. For most clones, growth of both stem and root were affected by NaCl and PEG concentrations compared with control samples both in 10 and 21 days time-course experiments.In order to contribute to the understanding of the mechanisms that make A. donax able to withstand severe water and salt stresses we measured some molecular parameters (expression of genes involved in drought and salt stress, antioxidant capacity, proline, etc.) that are known to contribute to drought and salt stress tolerance.This work was supported by the Project ENERBIOCHEM PON01_01966, funded by the Italian Ministry of Education, University and Research (MIUR), PON R&C 2007-2013.