Triticale (x Triticosecale Wittmack) grains synthesize and accumulate starch as their main energy source. Starch accumulation rate and synthesis activities of ADP-glucose pyrophosphorylase, soluble starch synthases, granule-bound starch synthase and starch-branching enzyme showed similar pattern of unimodal curves during endosperm development. There was no significant difference in activity of the starch granule-bound protein isolated from total and separated starch granules at different developmental stages after anthesis in triticale. Evans Blue staining and analysis of DNA fragmentation indicated that cells of triticale endosperm undergo programmed cell death during its development. Dead cells within the endosperm were detected at 6 d post anthesis (DPA), and evidence of DNA fragmentation was first observed at 21 DPA. The period between initial detection of PCD to its rapid increase overlapped with the key stages of rapid starch accumulation during endosperm development. Cell death occurred stochastically throughout the whole endosperm, meanwhile, the activities of starch biosynthetic enzymes and the starch accumulation rate decreased in the late stages of grain filling. These results suggested that the timing and progression of PCD in triticale endosperm may interfere with starch synthesis and accumulation.
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"The decrease in amylose content might be because of an increase in short chains and a decrease of the activity of the DBE (Lü et al. 2008). After that, the following increase in amylose content might be attributed to the enzymatic activity of the SS, which lengthens the amylose chains up to the end of grain development (Li et al. 2003Li et al. , 2010). These results might be considered as evidence that the amylopectin is synthesized before the amylose in triticale, which coincides with observations ofLü et al. (2008). "
[Show abstract][Hide abstract] ABSTRACT: Kernel development and maturation involve several well-characterised events, such as changes in ascorbate (ASC) metabolism, protein synthesis and storage, programmed cell death (PCD) of starchy endosperm and tissue dehydration. Despite many studies focusing on these events, whether and how they are metabolically related to each other, remains to be elucidated. In the present investigation, the changes in ASC-related metabolism, PCD occurrence, kernel filling and dehydration have been analysed during kernel maturation, over a 3-year period in plants grown under normal conditions and in plants displaying modified ASC synthesis. The obtained results suggest that ASC plays a pivotal role in the network of events characterising kernel maturation. During this process, a decrease in ASC content occurs. When ASC biosynthesis is improved in the kernel, by feeding the plants with its immediate precursor, L-galactone-γ-lactone (GL), the decrease in ASC, observed during kernel maturation, is delayed. As a consequence, ascorbate peroxidase (APX) activity is also enhanced. Moreover, a delay in the ASC decrease permits a delay in PCD occurring in kernel storage tissues and in kernel dehydration. Interestingly, the data emerging from the present investigation suggest that the delay in the decrease in ASC content and APX activity also improves kernel filling. The relevance of the ascorbate-dependent redox regulation for kernel productivity is discussed.