The effect of water stress on grain filling processes in wheat

The effect of water stress, commencing from the late cell division period, on in vivo grain growth was studied in relation to grain sucrose, water sta tus and in vitro starch synthesis. Detached ear experiments were conducted to assess the effect of sink dehydration on grain filling processes under n on-limiting source conditions. Water stress caused premature grain desiccat ion and resulted in a marked decline in grain sucrose and reduced grain wei ght. Both sucrose uptake and conversion to starch in vitro were increased b y mild water stress (solute potential (Psi (s))-0.8 MPa). However, a declin e in Psi (s) below this optimum resulted in reduced sucrose uptake and star ch synthesis not attributable to a reduced supply of sucrose. Stressed grai ns which failed to accumulate dry matter in vivo showed significant starch synthesis when cultured in vitro. Grains from in situ and osmotically stres sed plants showed a lower capacity for starch synthesis in vitro. The resul ts indicate that grain filling processes under stress conditions are limite d by (1) low substrate availability and low Psi (s) within the sink i.e. an unfavourable seed environment (non-lasting effect) and (2) reduced synthet ic capacity of the sink (carry-over effect).