Source and sink strength of different genotypes of wheat under water and non water stress conditions during reproductive stage

To investigation of physiological and biochemical basis of yield formation and drought resistance in two wheat cultivars differing in drought resistance and yield potential a set of experiments were conducted. In two experiments (field an greenhouse), exogenous application of cytokinine (CK) and absiscic acid (ABA) at cell division and grain filling stage of grain growth and in two other greenhouse experiments, the effect of different post anthesis water deficit (at cell division, grain filling, from anthesis until maturity) on source and sink related traits were studied. Under control condition grain yield, biomass production and 1000 grains weight of Marvdasht (high yield, sensitive to post anthesis water deficit) were higher than Zagrose (low yield, resistance to post anthesis water deficit). The different levels of Water deficit caused significant reduction in above mention traits in two cultivars, but the amounts of reduction in Marvdasht were more than in Zagrose. Exogenous application of CK at two stages caused significant increase in biomass and grain yield while ABA did not have significant effect on these traits. Highest concentration of IAA and ABA were observed at the cell division and the beginning of grain filling respectively. Exogenous application of ABA significantly decreased IAA and increased ABA concentration of grains while IAA had opposite effects. Under control condition, IAA and ABA concentration in the grains of Marvdasht and spermine, spermidine and putrescine were higher than in the grains of Zagrose. The different levels of Water deficit significantly increased ABA, spermine and spermidine concentrations and decreased IAA concentration in the grains of both cultivars. In contrast to Zagrose, The different levels of water deficit caused significant increase of putrescine concentration in the grains of Marvdasht. Under control in contrast to water deficit, the activity of vacuolar and apoplastic isoforms of invertase in the grains of marvdasht were higher than the grains of Zagrose. Maximum concentration of glucose and fructose in grains were observed contemporary with maximum activity of apoplastic, vacuolar and cytosolic isoforms of invertase during the cell division stage. Maximum activity of sucrose synthase was observed at the grain filling. Water deficit significantly increased activity of this enzyme in the grains of Zagrose. Under control treatment sucrose synthase activity had no significant difference in both cultivars. Water deficit decreased activity of this enzyme in the grains of Marvdasht more than in the grains of Zagrose. Maximum activity of sucrose synthase in the grains of both cultivars was observed at the grain filling stage. Water deficit decreased ADP-glucose concentration in the grains of both cultivars. Under control treatment the contents of estimated amino acids in the 181 grains of both cultivars were different. Water deficit increased asparagine, aspartic acid and valine concentrations in the grains of Zagrose but decreased them in the grains of Marvdasht. The efficiency and amounts of the soluble sugars mobilization in the penultimate, on average, in two cultivars were more than in the peduncle and in the Zagrose was higher than in the Marvdasht. Water deficit significantly increased mobilization from peduncle and penultimate to grains. Increasing of soluble sugars mobilization under water deficit in the Zagrose were more than in the Marvdasht. The concentration of fructan in the peduncle and penultimate was greater than the other soluble sugars. Water deficit in both cultivars caused significant decrease in photosynthesis rate, stomatal conductance, soluble proteins and chlorophyll contents of flag leaf. However, with increasing water deficit severity, reducing of these traits in the flag leaf of Marvdasht were more than in the flag leaf of Zagrose. CK in contrast to ABA significantly increased above mention traits of flag leaf in both cultivars. Water deficit decreased sucrose content in the flag leaf of Marvdasht in contrast to Zagrose. Water deficit caused significant reduction in the ratio of ATP/ADP in the flag leaf of both cultivars. Under water deficit, the proline concentration among of different amino acids had the highest variation in flag leaf. Water deficit increased 14 and 2 folds the Proline content in the flag leaf of Zagrose and Marvdasht respectively. The results suggest that under control treatment, high activity of vacuolar and apoplastic isoforms of invertase and the content of IAA at the cell division and ABA at the beginning of grain filling in the grains of Marvdasht maybe caused higher grain yield of this cultivar than Zagrose. Less decrease in the grain yield of Zagrose under water deficit treatment may be result of less decrease in Photosynthesis rate of flag leaf, higher efficiency in mobilization of soluble sugars in peduncle and penultimate, higher activity of invertase isoforms and sucrose synthase in the grains of Zagrose compare to Marvdasht.