Background: To identify genes that potentially regulate the accumulation, mobilization, and transport of photoassimilates in rice (Oryza sativa L.) leaves, we recently screened a mutant collection of rice by iodine staining to visualize leaf starch contents. From this screening, we isolated a rice mutant that exhibits hyperaccumulation of starch in leaves and designated it as the Leaf Starch Excess 1 (LSE1) mutant. Here, we report two other rice LSE mutants, LSE2 and LSE3.
Results: Unlike lse1 plants, lse2 and lse3 plants displayed retarded growth; lse2 showed an extremely dwarf phenotype and rarely survived in paddy fields; lse3 showed inhibited growth with pale green leaf blades, low tiller numbers, reduced height, and low grain yield. In lse2 and lse3 plants, the mature source leaves contained larger amounts of starch and sucrose than those in wild-type and lse1 plants. Furthermore, microscopic observations of leaf transverse sections indicated that hyperaccumulation of starch in chloroplasts of mesophyll and bundle sheath cells occurred in lse2 and lse3 plants, while that in vascular cells was noticeable only in lse3 leaves.
Conclusions: The distinct phenotypes of these three LSE mutants suggest that the LSE2 and LSE3 mutations occur because of disruption of novel genes that might be involved in the path of sucrose transport from mesophyll cells to phloem sieve elements in rice leaves, the mechanism for which has not yet been elucidated.