Survival strategies in two high altitude Sorghum species from western Himalayas

Elucidation of the structural and physiological adaptations developed against environmental determinants is a key to understand acclimation and capability to withstand cold in plants colonizing high altitudes. In the present study, two Sorghum species, S. arundinaceum and S. nitidum, were collected from three different elevations (800, 1800 and 2800 m a.s.l.) in the Neelum Valley, Azad Jammu and Kashmir. Above-ground biomass decreased but root growth increased along the altitude gradient in both species. The accumulation of ionic content in root and shoot was high in S. nitidum and low in S. arundinaceum. In S. nitidum, chlorophyll contents showed a significant increase from low to high altitude, while in S. arundinaceum, chlorophyll content decreased with increase in altitude. Both Sorghum species generally showed reduction in root epidermis thickness while metaxylem and phloem area increased along the altitude gradient. Stem and leaf area showed intensive sclerification and increased cortical cell area in S. nitidum, but sclerification in S. arundinaceum reduced from low to high altitude. Stomatal density and stomatal area were reduced in both Sorghum species from lower elevation to higher elevation. In S. arundinaceum, small angular prickles at the leaf margins were observed. It was concluded that narrow vessels, extensive sclerification and hairiness assisted both grasses to tolerate freezing-induced damage and their survival at extremely cold temperatures.