The upper leaf sheath of rice (Oryza sativa L.) serves as a temporary starch sink before heading, subsequently becoming a carbon source tissue to the growing panicle at the post-heading stage. The time of sink-source transition in upper leaf sheaths is highly correlated to the panicle exsertion. Here, we found that the expression profiles of starch synthesis genes such as ADP-glucose pyrophosphorylase large subunit 2, granule-bound starch synthase II, soluble starch synthase I, starch branching enzyme (SBE) I, SBEIII, and SBEIV were highly correlated with starch content changes during the heading period in the second leaf sheath below the flag leaf. In addition, the a-amylase2A and b-amylase were considered as major genes that were in charge of starch degradation at the postheading period. Of the five sucrose transporter (OsSUT) genes, OsSUT1 and OsSUT4 appeared to play an important role in sucrose loading into the phloem of source leaf sheaths. Moreover, the microarray-based data implied that the dominant processes associated with functional leaf sheath transition from sink to source were carbohydrate metabolism and the translocation of the carbon and nitrogen sources and inorganic phosphate.

In this report we show that the starch content decreased in NaCl-stressed rice (Oryza sativa L.) seedling leaves during the daytime. Because photosynthetic efficiency and starch degradation enzyme activity were not significantly affected by the high salt, it is likely that this effect results from repression of starch biosynthesis. To determine the regulatory mechanism, the activities of enzymes such as ADP-glucose pyrophosphorylase (AGPase), granule-bound starch synthase (GBSS), soluble starch synthase (SSS) and starch branching enzyme (SBE) involved in starch synthetic pathway were examined. Data suggest that NaCl-induced repression of GBSS activity was the most significant factor reducing starch accumulation. Based on real-time RT-PCR analysis, the effect of salinity on GBSS expression was primarily controlled on the transcriptional level. Furthermore, the salt-induced decrease of both GBSSI and GBSSII gene expressions could be mostly contributed by ion-specific effect and not by osmotic stress. Although the mRNA accumulation of GBSSI and GBSSII can be down-regulated by exogenous ABA, the negative influence of salt stress on GBSSI and II gene expression could be chiefly mediated via an ABAindependent pathway.

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Plant development is affected by the integration of light and phytohormones, including jasmonates (JAs). To address the molecular mechanisms of possible interactions between blue light and JA signaling in Arabidopsis thaliana, we used molecular and transgenic approaches to understand the regulatory relationships between FAR-RED INSENSITIVE 219 (FIN219)/JASMONATE RESISTANT1 (JAR1) and the blue-light photoreceptor cryptochrome1 (CRY1). FIN219 overexpression in the wild type resulted in a short-hypocotyl phenotype under blue light. However, FIN219 overexpression in cry1, cry2 and cry1cry2 double mutant backgrounds resulted in phenotypes similar to their respective mutant backgrounds, which suggests that FIN219 function may require blue light photoreceptors. Intriguingly, FIN219 overexpression in transgenic plants harboring ectopic expression of the C terminus of CRY1 (GUS-CCT1), which exhibits a hypersensitive short-hypocotyl phenotype in all light conditions including darkness, led to a rescued phenotype under all light conditions except red light. Further expression studies showed mutual suppression between FIN219 and CRY1 under blue light. Strikingly, FIN219 overexpression in GUS-CCT1 transgenic lines (FIN219-OE/GUS-CCT1) abolished GUS-CCT1 fusion protein under blue light, whereas GUS-CCT1 fusion protein was stable in the fin219-2 mutant background (fin219-2/GUS-CCT1). Moreover, FIN219 strongly interacted with COP1 under blue light, and methyl JA (MeJA) treatment enhanced the interaction between FIN219 and GUS-CCT1 under blue light. Furthermore, FIN219 level affected GUS-CCT1 seedling responses such as anthocyanin accumulation and bacterial resistance under various light conditions and MeJA treatment. Thus, FIN219/JAR1 and CRY1 antagonize each other to modulate photomorphogenic development of seedlings and stress responses in Arabidopsis.

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