Abstract
Large-panicle rice cultivars often fail to reach their yield potential due to the poor grain filling of inferior spikelets (IS). Thus, it is important to determine the causes of poor IS grain filling. In this study, we attempted to identify whether inferior grain filling of large panicles is restricted by superior spikelets (SS) and their physiological mechanism. SS were removed from two homozygous japonica rice strains (W1844 and WJ165) during flowering in an attempt to force photosynthate transport to the IS. We measured the effects of SS removal on seed setting rate, grain weight, grain filling rate, sucrose content, as well as hormone levels, activities of key enzymes, and expression of genes involved in sucrose to starch metabolism in rice IS during grain filling. The results showed that SS removal improved IS grain filling by increasing the seed setting rate, grain weight, sucrose content, and hormone levels. SS removal also enhanced the activities of key enzymes and the expression levels of genes involved in sucrose to starch metabolism. These results suggest that sucrose and several hormones act as signal substances and play a vital role in grain filling by regulating enzyme activities and gene expression. Therefore, IS grain filling is restricted by SS, which limit assimilate supply and plant hormones, leading to poor grain filling of IS.
Highlights
Rice is one of the most important food crops in the world, and its consumption is expected to increase with further population growth; improving the output per unit area is the only option for producing more rice on a limited land area (Khush, 2005)
The objectives of this study were to investigate whether inferior spikelets (IS) grain filling of large panicles is limited by SS through removal of some SS and examination of subsequent changes in seed setting rate, grain weight, grain filling rate, sucrose content, hormone levels, activities of key enzymes, and expression levels of genes involved in sucrose to starch metabolism in the IS during the grain filling period
Under T2 treatment, seed setting improved considerably; we focused on the effect of T2 treatment on IS grain filling
Summary
Rice is one of the most important food crops in the world, and its consumption is expected to increase with further population growth; improving the output per unit area is the only option for producing more rice on a limited land area (Khush, 2005). In order to increase rice yield, many scientists involved in genetic breeding are attempting to expand sink capacity by increasing the number of grains per panicle, cultivating large-panicle strains of rice (Kato et al, 2007). The capacities of a new type of rice from the International Rice Research Institute and a heavy panicle hybrid rice used for rice production have been significantly improved. Reason of Poor IS Grain-Filling (Peng et al, 1999). These cultivars, do not always produce higher yields due to low seed setting rate and grain weight of inferior spikelets (IS) (Zhang et al, 2009; Yang and Zhang, 2010). Improvements in IS grain filling would have a significant impact on the yield potential of large-panicle rice
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