Distribution of Assimilates to Each Organ in Rice Plants Exposed to a Low Temperature at the Ripening Stage, and the Effect of Brassinolide on the Distribution

Abstract

: Previously, we found that promotion of ripening by brassinolide (BR) in rice plants is attributable to the rapid translocation of assimilates from leaves to the panicle (Fujii and Saka, 1992). In this study, we examined the effect of BR treatment on the distribution aspects of carbohydrates (starch, sucrose, glucose and fructose) in upper organs including the panicle of the rice plant (cv. Nipponbare) grown in a low temperature condition(20,C in the daytime / 13,C at night) in a phytotron under natural daylight in summer. Rice plants in a greenhouse in summer were sprayed with BR (2 X I0-8 M and 2 X 10-9 M) twice at around the heading stage, and were then kept in the phytotron and in the greenhouse to examine the carbohydrate contents in leaf blades, leaf sheaths, culms, hulls and hulled grains at the milk-ripe and dough-ripe stages.At milk-ripe stage, the starch content in the plants grown in the greenhouse without BR treatment was overwhelmingly high in hulled grains with a low content in culm, leaf sheaths and hulls, whereas starch was hardly detected in the leaf blade. At the dough-ripe stage, starch was more accumulated in hulled grains. Sucrose content at the milk-ripe stage was low in hulls, but high in leaf sheaths and culms, especially in leaf blades. However, at the dough-ripe stage, a large amount of sucrose was accumulated in culms, and only a small amount in leaf blades. The content of glucose and fructose was 10 to 20% of that of sucrose in each organ, and did not differ so much between the two stages of ripeness.In the plants grown in the phytotron, the total amount of starch was markedly lower and the contents of sucrose, glucose and fructose were considerably higher than those in the greenhouse. The marked decrease of starch content in the phytotron was found in hulled grains while the content in leaf sheaths, culms and leaf blades increased. On the other hand, the increase of sucrose content resulted from the increase in vegetative organs with the decrease in hulled grains. An increase of glucose and fructose were also found in leaf organs at the milk-ripe stage.BR decreased the starch content in leaf sheaths and culms, and increased the contents of starch and sucrose in hulled grains in both temperature conditions. The contents of starch and sucrose in hulls were not influenced so much by BR. Neither did BR largely influence the contents of glucose and fructose. However, BR treatment strikingly increased the 1 ,000-grain weight and the percentage of ripened grains in the rice plant in both of the greenhouse and phytotron.Key words :Assimilate, Brassinolide, Promotion of Ripening, Rice ( Oryza sativa L.), Ripening Stage, Starch, Sucrose.The plant hormone brassinolide (BR) promotes the ripening of rice plants (Hirai et al., 1991) as well as isoprothiolane (Ohtsuka and Saka ,1989) and hydroxyisoxazole (Ota, 1981). In a previous study (Fujii and Saka, 1992), we found that BR applied at around heading time promoted ripening of rice plants through the promotion of the translocation of ass...

Does exogenous application of 24-epibrassinolide ameliorate salt induced growth inhibition in wheat (Triticum aestivum L.)?

“…Grain yield of a cereal crop depends on both number and size of grains (Grieve et al 1992), but from the results for different yield components as observed in the present study, it is clear that exogenously applied 24-epiBL did not improve the grain yield or yield components of hexaploid wheat. In the present study, 24-epiBL was applied to 41-days old plants, but it has been reported that the BR is effective for improving grain yield when it is applied at the heading stage, as has been found earlier in rice (Fujii and Saka 2001).…”

Boosting Crop Yields with Plant Steroids

“…Experiments involving exogenous BR application on wheat and soybean (Glycine max) plants and seeds suggest that BRs might significantly affect it (Janeczko et al, 2009(Janeczko et al, , 2010. In rice, treatment with BRs at anthesis increased starch content in kernels (Fujii and Saka, 2001). Additional studies on the BR effects on seed composition are needed if the BR pathway components are to be manipulated for grain crop improvement.…”

The effect of brassinosteroids on the morphology, development and yield of field-grown maize

“…(Ali et al , 2008aArora et al 2008;Hayat et al 2007;Janeczko et al 2009;Kartal et al 2009;Mazorra et al 2002;Ö zdemir et al 2004;Shahbaz et al 2008;Singh and Shono 2005). Photosynthesis, transpiration and nitrogen fixation in plants are also influenced by BRs (Ali et al 2008b;Fariduddin et al 2003;Farooq et al 2009;Hayat et al 2000;Li et al 2008;Sairam 1994a, b;Swamy and Rao 2008;Yu et al 2004), as well as the distribution of assimilates to various plant organs (Fujii and Saka 2001).…”