Abstract:

The ultra-structure of the vascular bundle phloem in rice rachilla and its time-course during grain filling period were observed for different positional rachillae within a rice panicle by using low-temperature embedding and electron microscopy technique, and CaM distribution in sieve element (SE) and companion cells (CC) of the central vascular phloem was investigated by immuno-gold localization. The results showed that there were obvious difference in the anatomical structure of the vascular bundle between different positional rice rachillae, with the relative large total vascular area, phloem area and vessel area in central vascular bundle for superior positional rachilla within a panicle, indicting that the superior rachilla had better structure for the assimilate transport compared to the inferior positional rachilla; the similar time-course in the degradation pattern of some organelles of SE and CC in central vascular phloem was observed in different positional rachillae at grain filling stage, with the relative delaying degradation and disintegration of SE,CC and phloem parenchyma cells for inferior positional rachilla; the abundant mitochondrion, chloroplast, starch granules and plasmodesmata, and numerous CaM labeling density were found in SE and CC of superior rachilla compared to inferior positional rachilla at beginning filling stage, while no significant differences between two types of rachilla at middle and late filling stages, implying that superior postional rachilla had relatively better transporting function at initial filling stage relative to inferior rachilla.

Key words: Rice(Oryza sativa L.), Rachilla, Positional variation, Ultra-structure, Calmodulin, Immuno-gold localization