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To identify the effects of grain phytic acid (PA) mutant on rice (Oryza sativa L.) grain filling and grain weight, the accumulating patterns of grain PA, total starch contents and also in relation with the carbohydrate translocation in different organs (leaf, culm, and sheath), and the activities of some enzymes involved in starch synthesis metabolism were investigated using 2 early indica genotypes differing in grain PA content-namely Xieqingzao and its low PA mutant (Os-lpa1). Compared with Xieqingzao, os-lpa1 had higher starch content and more carbohydrate accumulations in flag leaf, culm, and sheath, but much lower activities of ADPG pyrophosphorylase (ADPG-Ppase) and starch phosphorylase (SPase) in grains at filling stage, leading relatively decreasing grain weight, low grain starch accumulation and poor plumpness for os-lpa1. The activities of phosphate synthase (SP) and fructose biphosphorylase (FBPase) in sheath were generally lower at filling stage for os-lpa1 than those for Xieqingzao, despite relatively high starch content and sucrose accumulations in culm and sheath being shown for os-lpa1, implying that an obstacle of carbohydrate translocation from culm and sheath to grain at rice filling stage could be caused by grain PA mutagenesis, which might be one of major reasons for its poor plumpness and the reducing yield levels of os-lpa1.

The variation of amylose content (AC) among grains within a panicle and its relation to panicle morphology were investigated using 44 japonica rice cultivars differing in grain density (GD), panicle bending degree (BD) and palatability. Morphological traits of the rice panicle were poorly associated with mean grain AC on the average of the whole panicle, but closely related to AC variation and spatial distribution within a panicle, with the compact-panicle cultivars (GD>6.5 grain/cm and BD 70°). The extent of AC differences among the rachides within a panicle was also cultivar-dependent, and greater differences were found between middle and top rachides for the compact-panicle cultivars, and between middle and bottom rachides for the loose-panicle cultivars. The difference in spatial distribution of AC variation between Bing110 (a compact-panicle cultivar) and XS11 (a loose-panicle cultivar) indicated that grains with low AC were principally distributed on interior rachis of middle branches for Bing110, but on bottom-rachis for XS11. Such a distribution is basically associated with the difference in the timing procedure of floret initiation and development, and final grain weight.

The effect of grain position within a panicle on chalky occurrence, and its relation to phytic acid and protein content, were studied using 6 Japonica rice cultivars with compact panicles and through leaf and floret removal treatments to alter source-sink ratio. There were significant differences in total chalky grain (TCG), white core grain (WCG), white belly grain (WBG), and WCG/WBG among grains within a panicle, with the top and primary rachides having higher WBG than the bottom and secondary rachides. Alteration of source-sink ratio had a remarkable influence on chalky grain occurrence and its positional distribution within a panicle, and the extent of the influence varied greatly with cultivars. In comparison with WCG, WBG occurrence was more susceptible to the alteration of source-sink ratio. No significant correlation was found between chalky percentage and phytic acid and protein contents for the grains in the different positions within a panicle. Chalky occurrence had little effect on the nutritional quality.