Protein concentration in response to water stress in Themeda triandra Forsk

Abstract

The influence of water stress on the concentration of water-soluble protein growth reserves was determined during three growth stages (vegetative, pipe and reproductive) as well as in three plant parts (roots, stubble and leaves) for the indigenous C₄ semi-arid grass species, Themeda triandra. Four water stress treatments (T1 = 0–25%, T2 = 25–50%, T3 = 50–75% and T4 = 75–100% depletion of plant available water) were applied to plants grown in pots under greenhouse conditions. The water-soluble protein concentration (WSPC), determined in fractionated material obtained from stressed plants after drying in an oven, differed significantly (P<0.05) between plant parts as well as between growth stages. The WSPC in the leaves and stubble increased significantly with increased water stress for the vegetative, pipe and reproductive growth stages, while a similar increase was observed in the roots during the reproductive growth stage. The WSPC in the roots was variable among treatments during the vegetative and pipe growth stages. The results illustrate that under severe water stress, the decrease in aboveground vegetative growth causes an increase of water-soluble protein in aerial plant parts. Therefore, under severe drought conditions, the same number of animal units can still be carried owing to the higher nutritional value of the available fodder. This amplifies the importance of careful grazing and stock management in T. triandra dominant grassland, thus ensuring sustainable production and survival in an ecologically sensitive semi-arid climate.