Exogenous Application of Abscisic Acid or Gibberellin Acid Has Different Effects on Starch Granule Size Distribution in Grains of Wheat

Granule size distribution of wheat starch is an important characteristic that can affect its chemical composition and the functionality of wheat products. Two high-yield winter wheat cultivars were used to evaluate the effects of the application of exogenous ABA or GA during the reproductive phase of the initial grain filling on starch granule size distribution and starch components in grains at maturity. The results indicated that a bimodal curve was found in the volume and surface area distribution of grain starch granules, and a unimodal curve was observed for the number distribution under all treatments. The exogenous ABA resulted in a significant increase in the proportions （both by volume and by surface area） of B-type （〈9.9 Ixm in diameter） starch granules, with a reduction in those of A-type （〉9.9 ~tm） starch granules, while, the exogenous GA3 led to converse effects on size distribution of those starch granules. The exogenous ABA also increased starch, amylose and amylopectin contents at maturity but significantly reduced the ratio of amylose to amylopectin. Application of GA3 significantly reduced starch content, amylopectin content but increased the ratio of amylose to amylopectin. The ratio of amylose to amylopectin showed a significant and negative relationship with the volume proportion of granules 〈9.9 μm, but was positively related to the volume proportion of granules 22.8-42.8 μm.

Polyamines mediate the effect of post-anthesis soil drying on starch granule size distribution in wheat kernels

Polyamines(PAs) are important endogenous plant growth regulators responding to environmental stress and mediating many physiological processes including grain filling in cereals.This study investigated whether PAs mediate the effect of post-anthesis soil drying on starch granule size distribution,starch content,and weight of superior and inferior kernels of wheat(Triticum aestivum L.).Two wheat cultivars were grown in pots.Three treatments,well-watered(WW),moderate soil drying(MD) and severe soil drying(SD),were imposed from 9 days post-anthesis until maturity.PA levels in kernels and small,medium and large granules were measured.The results showed that superior kernels had much higher free spermidine(Spd) and free spermine(Spm) concentrations,larger volumes of medium starch granules,and smaller-sized large granules than did inferior kernels under all the treatments.Compared to WW,MD significantly increased the concentrations of free Spd and free Spm,activities of soluble starch synthase and granule-bound starch synthase,volume of medium granules,and starch content and kernel weight of inferior kernels,and decreased the size of large granules.SD produced the opposite effect.Application of Spd or Spm to spikes produced effects similar to those of MD,and application of an inhibitor of Spd and Spm synthesis produced effects similar to those of SD.These results suggest that PAs mediate the effect of post-anthesis soil drying on starch biosynthesis in wheat kernels by regulating key enzymes in starch synthesis and that elevated PA levels under MD increase the volume of medium granules and kernel weight of inferior kernels.

LH Plays a Role to Enhance the Nuclear and Cytoplasm Synchronization During In vitro Maturation of Ovine Oocytes

This study is aimed to investigate the effect of luteinizing hormone （LH） on maturation and fertilization in vitro of ovine oocytes. The ovine oocytes were cultured in vitro in medium with or without LH, and then checked by confocal laser scanning microscope to observe the distribution of cortical granules stained with FITC-LCA during different maturation periods. Similarly, some in vitro matured oocytes were also fertilized in vitro for analysis of their developmental potentiality further. After being cultured in vitro for 4 h, there were significant differences about the rate of germinal vesicle break down （GVBD） between the treatment （with LH） and the control groups （without any hormones） （36.76% vs 18%, P〈0.05）. Further, there were also significant differences of the cleavage and blastocyst rates between these two groups （67.15% vs 42.37%, 21.9% vs 12.71%, P〈0.05, respectively）. The distribution of cortical granules appeared to spread from the edges to the central site of sheep oocytes following their delaying durations of maturation in vitro. It can be concluded that LH may play a role to delay the occurence of GVBD, prolong the maturation duration of cytoplasm, and enhance the nuclear and cytoplasm synchronization of ovine oocytes matured in vitro and finally improve their in vitro developmental potentiality.