|Keywords (Extracted from title, table of contents and abstract of thesis)
drought, high temperature tolerance, wheat, triticum aestivum, water stress, drought tolerance, iaa content, ga3 content, aba content, proline content
In arid and semi arid regions water scarcity and high temperature are major production constraints. Plant water deficit during grain filling in wheat has been found to substantially affect grain yield. The study was aimed 1) to determine the physiological and biochemical response of plants to the variation in the temperature and moisture in plants grown in fields of arid, semi arid and high temperature areas during milky stage of grain formation. 2) To compare the performance of plants grown in pots at critical stages of grain filling under drought stress induced at anthesis stage. Furthermore, the effect of abscisic acid (ABA) and benzyladenine (BA), the two important hormones involved in stress tolerance applied at anthesis stage were studied on the physiology and biochemistry of plants at different developmental phases of grain filling viz. anthesis, watery ripe, milky, soft dough and hard dough stages.
Wheat samples collected from high temperature areas and arid and semi arid areas of Pakistan were analyzed for sugar, protein, proline and phytohormones-Indole-3-acetic acid (IAA), Gibberellin (GA3) and abscisic acid (ABA) content of flag leaves and spikes. The amount of sugar content decreased in both flag leaves and spikes of plants collected from both high temperature and arid and semi arid areas but the plants collected from high temperature region showed greater decrease than that of arid and semi arid areas plants. Protein content was increased with the increase in temperature. The concentration of growth promoting hormones, Indole-3-aceticacid (IAA) and Gibberellin (GA3) decreased whereas, that of stress hormone abscisic acid increased with increase in temperature and decrease in moisture content of soil. Sugar, protein, proline, IAA, GA3 and ABA contents of spikes were higher than that of leaves under both the stresses. The effect of high temperature was more marked than that of arid and semi arid areas.
Seeds of two wheat varieties (Triticum aestivum L.) cv Margalla-99 (cvl) and cv Manthar-2003 (cv2) were .sown in pots under natural climatic conditions. Stress treatments were imposed immediately after anthesis by withholding water supply for a period of 10 days. Aqueous solution of growth regulators, abscisic acid (I 0-6 M) and benzyl adenine (10-6M) were sprayed on the leaves at anthesis stage. Drought stress treatments were imposed immediately after anthesis and measurements were made subsequently at each successive stage of grain filling viz. anthesis, watery ripe, milky, soft dough and hard dough stages. Leaves and spikes were analyzed for protein, proline and sugar content and endogenous level of IAA, GA3 and ABA.
Under drought stress the relative water content, water potential, osmotic potential, sugar, protein, IAA, GA3 , grain yield, grain moisture content, grain weight, shoot biomass was found to be decreased while the application of abscisic acid and benzyl adenine partially ameliorated the inhibitory effect of drought but the effect of abscisic acid was more marked than that of benzyladenine. In all cases decrease was more in cv2 Manthar-2003 than in cvl Margalla-99. Application of both ABA and BA was to maintain the water budget and regulation of osmotic imbalance by regulating the relative water content of flag leaves and production of proline. IAA and GA3 content and IAA/GA ratio decreased under drought conditions in both flag leaves and spikes. ABA and BA application increased the IAA and GA3 content and ratio of IAA and GA3 over drought. Highly significant positive correlations existed in RWC, osmotic and water potential of flag leaves.
The adverse effect of drought started at anthesis stage reaching maximum at hard dough stage. ABA was more effective at the later stages (soft and hard dough stages) of grain filling whereas, BA was more effective at early stage (anthesis, watery ripe and milky stage) in most of the cases. The high temperature at the reproductive phase as well as the ABA application at anthesis stage accelerated the grain filling rate to escape the period of stress which appears an adaptive mechanism to increase the grain yield. Exogenous application of terpenoid analogue of ABA may be used for commercial use in the field to provide tolerance to plants against moisture stress.